Pe ee RT ON 4 em ee wet Ses oe Mtl Soot bre ernest 0) poe Meer Siew en ge me Te ee on S02F PTR PA SK ES PE meine: el bee Tere ee Fe tap cages o ad oat ae cel Spe Gaal Sa, Saas Toe hve Pes in ha ih 3 livaededes i baeineuand My Ph cgth Py°§ Jyanne at aa ty Aa Waly Jy te Relient yey ee ‘ pheteys tht Gy PO bee argo distareatAtiace erhu4e Siisiaave Hest i FE SIRIP nine CR AER wide & eho es F) Sam taas balys ¢ Vee eee Co eS i : . ah ehedy byhy sites : fee ae ati ia sdecstyes Natasatinet eta tenth ata iy Ke rh aint ot : rks fig tit ¥ Aneta reese Fi jabato Pacteh eel iictteniser: es sthdahubrarns 1 Neihhd pm Says, f ‘ ; : > var mesa econ aio hes we BAN ms he ionceses Nw Win "; rhea et ws OE ee Han Paeen iy Paerd) Har ere rT § OP Dbit ye Fy rire thedd we ant Joc ak the bee beeeh “ cig ren Lt * p> * A veh lig © Ass oe pet} Sy Me AOD PLAN Pree aa hats INST HCG AT, ¢ Wf AU 608 savy tarly es Gad 944, ict NTA y yt Lb» ae pn boo] 4 7 ce ne ae eet 1et heed Bag ts wuts a4 svi ta sated baa a Wry ae" euicataly at 4 Oe HSCS at Pee tioart ac pecate es © ae Pte te rs eevee sea semeihe xs a sae btha3 idence mana He botey bo ead cd ies Pita ha! PEE SENS 848 cee Meh $id isle xt jioeistes of Pee e Lys iy itert yea) IGE ii oeres iter ty J isaetmcadar tS RIS TIAGO Meio hes ics SAMA ES i irs TL mi DAN AIG elk gee a. thee : ii +: LoS ears tie se es ais et Se tee SIE-§ < Wate wd A Sieh nece, a Wh RL eR SEO Rem ay ge PACHNRAAG ¢ Nee aterreuase a i f i & reiaaitt oat ‘ei a sea Sen Ptat heat Gaye if a De FPGS AEST ae At Seta “th AGIA Cig a AV Ard AE RTs Meta ota baat Siditontsta at AUUA4N Vague Nes alate Aah imate? ta ea tas atti i sad das abhed Sag arp Lite roi cat : Rie PEE TAA GATE RAS TOE ray b+ RateT eeatks Mae once valieet eeorin TS ae POLIS ug oa NOME LUO DN ONT EE AAO tga Se eh PASS C84 0 UES Ped Et Prt YESH a cide ys eee, st crysewagey GAG as in 4) POE Ves 89 48 95, Py SICA Tad a Kae SUEIS oh Si09 heed terct eet agecte Yeh Lat abt ii Wigas ie rete ta TeShees seettens ue trorter eed erent cd Myf 4 et Tere tne seis iets : RAE SKE sane gale iA Alert th chi tay 4; 4 lsat se. Keep eur NALS tate i hare, 4 1a. hoe 2 hos Rat * Mites ave eorr peiecat Bt ein ene Pybieutiy 2. were sss aaa iergae hott fein aig ee picnics gegen id tecaace is $3 Ate ts < uate 5 Ve hae PACHA NE HF. Pate me eae ri ites: ‘ Ate talc Yates al Ape at at Meola i SAF steve ‘beet Bee AD Sh APs ae Ne tiie bei + $ 2 2 See gue er ee? ay x pat ae Bare Rees hint iat thee pdebe ASF f we baad we bs 8 sachgaet the. : te ealedin : 7 i F ran teh y] PORE ( fet! i tne EAE a hate Pe % . ¥ appre rete: acca ; ; hy Ptteneeaten ne patie & ai Hi koa Abita bl Abn ier eae ierepirces > ven ‘5 ety yas sadhana teeter cpitrpeatnet tga yn gn et e Ae Dayne HT ay TS 9 ee ye Digitized by the Internet Archive in 2008 with funding from Microsoft Corporation http://www.archive.org/details/evolutionracialhOOguliuoft al EVOLUTION, RACIAL AND HABITUDINAL. BY REV. JOHN T. GULICK. WASHINGTON, D. C.: PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON. AUGUST, 1905. CARNEGIE INSTITUTION OF WASHINGTON. PUBLICATION No. 25. AIBRARy SEP 0 4 tyb9 yy 9 HeRsiny oF wOS PRESS OF GIBSON BROS. WASHINGTON, D. C. PREEFAGE. In the present volume I have brought together in one connected presentation the chief results of my investigations concerning the factors of organic evolution. Portions of my theory of divergence which were published in the Linnean Society's Journal are repro- duced in the Appendix, with careful revision; but the fullest exposi- tion of the fact that all evolution, as we now observe it, is divergent, and that other factors besides natural selection are absolutely neces- sary both for the origin and the continuance of this divergence, is given in the new chapters constituting the body of the volume. These chapters have been written while considering the most recent biological investigations bearing on the general theory of segregation. The first four chapters of the volume are introductory, in that they present many facts of divergence and distribution in both natural and domestic species, which remain complete enigmas till the forms of racial and habitudinal segregation have been fully recognized. Chap- ters V, VI, and VII present the fundamental laws of segregation, and the interaction between the different classes of factors—between isolation and selection, between racial segregation and habitudinal segregation, between autonomic factors and heteronomic factors. In Chapter VI, $ I], 14-17 (pp. ro1—111), will be found a fuller exposi- tion than has been presented in any of my essays published by the Linnean Society, of the tendency of certain combinations of partially segregative e:}dowments to become more intense in successive genera - tions. Itis shown that this is especially the case when endowments, tending toward the mating of like forms with each other, are reinforced by varying degrees of mutualinfertility and incompatibility between unlike forms. Appendix II, $ IV, 3 (pp. 241-243), briefly indicates several methods of constructing what I have called the permutation triangle. It was first constructed in order to show that the sterility of cross-unions between divergent forms (whether they be varieties, species, genera, or higher groups), would lead rapidly to the extinction of most of these forms, if instincts and other endowments did not facilitate the union of compatible forms. The table thus constructed is found to be a concise presentation of certain classes of probabilities that arise in the pairing of things by chance. ll iv PREFACE. The principles molding segregation, and so controlling variation and heredity, and the effects on racial and social evolution produced by such control, are presented with considerable fullness of illustra- tion on the biological side. For my purpose it did not seem necessary to dwell at equal length on the social aspects. Another broad department of the subject is referred to in only the briefest way. This is the effect of amalgamation or regressive segrega- tron, both racial and social. I have, however, pointed out that in the history of man segregation was the leading factor through countless generations when races, languages, and institutions were becoming increasingly subdivided; and that it is only in modern times that the barriers to free intercourse have been so rapidly yielding that regres- sive segregation has been the predominant feature in human history. I have presented evidence that, even in the case of invertebrate animals, members of the same species, exposed to the same environ- ment in isolated groups, will often arrive at divergent methods of dealing with the environment, and so subject themselves to divergent forms of selection. If my contention is in accord with the facts, the assumption which we often meet that change in the organism is controlled in all its details by change in the environment, and that, therefore, human progress is ruled by an external fate, is certainly contrary to fact. It is of no little interest that the recent developments of biological science, in both Europe and America, are pointing, not only to the power of the organism to deal with the same environment in different ways, and so to determine the forms of what I have called active (or endonomic) selection, but also the power of many animals to deal with sudden changes in the environment in such a way that the group is saved from extinction till ‘‘coancident variations” have time to arise, insuring completer adaptation to the new conditions through selection. The teachings of biology are thus coming more nearly into accord with that school of sociology which has for years. maintained that the social group may learn to determine the form of its own social evolu- tion. We are thus led to hope that man will in time determine his own evolution, racial as well as social; for when sufficiently advanced to realize the breadth of the responsibilities resting upon him, the form of his racial inheritance will naturally be determined by the ideals shaping his social organization. In the third chapter, and again near the end of the last chapter, attention is called to the fact that, in accommodational and anticipa- tory action, and in codperation for the attainment of future results, all forms of life, from the earliest protozoa till we reach the highest I a PREFACE. Vv types of spiritual life in man, present activities entirely unknown in the inorganic world. In the degrees of attainment reached in codpe- rative action (with the division of labor and community of interest), and in anticipatory and discriminative action (securing adaptation to future conditions), we find a definite test of the stages of evolution reached—a test that is applicable to the lowest as wellas to the highest living creatures. Of my papers previously published, the one on Divergent Evolution has received the most attention. This is perhaps due to the fact that it was not only published in London in the Linnean Society’s Journal for 1887, but was reproduced in this country in the report of the Smithsonian Institution for 1891. I wish, however, to emphasize the importance of the factors enumerated and illustrated in the one on intensive segregation (see Appendix II). If we would fully com- prehend the factors producing the segregation of organic types, we must recognize not only the forms of isolation by which groups are first set apart; but also the physiological and psychological forms of segregation by which the slightly divergent forms are held perma- nently apart, and still further, the factors producing divergence in these isolated groups, and so resulting in intensive segregation. I show that intensive segregation is due not only to the exposure of isolated groups to different environments, but also to the different methods of dealing with the same environment adopted by the iso- lated groups. I also point out other factors that are subject to change without any change in the activities lying outside of the species; and all such I class as autonomic factors. Throughout all the chapters the underlying purpose has been the investigation of the autonomic as well as the heteronomic factors controlling evolution. The chief hindrance to the increase of our knowledge of the method of evolution is the tendency to regard some one of the several prin- ciples influencing segregation as the one principle controlling the whole process. I believe Prof. H. F. Osborn makes no mistake when he suggests that the ruling method of the next important advance in the interpretation of evolution must be one recognizing the complex action of diverse principles, and at the same time grasping the under- lying unity of the process. In the present volume the question is raised whether segregation, with its controlling influence in the spheres of both racial and habitudinal evolution, is not the underlying principle we are seeking. It must, however, be carefully noted that segregation as defined in this volume covers a much wider sphere than isolation. In order to reach the more pronounced results of racial segregation, the separate groups produced by isolation must v1 PREFACE. for several generations be subjected to divergent forms of selection; and in all the forms of animal life that are capable of learning by experience, accommodation, controlled by the principles producing habitudinal segregation, is constantly guiding and shaping racial segregation. Though more familiar words have been chosen for the title of this volume, the subject here treated would have been clearly expressed if the title had read: ‘‘Habitudinal and Racial Segregation; or, the origin and intensification of organic types, guided by innovation and tradition acting under segregate association, and established by variation and heredity acting under segregate intergeneration.” Joun T. GULICK. OBERLIN, OHIO. CO Nel Nes. CHAPTER I.—INTRODUCTION. ete es ACAI FOL PSC MOA thOM ini fon ces'a. ge oo dons ous e WE Gn eee een I=3 Small Areas of Distribution for Species of Hawaiian Snails......... I pet iter OrAGine OF epCeles te fa 0 «29ers cp eee ae nee eee es ae 2 Selectioninot Always. the Cause of Divergence .....52. 5005.0 cn5 es caus 3-6 In Many Cases Sextial Selection not the Cause... 2.2.56 6.0..5080 3 In Many of the Same Cases Natural Selection not the Cause........ 4 May not the Prevention of Free Crossing be an Explanation............ 6 Investigation of Causes and Effects of Segregation.................... 7 Segregation the Unifying Principle in Evolution..................... 7 CHAPTER II.—BIoNomic LAws. Wetitodioilmy esti ccitotiy: e. fyeci dayicen o fatiie oie cce dg) feue oe cry glee 2 eae ene #2 cae 9-13 MICOS OMS (OMOMIICS sits seas thee eiy epee nue sessed 1 somos acs vb len ae @-6y< ene 9 Why we Commence with the Method of Evolution................ 9 Neediotlnvestication(ofall Bactors.< 4 s..02o0t.25 cee se sae oes 10 Natural and Sexual Selection not the Only Factors............... Il Comparison of Conditions in Natural Species and in Domestic Varie- TES fas eeu tie tes te Pan chases. adidiah Gua esis oi ds ok sarang 12 REOCUcMOlmmOl WOmeStiC RCC (ek, a2: ba ea ete Petes cred uss aie aft saver eis Gs 13-22 (Grey snishahbee wok e{='(0) had se Kelels paren Neer teeter cee aie eee ae reece 13 UiramStocmenti OI OL NaACeSue, a isk. 5 rtteeistneees ces else ae ee senate Ge ns = = 14 Miner ence Ol RACES a aie See cise bess hee aes wiolnseees Fa S54 9.05 17 DIR DINEY ACCS Nine shhe oy orae MO ore ee hia ws es28 8 19 Arialpamatton Of RACES ics oe Lak ee aes 36 oat Ble adles Snel 0d 20 Influence of Acquired Characters on Racial Characters..........-. 20 CHAPTER III.—THE EVOLUTION OF NATURAL SPECIES. LORo\ (en tge hors Wal BLE c10: | 9 eee eee Oe ae re ec 23-29 Darwin's Pxplanatiomot Unity... 06s. esis aes e cee eee eres 23 Divergence Through Variation under Isolation and Unity Through Comimitmityeor DESCeN ites oq so nae sco as cmb ees whe epee Z Facts in Distribution of Hawaiian Snails.............0+-++-eseees 26 Diversity of Natural Selection not a Sufficient Explanation........ 27 Divergence through Independent Transformation... ............-- 28 Natural Selection as Explanation of Evolution..............-.-++545: 29-34 What Natural Selection does not Explain. .........-.--.-+-+255. 29 Selection, how Far Determined by External Nature.............- 31-34 DISCOMUMMIUITYAOL SPECIES terete ee srs. ae eae a cot we te Ge mol eye Yee e ye ei) ouel 34-36 CHAPTER IV.—DIVERGENCE UNDER THE SAME ENVIRONMENT. Explanation on Pinte fa 26 0 ocean Stel ech ap ecte s oA ees ater ener 37 Explanation GO? Plate Mls. 054 gsens oe pate seine AE Bales wea eee 39 vii Vili CONTENTS Explanation of Plate II].........-- ++. eee eee e eee ree teense 41 Oahu the Metropolis of the Achatinellide.................-ee0 sees 42 Plate A. Map of the Hawaiian Islands. Plate I. Eight Genera of Achatinellide. Plate B. Map of Oahu, Hawaiian Islands. Plate II. Twenty-five Species of Achatinella. Plate III. Variation and Intergrading of Bulimella. Explanation of Plate B......... 2... eee c cece cece ee eee eee eee eeeee 43 CHAPTER V.—THE Four SEGREGATIVE PRINCIPLES. Racial and Habitudinal Segregation. (1.22 5555% 3. bine 0105 ae ee tee 45-50 Interaction of Acquired and Inherited Characters...............- 45 Sesrepation a: bundamentallyl awe sci tem terete eect eee ete 47 Segregate Associations.c er sates cc rect e e ee 48 Interaction of Racial and Social Factors..................-..05- 49 Determinate Evolution of Evolutionary Terminology............. 50 Segregation the Combined Result from Four Principles............... 51-55 Racial Segregation Controlled by Two Principles and Habitudinal Secregation’ by LT wOSeeract ote tee ee hea eee enor ede 51 importance of Jsolation:.2 y-.e eee es eee oe eal eee 51 Definitions of the Four Segregative Principles................... 53 Objections to the Teruis..7 3552s bk Sere een scien eee 54 Interaction of the Four Principles:.20.). 2% 2400 - s ee e ee 55-78 Repeated Action of One or Combined Action of Several Principles. . 55 Importanceof Each of'the;Principles. 207 7 94)4.26 te 56 Two Methods of Generalizations, .< ccc circ feyers's ote sets nso hetero 58 Change/of Tradition in’ Chimney Swifts... 25.720 3.-220506-.2-. 6 59 Variation and Accommodation Two Methods of Adjustment....... 59 Conditions Suddenly or Gradually Encountered.................. 60 Accommodationiim Mant «2 2r-..2,. cede ee eproae cea eae ane 61 Endonomiuc Selection: 2 se 4.0 Puente c eo. te olsun elapse e nae 132 Tai GiSCrienl Nace PNCElOtc amie che cesck alcuey eh AER ore oe RI Atta 133 Contrastsrmduncin Ne tons ashlee ae ee 134 Table of Discriminate and Indiscriminate Modes of the Four PRINCl Plese ay es eee ene so Sie eh a alee rei Hee caren Gwe a Ss 136 viii CONTENTS Explanation of Plate II]. ....... 6... 60sec eee eee teeter eens 41 Oahu the Metropolis of the Achatinellida.............-....+-+--005- 42 Plate A. Map of the Hawaiian Islands. Plate I. Eight Genera of Achatinellide. Plate B. Map of Oahu, Hawaiian Islands. Plate II. Twenty-five Species of Achatinella. Plate III. Variation and Intergrading of Bulimella. Explanation of Plate B...... 22.105. serene eee bee rae seers 43 CHAPTER V.—THE FOUR SEGREGATIVE PRINCIPLES. Racial and Habitudinal Segregation% (5255 fo ae os sete eee eee 45-50 Interaction of Acquired and Inherited Characters................ 45 Sepregation.a Fundamental Paw S = the majority are dextral; S > D = the majority are sinistral; S— D coo = Sinistral with the exception of about 1 in 500. 5 NOTES ON THE SPECIES. Fic. 1. Carelia cocklea (Rv.) D. From the island of Kauai. Examination of the organs will probably place it with the Achatinellide. lic. 2. Amastra nucleola (Gould) D. From Waiole, Kauai. Fic. 3. Aurtculella auricula (Fer.) D > S. This species, like others of this genus, is found on the leaves of trees and shrubs. Its habitat is the eastern por- tion of the forest region of the island of Oahu. This specimen is from the valley of Palolo. Fic. 4. Apex apicatus (Nwe.) D> S$. From Wahiawa, Oahu. Also found in Helemano and Ahonui. Fic. 5. Leptachatina fjumosa (Nwe.) D. Found on the ground under dead leaves, in damp forest regions from Nuuanu to Palolo, on the island of Oahu. This specimen is from Palolo. Fic. 6. Laminella sanguinea (Nwe.) S. Found in Helemano and Wahiawa and the intervening regions on the island of Oahu. ‘This specimen is from Helemano. Fic. 7. Lamznella citrina (Migh.) S. From the island of Molokai. Fic. 8. Laminella tetrao (Nwe.) S. From the island of Lanai. Fic. 9. Laminella venusta (Migh.) S. From Lahaina, West Maui. Fic. 10. Laminella bulbosa (Gk.) S. From Kula, East Maui. Fic, 11. Partulina dubia (Nwe.) D. ‘This is a rare species distributed over a number of valleys of the island of Oahu from Waianae to Kalihi. This specimen EXPLANATION OF PLATE II. 24 is probably from Kalihi. No other species from the Hawaiian Islands seems to so closely resemble the Partula found on many of the islands of the Pacific. Still it must belong to the Achatinellida, for it completely intergrades with Partulina denstlineata, which presents the peculiar twist of the columella, the most constant shell-character of the Hawaiian family of snails.* Fic. 12. Partulina virigulata (Nwe.) D>>S. From the island of Molokai. Fic. 13. Partulina variabilis (Nwe.) S. From the island of Lanai. Fic. 14. Partulina splendida (Nwe.) D> S. From Lahaina, West Maui. Fic. 15. Partulina plumbea (Gk.) D. From Kula, East Maui; found on the trunks of trees several thousand feet above the sea level. Fic. 16. Newcombia cumingit (Nwe.) S. From Makawao, East Maui. Fic. 17. Amastra turritella (Fer.) D. Found on dead trees from Waiawa east- ward to Keawaawa, island of Oahu. This specimen is from Palolo. Fic. 18. Amastra violacea (Nwe.) D. From the island of Molokai. Fic. 19. Amastra magna (Adams) D. From the island of Lanai. Fic. 20. Amastra masterst (Nwe.) D. From Lahina, West Maui. Fic. 21. Amastra nigra (Nwe.) D. From Kula, East Maui. The Darwinian theory explains the unity of form in the different genera and species of one family by the theory that they are all de- scended from one original intergenerating stock. The diversity in the forms is explained as the result of variation, with diversity in the forms of selection produced by exposure to difjerent environments. In explain- ing the divergence in the genera of this family, I think, we shall come nearer to the facts if we attribute the diversity in the selection, to which they have been exposed for countless generations, to diversity an the methods of using the environment adopted by completely isolated groups. The divergence in many of the closely related species, found on the same species of trees in successive valleys on the same moun- tain range, is, I think, due to isolation and variation, without any dijjer- ence in the forms of selection. EXPLANATION OF PLATE II. This plate presents 25 species of Achatinella, a genus of arboreal snails found on the island of Oahu, and most of them confined to dis- tricts from 1 to 3 or 4 milesin extent. Achatinella is one of ten genera of the Achatinellide, of which there are between 200 and 300 species and over a thousand varieties, on this island only 40 miles long. Eight of these genera are given on Plate I, andoneon Plate III. This plate illustrates the relationship of species distributed in different valleys on the same island. The letter attached to each figure desig- nates the valley or small district in which the specimen figured was found. ‘The position of this valley or district on the island is easily * A careful comparison of the internal structure of this species with the struc- ture of the Partula of the South Pacific might perhaps reveal points of special interest in the relations of the two groups. 40 DIVERGENCE UNDER THE SAME ENVIRONMENT. discovered by reference to the map of Oahu preceding Plate II, where the same letters are used to designate positions. It will be observed that underscored letters are used to designate positions on the north- east side of the main mountain range, and that Roman letters are used to designate the positions on the southwest side of the same range. These are so arranged that the valleys indicated by the two forms of any one letter are nearly opposite to each other. The twenty-five species presented in this plate would have to be considered as one species if we accepted the statement that the find- ing of completely intergrading forms between two types proves that they are varieties of the same species. If, on the other hand, we adopt the statistical method of testing species,* these, and many more found in the forests of the same mountain range, will have to be classed as species. The collection of the species and varieties of this genus, made by me from 1850 to 1852, present a complete series of intergra- dations between the larger forms found on the trunks of the candle- nut tree in the eastern valleys of Oahu, and the small forms found on the leaves of the lobelia and other shrubs in the western valleys of the island, where groves of the candle-nut tree abound, occupied more or less by species of Bulimella, but neglected by the representatives of the genus Achatinella. Asno one will maintain that these most diver- gent types of the genus belong to the same species, the existence of such a series of intergrading links becomes a strong argument for the belief that divergent forms properly ranking as species have arisen from one original species, through the cumulative effects of variation codperating with a series of isolations, each isolation lasting for many generations before the next occurs. i The genera most characteristic of Oahu are Achatinella, Bulimella, and Apex; for, with the exception of two or three species of Achati- nella found on the island of Molokai, they are limited in their distribu- tion to thisisland. ‘Their distribution in the different districts of the island is probably due to the adaptation of Bulimella to a damp cli- mate, and of Achatinella to a region of dense shade, but of less rain, and of Apex to a comparatively dry climate. As regards rainfall, the northeast side of the main range catches the trade winds as they come from the ocean, and receives the heaviest fall; on the southwest side of the same range there is less rain; and on the shorter range, on the southwest side of the island, there is still less rain. In the first region we find Bulimella and a very few Achatinella; in the second region * The explanation of Plate III brings out the fact that the individuals represent- ing intermediate forms are very rare compared with those of typical forms. Sucb species meet the statistical test. EXPLANATION OF PLATE III. 41 both Bulimella and Achatinella in the shady valleys, with Apex on the comparatively sunny ridges; and in the third, several abundant species of Apex, and but one species of Bulimella, and but one of Acha- tinella, both of these being extremely rare. NOTES ON THE SPECIES. Fic. 1. Achatinella zonata (Gk.) S. From Pupukea. Fic. 2. Achatinella albescens (Gk.) S. From Pupukea. Fic. 3. Achatinella recta (Nwe.) 8. From Kawailoa. Fic. 4. Achatinella herbacea (Gk.) S. From Kawailoa. Fic. 5. Achatinella delta (Gk.) S. From Wahiawa. Fic. 6. Achatinella rhodorhaphe (Sm.) 5... From Wahiawa. Fic. 7. Achatinella pygme@a (Sm.) S. From Ewa. Fic. &. Achatinella ligata (Sm.) D. From Ewa. Fic. 9. Achatinella analoga (Gk.) 8. From Halawa. Fic. 10. Achatinella colorata (Rv.) S. From Halawa. Fic. 11. Achatinella adusta (Rv.) S. From Pauoa. Fic. 12. Achatinella castanea (Rv.) S$. From Pauoa. Fic. 13. Achatinella olivacea (Rv.) S$. From Pauoa. Fic. 14. Achatinella dunkeri (Cuming) S. From Makiki. Fic. 15. Achatinella producta (Rv.) D> 3S. From Makiki. Fic. 16. Achatinella buddii (Nwe.) S. From Makiki. Fic. 17. Achatinella johnsoni (Nwe.) S_> D. From Manoa. Fic. 18. Achatinella stewartiit (Green) D > $5. From Manoa. Fic. 19. Achatinella fuscozona (Sm.) S. From Manoa. Fic. 20. Achatinella trilineata (Gk.) S. From Palolo. Fic. 21. Achatinella varia (Gk.) 5 — D ao From Palolo. Fic. 22. Achatinella bacca (Rv.) D. From Paloto. Fic. 23. Achatinella plumata (Gk.) 5. From Waialae. Fic. 24. Achatinella diversa (Gk.) 5. From Waialae. Fic. 25. Achatinella abbreviata (Rv.) D. From Waialae. EXPLANATION OF PLATE III. The purpose of this plate is to illustrate the variations and inter- grading forms of closely related species of the Achatinellide. The 25 shells figured in this plate are found in the northwestern portion of the island of Oahu, and are regarded as belonging to four species, of which Bulimella ovata Nwe. is presented under ten variations, five being of the dextral form (see figs. 6 to ro), and five of the sinistral form (see figs. 11 to 15). Of these figure 10 is found in Hakepuu, and the rest in Kahana. Figures 1 to 5 are of Bulimella bulimoides Swn., found in Kawailoa; figures 16 to 20 are of Bulimella obliqua Gk., found in Kahana; figures 21 to 25 are of Bulimella rosea Swn., of which figures 21 to 24 are found in Wahiawa, and figure 25 is found in Helemano. Intergrading forms are found between figure 5 of this plate and Bulv- mella glabra Nwe.; between figure 8 of this plate and bulimella oomor- pha Gk.; between figure 15 of this plate and bulimella rotunda Gk. 42 DIVERGENCE UNDER THE SAME ENVIRONMENT. The relative numbers in which these different variations occur are roughly indicated in the following table, in which the numbers not inclosed in parentheses correspond with the figures in Plate III, while the number in parentheses below each one of these indicates approxi- mately the relative frequency in which it was found. 7 8 10 rT LZ I 6 7 ‘ 3 0) (200) (200) (200) (200) (100) (200) (200) (200) 2 3 + (200) (150) (100) (60) (; ~d aun Dee 14 15 16 17 18 19 20 21 23 24 25 (100) (60) (1) (200) (200) (200) (60) (30) (300) (45) (15) (15) The metropolis of Bulimella rosea is Wahiawa, where the most abundant type of coloring is seen in figure 22, which is snowy white with a pink lip. In Helemano district, the shells of this species are somewhat smaller, with the lip more frequently white, and the body of the shell not as snowy white as is usually the case in the metropolis. Figure 21 isa comparatively rare variety of B. rosea, white throughout and intergrading with B. ovata through a nearly white variety of the sinistral form of that species, occurring in Kahana in the proportion of perhaps one to a thousand of the normal specimens of the species. Again, in figure 16, we have a very rare form connecting Bulimella obliqua with Bulimella ovata. OAHU THE METROPOLIS OF THE ACHATINELLIDAS. The island of Oahu may be regarded as the metropolis of the Acha- tinellidz, for on this island we find 8 of the ro genera, while on Maui and Molokai together we find 7 genera, and on Kauai 3 genera. Suf- ficient attention has not been given to the land snails of Hawaii to enable us to give a full report; but I am told that there is an unusual development of Succinea on that island, while the Achatinellidz are but very meagerly represented. One explanation of the small devel- opment on the island of Hawaii of the family of snails which is so fully developed on the island of Oahu is found in volcanic eruptions, which on the island of Hawaii have from time to time destroyed the forests till recent years; while on the island of Oahu it is probably hundreds of thousands of years since such complete destruction of the necessary conditions of existence for these creatures has occurred. Di / ae ae en ‘an er j in ia 7 ie aa ie 7 Y ry i 7 7 nes? hiv it 1 ait MP ap tarl 5 ph ta" a oes | iy ; ‘t wé : PRs -44 anil j a7 : kt e.! ‘ meal ‘ ' : P] ; He © are | ( ; nef 5 ‘ ra te ed eq) J i ‘ nn sce a 0 a ae Peel, «fii Mer rs Caen 4 Hryeds Ter) Wei nit pets onl f q ‘oer UL as noe no farih ve 44; A } Oa ee nl a HOY Frei dy aby Fay wey Be 4h ahs < Remy Hl Asch tvprt Hiedle Si) me leaner (jd Dy i Bf a es , a 7 1h i ay j a 7 : hs ‘ ny J Sy ae 7 PLATE A. YPIMUZ 24D ZS) wou sam o BGI GS SS ee 6! fe : eyeyeuney n[nfouoyy "Iq Ndeyen om, uoquog oyoouny \% 4 09 or 02 “tq Pusey SJIUW 40 31V9S 9 PNperAy SANV ISI NVIIVMVH AWHIIN oO HO dvnt ADT mamnrmpyy Sonne Roe, }ivave 1 j@reury SS Za Ty Sar PLATE CGULICK INVNN ‘@ TOVIN “AA SONV1S] IVNVI 61 4Al4 WOUS AVGINIANILVHOYV JO VYAN3S5) LHOIW IVMO'TIOIN QIVO IVAVS Kahuku Pt. ISLANDS HAWAIIAN yw YROVNS fms SOOT NUN i ALITY FANNIN SVE DET \ Mokapu Pt. bY \) Wyre! awn Lahilahi Maun Pokat Bay Barbers Pt. GULICK PLATE || — — — 4 bi yb 2b DISTRIBUTION OF TWENTY-FIVE SPECIES OF ACHATINELLA FROM TEN YALLEYS GULICK PLATE III jd vd | % Ati ly moans Y an. | gh 10) 11h {2h 168 va 18h Loh 20h 25t 218 232 VARIATION AND INTERGRADING OF FOUR SPECIES OF BULIMELLA EXPLANATION OF PLATE B. AB LETTERS USED ON PLATE B, TO DESIGNATE THE VALLEYS AND DISTRICTS ON THE ISLAND OF OAHU. a, Waialei a, Kahuku. b, Pupukea. b, Malaikahana. c, Waimea. c, Laie. d, Kawailoa. d, Hauula. e, Opaiula. e, Kaliuwaa. f, Helemano. j, Waiolu. g, Wahiawa. g, Punaluu. h, Ahonui. h, Kahana. i, Kalaikoa. 1, Keawa. j, Waipio. 7, Hakepuu. k, Waiawa. k, Waikane. {Ew { Waimano. 1, Waiahole. , Ewa ; Waimalu. m, Halawa. m, Kaalaea. n, Moanalua. n, Kahaluu. 0, Kalihi. o, Heia } Abuimanu. ' Toleka. p, Nuuanu. pb, Kaneohe. q, Pauoa. r, Makiki. q, ¥, S, Kailua § Pohakunui. ( Olomana Peak s, Manoa. t, Palolo. u, Waialae. t, u, v, w, Waimanalo. v, Wailupe. w, Niu. x. Keawaawa. M, Mokuleia. L, Lehui. W, Waianae. {Italic letters in the second column are to be regarded as the equivalent of the underscored setters on the map.] CHAPTER V. THE FOUR SEGREGATIVE PRINCIPLES. I. Tue NEED oF A NOMENCLATURE DISTINGUISHING BETWEEN RACIAL AND HABITUDINAL SEGREGATION, 1. The Interaction of Acquired and Inherited Characters. The interaction of the factors producing racial segregation and those producing social or habitudinal segregation should, I think, be clearly recognized, and a suitable nomenclature used for presenting the same. Increasing attention is being given to this interplay of influences; but clear expression of the relations of the factors is con- stantly obscured by lack of terms for designating the processes of segregation relating to acquired characters or habitudes. In my paper on ‘‘Intensive Segregation”’ I emphasize the impor- tance of the forms of reflexive selection ‘‘due to the relations of the members of the same species to each other, and liable to change with- out any change in the environment,”’ and of active (or endonomic) selection ‘‘due to change in the successful use of the powers of the organism in dealing with the environment.’’ In another paragraph I say: ‘‘ Diversity in the uses to which different sections of one species put their powers when appropriating resources from the same envi- ronment must produce diversity in the forms of variation that are most successful in the different sections. This I call active selection as contrasted with passive selection, which varies according to differ- ences in the environment. All diversities of environal selection that do not vary according to differences in the environment must be classed as diversities of active selection, for they must have originated in some variation in the powers of the organism, or in the diversity of uses to which it has putits powers.’’* The power of the organism to determine industrial segregation is considered in my paper on ‘‘ Diver- gent Evolution,” read before the Linnean Society in 1887. In 1896, Professors Baldwin, Osborn, and Lloyd Morgan were inde- pendently led to consider the influence of individual powers of accom- modation in enabling representatives of a species to survive in an environment that would otherwise be fatal, and so ‘‘giving time to the species to develop coincident variations (7. e., congenital varia- * See Appendix II, Section I, 8, (4) and (18). 45 46 THE FOUR SEGREGATIVE PRINCIPLES. tions in the same direction),’** which are gradually accumulated by selection. Another point presented by the same writers is the conti- nuity of tradition, secured by training, suggestion, and example on the part of the parents and imitation on the part of the young. The effects of tradition have also been very clearly illustrated by F. W. Headley in his recent book.f I quote a few sentences in which he summarizes the effects of accommodation and tradition: The result is that among the higher plastic classes of animals evolution proceeds more rapidly. But obviously the quickening up of evolution is not all. The individual gains in importance. He improves his powers, is able to face a change of environment that otherwise would have been fatal. He makes an environment for his young in which intelligence can be developed; he chooses the environment which they shall have when out of the nursery, and so decides to some extent what qualities shall be the winning qualities in life. In fact, he is beginning to take the helm and steer the species. Or we may put it in this way: When the individuals of one generation decide the environment in which the next shall grow up, selec- tion ceases to be purely natural; it isin part artificial. These quotations are sufficient to show that there is increasing recognition of the fact that there may be changes in the organism that are not dependent on changes in the environment, and are there- fore not dependent on change in the form of the natural selection. In choosing terms for designating these processes I think we should care- fully follow Professor Baldwin’s suggestion ‘‘that selection in the Darwinian sense should be used only when the essential conditions of organic progress by survival are present, namely, variations and physical heredity.’’s In my own usage, selection has been applied only to processes secur- ing the survival of part of the variations of a race or species with the exclusion of other variations, and so.influencing its powers of heredity ; and isolation has been limited to the prevention of free crossing be- tween co-existing groups. In order to do this, and at the same time clearly present the principles controlling the evolution of habitudes, it has been necessary to find two terms that might hold the same rela- tion to innovation and tradition that selection and isolation hold to variation and heredity. The best words I have found are election * See letter from J. Mark Baldwin in Nature for April 15, 1897; also the same in Science for April 23, 1897, on ‘’Organic Selection.’”’ In this letter will be found references to discussion on the subject during the previous year in various books and journals. + Problems of Evolution, pp. 120-128. London, Buckworth & Co., 1900, and New York, Crowell & Co., 1901. t Problems of Evolution, p. 128. § See Science May 8, 1898. ‘The same limitation is also advocated in his Social and Ethical Interpretations, Appendix B. SEGREGATION A FUNDAMENTAL LAW IN THE ORGANIC WORLD. 47 and partition. The need of such terms will, I am sure, be recognized by many, though some may not consider the words I have chosen the best. 2. Segregation ts a Fundamental Law in the Organic W orld. One sphere in which it operates is racial (or aptitudinal) segrega- tion, produced by the intergeneration of individuals with like innate characters. Another sphere is social (or habitudinal) segregation, produced by the association with each other of individuals with like acquired characters. Segregate generation (i. e., the generation of like with like), 7s a condition on which the present structure of the organic world depends. Without segregate generation the differences of races, species, genera, and the higher groups could never have arisen, and if it were possible that it should cease, all these distinctions would ere long be obliterated. The fact that race characters are hereditary renders it certain that freely intergenerating races will, in a few generations, become one race. But the fundamental nature of the organic world is such that the only cases in which the law of segre- gation can be broken down are those in which the divergence is com- paratively small. When amalgamation takes place it is usually varieties of the same species that unite. When physiological incom- patibility has once been fully established, the segregation is never broken down; but, on the other hand, as long as there is any plasticity in a race, it is possible that new segregations may be introduced and one race divided into two or more races. Having observed that segregate generation is the fundamental principle by which the world of sexually reproducing organisms is maintained, and having discovered that the art of breeding, by which the multitude of domestic races has been produced, rests on the control of segregate breeding, we propose to make careful investiga- tion of the different forms of control influencing this principle and of the effects thus produced. As an equivalent for segregate generation (or the breeding of like individuals with like), Romanes has proposed the term ‘‘homogamy.”’ An objection to its use in this meaning is, however, found in the fact that in botanical language the same term has a somewhat different meaning. It should be noted that this statement concerning the breeding of like with like does not imply that creatures freely mating with each other are entirely free from differences. Of multicellular organisms no two were ever found to be exactly alike; if, therefore, there is any mating of these creatures, it must be the mating of creatures that are not completely the same, either in structure or function. The 48 THE FOUR SEGREGATIVE PRINCIPLES. point is that the greatest difference existing between any form of organisms and any other form that is capable of crossing with it, is very small compared with the differences presented by the vast world of organisms that are incapable of crossing with it. Cross- fertilization secures the blending of elements from individuals that are more or less divergent; but the degree of divergence that may exist without resulting in sexual incompatibility, either physiological, morphological, or psychological, is very small compared with the divergences that lie beyond the limits of compatibility. Again, we find that in some cases species incapable of crossing are so similar in visible characters that the naturalist finds difficulty in distinguishing them. 3. Segregate Association,* a Fundamental Law on which the Social Structure of Each Species that is not wholly guided by Instinctive Aptitudes must rest. The necessity of a common language for a social group will be rec- ognized by all. There must be a system of signs or signals by which the members of one group may call to each other when they wish to come together, may warn each other of approaching danger, and may in other ways codperate in securing the sustenance, protection, and propagation of the group. If these signs are not instinctively made and instinctively understood, they must depend on suggestion, train- ing, and imitation; and this suggestion, training, and imitation is made possible by the association maintained by the social group. It is a universal fact that the social characteristics of individuals of the same associating group are gradually unified by association. Again, it is certain that a group of freely associating and freely intergenerat- ing individuals of different races of mankind will in time become assimi- lated in language, manners, and customs, and finally in race, however different they may have been when first brought together. The blending of two strongly marked species is usually prevented either by instinctive aversion, by unfruitful crossing, or by the sterility of the hybrid offspring, as in the case of the mule; while the blending of two civilizations is liable to be prevented by the superior power of one completely overshadowing the influence of the other. Moreover as long as racial barriers are not broken down, distinctions of social types are not often wholly obliterated. This is naturally the case as long as the training of the young, and so the transmission of tradition, remains chiefly with the parents. Segregate association, that is, the association of like with like, is the fundamental factor in the production of habitudinal segregations; * That is, the association with each other of individuals with like acquired char- acters. THE INTERACTION OF RACIAL AND SOCIAL EVOLUTION. 49 and, as will be more fully explained in another chapter, it is brought about by the codperation of habitudinal demarcation through parti- tion, and habitudinal intensification through election. The methods of this election are first through the different forms of approval and disap- proval used in training the young, and second through the promotion and wide influence given to individuals attaining the highest recog- nition of public opinion and the suppression of individuals falling below the lower limits set by the laws and customs of the community. Divergent forms of civilization can neither be established nor main- tained without the continuous operation of segregate association. For designating the effects of segregate association I often use the term ‘‘habitudinal segregation”? rather than ‘‘social segregation,” because in creatures entirely guided by instinct there may be elab- orate forms of social organization, and therefore forms of social segre- gation, that rest mainly, if not entirely, on racial characters produced by racial segregation; while under “ habitudinal segregation’ I wish to consider the evolution of acquired characters under the operation of segregate association. If ants and bees learn by training and imita- tion incorporated in traditions, then the growth of their social organ- izations should be treated under this department of segregation; but, if not, then their evolution, both physical and social, comes under the department of racial segregation. 4. The Interaction of Racial and Social Evolution must be considered. The interaction of racial and social (or habitudinal) evolution and the exposition of the laws regulating the same, by which man is to gain control of his own evolution, is the broad sphere in which the biology and sociology of the future will expand. Ward, Giddings, Baldwin, and other Americans are exploring this field, and in Europe the trend is in the same direction, if I judge rightly. The nomen- clature which I propose and illustrate in the following pages will, I think, aid in discussing the problems of biology and sociology that are now coming to the front. I should not have had the patience and courage to attempt to present a scheme for so wide a field if I had not seen the pressing need for such a method from the side of biology. I also believe it will be a great advantage for sociology if a harmonious and correlated nomenclature can be brought into use in both biology and sociology. Some sociologists, recalling the nomenclature and exposition introduced by Herbert Spencer on the basis of an assumed correspondence between the biological and the social organism, will instinctively shun the use of a terminology that suggests a correspon- dence and interdependence between the two spheres of evolution. There will, however, be others, who have come into sufficiently close 50 THE FOUR SEGREGATIVE PRINCIPLES. contact with the problems of evolution, in both realms, to realize that great illumination for each will be found in the study of the interac- tion between the two realms. Those who are doubtful concerning the interaction of the two spheres will gain light from Baldwin’s Social and Ethical Interpretations and his Development and Evolu- tion, and from the discussions on organic selection given by Osborn, Baldwin, and others in Science and The American Naturalist during 1896-98. 9 8 7 : 5 4 ca oe | ¥ Dee e ee See or ae 8 | 14 | 20 | 2 | 32 38 | 43 | | - Z 9 8 7 6 5 4 3 2 1 eg eS =P 0 10 20 30 | 40 | 50. 60 70 80 | om il _ 9 8 7 6- 5 40 co 2 ' ig 90 790 | 200 | 390 | 490 590 690 790 890 Bhs wl + 9 | 8 7 6 | _5 4 ns bo 1 Te ='s550' eM EHP ™ | 65 | 1990 | 2990 | 3990 | 4990 5990 6990 7990 | 8990 * Formulas (1) and (2) were given in my paper on Divergent Evolution (see Appendix I). 106 ANALYSIS OF THE FOUR PRINCIPLES. Method of Testing Table A. Let M=10; m=7; c= 7 then © according to the table. P — NONI We now place under pure-breeds any number, and under cross- breeds 34 times that number. Pure-breeds. | Cross-breeds. 5 In nth generation, 2 | In nth generation, 7 | f (n+ 1)th “ = 2(M — Mc)'= 15 | In (2+ 1)th gen., 49 + Z i (n+ 2)th “ ) ( 2(75)") (424 (15x) ) ' Le = 12h |) Se Wis oe = 2(M — Mc)? \ / : 2(56.4) \ = 343 + 244 a 264 2 Starting with the fraction Z given in Table A, as correct for the a nth generation, we find that p= =f is correct for all subsequent gene- rations; and this proves the formula to be correct. If the denominator of the fraction representing the value of = is o, or less than 0, the disproportion increases with each generation; that is, cross-breeds become the overwhelming element. In this case by which we are testing the correctness of Table A, suppose the pure-breeds to be 2 and the cross-breeds to be 7 in the generation with which we commence. In the next generation, which we designate as the (n + 1)th generation, the pure-breeds will be 2x (M —Mc)!=2 | 10 — 2 = 15. In the (n+ 2)th generation the pure-breeds = 2 X (M — Mc)? = 2 X (7.5)?:= 112.5. The enae-tveede in the (n+ Sih generation = 7 X the cross- breeds of the previous generation, plus 7 < one-quarter of the pure- breeds of the previous generation = 7? + f In the (7 + 2)th gen- eration the cross-breeds will be 7 x the cross-breeds of the (m x 1)th generation, plus 7 * one-quarter of the pure-breeds of the (n + 1)th generation = 73 + is + [ 35» tS x <7] = 203275: \2 USE OF THE TABLES. 107 16. The Use of the Tables. The first object of this computation is to show that a partial posi- tive segregation that is ineffectual in preserving a new variety from the swamping effects of crossing becomes very effectual when a mod- erate degree of segregate fecundity codperates with it. It should be observed that when considering partial segregation codperating with segregate fecundity I assume that the two varieties that are compet- ing on the same area are equally adapted to the environment, and that the action of other principles is equal in each, in order that I may © compute the effects of the two factors under consideration when free from disturbing influences. It has been objected that, according to my Table I,* the eighteenth generation is many thousand times larger than the initial number, which is not the usual result under the condi- tions surrounding natural varieties. In reply I would say that even in natural varieties it is not at all impossible that the number should double with each generation for at least a few generations, especially when a variety has gained the use of resources heretofore unused, and that for the purpose of showing the ratio in which half-breeds and pure-breeds stand to each other it is entirely immaterial whether we assume that the number that arrive at maturity are the same in each generation, or that each successive generation is nearly double that of the preceding generation. But does not the assumption that the ratio of cross-breeding re- mains the same in successive generations vitiate the whole computa- tion and render it worthless? I think not. My contention is that when segregate fecundity comes to the aid of such a principle as pre- potential segregation (which is only partial in its action, and therefore by itself unable to prevent swamping), the result is the progressive action of both principles in each successive generation. But before we can show how this cumulative action arises we must have some formula for showing.the natural result of any given degree of segre- gation combined with a given degree of segregate fecundity; and the proper formula for this purpose seems to be the result that would be reached, if the principles should continue at the given degrees for a considerable number of generations. Take for example the case represented in Table I.* What is the -tatio between half-breeds and pure-breeds that most truly represents the case? Shall we go to the end of the first generation and say that, aoe or go to the eighteenth generation and find that = * See my paper on Divergent Evolution, Appendix I. 108 ANALYSIS OF THE FOUR PRINCIPLES. Undoubtedly the latter is the one we need to represent the result toward which the given conditions tend, though before the eighteenth generation is reached the degree of segregate breeding will have become more stringent. Having obtained a formula giving the results that would be reached if the ratios of cross-breeding and of attendant infertility were con- tinued at a given level for a number of generations, we next inquire whether there is any reason to believe that the degrees of segregate breeding will become more stringent in successive generations, and whether the infertility of cross-breeds will be increased. 17. Cumulative Segregation Resulting from Segregative Endowments. Let us consider a partially segregated variety of a plant species in which there is some variation in the segregative endowments. We will suppose that the species is one whose pollen is freely distributed by the wind and whose stigma is susceptible of fertilization for ten hours. Though the individuals of the new and partially segregated variety are very few as compared with the original stock, yet the pollen of the new kind reaches every stigma of the same kind before the ten hours of its susceptibility have passed, while pollen of the original kind, be- ing far more abundant, is sure to reach every stigma soon after their flowers have opened. The positive segregation of the new variety we wiil suppose is se- cured by prepotence of the pollen of the variety on the stigmas of the same variety, one variation being prepotent for about five hours, with the result that one-half of the individuals breed pure and one-half are crossed; that is, c=4; while another variation is prepotent for about 63 hours, with the result that two-thirds of the individuals breed pure and one-third are crossed; that is c = 4. The negative segregation of the new variety we will suppose is se- cured by segregate survival; for the pure-breeds, through different degrees of adaptation to the new station, enjoy different degrees of success in leaving offspring that come to maturity, the less adapted variations being multiplied by 1 in each generation, and the better adapted multiplied by 2 in each generation, while the cross-breeds ar» so lacking in adaptation as to be multiplied by + in each genera- tion. We therefore have two values for M, each occurring under c=4, and again under c= 4. In one variation we have M=1, and m=+,the proportion being as M = 10, and m~2; and in the other variation we have M = 2,and m= +, the proportion being as M = 10 and m = 1. CUMULATIVE SEGREGATION THE RESULT. 109 Solution reached by means of Table V.—\ooking in Table V,* we find that when c = 4, and M ~ 10, (var. 1) then with m = 2, half-breeds pure-breeds x 2; (var. 2) and with m 1, half-breeds = pure-breeds = ii F that when c = 3, and M = (var. 3) then with m = 2, half-breeds - pure-breeds X (var. 4) and with m = 1, half-breeds = pure-breeds + Now, it is evident that the ee on the next generation of the variation marked as var. 4, which is the most highly segregated, will be much greater than that of any other one of the variations. Solution reached by means oj Table A.—If we consult Table A, w shall find an equal contrast, for it gives for (var. 1) cross-breeds — pure-breeds * 2 (var. 2) cross-breeds = pure-breeds « + (var. 3) cross-breeds = pure-breeds X 2 (var. 4) cross-breeds = pure-breeds Solution reached by direct computation.—A sinnitte conclusion may be reached by computing the result for a few generations. Let us suppose that for one-half of the new variety the average prepotence allows one-half of the individuals to form cross-unions, and that for the other half of the variety the average prepotence allows only one- third of the individuals to form cross-unions; and also that one-half of each of these variations is so adapted as to multiply by 2 in each generation, while the other half multiplies by 1. As in the previous computation cross-breeds are multiplied by + in each generation. Let us now assume that in a given generation there are 1,000 indi- viduals in each of these variations, and what will be the number of pure-breeds of each of the four variations that will come to maturity in the next generation, and a the number of cross-breeds? In var. 1,c =4, M=1, m=; (1. e., pure-breeding 500; crossing SOQ); a" pure-breeds 500; fall bieeds 100. In var. 2, c= el M=2, m=+4; (@. e., pure-breeding 500; crossing 500), .. pure-breeds case half-breeds too. In var. 3, c= 4, M=1,m=4; (t. ¢., pure-breeding 666; crossing 333), -'. pure-breeds 666: half-breeds 66. In var. 4, c= 31, M=2, m= 1; (0. e., pure-breeding 666; crossing 333), ... pure-breeds 1,332; half-breeds 66. The sum of the pure-breeds of all the variations 3,408. It will be observed that in one generation the pure-breeds have decreased from 4,000 to 3,498; that is, their numbers have dimin- * See my paper on Divergent Evolution, Appendix I, 1IO ANALYSIS OF THE FOUR PRINCIPLES. ished one-eighth. In the second generation the result will be quite different; for variations 2 and 4 already constitute two-thirds of the whole number of pure-breeds. Second Generation— Pure-breeds. Of variation . . : : : : : : 250 Of variation 2 . : : ; : : : ; 1,000 Of variation 3. ; ; . : : : ; 444 Of variation 4 . : ; : . : : , tT. 776 3,470 In this generation the decrease is only 28 individuals, or about ;4. Third Generation— Pure-breeds. Of variation . i : : ; F ; ; 125 Of variation 2. : : : : ; 3 : 1, 000 Of variation 3. ; ; . : . F : 296 Of variation 4 . : : : : . . : 2, 368 3, 789 In this generation there is an increase of 319 individuals, or a little over ;. Fourth Generatton— Pure-breeds. Of variation: . : : . . ; : . 62 Of variation 2. : : : : : ‘ : 1,000 Of variation 3. ; : : : : : : 198 Of variation 4. : , . : : . : 3,156 4, 416 In this generation there is an increase of 627, or of nearly }. Tenth Generation— Pure-breeds. In variation1 . : ; . : : : : 0.98 In variation 2. : ¢ F ‘ : ; ; I, 000 In variation 3. : : . : . : : 16 In variation 4. , . . : , : = 17,759 18,775 Var. 4, of Tenth Generation = 1,000 (1.33334)'° computed by logarithms. We therefore observe that in the tenth generation variation 1 has become less than 1, and variation 4 has become the predominant type. For the next ten generations the average positive segregation will be advanced, (1) by the preponderance of variation 4, and (2) by the fact that the new variety occurs in much larger masses than at the beginning of the computation, and will therefore be less exposed to cross-fertilization. Now that the mass of pure-breeds is increased more than fourfold, it is reasonable to suppose that the ratio of pure-breeding advances. INSTITUTIONAL AND PRUDENTIAL SELECTION. Dit We may also assume that increased segregate fecundity and vigor will make the multiplier for pure-breeds = 2, and the multiplier for cross-breeds = ,. And when another ten generations have passed, still higher degrees of segregation will be the natural result. Conclusion.—We have now approached in three different wavs the proof of cumulative advance in a set of innate qualities, which by their combined action produce in moderate degress both positive and negative segregation. The result seems to be that when M/ by any chance comes to be larger than A/c + m, then the fraction b § mc : , 2 -, which gives the ratio of cross-breeds to pure-breeds,* M—Mc—m becomes a positive quantity, and a given proportion of the whole stock remains unaffected by crossing. This point having been reached the subsequent tendency is toward a constant increase in the segre- gative endowments. 18. /nstituttonal and Prudential Selection. Institutional and prudential selection stand in the same relation to the other forms of reflexive selection that artificial selection holds in relation to natural selection. They are the forms of reflexive selec- tion established in communities of rational beings for the purpose of securing ends that are more or less fullv apprehended as the goal. It should be observed that inherited instincts have an important part in each of the forms of conjunctional selection, that is, in sexaal, social, and filio-parental selection; and again in the forms of impreg- national selection and impregnational isolation just discussed, the coordinations are due to inherited characters, either morphological or physiological; but in institutional and prudential selection the processes are guided by conscious and reflective purpose. It will, therefore, be seen that the conscious regulation of relations between husband and wife, between man and man, or between parents and children, when it affects the form of survival, belongs to either insti- tutional or prudential selection, and not to conjunctional selection in any one of its three forms. In the past history of man the three forms of conjunctional selection have been of prime importance; but as civilization advances increasing control is given to institutional and prudential selection. Moreover, in the case of civilized man, domina- tional selection through intra-group struggle has in a large measure ceased to be a struggle for life or for the opportunity to have a full share in producing the next generation, and has become chiefly a struggle for influence in society and for escape from certain forms of *See Formula (4), on page 105. DE2 ANALYSIS OF THE FOUR PRINCIPLES. drudgery. If degeneracy is threatened, the remedy will not be found in restoring the conditions of savage life, in which the imbecile and the insane, the deaf and the diseased, are all eliminated by starvation; but rather by such forms of institutional and prudential selection, enforced by public opinion and law, as will prevent the marriage of those who are specially liable to have defective offspring. It thus appears that institutional selection and prudential selection, both of which may be subjected to rational control, are the chief factors by which man may hope to maintain and control his own evolution. The powerful influence of institutions on human evolution will be recognized by those who consider the effects that must be produced on the vigor and vitality of a nation when military organization and destructive wars prevent many of the most vigorous men from having anv share in producing the next generation, while many others who leave children are suddenly removed by death when their families most need their aid. Again, the institutions in which the community combines for the maintenance of justice and order and the training of the young must have a profound influence on the physical inheritance of the race, through the advantage it gives to the peaceful and law- abiding. In the evolution of civilized man the law of natural increase is liable to be set aside in a way that often becomes extremely abnormal. I refer to the effects of prudential selection in limiting the size of families, both by delaying marriage and by restraint after marriage. Of course, both methods of using the reason are legitimate if the end sought is not a selfish desire to be free from care and responsibility. The evil has grown to such proportions in certain communities that the very existence of these groups is threatened. The fundamental difficulty seems to be that public opinion has failed to set before the men and women of force and character—before those who are the back- bone of the nation—the double ideal of maintaining a vigorous life and civilization during their own generation and of transmitting the same to a posterity of unabated vigor and of high native character, as well as of high training and culture. It is impossible that this standard should be attained if there is unwillingness to establish family relations until the battle of life has been fought out and won. Nor can it be realized if after marriage those who should become parents wish to reserve the chief portion of their energy for social entertainments or for the pleasures of art, science, literature, and travel, with no consideration of how these great gifts of past genera- tions can be best transmitted and rendered continuously progressive INSTITUTIONAL AND PRUDENTIAL SELECTION. I13 in the hands of those who are capable of receiving, maintaining, and transmitting the same.* This factor is probably having a profound influence on the present evolution of the most highly civilized nations. In his volume on The Chances of Death, Karl Pearson says in a note (see p. 83): Mr. Francis Galton tells me that he was recently informed by credible medical authorities in Paris that the French population is becoming Breton, owing to the fact that this element of the population does not limit its fertility to anything like the same extent as other elements. Nearly all large families are found to be of Breton extraction. Similar changes of population are taking place in New England and in other countries, and in some of these cases the cause is probably the one we are now considering. The continuance of any human race depends not only on its power to produce vigorous and adapted off- spring in sufficient numbers, but on its willingness to exercise this power and to assume the heavy responsibilities of rearing and train- ing the young. If the Bretons are willing, and persist in being willing, France may become their inheritance: if they give way, the inheri- tance will pass to others. But the French are not the only people that are threatened by this selfish individualistic civilization. Its blighting effects are apparent among the professional and commercial classes in other countries. The statistics obtained by Karl Pearson, some relating to families of Anglo-Saxon extraction and others relat- ing to Danish families, do not give the proportion of the same classes that remain unmarried; but careful analvsis of the facts given leads him to remark: There are clear traces in the statistics of some special action influencing fertility in families with between 3 and 7 children. * * * It is noteworthy also that this characteristic is less marked in statistics drawn from pedigrees than in more recent natal statistics. I can not, therefore, avoid the conclusion that the dip between 3 and 7 is not due to compoundness; that its origin is comparatively recent, and that it is an artificial break in the natural smoothness of the curve of fertility. I believe it to be entirely due to a Malthusian restraint on population. Families which reach 7 and over appear to be those in which no check is placed on the ‘‘natural’’ growth. Below 7 there is a tendency to restraint which is * Since this paragraph was written Mr. Francis Galton has delivered the second Huxley lecture of the Anthropological Institute (of London), in which many suggestions are made for reversing the present unfavorable action of prudential selection. The lecture is entitled ‘‘The Possible Improvement of the Human Breed under the Existing Conditions of Law and Sentiment,” and is published in ‘‘Nature’’ Oct.31, 1901. In his view the high racial development of the most gifted fiftieth part of the human race is of more importance than the suppression of the lowest type, though he recognizes both methods as needed for reaching the best results. II4 ANALYSIS OF THE FOUR PRINCIPLES. marked by a transference of frequency from families which should lie between 4 and 7 to those lying between o and 4. * * * While the theoretical curve will be found to give only 6 to 8 per cent of marriages without issue, we find in modern statistics 11 to 18 per cent of marriages with no issue * * * and this even in countries like England and Denmark, where restraint is not usually supposed to be so prevalent as in France.* Again, he remarks: ‘‘The prudential restraint on marriage and parentage in the more educated members of the community, which we are apt to regard as a social virtue, may after all have its dark side.’ 19. Institutional Election, Partition, and Isolation. Institutional election arises through the influence of public opinion giving prominence, influence, and success to individuals who conform most fully to the social standards of justice and propriety; and is rein- forced by the law which puts a definite check on individuals whose actions fall so far below these standards that the community will not tolerate the offenders. Again, each community has its language, its industrial methods, its arts and sciences, and its forms of etiquette, which must be transmitted by tradition from generation to generation, for these attainments can not be transmitted by racial heredity, and their continuance in the community depends on example, education, and training on the part of the older generation, and on the part of the younger generation imitation, study, and practice. Now, insti- tutional election includes the superior success and influence of the individuals who attain the most complete equipment in these acquired characters that belong to the community. Institutional partition arises when local isolation and partition has resulted in divergence in language, religion, and education, preventing the possibility of association in one community when local isolation and partition has ceased. Institutional isolation.—Again, the differences in language, religion, and education, which prevent free association, will also prevent free intermingling of race, and the result is institutional isolation. Exam- ples of institutional partition and isolation are seen in the Mohamme- dan and Christian communities occupying the same regions in Turkey. * See Chances of Death and Other Studies in Evolution, pp. 67-69. qibid., p. 102. CHAPTER VIE. ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED), I. THE METHODS OF THE ENVIRONAL MODE OF EACH PRINCIPLE, WITH THE FORMS OF EACH METHOD. Producing demarcation of habitudinal Producing intensification of habitudinal groups: Environal partition. Endonomic partition, Industrial partition. Migrational partition. Heteronomic partition. Transportational partition. Geological partition. Artificial partition. Producing demarcation of racial groups: Environal isolation. Endonomic isolation. Industrial isolation. Chronal isolation. Seasonal isolation. Cyclical isolation. Migrational isolation. Heteronomic isolation. Transportational isolation. Geological isolation. Fertilizational isolation. Artificial isolation. groups: Ienvironal election. Endonomic election. Habitudinal election. Aptitudinal election. Heteronomic election. Natural election. Artificial election. Producing intensification of groups: Environal selection. Kndonomie selection. Habitudinal selection. Aptitudinal selection. Heteronomice selection. Natural selection. Artificial selection. racial Having completed our analysis of the methods and forms of the reflexive mode of influence, we will now briefly survey the forms of the environal mode. Under each or the four principles, when we find that the relations between the group and its environment are determined by conditions within the group, we call the influence endonomie selec- tion, election, isolation, or partition, as the case may be; or if the relations are determined chiefly by conditions lying outside of the group, we then speak of the influence as heteronomic. 1. Environal Selection and Environal Election. Environal selection, as we have just seen, may be either endonomic or heteronomic. Divergent forms of endonomic selection often arise through divergent habitudes or aptitudes of the individuals starting the isolated colonies, or through the accidents attending the entrance oj small groups into isolated i15 116 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). districts presenting the same environment,—In my paper reproduced in Appendix II of this volume I have emphasized the fact that it is true of a very wide range of species that any one species distributed in small sections in several isolated districts, presenting the same envi- ronment, will often use the environment in different ways, and so be subjected to different forms of selection. Selection thus determined by the relations in which the organism puts itself to the environment I call endonomic selection. We shall here consider in fuller detail the different conditions that may produce divergent forms of selection in isolated groups, exposed to the sameenvironment. Let us first consider cases in which the isolated groups are very small, and from a species with many variations through adaptations to a complex environment, and in which the new dis- tricts to which they are brought present the same environment as is found in the original home of the species. That the conditions may be clearly apprehended, let us suppose that we are considering a species of Hawaiian tree-snails on the southwest side of the main mountain range of Oahu, confined to the shady groves of a single val- ley, shut in on either side and at the head of the valley by high ridges covered with open brush, and at the mouth of the valley bv grassy slopes that extend to the sea. This snail lives continuously on the trees, clinging to the trunks and large limbs of five or six species, and presents many variations of color and some divergences in acquired habitudes according to the species of tree on which it has lived. If for many generations a certain strain should live entirely on one species of trees (perhaps occupying a single grove which includes no other trees), it would present innate aptitudes for that kind of life, devel- oped by selection. Now, suppose that by some very rare accident a man, bearing a branch of a tree, unconsciously transports a single impregnated individual of this species of snail into the neighboring valley on one side, and within a few years a similar occurrence carries another individual of the same species, but occupying another kind of tree, into the valley on the other side. Each individual has occu- pied but one kind of tree for its whole life, and having formed habi- tudes strongly favoring the kind it has so far used, seeks and finds the same kind in the new district to which it has been brought. As there is no pressure of population in their new and previously unoccupied districts, the descendants of each remain for a hundred years or more in the grove in which the first comer settled down; and the two colo- nies have, perhaps for a hundred generations, been subjected to some- what divergent forms of selection; for the habits of feeding have been different, and there has been no crossing between those of different ENDONOMIC AND HETERONOMIC SELECTION. 1 7 habits, as was the case in the original home. This is an illustration of what I call ‘‘habitudinal selection.’ We shall next consider an illustration of aptitudinal selection, which will be gained by changing the illustration just given at one point. Instead of taking the two individuals which start the two colonies from those which for a genera- tion have been feeding on different kinds of trees, we must take them from two separate strains which have, for many generations, had their separate methods of feeding, so that not only their habitudes but their aptitudes must be somewhat different. Again, we may consider conditions that would produce what we might call ‘‘acc?- dental selcction.”” This might occur if the two individuals starting the two colonies were from the same strain and had both of them gained various experiences by feeding on different trees, so that their habits were not fixed. One of them we will suppose was brought by accident to a fine grove of candle-nut trees in the new district, and for a hundred years finds no cause to go elsewhere; while the other one, in another valley, is brought to a grove of what the Hawaiians call ohia trees, and there remains for an equal number of years. Is it not certain that the selection will be somewhat divergent; and to what determining cause shall we attribute the divergence if not to accidents that started these individuals of varied attainments in separate colo- nies, and in groves of different kinds of trees? As the valleys are near together and on the same side of the mountain range, the rain- fall and other features of climate must be essentially the same. If the creatures under consideration were insects endowed with higher powers for exploring the environment, I recognize that accidents of the kind here suggested would have little or no effect in determining the forms of selection; for, in such cases, slight differences of aptitudes or habitudes would be sure to control the method of using the environ- ment. Moreover, such species would not fall into isolated groups through their occupying separate valleys. When an isolated individ- ual or pair deals with an environment possessing resources that are varied but familiar and easily explored, previous habitudes and apti- tudes are the chief factors controlling the methods of using the environment. If the power of using different resources is great and the power of exploration small, the method of using the envi- ronment may be determined by the kind of resources first reached on entering the district. Heteronomic selection is of two forms—natural selection, produced by conditions in the environment that are independent of any purpose to control the forms of survival, and artificial selection, which is deter- mined by more or less distinct purpose to control survival. If in the 118 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). case of the snails just considered some of them are brought to groves on the northeast side of the mountain range, they will be exposed to a somewhat greater rainfall, and will probably be subjected to some change through the resulting selection. Again, suppose a colony is planted on either side of the range, in a valley where but one kind of shade trees is found, and this a kind that has never before been occu- pied by the species. In both these cases we should have heteronomic selection of the form that has been called natural selection. If any of these snails should be discovered by man to be good for food or medicine, and should be subjected to selection for the purpose of improving the qualities sought, the result would be heteronomic selection of the artificial form. Environal election corresponds with environal selection in the general influences by which it is shaped; but it differs in the results produced, for it relates to the intensifying of habitudes and acquired characters within the associating group. The higher the grade of intelligence the more marked are the changes and divergences intro- duced by acquired habitudes and characters, and accordingly, in such cases, endonomic election becomes the leading factor by which some new adjustment to the environment is developed into an established method of sustaining life; and if the inherited endowments are not in complete accord with the new life, coincident selection carries the adjustment to higher degrees; for variations favoring the conditions imposed by the new tradition will have the advantage. Examples of endonomic election preceding and introducing coincident selection are seen in the tree-climbing rats mentioned above,* and in the cats that have taken to wading and fishing.t Heteronomic election is either natural or artificial. Avrtzficzal election is seen in dogs and other domestic animals that have been subjected to training. Natural election is seen in the case of the chimney swift, which, in a large meas- ure, having lost the hollow trees in which it used to build its nests, has been forced to find a substitute in the chimneys built by the intruders who cut down its trees. The new habit is undoubtedly being reinforced by instincts gradually established by coincident natural selection. 2. The Methods of Environal Isolation. Endonomic isolation.—lt is evident that, when varieties of the same species of plant occupying the same areas are prevented from crossing by flowering at different seasons, the process which I call seasonal isolation is rightly classed as a form of endonomic isolation. The * See page 101. T See pages 67-68. INDUSTRIAL ISOLATION. 119 same is true of the cyclical isolation between two broods of the period- ical cicada when occupying the same district.* | As each brood lives nearly seventeen years burrowing in the ground, and then spends the few last weeks of its allotted life above ground breeding in the trees, it never hasa chance to cross with the other brood, whose time for breed- ing comes on another year, and each seventeenth year thereafter. f Industrial isolation and mtarational isolation, so far as they are deter- mined by diversity in the habits or instincts of the members of the species, must also be classed as forms of endonomic isolation. Heteronomic rsolation.—In the four remaining torms of environal isolation, namely, transportational, geological, fertilizational, and artificial isolation, heteronomic influences must prevail. 3. Industrial Isolation. Industrial isolation is isolation arising from the activities by which the organism protects itself against adverse influences in the environ- ment, or by which it finds and appropriates special resources in the environment. The different forms of industrial isolation are sustentational, pro- tectional, and nidificational isolation. For the production of industrial isolation it is necessary that there should be, in the same environment, a diversity of fully and of approx- imately available resources more or less separated, and in the organ- ism some diversity of adaptation to these resources, accompanied by powers of search and of discrimination, by which it is able to find the resources for which it is best fitted and to adhere to the same when found. The relation in which these causes stand to each other and through which they produce segregation may be described as separation according to endowment produced by endeavor according to endow- ment. From the nature of the process it produces segregation; for those of like aptitudes are brought together. It is evident that if initial variation presents in any case a diversity of adaptations to surrounding resources that can not be followed without separating those differently endowed, we shall have, in the very nature of such variation, a cause of segregation and of divergent evolution. Some slight variation in the digestive powers of a few individuals makes it possible for them to live exclusively on some abun- * For a full statement see U. S. Department of Agriculture, Division of Ento- mology, Bulletin No. 8, and Bulletin No. 14, New Series, 1898. + For a comparatively full account of the different broods of this species, and the problems raised by the remarkable facts, see Appendix IT, Sec. I11, 3. 120 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). dant form of food, which the species has heretofore only occasionally tasted. In the pressure for food that arises in a crowded community these take up their permanent abode where the new form of food is most accessible, and thus separate themselves from the original form of the species. These similarly endowed individuals will, therefore, breed together, and the offspring will, according to the law of divergence through segregation, be still better adapted to the new form of food. \Vhen other forms of isolation arise, they may be entirely independent of change in the environment, the only change being in the forms or functions of the organism. This special form of segregation is as dependent on psychological causes which guide the organism in finding and in adhering to the situation for which it is best fitted as it is on the initial divergence of the more strictly physiological adaptations by which it is able to appropriate and assimilate the peculiar form of resource. In the case of freely moving animals the psychological guidance is an essential factor in the success of the individual, while in the case of plants and low types of animal life the suitable situation is reached by a wide distribution of a vast number of seeds, spores, or germs, and the same situation is maintained by a loss of migrational power as soon as the germs begin to develop. In these lower organisms it is evident that the success of the individual must depend on its physiological rather than on its psychological adaptations; and if variation results in a slight difference in the kinds that succeed in germinating and in prop- agating in contrasted situations, we have diversity in the forms of natural selection affecting the seed, and the separation is what I here- after describe as local isolation passing into local segregation. We therefore see that what I here call industrial isolation depends on psychological powers acting in aid of divergent physiological adapta- tions to the environment, or in aid of adaptations that are put to different uses. Observation shows that there are a multitude of cases in which endeavor according to endowment brings together those similarly endowed, and causes them to breed together; and when the species is thus divided into two or more groups somewhat differently endowed, there will certainly be an increased divergence in the offspring of the parents thus segregated; and so on in each successive generation, as long as the individuals find their places according to their endowments, and thus propagate with those similarly endowed, there will be accu- mulated divergence in the next generation. Indeed, it isevident that endeavor according to endowment may produce under one environ- ment what natural selection produces when aided by local separation INDUSTRIAL ISOLATION. 121 in different environments. As it produces the separate breeding of a divergent form without involving the destruction of contrasted forms, it is often the direct cause of divergent transformations; while natural selection which results in the separate breeding of the fitted through the failure of the unfitted can never be the cause of divergence unless there are concurrent causes that produce both divergent forms of natural selection and the separate breeding of the different kinds of variations thus selected. Again, endeavor, according to endowment, often secures separation according to endowment; and this gives an opportunity for the inher- itable effects of diversity of endeavor (if there are such effects), to be accumulated in successive generations. In the relation of endowment and endeavor we have a striking example of the peculiar interdependence of vital phenomena. —Diver- sity of endowment is the cause of diversity of endeavor and of segre- gate breeding according to endowment, and segregate breeding accord- ing to endowment is the cause of increased diversity of endowment. It is very similar to the relation between power and exercise in the individual. Without power there can be no exercise, and without exercise there can be no continuance or growth of power. The effects of industrial isolation are specially liable to be enhanced by that form of intensive segregation which I have suggested should be called suetudinal intension. Simple and familiar as the principles of industrial isolation and sue- tudinal intension may seem, their consistent application to the theory of evolution will throw new light on a wide range of problems. This law of divergent evolution through industrial segregation rests on facts that are so fully acknowledged by all parties that it seems to be a superfluous work to gather evidence on the subject. It may, however, be profitable to consider briefly whether the cases are fre- quent in which different habits of feeding, of defence, or of nest- building become the cause of separate breeding by which the same habits are maintained in one line of descent without serious interrup- tion for many generations. It isimportant to remember (1) that the separate breeding will arise with equal certainty whether the diversity in the habits has been initiated by original diversity in the instincts and adaptations of the different variations, or by competitive disrup- tion, through the crowding of population inducing special efforts to find new resources, and leading to diversity of endeavor; and (2) that in either case the result is what is here called industrial segregation. In the first case, when the creatures are guided by some diversity of inherited instincts, the process is directly segregative, while in ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). ~ t i) the second case it is primarily separative, but inevitably passes into segregate breeding. Divergence through diversity of use, and the resulting diversity of acquired characters, whether inherited or not, will operate as surely in the one case as in the other. Sustentational isolation arises from the use of different methods of obtaining sustentation by members of the same species. There can be no doubt that of the innumerable cases where phyto- phagic varieties (as they are sometimes called) of insects exist, a con- siderable proportion would be found on investigation to be permanent varieties, producing offspring that are better adapted to the use of the special form of food consumed by the parents than are offspring of other varieties; and it is evident that if the peculiar habits of each variety had no tendency to produce segregative breeding this result would not be reached, for each variety would be promiscuously min- gled with every other, and, though the tendency to variation might be greatly increased, the regular production of any one variety of young would be prevented. Protectional tsolation is isolation from the use of different methods of protection against adverse influences in the environment. When a new enemy enters the field occupied by any species, different methods of escape or defence are often open to the mem- bers of the one species; and the use of these different methods must sometimes result in segregating the members according to the methods adopted. Some may hide in thickets or holes, while others preserve themselves by flight. Supposing the species to be an edible butter- fly occupying the open fields and the new enemy to be an insectivorous bird also keeping to the open country, certain members might escape by taking to the woodlands, while others might remain in their old haunt, gaining through protectional selection more and more likeness to some inedible species. Nidificational tsolation.—Let us now consider the effects of diver- gent habits in regard to nest-building. It is well known to American ornithologists that the cliff swallow of the eastern portions of the United States has for the most part ceased to build nests in the cliffs that were the original haunts of the species, and has availed itself of the protection from the weather offered by the eaves of civilized houses; and that with this change in nest-building has come a change in some of its other habits. Now, there is reason to believe that if the number of houses had been limited to a hundredth part of those now existing, and if that limited number had been very slowly supplied, this gradual change in some of the elements of the environment would have resulted in divergent forms of adaptation to the environ- CHRONAL ISOLATION. £23 ment in two sections of the same species. One section would have retained the old habit of building in the cliffs, with all the old adapta- tions to the circumstances that depend on that habit, while another section of the species would have availed itself of the new opportuni- ties for shelter under the eaves of houses, and would have changed inherited adaptations to meet the new habits of nest-building and of feeding. It is also evident that the prevention of free interbreeding between the different sections caused by the diversity of habits would have been an essential factor in the divergence of character in the sections. It simply remains to consider whether the industrial habit that separates an individual from the mass of the species will necessarily leave it alone, without any chance of finding a consort that may join in producing a newintergenerant. The answer is that there is no such necessity. Though it may sometimes happen that an individual may be separated from all companions by its industrial habit, it is usually found that those which at one time and in one place adopt the habit are usually sufficient to keep up the new strain if they succeed in securing the needed sustenance. 4. Chronal Isolation. Chronal isolation is isolation arising from the relations in which the organism stands to times and seasons. I distinguish two forms—cyclical and seasonal isolation. Cyclical isolation is isolation arising from the fact that the life-cycles of the different sections of the species do not mature in the same years. A fine illustration of this form of isolation is found in the case of Cicada septendecim, whose habitat is the northern portion of the Mississippi Valley and of the Atlantic States, though many outlying broods are found in other regions. The typical form has a life-cycle of seventeen years, but there is a thirteen-year race (Crcada tredecim Riley) found chiefly in the Southern States, and therefore separated from the typical form, both locally and chronally. As the life- cycle of this race is thirteen instead of seventeen years, in a district where the habitats of the two races overlap, even if there were no physiological or psychological incompatibility to overcome, inter- breeding could occur between the two forms only once in 221 years, that is, once in 13 generations of the longer-lived race, and once in 17 generations of the shorter-lived race. The distribution of the two races in different districts seems to indicate that local isolation under different climatic conditions has had an important influence in their development. It is manifest, however, that if during a period of 124 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). local separation, or if during the period of 221 years of cvclical separa- tion after the thirteen-year race was first formed, this race should become modified in the season of its appearing, there would after that be no mingling of race, though brought together in the same districts. This would be seasonal isolation, which we consider in a following paragraph; but what is of special interest here as examples of com- plete cyclical isolation is the fact that in each of several limited dis- tricts there are found two broods of the same race whose appearance above ground is always separated by the same number of years.* In any species where the breeding of each successive generation is separated by an exact measure of time which is very rigidly regulated by the constitution of the species, cyclical isolation wil] follow, if, through some extraordinary combination of circumstances, members sufficient to propagate the species are either hastened or delayed in their development, and thus thrown out of synchronal compatibility with the rest of the species. If, after being retarded or hastened in development so that part of a cycle is lost or gained, the old constitu- tional time measure reasserts itself, the isolation is complete. In such cases, so far as the time of maturing is concerned, the differ- ence is segregative, while in every other respect it will be simply separative, except as separation passes into segregation. If the periodical cicada was as variable in form and color as is the Achatinella (as well as other genera of Hawaiian snails), we should probably find each brood characterized by easily recognized divergences. Seasonal isolation is produced whenever the season for reproduction in any section of the species is such that it can not interbreed with other sections of the species. It needs no argument to show that if, ina plant species that regularly flowers in the spring, there arises a variety that regularly flowers in the autumn, it will be prevented from interbreeding with the typical form. The question of chief interest is, under what circumstances are varieties of this kind likely to arise? Is a casual sport of this kind likely to transmit to subsequent genera- tions a permanently changed constitution? If not, how is the new constitution acquired? One obvious answer is that it may arise a For the fullest statement yet made of the habitats and years of appearance of the 14 broods of the 17-year race and the 7 broods of the 13-year race, see Bulletin 14, New Series, of the Division of Entomology, U.S. Department of Agri- culture, 1898. As an example of the overlapping of the habitats of two broods of the same race, observe that, on pp. 48 and 49 of this Bulletin, three of the counties of Iowa and three of Missouri are given as part of the district where Brood XIII will appear in the year 1912, and also as part of the district where Brood XIV will appear in 1913, both broods being of the 17-year race. Broods XXI and XXII, of the 17-year race, are also reported as appearing a year Spake in Wilkes County, North Carolina. CHRONAL ISOLATION. 125 under some special influence of the environment upon members of the species that are geographically or locally isolated from the rest of the species. But may not variation in the flowering season of a fairly homogen- eous species tend to produce greater variation in that respect in the next generation, and so on, till the divergence in the constitutional adaptation to season is carried to the greatest extreme that is com- patible with the best adaptation to the environment? 1 believe that it not only may, but must have this effect; and that the result will be that the average form which flowers at the most favorable season will so vastly predominate over the extreme forms that the latter will be but stragglers in comparison. In regard to the one point of the season of readiness for propagation, this principle is segregative, but in other respects it is simply separa- tive, unless through the principle of correlated variation other charac- ters are directly connected with the constitution that determines the season. It will be observed that seasonal isolation is produced by a parallel and simultaneous change in the constitution of members in one place sufficient to propagate the species; while cyclical segre- gation is produced by a simultaneous acceleration or retardation in the development of members in one place sufficient to propagate the species without disturbing the regular action of the constitution under ordinary circumstances. 5. Spatial Isolation. Spatial isolation is isolation arising from the relations in which the organism stands to space. I distinguish two forms, viz, geographical and local isolation. Geographical isolation is isolation that arises from the distribution of the species in districts separated by geographical barriers that prevent free interbreeding. Decided differences of climate in neighboring districts may be classed as geographical barriers. Local isolation is isolation that arises when a species with small powers of migration and small opportunities for transportation has been, in time, very widely distributed over an area that is not sub- divided by geographical barriers. The segregation in this case is due to the disproportion between the size of the area occupied and the powers of communication existing between the members of the species occupying the different parts of the area. Though it is often difficult to say whether a given case of isolation should be classed as geographical or local, still the distinction will be found useful, for the 126 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). results will differ according as the isolation is chiefly due to barriers or to wide diffusion of the species. In geographical isolation the result is usually the development of well-defined varieties or species on oppo- site sides of the barriers; but in local segregation it often happens that the forms found in any given locality are connected with those in surrounding localities by individuals presenting every shade of intermediate character, and in general terms it may be said that the forms most widely separated in space are most widely divergent in character. It is, of course, apparent that when the divergence has reached a certain point the differentiated forms may occupy the same districts without interbreeding, for they will be kept apart by some, if not all, of the different forms of autonomic isolation. Three different forms of spatial segregation may be distinguished according to the causes by which they are produced, viz: Migrational isolation, caused by powers of locomotion in the or- ganism. Trans portational isolation, caused by activities in the environment that distribute the organism in different districts. Prominent among these are currents of atmosphere and of water, and the action of migratory species upon those that can simply cling. Geological isolation, caused by geological changes dividing the ter- ritory occupied by a species into two or more sections. For example, geological subsidence may divide the continuous area occupied by a species into several islands, separated by channels which the creatures in question can not pass. Migration differs from transportation simply in that the former is the direct result of activities in the organism, and the latter of activi- ties in the environment, and though the distribution of every species depends on the combined action of both classes of activities, it is usually easy to determine to which class the carrying power belongs. The qualities of the thistle-down enable it to float in the air, but it is the wind that carries it afar. Some degree of local isolation exists whenever the members of a species produced in a given area are more likely to interbreed with each other than with those produced in surrounding areas, or when- ever extraordinary dispersal plants a colony beyond the range of ordi- nary dispersal—in other words, when those produced in a given dis- trict are more nearly related with each other than with those produced in surrounding districts, there local isolation has existed. There is one important respect in which spatial isolation differs from all other forms of isolation, namely: In its ordinary operation it does SPATIAL ISOLATION. 127 not bring together those of similar endowments, and does not depend ondiversity. The dispersion of the members of a species would not be prevented if each was exactly like every other; though, of course, if there were no power of variation, separate breeding would have no influence in producing divergence of character. It follows that every species is more or less liable to be affected by spatial isolation; and it often happens that other forms of isolation arise through the previous operation of this form; but as spatial isolation prevents organisms from crossing only when separated in space, it must always be reinforced by other forms of isolation before well-defined species are produced that are capable of occupying the same district without interbreeding. Many slightly divergent forms arising through local isolation are reintegrated with the surrounding forms, new diverg- ences constantly coming in to take the place of the old; but if, during its period of local divergence, industrial or chronal isolation is intro- duced, the variety becomes more and more differentiated, and, as one after another the different forms of reflexive segregation arise, it passes into a well-defined species. As spatial isolation does not necessarily depend upon diversity in the qualitiesand powers of the organisin, it usually fails of distributing the varieties of a species in different localities according to their differences of endowment. The causes that produce it are primarily separative, not segregative. Migration is produced by the natural powers of the organism acting under the guidance of instincts that usually lead a group of indi- viduals, capable of propagating the species, to migrate together; while organisms most dependent on activities in the environment for their distribution are usually distributed in the form of seeds or germs, any one of which is capable of developing into a complcte community. The causes of isolation between the different sections and of inte- gration between the members of one section are, therefore, sufficiently clear; but what are the causes of differences of character in different sections, especially when they are exposed to the same environment? These causes all come under what I call typal intensification through diversity of success and diversity of survival. 128 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). 6. Fertilizational Isolation. Francis Galton’s short article on ‘‘The Origin of Varieties,’ which was published in Nature, vol. xxxIv, p. 395, refers to this cause of isolation. He says: If insects visited promiscuously the flowers of a variety and those of the parent stock, then—supposing the organs of reproduction and the period of flowering to be alike in both, and that hybrids between them could be produced by artificial cross-fertilization—we should expect to find hybrids in abundance whenever members of the variety and those of the original stock occupied the same or closely contiguous districts. It is hard to account for our not doing so, except on the supposition that insects feel repugnance to visiting the plants interchangeably. It is evident that isolation of this form depends on divergence of character already clearly established, and, therefore, on some other form of isolation that has preceded. It is also segregative rather than separative, in that it perpetuates a segregation previously produced, which might otherwise be obliterated by the distribution of the differ- ent forms in the same district. The form of isolation that precedes fertilizational isolation, producing the conditions on which it depends, must, in the majority of cases, be local isolation. Chronal and impregnational isolation, when imperfectly established, might be for- tified by fertilizational isolation, but, in the case of plants, these are usually dependent on previous local isolation. 7. Artificial Isolation. Artificial isolation is isolation arising from the relations in which the organism stands to the rational environment. The tmportance of environal rsolation.—We must not assume that the various forms of environal isolation are of small influence in the formation of species because sexual or impregnational incompatibility is a more essential feature, without which all other distinctions are liable to be swept away. The importance of the environal forms of isolation lies in the fact that they often open the way for the entrance of the more fundamental forms of segregation, even if they are not essential conditions for the development of the same. Though myriads of divergent forms produced by local and industrial isolations are swept away in the struggle for existence, and myriads are ab- sorbed in the vast tides of crossing and intercrossing currents of life, the power of any species to produce more and more highly adapted variations, and to segregate them in groups that become specially adapted to special ends, or that grow into specific forms of beauty and internal harmony, is largely dependent on these factors. REGRESSIVE MODES OF THE PRINCIPLES. 129 8. Environal Partition. Environal partition depends on influences quite similar to those producing environal isolation, except that the seasonal, cyclical, and fertilizational forms are wanting. This is because these forms depend on inherited characters rather than on acquired habits, while envi- ronal partition is due to incompatibility in the acquired habits of individuals usually belonging to groups that have been locally sepa- rated fora time. Industrial and migrational partition tend more or less directly to produce groups with somewhat divergent habits, while transportational, geological, and artificial partition open the way for divergent forms of innovation, tradition, and election, to establish divergent types of habitudinal groups. Moreover, these forms of par- tition tend directly to produce isolation and consequently divergent racial groups. II. THe REGRESSIVE MODE oF EACH SEGREGATIVE PRINCIPLE. Regressive selection may be produced either by the cessation or by the reversal of a long-established form of selection. Near the end of the last chapter we referred to the Old World cuckoo and the American cow-bird as examples of degeneracy in the instincts for nest- building, for incubation, and for the feeding of their own young—a degeneracy that seems to have been produced by the gradual cessa- tion of the selection by which these instincts had for countless gener- ations been maintained. We also found that there was reason to believe that the discovery of substitutes for mother’s milk is, in certain races of mankind, leading to decay of the power to give suck, through the survival of the children of mothers who, under the con- ditions of primitive times, would have entirely failed of having any share in the parentage of the next generation of parents. Examples of the reversal of selection are found in the history of species that, through the coming and going of the ice age, have for many genera- tions been subjected to increasing cold, and then for many generations to increasing warmth. Regressive election arises when any tradition or acquired character that has long been necessary for success in a given community ceases to be so. It often prepares the way for regressive selection. For certain races of dogs the traditional methods of finding food are very different from those that were current with their primitive ancestors, and the cessation of the necessity for the strenuous life of the old times has brought regressive selection, resulting in the decay of some of the old instincts. 130 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). What is usually called the amalgamation of races is regressive tsola- tion. Itis a form of racial demarcation, in which the boundaries are so changed that two or more slightly divergent varieties or races are interfused and become one. But, as I have already suggested, the limits within which regression of this kind can take place are compar- atively small. Regressive partition takes place when divergent forms of civiliza- tion become commingled and blended. In the case of human races it often introduces regressive isolation. The most familiar of these four regressions is regressive isolation, that is, racial amalgamation, to which Darwin’s work on cross and sel} fertilization has called attention. The chief significance of the prin- ciple lies in its producing a certain limited undoing of isolation and in its giving plasticity and variability to the compounded stock. Amal- gamation usually arises through the entrance of divergent races into the same region before their sexual and social instincts or the physio- logical and structural coadaptations of the sexes have become so divergent as to prevent interfusion. Under such conditions what- ever determines the bringing together of the races in the same region determines the nature of the amalgamation. When human races are brought together in the same region, the rapidity of amalgamation is determined largely by racial instincts and social conditions. 1. Reversal of Partition and Isolation in Man. The most remarkable feature in the evolution of civilized man is the | veversal of the processes of partition and of tsolation and the breaking down of the social and racial segregations that have been progressing for countless generations. The leading factors in this process of coalition are social rather than racial; but the final result will un- doubtedly be a great reduction of the number of races, and possibly a blending of all in one generalized type, resulting from the amalgama- tion of all the racesin one. It is, however, possible that the barriers preventing marriage between certain races of men will become more fixed than ever, even though the intercourse of industrial, commercial, and national life becomes increasingly intimate. The era of commer- cial intercourse has been inaugurated and will never be reversed. Again, the smaller nations are being absorbed into the larger nations ; but what the final result will be on the multitude of races and castes can not be easily foretold. NO REFLEXIVE SELECTION BETWEEN GROUPS. 131 2 Isolation Prevents Reflexive Selection between Groups. Weare now prepared to understand one reason why isolation result- ing from indiscriminate separation is in time transformed into segre- gation. Isolation 1s in its very nature the suspension, not only of one jorm, but of all forms of reflexive selection between the separated portions of the species. The importance of the cessation of natural selection in producing the different stages of the degeneration of organs that have ceased to be of use has been fully discussed by Romanes (see Nature, Vol. 41, p. 437, and previous communications there referred to), who points out that, as the power of the special form of heredity by which any organ has been produced has been built up by many generations of natural selection that have acted in favor of the organ, so the gradual weakening of that power follows the cessation of the natural selection. Professor Weismann seems to appeal to the same principle when he attributes the reduced size of ‘‘rudimentary organs” to the action of ‘‘panmixia.”’ Now, since isolation always includes the complete cessation of reflexive selection between the separate groups, a similar principle is introduced, and the result must be the weakening of the power of heredity by which the portions of the species were held in correspondence with each other before their sepa- ration. I have elsewhere shown that isolation necessarily disturbs unstable adjustments; and we here see that the most stable of the adjustments by which each part of a species is kept in correspondence with every other part gradually becomes unstable, under the con- tinued influence of isolation. Whenevera species is divided into two portions that do not interbreed, the forms of reflexive selection above described will cease to act between the two portions, and they will continue in sexual, social, physiological, and industrial harmony with each other only in so far as the force of the old heredity holds them to the old standards. But the force of heredity in these respects will in time fail if the reflexive selection that held the original stock in accord is entirely removed in its action between the two portions. Ii the separate breeding is long continued, incompatibility in all these re- spects tends gradually to arise; but it is manifest that incompatibility of industrial habits implies diversity in the forms of environal selec- tion shaping each portion. I therefore maintain that separation, which necessarily includes the cessation of reflexive selection between the portions separated, is a cause of segregation and divergence and that it introduces diversity of environal selection, which is a still further cause of divergence. 132 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). III. DiscRIMINATE AND INDISCRIMINATE ACTION OF THE SEGREGATIVE PRINCIPLES. * 1. Discriminate Action. Under each of these four segregative principles we may raise the question as to the difference in the results; first, when the principle under consideration is guided by some discriminative influence, continued from generation to generation, and, second, when it acts without discrimination and without cumulative results in sutcessive generations. It is evident that discriminative survival, which is the same as selection, when continued in the same form for successive generations, must be cumulative in its effects. Duscriminative 1s0- lation, that is, segregate intergeneration, arises whenever adapta- tion for appropriating certain resources brings together in one iso- lated group those that are by innate qualities and aptitudes the better adapted. In most of these cases it is not possible that another group should arise within this first group simply through being more highly endowed in the same respect. Cumulative isolation is for the most part produced by the subdivision of groups that have already been established, and the agencies producing the successive divisions are likely to be different in their nature, and, therefore, not cumu- lative in their effects upon any one character. This, however, does not prevent each isolation from being more or less segregative in regard to some of the characters. Election, that is, the discriminate success of individuals through the attainment of certain habitudes and acquired characters, is likely to be cumulative in the effects produced on successive generations; for, as long as increased facility in the performance of certain acts is an advantage, both habitudes and aptitudes aiding in the performance will be combined in an increasing degree in each generation. Discriminate partition, that is, segregate association, arises when- ever adaptation for dealing with either the environment or the social conditions brings together in one separate group those that are by habitudes (that is, by acquired characters), the best adapted. It is manifest that among social organizations occasions producing such partition must often arise; and it seems probable that among even the least-endowed creatures great advantage must sometimes come to those who have in some degree acquired characters enabling them to meet new conditions in the environment, which come upon the spe- cies with a sweep that none who are unprepared can withstand. Such * See Table of ‘‘ Discriminate and Indiscriminate Forms,” page 136. INDISCRIMINATE ACTION OF THE PRINCIPLES. tee ee | changes are sometimes experienced in temperature; or in the salinity of the water, in the case of water plants and animals. 2. Indiscriminate Action of the Segregative Principles. Again, let us consider what the results are when the action of these principles is indiscriminate. Jndiscriminate survival takes place in regard toany given character of a species when the presence or absence of the character has no effect on the adaptation of the individual. For Anglo-Saxons the possession of blue eyes or gray eyes is a matter of non-selective importance, and selection does not determine which shall prevail. There is, however, another form of indiscriminate survival which may have definite influence in determining the subsequent form ofaraceorspecies. I refer to the indiscriminate destruction of all but a small portion of the intergenerating group. Against heavy volcanic convulsions the varying endowments of different individuals of any one species usually count for nothing, and therefore the destruction falling upon them is indiscriminate; but if only a pair or two are left to propagate the species, the probability is that the type will be more or less changed in one or more of its characters. Indiscriminate tsolation of only a small fragment of a species is liable to result in important divergence in one or more of the characters of the species. Ifa single gravid individual, of a variable species of Hawaiian tree snails, is carried for a mile or two from its native val- ley while clinging to a leaf borne by a bird or a strong wind, it may fall in a neighboring valley, among groves and thickets of the same trees and shrubs that furnished its natural station in its original home. Is there now any probability that the colony descending from this individual, completely isolated from the original stock, but living in a valley with the same climate, and vegetation, and birds, and insects as are found surrounding their relatives in the original valley, will, by any chance, reproduce all the variations and varie- ties of the original species, and in the same proportions, and at the same time avoid producing any new varieties?) My knowlege of var- iable animals in general, and my observations on Hawaiian snails in particular, make it impossible for me to believe that such a case could everoccur. If anyone says that an isolated portion of a species under absolutely the same environment as the original stock must produce the same varieties, as Wallace maintains in his volume entitled ‘‘ Darwin- ism,”’ I suspect he is using the word ‘‘ environment ’’ as equivalent for all the conditions that may cause divergence, whether they lie within the species or belong to what lies outside of the species. This seems to bein part the explanation of Wallace’s position ; for in enumerating the 134 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). conditions in the environment that may have an effect in producing divergence, he calls attention to the fact that the small isolated por- tion of the species ‘‘is at once in a different position as regards its own kind.’’ Now, this is exactly what I mean when I say that the iso- lation of a small portion has some effect in producing divergence, even if the conditions outside of the species could be absolutely the same as in the original habitat. Still further, as | have abundantly shown in the paper reproduced in Appendix II, it is very possible that the isolated portion will, early in its career, if not from the very first, be subjected to new forms of selection, through the adoption of habits of feeding that are wanting, or unusual, in the original habitat; for a rare habit in the original valley might become the predominant habit in the colony that arises in the newly occupied valley, even if the envi- ronments were absolutely the same. This form of selection I have called active (or endonomic) selection. Indiscriminate success will arise in regard to any given habitude, or form of acquired efficiency, when the attainment or the non-attain- ment of the habitude has no effect on the success or influence of the individual. Another form of indiscriminate influence may be intro- duced by the indiscriminate slaughter of all but a few individuals of a community, in which case the habits of the few remaining indi- viduals will have great influence on the habits of the new community arising through the multiplication of the few survivors. Indiscriminate partition arises whenever the occasion that brings a number of individuals of a species together in a separate position does not determine that they shall be of any particular type of habitudes, of culture, or acquired skill. Partition due toan island being divided by partial submergence is usually indiscriminate; while migration often produces discriminate partition, as when it brings to a distant island men who are skilled in canoe building and sailing. 3. Contrasts in Discriminate and Indiscriminate Forms of Action. These considerations bring to light the following facts: (1) In the survival of innate characters and the success of acquired characters the discriminate forms (7. e., selection and election) are of prime importance; for in one way or another they are continually acting on nearly every generation of nearly every species. The cases must be rare in which equal success and survival are attained by all the variations; for if variations in other respects have no effect, its variations in vigor will have relation to the degree of survival. In some rare cases there will occur the indiscriminate elimination of all but a very few members of a race or species; and the results DISCRIMINATE AND INDISCRIMINATE ACTION. 135 in such cases are liable to be of importance, through the original average character of the species not being fully represented and through the fact that this initial bias often leads to some new form of selection, which continues to act with cumulative force through subsequent generations. No single pair can exactly repro- duce the average character of the species in all its aptitudes and habitudes, and therefore the methods of dealing with the environ- ment adopted by the descendants are liable to be different. (2) In isolation and partition there is less opportunity than in selection and election for cumulative effects in each generation. Moreover, in many of the cases, the isolation is indiscriminate till divergent forms of selection codperate. But it should be noted that the isolation of asmall number of the species is of frequent occurrence, and the failure of these small groups to represent the average charac- ter of the group or race either in habitudes or aptitudes introduces slight divergences determining new forms of autonomic selection which are of great importance in molding new types. And even when large masses are indiscriminately isolated all selection pro- ducing codrdinations between the members of the separate groups ceases; and the probability is that in the course of many generations divergent forms of selection will arise, through different methods of coordination between members as wellas through different methods of dealing with the environment adopted by different isolated groups. This probability rests not so much on the probability of a difference in the average character of the two large sections as on the probability that in one section some new habitude will arise that does not arise in the other section. The importance of isolation in producing diver- gence is seen not only in its being the absolute condition on which divergent forms of selection become of avail in producing divergence, but in the fact that the isolation of a few individuals often introduces from the first a divergent form of autonomic selection, though the environment is the same, and in the fact that the isolation of a large section of a species opens the way for a similar divergence of selection, though it may require many generations for the result to become apparent. Moreover, discriminate isolation (as when different indus- tries have led individuals to form intergenerating groups according to their aptitudes), leads from the first to divergence in adaptations and to the intensification of adaptations. The table on page 136 will be useful in enabling us to keep in mind the importance of these distinctions when applied to some of these prin- ciples. Discriminate survival, which is usually called selection, is of such importance that many terms have been needed to present the 136 ANALYSIS OF THE FOUR PRINCIPLES (CONTINUED). different influences through which it arises; while indiscriminate survival and its equivalent, indiscriminate elimination, seem to be sufficient for the designation of a process which, as compared with selection, is rarely effective in producing the transformation of races. 4. Table of the discriminate and indiscriminate forms of the four segregative . Indiscriminate success = principles. THe EIGHT Forms. THE RESULTS. PARTITION. . Discriminate partition = segregate asso- . Grouping of individuals according to habi- ciation. . Indiscriminate partition with more or less loss of power to perpetuate the original habitudes unchanged. SUCCESS. . Discriminate success = election. indiscriminate failure. ISOLATION. . Discriminate isolation = segregate inter- generation. . Indiscriminate isolation with more or less loss of power to reproduce the complete average of the innate characters ot the orig- inal stock. SURVIVAL. . Discriminate survival =— selection. . Indiscriminate survival — indiscriminate elimination. tudes and acquired characters, and so producing habitudinal segregation, and giving an initial tendency toward segre- gate breeding. . More or less divergence in the habitudes and acquired characters of the separated groups, especially when the groups are very small, and so producing initial habi- tudinal segregation. . Success and influence of individuals accord- ing to their acquired fitness for the condi- tions, both social and physical, in which they are placed, producing intensified habitudinal segregation. . When the number of individuals that es- cape from a sweeping catastrophe is very small, they will be unable to perpetuate the original social organization unchanged. . Grouping of individuals according to their aptitudes and innate characters, and so directly introducing segregate breeding with divergence of characters, 7. e., racial segregation. . More or less divergence in the aptitudes and innate characters of the isolated groups, especially when at the time of the first setting apart the group is represented by but one, or but few, individuals, and so producing initial racial segregation. . The efficiency of individuals in living and propagating will vary (and sotheir survi- val will vary) according to their innate fitness for the struggle of life, and thus the fitness of the race will be increased. . When those indiscriminately surviving are very few, it will be impossible for them to reproduce all the innate characters of the original stock unchanged. CHAPTER VIII. CLASSIFICATION OF THE FORMS OF THE PRINCIPLES PRODUCING ALLOGAMIC EVOLUTION. J. TABLES OF ForMS, WITH BRIEF EXPLANATIONS The analysis presented in the two preceding chapters has revealed many factors, which are here brought together in tables so arranged as to show the more important of their relations to each other. (See pages 138-139.) 1. Allogamic, Autogamic, and Agamic Evolution. A complete classification of the factors of organic evolution must include the principles producing differentiation of organisms multi- plying asexually, as wellas of those reproducing sexually. Moreover, the reproduction of self-fertilizing speciesis so unlike that of species in which cross-fertilization takes place (either in each generation or at the end of a series of generations), that it seems necessary to consider their methods of transformation separately. Following these dis- tinctions, organic evolution needs to be divided into three depart- ments, which may be called: Allogamic evolution, which relates to the evolution of cross-fertiliz- ing organisms; Autogamic evolution,* which relates to the evolution of self-fertil- izing organisms; and Agamic evolution, which relates to the evolution of organisms whose reproduction is continuously asexual. The investigation presented in this volume relates to allogamic evolution. * Karl Pearson, in 2nd ed. of ‘‘ The Grammar of Science,’’ London, 1900, p. 423, uses the term ‘‘Autogamic Mating”’ to designate self-fertilization. 137 138 9 “=. CLASSIFICATION OF THE FORMS OF THE PRINCIPLES. Allogamic Evolution Controlled by the Four Principles of Segregation. =I + association autonomic Habitudinal segregation *." III, and heteronomic association = V + VII, controlled by eneration = JI + IV, and heteronomic in- || B- ‘autonomic interg Racial segregation °. tergeneration = VI gregate intergeneration of indviduals | | + VIII, controlled by segre according to their innate aptitudes and restin racial generalization and adaptation. according to their ac- on tradition and innov ition of individuals assocl segregate g on heredity and variation, with | ation, and resting quired habitudes with habitudinal generalization and accommodation. C. Typal demarcation *.. autonomic demar- eation =~ 1+ I1I, and *.. heteronomic demar- cation = V + VI. (E) Habitudinal demarcation, through par- tition. {a. Reflexive partition. } 1. Conjunctional partition. - (1) Family partition. : (2) Social partition. a 2. Institutional partition. o es (3) Linguistic partition. 8 nS (4) Religious partition. c mE = (5) Educational partition 0 g (6) Sanitary partition. 5 < 6. Environal partition. z. 9 3. Endonomic partition. B g (7) Industrial partition. 3S (8) Migrational partition. J = 4, Heteronomic partition. } Ea (9) Transportational par- ! = . tition.w t som (10) Geological partition. w | os 5 (11) Artificial partition. J =.9 c. Regressive partition. w. Indiscriminate partition. dD. Coincident election. Typal intensification *.* autonomic intensifiea- tion = III + IV, and *.: heteronomic intensifi- cation = VII + VIII. (G) Habitudinal intensification through success (through election when discriminate). { g. Reflexive election. ) 10. Conjunctional election. (29) Sexual election. | (30) Social election. | (31) Filio-parental election. 11. Dominational election. J ’ 12. Institutional election. (32) Religious election. (33) Educational election. (34) Sanitary election. (35) Penal election. Environal election. 13. Endonomic election. (36) Habitudinal election. h. ‘WOT}Da]9 StMIOUOINY “TIT (37) Aptitudinal election. J 14. Heteronomic election. VII. Hete- (38) Natural election. ronomic (39) Artificial election. election. l 1. Regressive election. y. Indiscriminate failure. (F) Racial demarcation through isolation. d. Reflexive isolation. 5. Conjunctional isolation. (12) Sexual isolation. (13) Social isolation. 6. Impregnational isolation. (14) Dimensional isolation. | (15) Structural isolation. Physio- ¢(16) Potential isolation. logical { (17) Segregate fecundity. | isolation | (18) Segregate vigor. | (19) Segregate adaptation , (20) Segregate freedom from competition. (21) Segregate escape from enemies. 7. Institutional isolation. ‘MOLIOSI DIMOU NY “TY ( @ Environal isolation. 8. Endonomic isolation. (22) Industrial isolation. (23) Chronal isolation. Seasonal isolation. Cyclical isolation. (24) Migrational isolation. J Coincident isolation. 4 9. Heteronomic isolation. 7) | (25) Transportational iso- | lation.x Bas (26) Geological isolation.x | BO * (27) Fertilizational isola- | 8 gos (28) Artificial isolation. 7. Regressive isolation. L x. Indiscriminate isolation. tion. | J Coincident (or organic) selection. (H) Racial intensification through survival (through selection when discriminate). { 7. Reflexive selection. ) 15. Conjunctional selection. (40) Sexual selection. (41) Social selection. (42) Filio-parental selection. 16. Dominational selection. (43) Sustentational domination. (44) Protectional domination. (45) Nidificational domination. (46) Mating domination. (47) Prepotential domination. 17. Impregnational selection. (48) Dimensional reflexive se- lection. (49) Structural reflexive selection. (50) Potential selection. (51) Fecundal selection. 18. Institutional selection. (52) Ecclesiastical selection. (53) Military selection. (54) Sanitary selection. (55) Penal selection. 19. Prudential selection. k. Environal selection. 20. Endonomic selection. (56) Habitudinal selection (57) Aptitudinal selection —— “HOTOa[as OfurOuUOINY “AT 21. VIII. He- teronomic selection. Heteronomic selection. (58) Natural selection. (59) Artificial selection. l. Regressive selection. z. Indiscriminate elimination. f{tOrganic (or Coincident) selection is determined by accommodation that protects the group from extinction till coincident variations have time to arise. TABLES OF FORMS. 139 3. The Forms of Selection Defined. j. Reflexive selection, based on relations within the group. *t15. Conjunctional selection, *.. cobperation of individuals especially *.” the codrdination of instincts and habits with qualities. (40) Sexual selection’. codrdination of sexual instincts and qualities. (41) Soctal selection *.. codrdination of social instinets with qualities. *+(42) Filvo-parental selection’. cobrdination between the powers and char- acters of the parents, and the size, number, form, and instincts of the young. 16. Dominational selection *.. power to outdo, outrun, and overcome others of the same group in appropriating needed resources. (43) Sustentational domination’. taking food. (44) Protectional domination’. taking positions affording safety. (45) Nidificational domination’. taking positions for breeding. (46) Mating domination *.. monopolizing mates. (47) Prepotential domination *. superior potency of pollen. *17. Impregnational selection *.. structural and physiological coordinations that secure a sufficiency of impregnated germs with least waste. (48) Dimenstonal selection’... cobrdination in length of pistils and pollen tubes, and in size of other impregnating organs. (49) Structural selection *.. cobrdination of clasping organs, ete. (50) Potential selection *.. codrdination of the sexual elements. (51) Fecundal selection *.. codrdination in the relative number of the male and female elements preventing waste. F18. Institutional selection *.. suppression of reproduction for (52) Eccle- siastical, (53) Military, (54) Sanitary, and (55) Penal reasons; or the favoring of certain types. t19. Prudential selection’. delay of marriage and prevention of reproduction for economic and other personal reasons. k. Envtronal selection *.’ relations of the group and the environment. 20. Endonomic selection, determined by activities in the group. (56) Habitudinal selection, determined by acquired habitudes. *(57) Aptitudinal selection, determined by innate aptitudes. t21. Heteronomic selection, determined by activities in the environment. (58) Natural selection, determined by the irrational environment. (59) Artificial selection, determined by the rational environment. §1. Regressive selection, as when accommodation preserves those of inferior racial endowments. Explanation of the signs used in Sections 2 and 3. = Equalto. + Combined with. ‘. By means of; produced by; through. * Determined by previously attained aptitudes. f+ Determined by previously attained habitudes. *+ Determined by aptitudes and habitudes. t~ Determined by conditions in the present environment. § Determined by one or more of these influences. "AI +e IULIaJIp ‘UorpIajas IMuOoUQINW - sapnyiqey ayy Aq peu ‘dnois yovo yo sopnande puv "TTTAT 140 CLASSIFICATION OF THE FORMS OF THE PRINCIPLES. 4. Conditions Determining the Forms of Selection. The forms of selection depend on the following conditions (the letters and numbers are those used in the tables on pages 138-139): j. The relations in which individuals of the same group stand to each other; that is, the reflexive conditions. First, the aptitudes (1. e., instincts and other inherited powers), that shape these relations to each other; second, the habiztudes (v1. e., habits and other acquired powers), that shape their relation to each other; and, third, the physical characters of the individuals, must be coérdinated. k. The relations in which the group stands to the environment, that is, the environal conditions (arising from the action and reaction be- tween the group and its environment), must be harmonized. 20. The conditions within the group that shape these relations to the environment; that is, the endonomic conditions, being (56) the habitudes, and (57) the aptitudes that enable the isolated group to determine how it will use the environment, must be kept in the fullest possible accord with these uses and with each other. 21. Heteronomic conditions, (58) natural and (59) artificral; that is, conditions in the environment that constitute a limit to the possible methods of escape from destruction. Small colonies of Hawaiian snails, of the same species, isolated in neighboring valleys, but occu- pving the same species of trees and feeding in the same way, and all exposed to the same enemies, it seems to me are probably subject to the same forms of heteronomic environal selection. Any snail, capable of living on several species of trees growing in thick, shady groves, when brought to a valley where only one species of such trees is found, is subjected to heteronomic conditions, for but one method of survival is open to it. But even under these conditions we find divergence taking place in isolated groups. Shall we attribute such divergence to diversity of selection or to the diversity presented in the average character of the groups when first isolated? I believe this latter explanation is the more reasonable. If each colony was originated bya single snail, we knowit is impossible that these original progenitors of the different colonies should in every respect have possessed the same characters. It is also impossible that the varia- tions occurring in an isolated colony springing from a single pair should be exactly the same variations, presented in exactly the same proportions, as in the mother colony from which they were separated. The influences determining the forms of isolation, partition, and election are also presented under the aspects of reflexive influences and environal influences, and in constructing terms for the different AUTONOMIC AND HETERONOMIC INFLUENCES. I4t forms of these three principles we are able to avail ourselves of the adjectives that have been used in designating the different forms of selection. This is a great aid in presenting the relations between the four principles in their different forms. In many of the places where the sign *.* (meaning caused by) is used after the forms of reflexive selection, it might with equal correctness be changed to .. (meaning causing). For example, social selection may be described on the one hand as depending on the codrdination of social instincts and qualities, and on the other hand as budding up and matntaining the social instincts and the characters on which they depend. Taking a special case: Without any possible method of recognizing each other there could be no social selection; but, on the other hand, when a new race is formed, it is social selection that seizes on some new and fluctuating character, emphasizing, intensifying, and rendering it permanent; and so, in an important sense, it may be said that social selection produces the recognition marks and calls and codrdinates them with the special instincts of the race that recog- nize these marks and respond to these calls. II]. AUTONOMIC AND HETERONOMIC INFLUENCES. 1. Autonomic Influences Include Endonomic ani Rejlexive Influences. The nomenclature given in this volume calls.attention to the fact that endonomic selection is determined by habitudes and aptitudes for dealing with the environment, and is subject to diversity without any corresponding diversity in the environment; and that the forms of reflexive selection are determined by the necessity for sexual, social, and other codrdinations between the members of the same intergen- erating group, also undergoing change without reference to change in the environment. The forms of endonomic and reflexive selection are, therefore, brought together under the term autonomic selection, which sets them in strong contrast with heteronomic selection, which is always determined by conditions in the environment surrounding the intergenerating group. But the effects of changes of activities within the intergenerating group, and not depending on changes in the environment, are not all covered by autonomic selection. We must also consider the autonomic forms of tsolation, election, and partition, for they are all of importance in segregating and molding the types of allogamic organisms. Autonomic tsolation includes both endonomic isolation, produced by industrial, chronal, and migrational isolation, and reflexive isola- tion, produced by sexual and social instincts, by impregnational incompatibilities, and by institutional requirements. Itisin contrast with heteronomic isolation, which is determined by conditions outside 142 CLASSIFICATION OF THE FORMS OF THE PRINCIPLES. of the organic group, as, for example, geological subsidence, or causes resulting in transportation to an isolated position. Autonomic selection codperating with autonomic isolation produces autonomic generation; and heteronomic selection codéperating with heteronomic isolation produces heteronomic generation. Autonomic electron includes endonomic election, produced by the success of different acquired methods of dealing with the environment, and reflexive election, produced by the social promotion or suppression of individuals according to the success of their habits in relation to others of the same group. It is in contrast with heteronomic election, which is determined by conditions outside of the organic group. Autonomic partition includes €ndonomic partition and reflexive partition, and secures the grouping of individuals as regards their habitudes, through the influence of activities that lie within each asso- ciating group. It isin contrast with heteronomic partition, which is the grouping of individuals as regards their habitudes, through the influence of activities in the environment. Autonomic partition combining with autonomic election produces autonomic association; and heteronomic partition combining with heteronomic election produces héteronomic association. Habitudinal intensification may arise from activities entirely within the group of organisms, of which social promotion and social suppres- sion* of habitudes are familiar examples, and the combined effects of these activities on the habitudes of the group is appropriately called autonomic election; but we need a term to designate the combined influence of autonomic election and autonomic selection, producing the intensification of inherited aptitudes, in addition to the intensifica- tion of acquired habitudes. Such a term is autonomic intensification. It signifies the molding of types by activities within the intergene- rating and associating group. Incontrast with autonomic intensifi- cation, we have intensification produced by the combined action of heteronomic election and heteronomic selection, which may appro- priately be called heteronomic intensification. The codperation of autonomic partition and autonomic isolation I call autonomic demarcation; and the codperation of heteronomic partition and heteronomic isolation I call heteronomic demarcation. The codperation of autonomic intensification with autonomic demarcation produces autonomic segregation; and the cooperation of heteronomic intensification with heteronomic demarcation produces heteronomic segregation. * Baldwin defines social suppression as ‘‘ Suppression of the socially unfittest by law, custom, etc.’’ (See ‘‘Social and Ethical Interpretations,” Appendix B.) PARTITION CONTROLLING ISOLATION. 143 2. Autonomic Partition Produces Autonomic Isolation. In the evolution of the European races of man the tendencies which break down ancient segregation, whether resting on habitudes or aptitudes, are so strong that it is difficult for us to apprehend the conditions of society in which segregative tendencies are in full force. The caste system of India not only maintains with absolute strictness the old barriers based on traditions received from remote genera- tions, but tends to create new divisions, resting at first on industrial habits, but in time reinforced by separate social customs, separate ideals, and separate methods of training, and are finally intrenched behind restrictions forbidding marriage with those who were once considered as belonging to the same caste. Professor Reinsch states* that there are no less than 3,000 castes in India; and missionaries who have studied the institutions of the country most carefully assure us that if a caste is defined as an intermarrying group that iscompletely excluded from marriage with all other groups, then the castes of India number many thousands. Of the Brahmins, who are considered the highest caste of India, there are over 1,800 such sub-castes. Rev. J. P. Jones, D. D., of Pasumalai, South India, informs me that during his residence in Southern India a branch of a certain barber caste has taken up the trade of weaving; and feeling that their occu- pation, which is being transmitted from father to son, sets them above the barber caste, they are now beginning to require that the son of a barber desiring to marry the daughter of a weaver must give up bar- bering and become a weaver. , The one remaining step required for the full establishing of the new caste will probably come within a few years, and will be the objecting to additions to the guild from those who have not been born within its ranks. Though railroads and other influences from Europe tend toward freer intercourse, these new castes are struggling into exist- ence; and the tendency is to fortify the spirit of segregation by refus- ing to eat or have close fellowship with any outside of the caste that has thus recently come into being. The caste system as developed in India is as unlike the democratic conservatism of China as it is opposed to the progressive individual- ism of Europeanraces. It may be doubted whether the caste system of India can ever develop into a truly progessive system. But the essentially democratic life of China stands in a very different relation to the progressive element of European civilization. In innate racial qualities no people can surpass the Chinese; and their vitality and power of adaptation is such that they seem to be equally fitted for suc- * See ‘‘ The Forum”? for June, 1901. 144 CLASSIFICATION OF THE FORMS OF THE PRINCIPLES. cess in all climates and inall countries. Moreover, under the stimulus of intercourse with European civilization, there are evident signs that new and progressive elements will be added to the old ideals tilla truly progressive spirit is attained. The remarkable power of accommoda- tion to different climates and health conditions possessed by the race, especially by the branch occupying the southern provinces of China, is such that few races are able to endure free competition with them even when the country and climate are so chosen as to give the best pos- sible chance to their rivals: Members of the Teutonic race, when sub- jected to the climate of India, suffer from the effects of the heat; and their small power of individual adaptive modification in that direction gives them but little prospect of becoming completely adapted through the effects of natural selection; for, if their children remain contin- uously in the country, they have not sufficient energy for the battle of life. On the other hand, the Chinese from Canton, with high powers of accommodation, are fully successful as permanent settlers, both in the cold of Manchuria and in the heat of the Malay Peninsula, Borneo, and the Philippine Islands, and if completer racial adjustment is needed, they are sure to attain to it in the course of generations, through the accumulation of coincident variations. In the last chapter of his Problems of Evolution, Headley discussed from a biological point of view some of the problems arising in the intercourse of eastern and western races. III. AN UNWARRANTED ASSUMPTION. In discussing the influences producing evolution some writers have assumed that all diversity of survival in different groups of individ- uals of the same species is due to diversity in the environments to which the groups are exposed; and as natural selection is defined as the influence of the environment in determining what individuals shall survive, the inference is reached that diversity of natural selection is the only influence producing diversity of survival. A careful study, however, of causes producing diversity of survival in isolated groups shows that this assumption is without foundation. In the first place, it ignores the fact that diversity in sexual selection, and in any one of the other forms of reflexive selection, depends on diversity in the influence of members of the group upon each other, and that these influences may pass through a considerable range of divergence without change in the conditions lying outside of the species. In the case of man the forms of reflexive selection depend chiefly on the form of social organization, which may be subject to great change without reference to change in the environment of the AN UNWARRANTED ASSUMPTION. 145 group. Inthe second place, it ignores the fact that diversity of envi- ronal selection may be brought about either by diversity in the activ- ities of the environment (that is by heteronomic selection), or by diversity in the organism determining its methods of dealing with the environment (that is, by endonomic selection). Small differences may of course be found in the conditions presented in any two isolated positions; but when the divergence in the groups of organisms is not in accord with nor in proportion to these, it can not be attributed to them. If, however, we find that the form of selec- tion is determined by the methods of using the environment adopted by the group, and that this is determined by the innate aptitudes of the individuals that founded the colony, I call the principle aptitudinal selection. If again, the method of using the environment, and so the form of selection, is determined by the training and acquired habits of those founding the group, I call the principle habitudinal selection. Still further, there are strong reasons for believing that divergent forms of survival may arise in isolated groups, not only when the envi- ronment surrounding each group is the same, but when the habitudes and aptitudes of the individuals establishing the groups are the same. If we select two islands as completely alike in climate and resources as can be found, and plant upon the same two colonies of a few families each, selected in such a way that the average character of the colonies, in both innate and acquired characteristics, shall be as much alike as possible, and if we then subject them to complete iso- lation from each other and from the rest of the world, will they not in a few generations become divergent in language, in dress, in customs, in industries, and, if the experiment is continued through scores of gen- erations, even in race characters? This might be called spontaneous diversity of election in partitioned groups, producing divergence of habitudes, and finally divergence of habitudinal selection, and so divergence in race characters. In Professor Conn’s Methods of Evolution, 1900, will be found a very lucid statement of the importance of isolation as a primal factor in all divergent evolution; but his plan of exposition aims at giving in broad outlines the main factors, rather than a complete analysis of the influences producing each. CHAPTER IX. SUMMARY AND CONCLUSION. I. SUMMARY. 1. Segregation. As segregate breeding is the fundamental principle producing racial segregations, and as isolation and selection codperate in controlling the degrees and forms of segregate breeding, and therefore in control- ling variation and heredity, so also it will be found that segregate association is the fundamental principle producing habitudinal segre- gation, and so partition and election codperate in controlling the forms of segregate association, and therefore in controlling innovation and tradition. It is also evident that the initial racial segregation introduced by discriminate isolation, or by the indiscriminate isolation of a few pairs, may be greatly hastened and intensified by the exposure of the isolated groups to diverse forms of selection; and it is no less certain that, even when the environment is virtually the same, diverse forms of selection may be introduced by diverse methods of using the environ- ment that are liable to be adopted by the isolated groups. Moreover, it is equally evident that the initial habitudinal segregation intro- duced by discriminate partition, or by the indiscriminate partition of a single pair, may be greatly hastened and intensified by the exposure of the separated groups to diverse forms of election arising from the various forms of success, which are determined by the activities that become habitual in each group. The evolution of organic types is originated and maintained by partition and election producing habitudinal segregation, and by isolation and selection producing racial segregation. Without these principles producing their intensifying and ramifying effects on organic types, the complex world of life could never have arisen out of the simple forms of primitive life; and without the continuance of the segregations thus produced the diversity that has been reached would soon be dissolved and the whole world of life would be reduced to but one species. But the history of races and species shows, on the one hand, that segregate breeding when fully fortified by physiologi- cal and psychological incompatibilities is never removed ; and, on the other hand, that whenever increasing stringency of segregate breed- ing is in any way introduced, there we have either the transforma- 147 148 SUMMARY AND CONCLUSION. tion of some existing species or the setting apart of new groups that grow into new species unless reabsorbed by crossing or exterminated by competition. The whole process of bionomic evolution, whether progressive or retrogressive, whether increasingly ramified and divergent, or increas- ingly convergent through amalgamation, is a process by which the limitations of segregate breeding are either set up and established or cast down and obliterated. But, as we have already seen, on the side of amalgamation an impassable barrier is in time reached in the physiological and psychological incompatibilities of long-established types, while on the side of advancing segregation the possibilities are constantly increasing. The general result is that new isolations and incompatibilities are constantly arising, forming new races and species, which in time become so divergent that it is impossible for them to coalesce under any conditions. 2. Unbalanced Propagation. If we wish to find a principle which, if continued from generation to generation, will steadily tend towards the transformation of type, it is unbalanced propagation continuously of the same sign. That is, if the result desired is increase of the character under consideration, the selection in successive generations must be of those individuals that possess the character in more than the average degree; and such selection may be said to be continuously of the plus form. If the in- dividuals selected in each generation depart from the type, but are so selected that those above the average are exactly sufficient to balance those from below the average, the average character of the mixing mass will be the sameas the average of the original stock; and again, if the selection is plus in one generation and equally minus in the next generation, the result will be uncertain, even though long continued, for the effects of selection in one generation will be balanced by the effects of selection in the next generation, and we shall have one form of balanced selection. Witha definition of balanced propagation that includes balancing of both the kinds just mentioned, we may say with confidence that unbalanced propagation, if continuous, will produce transformation, and that balanced propagation of the type, if con- tinuous, will produce stability of type, and that balanced propagation of forms, some of which are considerably above the type and others of which are considerably below the type, will produce fluctuating variation. We may next ask, how is unbalanced propagation brought about? The answer is that, in both natural and artificial breeding, it may be UNBALANCED PROPAGATION. 149 brought about either by the unbalanced effects of the processes sepa- rating the individuals into coexistent groups that are prevented from intergenerating, or by the unbalanced effects of differing degrees of survival for different forms of variation. The former principle is called ‘‘isolation,’’ and the latter principle ‘‘selection.”” It is quite evident that in as far as selection prevents any form from propagating, in so far it prevents intergeneration between that form and the forms that produce the next generation; but, at the same time, I prefer to define isolation as the prevention of free crossing between coexisting groups, though the individuals of each group, so far as they survive, are freely intergenerating. When pointing out the correspondences between selection and isolation, I would say that both are principles by which the abiding principle of segregate breeding is modified and intensified; and that when either of them produces unbalanced propagation effected by the same signin successive generations, the result is transformation of type. During the process of domestication the reproductive powers of many species are so impaired that it is with difficulty that a perma- nent domestic race can be produced. Many individuals that thrive on the nourishment furnished fail to leave offspring, so that the race is perpetuated not by the offspring of those which are most pleasing to those who keep and select them, but by the offspring of those which have offspring. The same principle may produce transformation in species that are not under domestication. For if, among the many varieties, there arises one that, while retaining equal adaptation, is more fruitful than other varieties, it will be favored by fecundal selec- tion. The descendants of the most fertile will have the largest share in producing the next generation. ‘This will tend to produce increas- ing fecundity in succeeding generations. his isa form of discriminate survival; but we must remember that this fecundal selection will pro- duce accumulation of other characters besides fecundity only when fecundity is correlated with certain variations that do not represent the typical or average form; that is, only when it is unbalanced fecun- dity. This seems to be a necessary law. Asa corollary from this law, I judge that, in a stable intergenerating species or variety, the aver- age form will be found to be most fertile; or, at least, the forms that depart from the average will not be continuously endowed with higher fertility than the averageform. In considering the effect of selective survival we have to discriminate between balanced and unbalanced selection. Unbalanced selection is either the selection of individuals above the average producing an increase of the character thus selected or the selection of individuals below the average producing a decrease 150 SUMMARY AND CONCLUSION. of the character thus discriminated against. Balanced selection is usually secured by selecting individuals of the average form, and tends to produce increasing stability. 3. Cumulative Effects through the Cooperation of Different Principles. Two or more of the factors mentioned in this volume may co- operate in rendering a type more stable, or in rendering its previously attained characters more intense, or in diminishing its present char- acteristics while others are brought into prominence. If the organ- isms under consideration form but one intergenerant, any transforma- tion thus produced will be monotypic; butif through the codperation of isolation they form several intergenerants, any subsequent trans- formation will result in polytypic evolution. Again, if each factor working by itself would tend to produce the same result, the united influence of several factors working together will be much more decisive than that of but one of them working alone. 4. Cumulative Effects through the Operation of the Same Principle in Successive Generations. Once more it should be noted that the effect of unbalanced selection when continued through many successive generations is vastly greater than when lasting but for one generation. Indeed, on reflec- tion it becomes apparent that the great difference between selective survival and non-selective survival is that the former is continuous from generation to generation, while the latter is accidental, and, therefore, not continuous. Moreover, in non-selective survival the effects of survival in any one generation are liable to be in a measure neutralized by the effects of survival in succeeding generations. Dis- criminate isolation is more effective than indiscriminate isolation because it is more effective in bringing together in one groupa consid- erable number of individuals that belong to the same class; that is, that are either of average character, or above the average, or below the average. Indiscriminate isolation is less likely to bring together a special type and to repeat the process through many generations, and is, therefore, usually less effective than discriminate isolation in producing transformation. The probability that a cumulative result will be reached through the effects of indiscriminate isolation, dividing the whole species into, two large and nearly equal groups, without the codperation of selec- tion or without the continuous and cumulative effects of suetude (7. e., of use or disuse), is very small; but we must remember that when isolation has become effective in shutting out all individuals of other groups, divergent selection, divergent suetude, and different forms ‘a SOME OF THE FACTS EMPHASIZED. ESt and degrees of amalgamation are liable to arise. ‘his liability is enhanced in case the fragment indiscriminately separated is small; for there is then a possibility that, in some one of its habitudes or aptitudes, it will differ from the original stock in such a way as to insure its using the environment in a somewhat different manner. It is certain that isolation is a principle tending toward the introduction of diversity not only in the forms of environal selection affecting the species, but also in the forms of reflexive selection, of suetude, and of amalgamation. The distinction indicated by discriminate and indiscriminate isola- tion pertains only to the generations when group-formation is being shaped by additions brought in from the parent stock or from other groups, and these are usually the earlier generations of the new groups; but the influence of this primal shaping will continue through subse- quent generations. The action of discriminate survival and of suetude is, however, not at all confined to the earlier stages of group formation. 5. Amalgamation. After a group has been considerably differentiated, combination with other groups is described as amalgamation. Amalgamation, or the crossing of races that have been segregated for many generations, is a most effective process for introducing varia- tion; and, if the contrast is not too great, for adding vigor to the stock. 6. Some of the Facts Emphasized in this Volume. (1) That segregation is the underlying principle throughout the whole process of bionomic evolution. (2) That the causes producing and intensifying segregation are quite various, and can not all be included under the term “‘ selection,’’ and that in seeking the causes of organic evolution we must investigate all the natural causes modifying the action of segregate breeding. (3) That some of the most powerful influences in the control of seg- regation are due not to different forms of activity in the environment, but to diversity of activities in the organism, and may, therefore, be classed as forms of autonomic segregation. (4) That habitudinal demarcations, through partition, are the initial forms of grouping, which, when intensified by election, produce habitudinal segregations, and that habitudinal segregations are often the controlling factors leading to racial segregations. (5) That in reflexive selection (that is, selection produced by the relations of members of a species to each other), the influence of the environment in producing the special result is usually very obscure, 152 SUMMARY AND CONCLUSION. though there can be no doubt that it is sometimes operative. Social organization is often affected by the conditions in the environment; but though the environment remains unchanged, vast changes in social organization may take place. For example, while remaining in the same region, and without special change in the environment, a tribe of men may pass from the hunter stage of life, through some- thing of pastoral life, into agricultural and diversified industrial life. This has probably been the experience of the Chinese race. (6) That endonomice selection, resting on the power of different individuals of the same species to deal with the same environment in different ways, is a fruitful cause of divergent evolution in isolated sections of the same species. This diversity of power is sometimes due to diversity of aptitudes, producing what I call aptitudinal selec- tion; and sometimes to diversity of training and of habitudes, pro- ducing what I call habitudinal selection; and at still other times to different methods of using the same aptitudes and habitudes, for which a suitable name has not yet been suggested. (7) That organic (or coincident) selection is of great importance in securing a new adjustment when the organism is suddenly exposed to an environment very different from that to which it was previously adjusted. (8) That the indiscriminate isolation of a small fragment of a species leads directly to the modification of type in the descendants of the isolated fragment, for the character of a single individual (or even the average character of several individuals) seldom if ever represents the average character of the original stock in every respect. (9) That indiscriminate isolation of a large section of a species interrupts the unifying influences of tradition and of heredity between separated branches of the original stock; and, even though the environ- ment surrounding each branch is the same, the traditional method of dealing with the environment may in one or in both branches become modified, and the separate branches be thus subjected to divergent forms of endonomic selection. (10) That the indiscriminate elimination of all but a small fragment of an intergenerating group may be an important factor in introducing transformation, for one or two individuals may not be able to transmit all the traditions of the original group, or to reproduce in the innate characters of their offspring the unchanged average character of the original stock. (11) That advancing powers of accommodation, codperating with higher degrees of altruistic social organization, are in an ever-increasing measure setting aside both environal and dominational selection, and so lowering the racial standards of civilized man. A METHOD OF STUDY. 153 (12) That a perverted form of prudential selection is threatening the very existence of some nations that are counted highly civilized. (13) That the only remedy for these destructive tendencies lies in enlightened and renovated institutional and prudential selection, and the wide adoption of higher ideals. (14) That the most marked characteristic of modern human history is found in the breaking down of many of the minor segregations, both social and racial, of previous eras, and the ever-increasing intercourse between nations and races. (15) That, notwithstanding the general trend of the new era, among the millions of India many new castes have been established during the past century. II. CONCLUSION. 1. What has been Gained by Recognizing Habitudinal Segregation ? Having completed our study of the four principles of segregation, let us turn to the classification given in Appendices I and IJ, and consider what has been gained by the distinct recognition oj habitudinal segregation. In Appendix I the combined action of partition and election, produc- ing segregate association of individuals according to their acquired characters, and of isolation and selection, producing segregate inter- generation of individuals according to their innate characters, is pre- sented under the single term “ segregation.’ The action and reaction between the two spheres of segregation is not clearly presented, and, under the nomenclature there given, it would be difficult to consider all the aspects in which this interaction is manifested. In Appendix II, assimilational, stimulational, suetudinal, and emotional intension are used to designate intensification, produced by the different forms of accommodation and of acquired characters; while other terms are used to designate the intensification produced by the different forms of unbalanced propagation, securing the survival of certain types of variation in innate characters. The interaction, however, between habitudes and aptitudes is not as clearly presented in these earlier papers as in the chapters of this volume. 2. A Method of Study that should be fully Applied. I believe the facts of distribution to which I call attention are of great importance, and that the methods of collecting and of exhibiting by which these facts have been brought to light is worthy of being applied in other fields. This method may be regarded as a develop- ment of the study of ‘‘centers of creation,” initiated by Louis Agassiz and transformed by Darwin, Wallace, and others into the study of geographical distribution as affected by migration and divergent evo- 154 SUMMARY AND CONCLUSION. , lution. In order to perfect the method it is important that the ‘crea- tures under study should be labeled at the time of collection with the conditions (of feeding, ete.) under which each specimen was found, and should be exhibited on maps setting forth as fully as possible the conditions presented by the environment at each point. An impor- tant step in this direction has been made by the late Professor Hyatt, of the Museum of the Boston Society of Natural History, in construct- ing a model of the island of Oahu, on which the geographical relations of the species and varieties of snails from that district may be exhib- ited. It would, however, bea great gain if a model (or at least a map) of the island of sufficient size were so arranged as to allow the shells themselves to be placed upon it in their true positions, instead of being represented by letters and numbers. The advantage of both methods might be attained by having, in addition to the model of the island arranged according to Professor Hyatt’s method, a very large map on which the shells might be placed. The method might be further improved by the use of colors and other devices for indicating the species of plant on which each speci- men, was found. The influence of temperature, humidity, and other external conditions, and especially of the conditions interfering with free crossing, may also be studied by exhibiting the average character attained under different stages of the influence and the degree of seg- regation resulting from the full action of the combined influences. The degrees of segregation that have taken place in the inhabitants of a series of districts presenting different degrees of geographical isolation may also be studied by the determination of place-modes by statistical methods. Information on the mathematical methods that have been applied to this and other allied problems in biology will be found in the works of Francis Galton, Karl Pearson, C. B. Davenport, and others, and in ‘‘ Biometrika,” a journal for the statistical study of biological problems. 3. The Study of Conditions lavoring Segregation. A rich field for the study of organisms under conditions favoring segregation will be found in the fauna and flora of island groups. The most interesting conditions will appear where the majority of the species are able to distribute themselves with some degree of freedom from island to island, while some one organic form is unable to pass the water barriers, except on very rare occasions. In such a region we shall, I believe, always find a serves of nearly related varieties or species distributed in the midst of a comparatively uniform environment. Simi- lar results will undoubtedly be found wherever a group of organisms 2 AN EXAMPLE IN ACCORD WITH THE THEORY. 155 : that rs variable but of very limtted powers of migration has been for many generations surrounded by a mass of species possessing ordinary powers of vartability and ordinary facilities for distributing themselves. If this prediction is found to be in accordance with facts, it will show that the explanation of divergent evolution to which we have been led by the investigations presented in the foregoing chapters is essentially correct. 4. Prediction Confirmed by Partula of Tahttt. Since writing the preceding statement, I have read with the greatest interest Dr. A. G. Mayer’s memoir on ‘‘Some Species of Partula from Tahiti; A Study in Variation.’”’ The conditions of variation and migration which he brings to light in the case of some of the snails of Tahiti are a fine example of the conditions which I have found in the Hawaiian snails to be most favorable for the segregation of many closely related forms within a comparatively limited district, each section of which presents essentially the same environment. These conditions are, in the case of the closely related but divergent forms, a full degree of variability, but a very limited power of migration, and in the surrounding species the ordinary endowments in regara to variation and migration. Partu/a hyalina is found in all the valleys of the island of Tahiti; also on the Austral islands and on one of the Cook group. It may, therefore, have opportunities for migration that are not possessed by the other species of Partula found on Tahiti; and certainly it does not present the tendency to variation in form and color which we find in some of these species. Of these.other types I will refer only to three species which are found in four valleys, in which the character of the vegetation is essen- tially the same. On the north side of the island are three approxi- mately parallel valleys, Pire, Fautaua, and Tiperui. The first and last of these are about 3 miles apart, Pir lying on the east and Tiperui on the west, while Fautaua and several narrow gorges lie between them. These three valleys are, however, ‘broad and well- watered, and contain a luxuriant growth of wild plantains and Cala- dium, upon which the snails are found in large numbers.’’ Besides Partula hyalina, mentioned above as found in all the valleys of the island, there are two species of Partula found in these valleys. Par- tula filosa is found only in Pire, and though constantly dextral pre- sents divers shades of color. Partula otahcitana is found in all three of the valleys, but presents hereditary tendencies differing in each of the valleys; for example, in Pire it is constantly sinistral, in Tipeerui it is constantly dextral, and in Fautaua dextral and sinistral forms are found in nearly equal numbers. 156 SUMMARY AND CONCLUSION. On the south side of the island, about 27 miles from the three valleys just mentioned, is the valley of Vaihiria, where Partula sints- trorsa isfound. Thisspecies, though closely related to the two species last mentioned, has adopted a different habit of feeding. ‘‘The Caladium and the wild plantain grow here in abundance, but most of the snails were found upon the wild turmeric, almost none being dis- covered upon the Caladium, and but few upon the leaves of the wild plantain.”” It is very variable in color, but easily distinguished from those of similar color in the valleys first mentioned by its lack of a tooth on the body whorl, by its relatively thin and fragile lip, by its more constricted suture, and by the lack of variation in the color of the young. Ofits individuals 90 per cent are sinistral and 10 per cent dextral. From these facts Doctor Mayer draws the following conclusions: Partula hyalina is very stable in all of the valleys, and gives rise to no varieties. All the other species, however, are remarkably variable, and give rise to numerous color-sports. These color-sports tend to breed true to themselves, and, therefore, to originate new color-forms and finally new species. This tendency is, however, held in check by frequent inter-crossing with the parent stock, and becomes effective only when the new color variety is isolated, or when it displays a remark- ably strong tendency to breed true. * * * It is probable that geographical isolation plays a most important part in the formation of new species. If two valleys be adjacent, their snails are closely related each to each, whereas the wider the separation between any two valleys the more distant the relationship between their snails. The ridges between the valleys, being either barren or covered with vegetation unsuitable to the snails, afford barriers over which the animals must find it more or less difficult to pass. Thus the Partula in the Tahitian valleys are isolated very much as are the Achatinellidae of Oahu in the Hawatian Islands. * * * As far as the very limited observation of the writer goes, there appears to beno differencein the character of the snailsin different parts of the same valley. The difference between any two adjacent valleys is, however, very marked. The full statement of these facts and conclusions will be found in Memoirs of the Museum of Comparative Zoology at Harvard College, Vol. XXVI, No. 2, published in 1902. 5. The Power of the Organism to Control its Relations to the Environment Increases with the Stage of Evolution Attatned. We have shown by direct observation that it frequently happens that the same species of snails, when distributed in isolated groups in districts furnishing the same environment, establishes divergent methods of dealing with the environment, and so determines the form of selection to which it is subjected in the different districts. More- over, this power of the organism to control uts relations to the environment is found to belong in a higher degree to vertebrate animals, and espe- cially to birds and mammals, while immeasurably the highest power TENTATIVE VARIATION WITH HEREDITY. 15 “SI of thus shaping his relations belongs to man. Civilized man not only changes his relations to the environment, but by agriculture and other arts transforms the environment to suit his own needs. In all its action inorganic matter is completely indifferent to the character of the results, either within the mass that is acting or in things external to it; but organic life is, throughout all its grades, striving to attain an increasing power of race preservation under given conditions, and, in its highest manifestation in man, it breaks largely away from the ancient thraldom, and assumes an ever-increasing control of the environment. 6. The Chief Method of Advance is Tentative Variation with Transmission to Offspring of the Endowments of the Survivors. Throughout this whole struggle for ascendency the principal method of advance is the sending forth of various tentative experiments in the form of variously endowed individuals presenting many methods of dealing with the environment, each individual that survives having some influence on the endowments of the next generation. This law of the survival of the fittest applies to all from the lowest to the highest; but the qualities that constitute fitness differ progressively. In one stage, strength and such weapons as teeth and claws are of the greatest importance; in another stage, the degree of intelligence and the power to produce artificial weapons is the test; and, in a still higher stage, the power of social organization and the ethical ideals that form the foundation for such organization become the supreme necessity for survival. But throughout itis the same law of survival, the survival of the fittest, the future continuance of those fitted to continue. Though plants are without conscious purpose, we neces- sarily regard their production of flowers and seed as anticipatory action; for the whole significance of the process is found in its helping to secure continued propagation. To an observer at the equator, the sun rises and sets each twenty- four hours, moving ina circle nearly perpendicular to the horizon, while to an observer at the North Pole the sun would rise and set but once in a year, and in each twenty-four hours would move through a complete circle nearly parallel to the horizon, traveling, as conven- tional language would say, from left to right; and to an observer at the South Pole, the same sun would rise and set but once in a year, and would circle in the reverse direction, that is, from right to left. Now, in such a case as this, we do not say that the cosmic process is changed. So also, in the case of ethical man, I would not say, as Hux- ley does, that his life is in opposition to the cosmic process, but rather that he has attained to one of the higher stages of that process, in which the meek are the ones who inherit the earth. 158 SUMMARY AND CONCLUSION. 7. Accommodation, Cooperation, and Anticipation. There are three spheres in which it is evident that progressive adaptation for beneficent action may take place, commencing with the smallest beginnings in the lowest organisms and progressing through each higher stage of evolution till the widest reaches are attained. These three spheres are accommodational action (whether tentative or directly discriminative), co perative action, and anticipatory action. Power for action in these spheres is characteristic of the realm of life, and is manifested in higher and higher efficiency till accommo- dation tries to prove all things, holding fast that which is good; and codperation, associated with division of labor and community of interest, reaches out to include in its beneficence the living universe; and anticipation, pressing forward in its unbounded aspirations and ideals, becomes the ever-advancing influence of foresight and predic- tion in the activities of the highest beings. 8. Increasing Recognition of Autonomic Factors. It will be observed that throughout the whole process of evolution there are two classes of factors, of which one class may be called hete- ronomic, in that they are subject to change through change in activi- ties lying outside of the group of organisms concerned, while the other class may be called autonomic, in that they are controlled by changes within the group of organisms. In the theory of evolution presented by Darwin, the importance of the heteronomic factors was empha- sized, though he pointed out one form of autonomic transformation, which he designated by the term ‘‘ sexual selection.’”’ ‘To some ex- pounders of evolution natural selection has seemed so completely sufficient that they have been ready to deny the influence of sexual selection (or of any other autonomic factor) in producing divergence. On the whole, however, there has been during the past ten or fifteen years an increasing recognition of the fact that not only sexual selec- tion but other autonomic factors are more or less effective in control- ling the forms of selection, and, therefore, in controlling the transfor- mations of organisms. Do we not thus reach one explanation of the continuous advance—the determinate evolution—of certain large classes of animals? The recognition of autonomic factors in the process of evolution is giving new insight into the self-developing endowments of the organic world. APPENDIX I. REFLEXIVE SEGREGATION.* fA small portion of ‘‘ Divergent Evolution through Cumulative Segregation.” ]T Reflexive segregation is segregation arising from the relations in which the members of one species stand to each other. It includes three classes, which I call ‘‘conjunctional,”’ ‘‘impregna- tional,’ and ‘‘institutional segregation.”’ It is important to observe that intergeneration requires compati- bility between members of the group in all the circle of relations in which the organism stands; but, in order to insure isolation between any two or more sections of a species, it is sufficient that incompati- bility should exist at but one point. If either sexual or social instincts do not accord, if structural or dimensional characters are not correlated, if the sexual elements are not mutually potential, or if fixed institutions hold groups apart, intergeneration is obstructed or prevented and isolation is the result, either as segregation or as sepa- ration that is gradually transformed into segregation. (a) CONJUNCTIONAL SEGREGATION. Conjunctional segregation is segregation arising from the instincts by which organisms seek each other and hold together in more or less compact communities, or from the powers of growth and segmentation in connection with self-fertilization, through which similar results are gained. I distinguish four forms—social, sexual, germinal, and floral segre- gation. * Under ‘‘Demarcational Segregation” I class the influences by which organ- isms are distributed in separate groups. It includes both environal segregation and reflexive segregation, and is equivalent to isolation as now generally used. In the section of this paper on Environal Segregation (not here reproduced), I considered the forms of isolation arising from the relations of the species to the environment. A classified table of the forms of segregation will be found near the end of this paper. + Read December 15, 1887. From the Linnean Society’s Journal, Zoology, Vol XX. 159 160 APPENDIX I—-DIVERGENT EVOLUTION. 10. Social Segregation Produced by Discriminative Action of Social Instincts.* The law of social instinct is preference for that which is familiar in one’s companions; and as in most cases the greatest familiarity is gained with those that are near of kin, it tends to produce breeding within the clan, which is a form of segregate breeding. If the clan never grows beyond the powers of individual recognition, or if the numbers never become so great as to impede each other in gaining sustenance, there will be but little occasion for segregation; but multiplication will lead to subdivision. Wherever the members of a species, ranging freely over a given area, divide up into separate herds, flocks, or swarms, of which the members produced in any one group breed with each other more than with others, there we have social segregation. It should always be kept in mind that social segregation arises at a very early stage, often holding apart groups but very slightly differ- entiated; while in the case of many animals the sexual instincts of the males tend to break up these minor groups. Though the barriers raised by social instincts are often broken over, their in- fluence is not wholly overcome, and in many instances the social segregation becomes more and more pronounced, till in time decided sexual segregation comes in to secure and strengthen the divergence. 11. Sexual Segregation 1s Produced by the Discriminative Action of Sexual Instincts. There can be no doubt that sexual instincts often differ in such a way as to produce segregation. But how shall we account for these differences? In the case of social segregation there is no difficulty, for it seems to be, like migration, due to a constant instinct, always tending to segregation. We also see that an endowment which pre- vents the destruction of the species through the complete isolation of individuals, and which codperates with migrational instincts in secur- ing dispersal without extinction, may be perfected by the accumulat- ing effects of its own action. And is there any greater difficulty in accounting for the law that regulates sexual instincts? If it can be shown that vigor and variation, the conditions on which adaptation depends, are in their turn dependent on some degree of crossing, there will be no difficulty in attributing the development of an instinct that secures the crossing to the selection of the individuals that possess it in even a small degree. On the other hand, whenever there arises a variety that can maintain itself by crossing within the same * Numerals are used to designate causes of segregation not depending on human purpose. Of these nine were mentioned in the section on environal segregation. SEXUAL SEGREGATION. IOI variety, any variation of instinct that tends to segregation will be preserved by the segregation. It needs no experiments to prove that if the members of a species are impelled to consort only with the mem- bers of other species, they will either fail to leave offspring or their offspring will fail to inherit the characteristics of the species. The same is true concerning the continuance of a variety that is not some- how segregated. The power of variation on the one hand, and the power of divergent accumulation of variations on the other hand, are prime necessities for creatures that are wresting a living froma vast and complex environment; and the former is secured by the advan- tage over rivals possessed by the variations that favor crossing, and the latter by the better escape from the swamping effect, and some- times from the competition of certain rivals, secured by the more segregative variations. We must, therefore, believe that whenever in the history of an organism there arise segregative variations which are able to secure sufficient sustentation and propagation to continue the species, the segregative quality of the forms thus endowed will be preserved and accumulated through the self-accumulated effect of the segregative endowments. It is probable that in many of the higher vertebrates sexual in- stincts tend to bring together those of somewhat divergent character, but the difference preferred is within very narrow limits; and beyond those limits it may be said that the general law for sexual attraction is that it varies inversely as the difference in the characters of the races represented, if not inversely as some power of such difference. The action of such a law is necessarily segregative whenever the diver- gence has, through other causes, passed beyond the limit of higher attraction. Before sexual segregation can arise, there must arise distinctive characteristics by means of which the members of any section may discriminate between those of their own and other sections. If there are no constant characteristics there can be no constant aversion between members of different groups, no constant preference of those of one’s own group. From this it follows that before sexual segregation can arise, some form of segregation that is not dependent on distinct characteristics must have produced the divergence on which the sexual segregation depends. Such forms are local, social, and some kinds of industrial segregation. When varieties have arisen through these causes it often happens that sexual segregation comes in and perpetuates the segregation which the initial causes can no longer sustain. As long as the groups are held apart by divergent sexual instincts, it is evident that divergent forms of sexual selection are almost sure to arise, leading to a further ac- cumulation of the divergence initiated by the previous causes. 162 APPENDIX I—DIVERGENT EVOLUTION. If there is any persistent cause by which local and social groups are broken up and promiscuously intermingled before recognizable char- acters are gained, the entrance of sexual segregation will be prevented. I therefore conclude that the chief influence of this latter factor is found in its prolonging and fortifying the separate breeding of varie- ties that have arisen under local, social, or industrial segregation, and in thus continuing the necessary condition for the development of increasingly divergent forms of intensive segregation, under which the organism passes by the laws of its own vital activity when dealing with a complex environment in groups that never cross. 12. Germinal Segregation is Caused by the Propagation of the Species by means of Seeds or Germs, any one of which, when developed, forms a community so related that the members breed with each other more frequently than with the members of other communities. If the constitution of any species is such that the ovules produced from one seed are more likely to be reached and fertilized by pollen produced from the same seed than by pollen produced from any other one seed, then germinal segregation is the result. In order to secure this kind of segregation it is not necessary that the flowers fertilized by pollen from the same plant should be more fertile or the seeds capable of producing more vigorous plants than the flowers fertilized by pollen from another plant. All that is re- quired is that the seeds produced by each individual plant shall be fertilized by the pollen of the same plant. This form of segregation is closely related to local segregation on one side and to social segregation ontheother. It, however, differs from the former in that it does not depend on migration or trans- portation, and from the latter in that it does not depend on social instincts. 13. Floral Segregation ts Segregation arising from the Closest Form of Self-fertiliza- tion, namely, of the Ovules of a Flower by Pollen from the same Flower. Some plants that in their native haunts are frequently crossed by the visits of insects depend entirely on self-fertilization when trans- ported to other countries where no insect is found to perform the same service for them. The common pea (Pisum sativum) is an example of a species that does not fail of propagating in England, though Dar- win found that it was very rarely visited by insects that were capable of carrying the pollen, and the pollen is not carried by the wind.* Darwin also mentions Ophrys apifera as an orchid which ‘‘has almost certainly been propagated in a state of nature for thousands of gen- erations without having been once intercrossed.’’ + * Cross and Self Fertilization in the Vegetable Kingdom, p. 161. t Ibid., p. 439 IMPREGNATIONAL SEGREGATION. 1623 GENERAL OBSERVATIONS ON GERMINAL AND FLORAL SEGREGATION. A fact of great importance in its bearing on the origin of varieties should be here noted. Any variation, arising as a so-called sport, in any group of plants where either of these principles is acting strongly, will be restrained from crossing, and will be preserved except in so far as reversion takes place. Now, there isalwaysa possibility that some of the segregating branches of descent will not revert, and that, through the special character which they possess in common, they will some time secure the services of some insect that will give them the benefit of cross-fertilization with each other without crossing with other varieties. The power of attaining new adaptations may be favored by self-fertilization occasionally interrupted by interbreeding with individuals of another stock; for the latter is favorable as intro- ducing vigor and variation, and the former as giving opportunity for the accumulation of variations. These two methods of propagation are so far removed from those found in the majority of species that it may be wise to consider any transformation arising under such conditions as belonging to a separate department of the process of evolution. Organisms that are self-fertilized in all their generations seem to stand innearer relation to species entirely without the power of sexual propagation than to species in which cross-fertilization is the usual method of propagation. (b) IMPREGNATIONAL SEGREGATION. Impregnational segregation is due to the different relations in which the descendants of one original stock stand to each other in regard to the possibility of their producing fertile, vigorous, and fully adapted offspring when they consort together. In order that impregnational segregation should be established and perpetuated, it is necessary, first, that variation should arise, from which it results that those of one kind are capable of producing vig- orous, adapted, and fertile offspring in greater numbers when breeding with each other than when breeding with other kinds; second, that mutually compatible forms should be so brought together as to insure propagation through a series of generations. In order to secure this second condition, it is necessary that, in the case of plants, there should be some degree of local, germinal, or floral segregation, and, in the case of animals that pair, either pronounced local segregation or partial local segregation, supplemented by social or sexual segregation. The action of the different forms of impregnational segregation I call negative segregation, for they rest on incompatibilities interfering with mixed unions or allowing of no offspring, or of but few or inferior offspring, as the result of mixed unions, and, unaided by positive seg- I 64 APPENDIX I—DIVERGENT EVOLUTION. regation, can do nothing toward bringing creatures together accord- ing to their compatibilities. The forms of segregation that place or draw together creatures of like innate characters I call forms of post- tive segregation. Of each form of segregation which we have up to this point con- sidered, the segregating cause has been one that distributes individuals of the same species in groups between which free intergeneration is checked; while the propagation of the different groups depends sim- ply on the original capacity for intergenerating common to all the members of the species. The intercrossing has been limited not by the capacity but by the opportunity and inclination of the members. Coming now to cases in which complete lack of capacity for fruitful crossing is the cause that prevents the production of mongrels, we find a dependence of a very different kind; for toinsure the propagation of the different groups it is not enough that the general opportunity for the members of the species to meet and consort remains unimpaired. There must be some additional segregating influence bringing the members together in groups corresponding to their segregate capacity, or they will fail of being propagated. The form of impregnational segregation which I call prepotential segregation is due to the prepotency of the pollen of a species or variety on the stigma of the same species or variety, and complete potential segregation is due to the potency of the pollen of the same species, with the complete impotence of the foreign pollen. When allied species of plants are promiscuously distributed over the same districts, and flowering at the same time, prepotency of this kind, aided by the free dis- tribution of the pollen by the wind, is one of the most direct and efficient causes of segregate breeding. The same must be true of varieties similarly distributed whenever this character begins to affect them. In the case, however, of dicecious plants and of plants whose ovules are incapable of being impregnated by pollen from the same plant, no single plant can propagate the species. If, therefore, the individuals so varying as to be prepotent with each other are very few, and are evenly distributed amongst a vast number of the original form, the probability is that they will fail of being segregated through failing to receive any of the prepotent pollen. It is thus apparent that when the mutually prepotent form is represented by comparatively few indi- viduals, their propagation without crossing will depend on their being self-fertile and subject to germinal or floral segregation, or on their being brought together by some other form of positive segregation. When a considerable number of species of plants are commingled and are flowering at the same time, their separate propagation is DIMENSIONAL AND STRUCTURAL SEGREGATION. 165 preserved, in no small degree, by the prepotential segregation of those that are most nearly allied and by the complete potential segregation of those that belong to different families, orders, and classes. ‘The same principle must come in to prevent the crossing of different spe- cies, genera, families, and orders of animals whose fertilizing elements are distributed in the water. When aided by this free distribution the combined effect is that of positive as well as negative segregation; for the free distribution of the fertilizing element, with the superior aflinity of the two sexual elements that are mutually prepotent, secures the interbreeding of the species or variety producing the mutually prepo- tent elements. Impregnational segregation generally exists between the different species of the same genus, almost always between species of different genera, and always between species of different families, orders, classes, and all groups of higher grade. And in all these cases it is associated with other forms of segregation, and when once complete the groups affected never coalesce. Though complete mutual ster- ility never gives place to complete mutual fertility, in every case where the descendants of the same stock have developed into different classes or orders, and in most cases where they have developed into different families or genera, the reverse process has taken place, and complete mutual fertility has given place to complete mutual sterility. Under impregnational segregation I distinguish dimensional segre- gation, structural segregation, potential segregation, segregate fecun- dity, segregate vigor, segregate adaptation, segregate freedom from competition, and segregate escape from enemies. 14. Dimensional Segregation (or Segregative Size) is caused by Incompatibility tn Size or Dimensions of the Individuals of the Different Breeds. As familiar illustrations of this form of segregation, I may mention the following: The largest and smallest varieties of the ass may run in the same pasture without any chance of crossing. I have also kept Japanese bantam fowls in the same yard with other breeds without any crossing. In many other species individuals of extreme diver- gence in size are incapable of interbreeding. 15. Structural Segregation (or Segregative Structure) ts Caused by Lack of Correlation in the Size of Different Organs and by other Incompatibilities of Structure. Darwin suggests that the impossibility of a cross between certain species may be due to a lack of correspondence in length of the pollen tubes and pistils. Such a lack of harmony would perhaps account for difference of fertility in reciprocal crosses, according as the male is of the one variety or of the other. 166 APPENDIX I—DIVERGENT EVOLUTION. Segregative structure does not usually arise till other forms of segre- gation have become so well established that difference of structure does not make any essential difference in the amount of intergenera- tion. It is not, however, impossible that species that would otherwise freely cross are thus held apart. In Broca’s work on ‘‘Human Hybridity’’* there is a passage quoted from Prof. Serres showing that it is very possible that this form of incompatibility may exist between certain races of men. 16. Potential Segregation (or Segregative Potency) in its Two Forms, Complete Potential Segregation and Prepotential Segregation. (1) Nature of the Principle.—It is caused by the greater rapidity and efficiency with which the sexual elements of the same species, race, or individual combine. Complete potential segregation is caused by the mutual impotence of the contrasted forms, as is always the case between different orders and classes; and prepotential segre- gation is caused by the superior influence of the fertilizing element from the same species, race, or individual, as contrasted with that from any other species, race, or individual, when both reach the same ovum at the same time, or sometimes when the prepotent element comes many hours after the other. That propagation may result compatible elements must meet. When pollen from a contrasted genus, order, or class has no more effect than inorganic dust, it seems appropriate that we should call the result complete potential segregation rather than prepotential segregation, which implies that the foreign as well as the home pollen is capable of producing impregnation. Prepotential segregation may be considered the initial form of potential segregation. The principle is fundamentally one, though it will be convenient to retain both names. The importance of this principle in producing and preserving the diversities of the vegetable kingdom can hardly be overstated. If pollen of every kind were equally potent on every stigma, what would the result be? What distinctions would remain? And if potential segregation is necessary for the preservation of distinctions, is it not equally necessary for their production? Amongst water animals that do not pair, the same principle of segregation is probably of equal importance. Concerning this form of segregation many questions of great interest suggest themselves, answers to which are not found in any investigations with which I am acquainted. * Enélish translation, published by the Anthropological Society of London, p. 28. POTENTIAL SEGREGATION. 167 Some of these questions are as follows: (2) Points needing investigation.—First. Are there many cases of prepotential as well as of complete potential segregation between dif- ferent forms of water animals? Second. Is prepotential segregation always accompanied by segre- gate fecundity and segregate vigor? Third. If not always associated, which of the three principles first appears? And what are their relations to each other? Fourth. When allied organisms are separated by complete environal segregation, are they less liable to be separated by these three prin- ciples? Darwin has in several places referred to the influence of prepotency in pollen, and in two places I have found reference to the form of pre- potency that produces segregation; but I find no intimation that he regarded this or any other form of segregation as a cause of divergent evolution. The effect of prepotency in pollen from another plant in preventing self-fertilization is considered in the tenth chapter of his work on ‘‘Cross- and Self-fertilization in the Vegetable Kingdom,” pp. 391-400. Some very remarkable observations concerning the pre- potency of pollen from another variety than that in which the stigma grows are recorded in the same chapter, but no reference is there made to the effect that must be produced when the pollen of each variety is prepotent on the stigma of the same variety. In Chapter XVI of ‘‘ Variation under Domestication ”’ it is suggested that prepotency of this kind might be a cause of different varieties of double hollyhocks reproducing themselves truly when growing in one bed, though there was another cause to which the freedom from crossing in this case has been attributed. Again, in Chapter VIII of the fifth edition of ‘‘The Origin of Species,’’ in the section on ‘‘The Origin and Causes of Sterility,’ Darwin, while maintaining that the mutual sterility of species is not due to natural selection, refers to prepotency of the kind we are now considering as a quality which, occurring in ever so slighta degree, would prevent deterioration of character, and which would, therefore, be an advantage to a species in the process of formation, and accordingly subject to accumulation through natural selection. In order to construct a possible theory for the introduction of sterility between allied species by means of natural selection, he finds it necessary simply to add the supposition that sterility is directly caused by this prepotency. He, however, for several reasons, concludes that there is no such dependence of mutual sterility on the process of natural selection. Concerning the pre- potency he makes no reservation, and I accordingly judge that he 168 APPENDIX I—DIVERGENT EVOLUTION. continued to regard it as strengthened and developed through the action of natural selection.* (3) Reasons for believing that potential segregation can not be accu- mulated by natural selectton.—Concerning this last point I wish to give reasons fora different opinion. I believe that qualities simply produc- ing segregation can never be accumulated by natural selection, for— lirst. When separate generation comes in between two sections of a species they cease to be one aggregate, subject to modification through the elimination of certain parts. Both will be subject to sim- ilar forms of natural selection only so long as the circumstances of both and the variations of both are nearly the same, but they will no longer be the members of one body between which the selecting pro- cess is carried out. On the contrary, if they occupy the same district each group will stand in the relation of environment to the other, mod- ifying it, and being modified by it, without mutually sharing in the same modification. Second. Though one may exterminate the other, the change that comes to the successful group through the contest is not due to its superiority over the other, but to the superiority of some of its own members over others. Third. Whenany segregate form begins toarise we can not attribute its success to the advantage of isolation, for it is not the success, but the separateness of the success, that is due to the isolation. Fourth, The power of migration, or any other power directly re- lated to the environment, may be accumulated by natural selection, and afterward lead to segregation, but, according to my method of judging, the advantage of segregation over intergeneration is not the cause of the preservation of forms endowed with segregative qualities, for they will certainly be preserved as long as they are able to wina bare existence, which is often a lower grade of success than the one from which they are passing. (4) How shall we explain the accumulation of potential segregation?— But if the accumulation of prepotential segregation is not due to nat- ural selection, how shall we explain it?) The divergence of a group can not take place without its being segregated from the original stock as well as from other types; and the potency of the sexual elements of the new group will be maintained in their relations to each other by some form of reflexive selection; but as there can be no reflexive selec- tion between the segregated groups, the potency of the elements for crossing outside of the group will in time be impaired; and then we * Since my comments on this passage were written I have discovered that Dar win has omitted it from the sixth edition. ACCUMULATION OF POTENTIAL SEGREGATION. 169 shall have prepotency of each group within the circle of its own group. This process may take place when a group is protected by complete isolation, however produced. Let us next consider a case in which a small group partially protected from mixture with the original type by incomplete local and industrial segregation produces a variation ‘whose ovules are more readily fertilized by pollen from the same group than by pollen from the original type. Is it not evident that this variation will gain with each generation an increasing prominence in the new group that maintains somewhat new methods of dealing with the environment in its partially isolated habitat? This will be so, first, because variations possessing but little or no prepotency with their own group will eventually coalesce with the original stock, and especially will this be the case if the new group becomes somewhat numerous and passes beyond the limits of its narrow habitat into districts where the original type abounds; and, second, because vari- ations possessing the prepotency with their own group in a superior degree will remain distinct, breeding with each other, and their de- scendants will become still more segregate and still more perma- nently divergent. Of the law of accumulation of segregative endow- ments, we may say that as the descendants oj the best fitted necessarily generate with each other and produce those still better fitted, so the de- scendants of those possessing the most segregative endowments necessarily generate with each other and produce those that are still more segregate. It will, however, soon be shown that unless the reproduction and power of survival is greater for the pure segregate forms than for the mixed forms, the proportion of pure forms to mixed forms will decrease in each generation. It is evident that when either segregate potency or segregate pre- potency is associated with the free distribution of the fertilizing ele- ment by wind or water, the combined effect must be in the former case complete, and in the latter case partial, positive segregation, for the breeding together of compatible forms is thereby secured, It may at first appear that a slight degree of segregate prepotence will prevent crossing as effectually as a higher degree, but further reflection will show that the efficiency of the prevention will vary in direct proportion with the length of time over which the prepotent pollen is able to show its prepotence, and this will allow of innumer- able grades. If, in the case of certain individuals, the prepotency is measured by about twenty minutes, while with other individuals it enables the pollen of the same variety to prevail though reaching the stigma an hour after the pollen of another variety has been applied, the difference in the degree of segregation will be sufficient to make the persistence of the latter much more probable than that of the 170 APPENDIX I—DIVERGENT EVOLUTION. former. ‘This form of segregation is evidently one of the important causes preventing the free crossing of different species of plants. It probably has but little influence on terrestrial animals; but how far it is the cause of segregation among aquatic animals is a question of no small interest, concerning which I have but small means for judging. I have, however, no hesitation in predicting that, unless we make the presence of this segregative quality the occasion for insisting that the forms so affected belong to different species, we shall find that amongst plants the varieties of the same species are often more or less separated from each other in this way. I do not know of any experiments that have been directed toward the determining of this point; but on the general principle that race distinctions are the initial forms under which specific differences present themselves, I can have no doubt that feeble prepotence precedes that which is more pronounced, and that part of this divergence in many cases takes place, while the diver- gent branches may be properly classed as varieties. Another reason for believing that prepotential segregation will be found on further investigation to existin some cases between varieties is the constancy with which, in the case of species, this character is associated with segregate fecundity and segregate vigor, which we know are sometimes characteristics of varieties in their relation to each other. 17, 18. Segregate Fecundity and Segregate Vigor. By segregate fecundity I mean neither segregation produced by fecundity nor fecundity produced by segregation, but the relation in which species or varieties stand to each other when intergeneration of members of the same species or variety results in higher fertility than the crossing of different species or varieties. In like manner segregate vigor is the relation in which species or varieties stand to each other when the intergeneration of members of the same species or variety produces offspring more vigorous than those produced by crossing with other species or varieties. Integrate fecundity and integrate vigor are the terms by which I indicate the relation to each other of forms in which the highest fertility and vigor are produced by crossing, and not by independent generation. 19. Segregate Adaptation.* Segregate adaptation is the relation in which species or varieties stand to each other when the intergeneration of individuals of the same species or variety produces offspring better adapted than the * This and the following paragraph were not in the paper as first published, though the advantage of escape from severe competition with members of the same species was set forth in the paragraph entitled ‘‘ Competitive disruption.” SEGREGATE FECUNDITY, VIGOR, AND ADAPTATION. in| offspring produced by crossing with other species or varieties. Nat ural selection is the survival of the best adapted of the variations that remain and breed with the stock under consideration, but it takes no cognizance of the fitness or lack of fitness of individuals or a race that separate themselves from the intergenerating mass. ‘The dilferent grades of fitness for their new life found among the individuals that form the new intergenerating group will be the ground for divergent natural selection in the new group; but they will not affect the type of the original stock. Now, whenever the conditions and aptitudes of the two groups are so different that the offspring of cross-unions are less fitted for life under either set of conditions than is either group of the pure-breeds for its own peculiar life, we shall have a new principle, different in its effects from natural selection. This I call segregate adaptation. Natural selection is the survival of the fittest that inter- generate; segregate adaptation is the superior fitness and survival of the offspring produced by segregate generation. 20, 21. Segregate Freedom from Competition and Segregate Escape from Enemies. Segregative endowments may be necessary to the enjoyment of cer- tain advantages which are gained not by superior adaptation to the environment, but by endowments that set them in a position where competitors and enemies are as yet few. These two principles I have called segregate freedom from competition and segregate escape from enemies. Segregate jreedom jrom competition or segregate access to unused resources results when the pure offspring have freer access to unused resources than do the cross-breeds or the original stock. Segregate escape from enemies (an advantage often of equal import- ance with that just mentioned) arises whenever the pure offspring of a divergent variety are able to occupy a position freer from enemies than that occupied by the original stock. (c) INSTITUTIONAL SEGREGATION. Institutional segregation is the reflexive form of rational segrega- tion. It is produced by the rational purposes of man embodied in institutions that prevent free intergeneration between the different parts of the same race. As the principal object of the present paper is to call attention to the causes of segregation acting independently of effort and contriv- ance directed by man to that end, it will be sufficient to enumerate some of the more prominent forms under which institutional segrega- tion presents itself, noting that some of these influences come in as 172 APPENDIX I—DIVERGENT EVOLUTION. supplemental to the laws of segregation already discussed, simply reinforcing by artificiai barriers the segregations that have their orig- inal basisin nature. The chief forms to be enumerated are national, linguistic, caste, penal, sanitary, and educational segregation.* CONCLUDING REMARKS. 1. Impregnational Segregation a Cause of Divergence in both tts Earlier and Later Stages. The negative forms of segregation would tend to produce extinc- tion if they were not associated with the positive forms of segregation. But in the case of organisms whose fertilizing elements are dis- tributed by wind and water, the qualities that produce these nega- tive forms of segregation are usually accompanied by those that produce potential segregation, and potential segregation codperating with this free distribution results in positive-segregation. But even prepotential segregation, when produced by mutual incompatibility between a few individuals and a numerous parent stock, depends for its continuance and development on some degree of local, germinal, or floral segregation, partially securing the intergeneration of the few that are mutually compatible. On the one hand, impregnational segregation depends on some degree of local, germinal, or floral segre- gation which is a constant feature in most species; and, on the other hand, not only do these initial forms of positive segregation fail of producing any permanent divergence till associated with impreg- national segregation, but the more effective forms of positive segrega- tion, such as industrial, chronal, fertilizational, sexual, and social segregation, often depend on impregnational segregation, inasmuch as the divergence of endowments which produces these depends on impregnational segregation. Moreover, in all such cases, increasing degrees of diversity in the forms of adaptation, and consequently of diversity in the forms of natural selection, must also depend upon these negative factors, which in their turn depend on the weak, initial forms of positive segregation. Divergent evolution always depends on some degree of positive segregation, but not always on negative segregation. Under positive * This completes the classification of the forms of isolation which are here pre- sented as forms of demarcational segregation. It is probably correct to say that with the exception of transportational and geological isolation, and perhaps some cases of migrational isolation, all the forms of isolation so far discovered are, from the first, more or less discriminative, and, therefore, segregative. Moreover, if transportational or geological action plants an isolated colony of only a few indi- viduals, the average type of the original stock is not fully represented in the colony and, therefore, the effect is more or less segregative from the beginning. SEXUAL INCOMPATIBILITY. L723 segregation of a rigorous form (as, for example, complete geograph- ical segregation), considerable divergence may result without any sexual incompatibility. Darwin has shown, by careful experiments, that entegrate vigor and fecundity is the relation in which the varieties of one species often stand to each other. This fact does not, how- ever, prove that the more strongly divergent forms, called species, which are prevented from coalescing by segregate vigor and fecundity, did not acquire some degree of this latter character before any perma- nent divergence of form was acquired. Their having acquired this segregating characteristic may be the very reason why their forms are now so decidedly different, for without it they would have been swal- lowed up by the incoming waves of intergeneration. Again, we must remember that forms only moderately divergent are habitually classed as different species if they are separated by segregate vigor and fecundity (that is, by some degree of mutual sterility), unless observation shows that they are of common descent. These two considerations sufficiently explain why the varieties of one species are so seldom reported as mutually infertile. Notwithstanding this, the experiments of Gartner and of Darwin seem to show that seg- regate fecundity and vigor may arise between varieties that spring from one stock. In view of these cases we must believe that in the formation of some, if not many species, the decisive event with which permanent divergence of allied forms commences is the intervention of segregate fecundity or vigor between these forms. Positive segregation, in the form of local, germinal, or floral segrega- tion, producing only transitory divergences, always exists between the portions of a species that has many members; but as it does not directly produce the negative segregation which is, in such cases, the necessary antecedent of permanent divergence, we can not, in accord- ance with the usage of language, call it the cause of the permanent divergence. Moreover, though it may be in accordance with ordinary language to call the negative segregation, which is the immediate antecedent of the permanent divergence the cause of the same, it will be more correct to call the coincidence of the negative and positive segregations the cause, and still more accurate to say that the whole range of vital activities (when subjected to the limitations of any sexual incompatibility that corresponds in the groups it separates to some previous but ineffectual local, germinal, or floral segregation) will produce permanent divergence. In many cases not only is the entrance of impregnational segrega- tion the cause of the commencement of permanent divergence, but its continuance is the cause of the continuance of the divergence. The 174 APPENDIX I—DIVERGENT EVOLUTION. clearest illustration of this is found in the case of plants that are fer- tilized by pollen that is distributed by the wind. All the higher, as well as the lower, groups of such plants would rapidly coalesce if each grain of pollen was capable of producing fertilization, with equal cer- tainty, promptness, and efficiency, on whatever stigma it might fall. We may also be sure that with organisms that depend upon water for the distribution of their fertilizing elements, impregnational segrega- tion is an essential factor in the development of higher as well as of lower taxonomic groups. It is important to observe that, in the cases under consideration, the inferior fertility or vigor resulting from the crossing of the incom- patible forms is as truly a cause of divergence as the inferior oppor- tunity jor crossing which from the first existed between the members occupying different localities or between flowers growing on different trees of the same species. The former has been called negative and the latter positive segregation, not for the sake of distinguishing different grades of efficiency, but for the sake of indicating the different methods of operation in the two classes of segregation. 2. Isolation Usually Somewhat Discriminate, and therefore Segregative, from the Furst. Ot the twenty-one natural forms of isolation enumerated in this paper, there are only two that are usually indiscriminate in their action. These are transportational segregation and geological segre- gation. And even these sometimes become discriminate in their action through the fact that those individuals that are similarly endowed are lable to be transported in the same way and to the same place, or to escape together from destruction in geological disturb- ances. Again, it may happen that by gradual subsidence a large island will be divided into two smaller islands, and thus certain species inhabiting the original island may be indiscriminately isolated. But even in such a case, unless the average inheritable character of each section of the species is exactly the same in all respects, the effect is segregative from the first. If one, or both, of the sections is very small, the probability of exact similarity in all respects entirely dis- appears, unless the species is wanting in plasticity and variability. 3. Principles Intensifying Segregation. Besides artificial and institutional segregation, which depend on the rational purpose of man, we have now considered 21 forms of seg- regation, resting on purely natural causes. At some other time I shall endeavor to present the natural laws that cooperate in intensifying the effects produced by the segregative PRINCIPLES INTENSIFYING SEGREGATION. 175 causes already considered. Segregation is not simply the indepen- dent generation of different sections of a species, but the independent generation of sections that differ. Though indiscriminate isolation of a small section of a species may produce an initial difference, it is evident that the degrees of difference may be greater or less, and that whatever causes a greater difference in two sections that are prevented from intergenerating will also be a cause of increased segregation, and may be classed as a form of intensive segregation. It has been observed that some of the causes enumerated in this chapter are primarily separative, and that no one of those that are primarily segregative is at any one time segregative in regard to many classes of characters. As several forms of segregation may codperate in securing a given division of a species, and one form is superimposed upon another, the aggregate effect must be great; but we easily perceive that it may be indefinitely enhanced by causes producing increased divergence in the segregated branches. The causes which produce monotypic evolution when associated with intergeneration must be equally effective in producing polytypic evolution when asso- ciated with isolation whether in its separative or segregative forms. But the discussion of intensive segregation must be reserved for another occasion. A Lack tn this First Classification of Segregative Principles.* The classification of segregative principles here given does not draw any clear distinction between those resting upon acquired characters and habitudes and those resting upon innate characters and aptitudes. For example, industrial segregation is defined as ‘‘Segregation arising from the activities by which the organism protects itself against adverse influences in the environment, or by which it finds and appropriates special resources in the environment.’ Now it is manifest that in some cases the different methods of using the environment may be determined by acquired habitudes rather than by inherited aptitudes, and the demarcation thus produced will, in the first place, be habitudinal, though in the end it may result in racial demarcation. The interaction between the principles producing racial segregation and those producing habitudinal segregation is discussed in Chapter V (pp. 45-78). It should also be noted that since this paper was brought before the Linnean Society, isolation has come into general use for designating the prevention of free crossing, by which the demarcation of racial groups is determined. This leaves the term ‘‘segregation”’ more free to designate the combined action of the prin- ciples producing the demarcation of groups and of those producing the intensifi- cation of the characters of the separated groups. Partition and isolation pro- duce habitudinal and racial demarcation, while election and selection produce habitudinal and racial intensification, and the combined action of the four principles produces segregation both racial and habitudinal. (Vor a fuller state- different form. 176 APPENDIX I—DIVERGENT EVOLUTION. 4. Classified Table of Forms of Segregation.* DEMARCATIONAL SEGREGATION [OR ISOLATION]. A. Environal segregation: (a) Industrial segregation. Sustentational. 72.4 PF Ne 3 The ote reer eieienie re ciate rei ssn I DOLENSEV.E j5)-5.c:01c1d s sunzaare ee once ies nears aes eee eat renee 2 Nidsficationall 253.000, disedavejade re Sicha hi stniees eto tereiers eke oe eae 3 (6) Chronal segregation. Cyclical sis. soreetniawia Wadena an He cee ete ee eee eee 4 seasonal oj cisco. sincetaierars oie: ects sein cltenas eRe See ERs 5 (c) Spatial segregation. Geographical ( MigtRtiOnal % 5.5 iccnisa tee sient eure salar 6 acai } iiransportational.0. ‘spao. > 2 z{ 26 8 IN—W, jy d... stysiya fs 3 : ; qequinu vy? Surq q pur ‘spsoiq-ypey Jo Joquinu oy} Suroq Fy *\ + m(oz — 1) 7 lS — san i a {| STUSAY AY? YOM Jo ‘suria} u SutuivzUOS 9-2 ‘uotyeisues 9y} JO Joquinu 9u1 Aq passoidxo vy} st surto} Auvul se Burutezuos f° 5 tt + ar Seow 4 + ] Solies oy} Jo F ums vy} Aq porydyypnur ’ 9g or 13 J qur i+ AQ Pesseidxe LY} Se aeUT ee ee u(t? — 1) Pee? 1d JOS YF. Aq Paley [—n(9J¥ — JY) Me = Spadiq-jyey jo uoteisuas YW ay} pue !(97y— JY) K t—uwPIV—W) FOF HOW — IV) F = Specrq-oind jo uorneisues Uy oy —'ajny pworag ‘m2 Aq paydrypnur spaaiq-aind jo uorjeisuas snoracid oy} Surppe pure woz — 1) Aq sposaq-jyey fo VOTPiouNs snotvoid aq} BurAydyynur Aq punoy oie vorvsauas Auv Jo spasiq-jyey oy? pure ‘spy — yy Aq spoorq-aimd jo uoneriouas snorsid oy} BuLAyanynar Aq punofy o1e uUOTeIOUNS Auv Jo Sposiq-aind oy ,—‘ayny ps4tog a + 4 ) " a ) + ( \+ | )) Ky — Jy)ouep = uornvioues yt | -uonvsoues yyw = =vw?W — W)V (ON —W) , PWN), -PN—W). .eM—W) see aie stoes (cone —Ww) * woz —1) * .w(oz — 1)) t (uz —1 )QW — Wey = voResus YF «2 OI — INIMOP + MOOT — 1). OI — WMO + (097 — I) OW — Jx)UoP 4+ g(m(9Z — 1)) 2p = UOTJRIDUDS YF | UOTeIINNS YF = ,(JY — W)Y “ZO — JV) UOp + M07 — TOW — W)Moy + .(me(o7 — 1))2ueP = UOTeIDUD, pE |° UOTeIINNs pe =, — W)Y ‘(VY — Jy) mop + m(oz — 1) WP = UOTPRIDUDS PZ |" UoOTeIoNAs pz = ,(9JY — W)P ‘IM = UOT eINUaS JST | ‘UOT}eIOU[D IST = IY — WW) “roquinu yeniuy = V “spooiq-j]eH ‘spoo1q-amg “spaasq-aand 04 spaaag-{ypF] fo woysodosd ayy Burs ‘Appunda.y ayvsaasay puv Uuoryvsassag avywsog sof vynuso.7 padojaaaq— |] WAV L, 180 APPENDIX I—DIVERGENT EVOLUTION. METHOD OF USING TABLE III (see p. 179). By supposing » to be an indefinitely high number, and by giving different values to J, m, and c, we shall have the means of contrast- ing the number of the pure-breeds with that of the half-breeds, when the process has been long continued under different degrees of posi- tive segregation and segregate fecundity. In the first place, let us take a case in which there is no segregate fecundity, that is \/ = m, and for convenience in computation let us make WM = 1,m = 1. In every case where there is not inte- grate fecundity, that is, where m is not larger than , the fraction (1 — 2c)m ae Y ag, is less than unity, and the sum of the geometrical pro- gression of our formula will fall within the limits of a number that can be easily computed by the well-known formula.S = . in which ’ — if a is the first number of the progression, which in this case is 1, and r is . ae . (1 — 2c)m : the ratio of progression, which in this case is SS ee the fraction we are now considering. Supposing c = a the fraction will be ( 2 ) Game” woe: ; 9 . = : : ER coe a —_ = me ee eS s2. 9 pa» becomes S Ro eae 10 1 9 =9. This number 9 is, therefore, equal to the sum of this progres- sion and can, therefore, be used as the value of the infinite progression in the formula for the nth generation when n is a high number. Substituting these values in the last formula of the table, we find that the nth generation of the half-breeds equals the nth generation of the pure forms, each being equal to 2 of A(M—Mc)*—!, A(M—Mc)*— is a vanishing quantity, for J — Mc is less than 1. Every form is, therefore, in time fused with other forms. But let us try higher ; I I : degrees of segregation. If we make c = —— or ——., we still find 100 1000 that half-breeds = pure-breeds, while the latter are constantly de- creasing, which shows that imperfect positive segregation, without the aid of some degree of segregate survival, can not prevent a species being finally fused with other species. The pure-breeds must de- crease as long as the whole number of each successive generation of pure-breeds does not increase by a multiple equal to or larger than ——. That is, if m=M, and Al < I ;_.¢ fusion will in time become complete. TABLE IV WITH FORMULA. 181 Let us now consider cases in which the segregation is ees but segregate fecundity comes in to modify the result. Let W/ = 2, I er . m=1,C=7. Substituting these values in our formula from Table 18 III, we shall find that the sum of the infinite progression is : Pe And M— Mc = 2 which makes the half-breeds = the pure forms cm; and cm = ary Let MV =2,m=1,c= zag then half-breeds = TO 100 I I payee pure forms x roo? bet M= 2, m = 1, c =~; then the infinite progression = 1, M — Mc =1, and the pure forms in each genera- tion will equal A, and the half-breeds A = *. ‘Therefore, half-breeds = I pure-breeds x 2 TABLE IV.—Simplified Formulas for the Proportions in which Halj-breeds stand to Pure-breeds when all forms of Segregate Survival are considered. In each formula VW may represent the ratio of those coming to maturity in each generation of the pure-breeds, and m may represent the ratio of success or failure of the cross-breeds in coming to maturity in each generation. From Table III we learn that H mc if (i= 2e)m (1 —2c)m)2, [ )3 7a. } 5 = Wa Xx | E+ ag (eae hiy | | 4 P M-—Mc L M — Mc L M—Mc J L | vel ; ie When (1 — 2c)m is less than ets is a decreasing geometrical progression, and we may obtain the value of the whole series by the formula S = —. Applying this formula we have Hm P~ M—Mc * on 1 —~"M—Me eee OG M— Mc ~ M—Mc” M—Mc—m-+ 2mc mec ones Formula (1) mc H=P~x FEE Formula (2) 182 APPENDIX I—DIVERGENT EVOLUTION. The following solutions, as well as those given in Table V, are obtained by substituting values for M, m, and cin formula (2): When M = 4, m = 3, then if c = 4, half-breeds = pure-breeds x ?. c = 3, half-breeds = pure-breeds x 3. c = 4, half-breeds = pure-breeds x 3. c = +, half-breeds = pure-breeds x 3. c = $, half-breeds = pure-breeds » #. TABLE V.—From Formula (2). | When M = 10 andm= 9. 8. ae | 6. re 4. 3. 25 i bes Ifc= then a c) 8 ea ass 5 4 3 2 i — pure-breeds x 10 | 10 10 | 10 10 10 10 10 10 eae oe 9 8 | 6 5 4 2. 2° 3) eh a a 11 12 13 14 15 i6 | 17 18 19 ae 9 8 7 6 5 4 3 2 re Sg 12 14 | 16 Te: |) 200" 99“ |'g4.7 | o61 |) Be | Se a 8 7 |, £68. S| es sa ee ae Tie = ge os 13 i6 Io | 22 W265.) ae "sr Se nag be 2 9) 8) 7 soe] Se! | oa ere Gin ce i | 18 | 22 | 26 | 30 | 34 | 38 | 42 | 46 net = 9 8 7 6 5 4 3 2. 1 ee es 15 | 20 | 25 | 30 | 35 | 40 | 45 | 50 | 55 liegt 9 8 oT 6 5 4 | 3 2 a ean pagaee Ac 17 624°) ate 38 las | Soe) 8os\\e cet) mgs Pesan Spe Se CR ae) et ae 10 is | 26 | 34 | 42 | 50 | 58 | 66 | 74 | 82 Iife=. H=Px 9 8 7 6 Dey ees [Se he ee ee 100’ 108 | 206 | 304 402 | 500 | 598 | 696 | 794 | 892 1G ye a ey eke CE a 7 6_| _5 csi ea | 2 | 1000’ : 1008 2006 3004 4002 | 5000 | 5998 | 6996 | 7994 | 8992 OBSERVATIONS ON TABLE V. This mathematical analysis of the effects of positive segregation and segregate fecundity when coédperating brings distinctly into view several important relations. First. Incomplete forms of positive segregation, that avail little or nothing in preventing a form from being absorbed in the course of time, become very efficient when strengthened by moderate degrees of mutual sterility. Take, for instance, the line of the table in which I c = —~. If 1 in every 100 unions is a cross with some other form, 100 OBSERVATIONS ON TABLE V. 183 the form will in time be overwhelmed, unless other causes come in to counteract; but here we see that, if segregate fecundity occurs in the ratio of 10 to 9, the pure form becomes 12 times as numerous as the half-breeds; and if in the ratio of 10 to 5, it becomes 100 times as numerous. Second. Again, if we take the proportional differences between the I different terms of the top line opposite c = —, we shall find them very 2 unlike the differences that appear in the bottom line opposite c = ane OOO In the former the first term is 9 times as large as the last, while in the latter the first term is more than 80 times as large as the last. This shows that when positive segregation is intense, differences in the degree of segregate fecundity produce greater contrasts than the same differences do when the positive segregation is slight. Third. A similar distinction is found when we compare the right- hand column with the left-hand column. The smallest term in the former is to the largest term in the same column as 1 to 899, while in the left-hand column the greatest is as 1 to roo. This shows that when segregate fecundity is strongly developed, differences in the degrees of positive segregation produce greater contrasts than the samme differences produce when the segregate fecundity is but slightly developed. APPENDIX II. INTENSIVE SEGREGATION, OR DIVERGENCE THROUGH INDEPENDENT TRANSFORMATION.* I, CLASSIFICATION OF THE FORMS OF INTENSIVE SEGREGATION. Ina previous paper on divergent evolution I have enumerated many classes of natural causes which produce either separate or segregate generation, and which, in their combined action, tend to produce cumulative segregation and divergent evolution in every part of the organic world. I have there shown, with sufficient fulness, that cumu- lative segregation always produces cumulative divergence or poly- typic evolution; but I have not fully shown how separation from the first involves more or less segregation, or how segregation, which at first divides the species into sections with reference to some one en- dowment, is always tending toward intensified segregation in which the sections present differences in regard to an increasing number of endowments. After expounding the principles on which these laws of divergence rest, I will give a few examples of divergence, calling attention to the complete correspondence between the facts of nature and the prin- ciples expounded in this and the previous paper. * From the Linnean Society’s Journal, Zodlogy, vol. xxi. Read December 19, 1889. + Separate generation, or separation, is the indiscriminate division of a species into sections that do not intergenerate. Segregate generation or segregation is the independent generation of different sections of a species when the sections are composed of somewhat divergent classes of variations. Isolation differs from selection in that the latter denotes the exclusion of certain kinds from opportunity to propagate, while the former denotes the division of those that propagate into classes that are prevented from intergenerating. Isolation, or the prevention of intergeneration, whether it be through separation or segregation, I also call independent generation. Darwin used isolation as equivalent to geographical separation, while later writers have come to use it as equivalent to independent generation. 185 186 APPENDIX II—INTENSIVE SEGREGATION. 1. Separation always Involves more or less Segregation, for no two Portions of a Species Possess exactly the Same Average Character. When a homogenous species is divided into two large sections, it may be difficult to prove by measurement that there is any difference in their average character; but on general principles we may assume that, at least in some points, there is a slight difference. It is evident that when the separated sections are small there is more likely to be diversity in the average character of the sections and that, roughly stated, the probability of divergence from this cause will be in direct proportion to the variableness of the species and in inverse proportion to the size of the different sections. When a few stragglers form a small colony in an isolated position there is the strongest reason to expect that they will not be able to propagate the characters of the species in exactly the same proportions in which they are produced by the main body of the species, or by any other small colony that is prop- agating independently ; and when the original stock has been rendered highly variable by the crossing of somewhat divergent varieties, the degree of difference that will probably be presented by any two inde- pendent colonies will be correspondingly increased. We must bear in mind that while specumens possessing an average character in any one respect are always abundant, those perfectly representing the average in every respect are rarely, if ever, found. Now, is it to be supposed that any one or any small number of these imperfect representatives of a species will, if separated from the rest, transmit all the characteristics of that species in the exact proportions presented by the average char- acter of the original stock? Mr. Francis Galton has conclusively shown* that in the children of parents whose heights deviate from the average of the race to which they belong, there will be a similar deviation amounting on the average to a certain fixed proportion of that presented by what he calls the mid-parentage. The mid-filial deviation in the groups investigated by him was about two-thirds of the mid-parental deviation. There is, therefore, a regression in the average character of the offspring toward the typical character of the group. It must be observed, how- ever, that this law can hold in full force only when there has been free crossing, for otherwise there will be no type from which the deviation can be measured. * See ‘Types and Their Inheritance,’’ an address before the Section of Anthro- pology of the British Association in 1885; also ‘‘ Natural Inheritance,” p. 97. TRANSFORMATION AND MONOTYPIC EVOLUTION. 187 2. Kight Forms of Monotypic Evolution Let us now consider how this initial segregation, which is always present in the case of a small colony, is enhanced and intensified by the cooperation of other principles, and how forms segregated through possessing different characters in some one respect come to diverge in other respects. For example, when differences of color become the occasion for sexual and social segregation, how does this open the way for divergent transformation in habits of feeding and in a thousand other respects? The principles codperating with independent genera- tion in producing this enhanced divergence are all causes of simple transformation, or monotypic evolution when there is free intergen- eration. Divergent breeds of domestic animals have always been produced when the different sections of a species in the care of different races of men have been prevented from interbreeding, thus securing their independent transformation during the process of domestication. So in nature, when any form of independent generation has been established, any cause of transformation that may afterwards arise will always produce more or less divergent evolution, and never that which is in every respect parallel. But we must defer the discussion of this subject till we have enumerated the more manifest of the prin- ciples of monotypic evolution: (1) Asstmtlational transformation, or modification due to deficiency with economy, or redundance with profusion, of growth, resulting from different degrees of assimilative power. ‘‘ Economy of growth”’ is a term already in use, but a term is needed that shall include both this and its opposite. (2) Stimulational transformation, or modification produced by changed motions in the fluids of the organism responsive to changed influences in the environment. Under this principle we may place the direct influences of light, heat, electricity, the dampness of the air or the saltness of the water in which the organism is bathed, the qual- ity of the food, and all stimulation from physical and chemical causes, exclusive of those resulting in muscular activity or the movement of the organs. (3) Suetudinal transformation, or modification due to the effects of use, disuse, and habitual effort in producing motions, and in resisting the strain of gravity and other forces tending to produce motion. Sue- tude is not found in the dictionary, but I venture to use it as including assuetude, which is being accustomed to, being practiced in, habitual use; and desuetude, which is disuse, discontinuance of practice. 188 APPENDIX II—INTENSIVE SEGREGATION. (4) Emotional transjormation.—Dr. C. V. Riley, late of the National Museum, Washington, has called attention to the influence of parental emotions (especially maternal emotions during the term of pregnancy) as a factor in evolution (Address ‘‘On the Causes of Variation,’’ before the Section of Biology, American Association, August, 1888; also in Popular Science Monthly, vol. xxxLv, pp. 811-816). (5) The cumulative development of adaptations through ‘‘the survival of the fittest’? when the fittest are other than average forms. This is the principle of unbalanced selection producing selectional transformation. (6) Transformation produced by the indiscriminate destruction of a portion of a species, with the accompanying probability that the remaining portion will not possess all the characters possessed by the species previous to the elimination. This principle I call ‘‘unbalanced tndiscriminate elimination,” producing indiscriminate eliminational transformation. (7) Transformation produced by different degrees of amalgama- tion of the varieties and races which have resulted from previous segre- gations. In most species there is a constant process of amalgamation by which thousands of minor varieties are absorbed; but when the process extends beyond ordinary limits, and the barriers that have divided well-marked races give way, transformation must follow. This principle I call diversity of amalgamation producing amalgama- tional transformation. (8) The cumulative development of the more fertile of the forms that are equally adapted. In other words, transformation produced by diversity in the relative fertility of varieties that are equally adapted to the environment and the constitution of the species, or by change in the degrees of fertility possessed by the same variety at dif- ferent times and in different places. This principle I call unbalanced fecundity, or unbalanced fecundal selection, producing fecundal trans- jormation. Of these principles all except the sixth, seventh, and eighth have been more or less discussed by writers on biology, though some of the forms of selection depending on the relations in which the members of a species stand to each other have never been pointed out, and many writers have failed to observe that selection often produces fixity of type instead of transformation, and that divergence can not be pro- duced through diversity in the kinds of selection without the codpera- tion of isolation, and may be produced without exposure to different environments. LAWS OF GROWTH NOT DISCUSSED. 189 Assimilational, stimulational, suetudinal, and emotional transfor- mation belong to a class of factors producing what are known as ac- quired characters.* Selectional, eliminational, amalgamational, and fecundal transfor- mation may be classed as principles of unbalanced propagation. The principles of unbalanced propagation are abundantly established as genuine methods of change in the average inheritable characters of species, not only by experience derived from the domestication of plants and animals, but by observation of similar effects produced by natural processes. 3. Principles of Vital Action not here Discussed. I have not mentioned ‘‘acceleration and retardation” as principles of transformation, for they seem to be but phases of the law of sue- tude; for, as explained by Cope, use or effort in the parents produces in the offspring accelerated inheritance, while disuse or cessation from effort produces in the offspring retarded inheritance.f So also Hyatt’s ‘‘Law of Concentration”’ (or ‘‘acceleration,”’ as he often calls it) seems to be a general law of inheritance relating to the transmis- sion of characters originating under any and every principle, the effects, whether progressive or retrogressive, being inherited at earlier and earlier ages in each successive generation.{ It is also doubtful whether correlated transformation should be considered a separate principle, for it seems to be simply the inheritance by offspring of characters that have for generations been united in the endowments * These four factors are included under what Prof. J. M. Baldwin calls accom- modation (see Nature, April 15, 1897, also ‘‘Development and Evolution,” pp. 94 and 151). Accommodation produces three classes of effects: (1) Habitual activity (that ts, repeated imitative and intelligent activities, aiding in self-preserva- tion, or in the preservation of ofjspring or of the communal group); (2) modification (that is, acquired physiological and anatomical effects of activity); (3) active (or endonomic) selection determined by the habitual activities of the group in dealing with the environment. Fora description of accommodation in lower organisms see Contributions to the Study of the Behavior of Lower Organisms, published by the Carnegie Institution, 1904, where Herbert S. Jennings has shown in a series of elaborate experiments with Ameba, with ciliate infusoria, and with flagel- lates, that their usual method of response to any given stimulus is in accord with what Lloyd Morgan has called ‘‘The method of trial and error.” This method I would describe as varied tentative action with repeated response till success is gained either by avoiding damage or by attaining advantage. + ‘‘Origin of the Fittest,” pp. 203-207, 228. t Proceedings of the American Association, vol. XXxU, pp. 352-361. 190 APPENDIX II—INTENSIVE SEGREGATION. of at least a portion of their ancestry, and the correlation of these endowments must have been produced through the action of other principles. The prevalence of males in times of pressure, with the prevalence of females in times of plenty, is regarded by Dr. W. K. Brooks, of Johns Hopkins University, as a characteristic established by natural selec- tion, by which the organism acquires variability or fixity of type according as either character is most needed; for according to his observations the males represent the former and the females the latter element. There can be no doubt that in many species the males are more variable than the females, and that in some of the same species the proportion of males increases with the degree of adversity; but this does not seem to be sufficient ground for maintaining that the increase in the proportion of males will increase the variability of the offspring. Increase in the number or amount of the variable element does not necessarily involve increase in the variability of either element or in the offspring of both. I find need of additional factors in order to bring these facts into any relation to the increase of variability. Granting that the sperm-cell is the source of variation and the germ-cell the source of fixity, and that increased tendency to variation in the offspring will be secured by an increased range of variation in the sperm-cells, it does not follow that increase in the relative number of males will increase the range of variation in the sperm-cells, and, therefore, in the offspring. But if conflict in the environment and the winnowing process of natural selection falls most heavily upon the males, there must be some advantage in having their relative numbers increased in times of adversity; and if the exposure of parents to hardships increases the variability of either male or female offspring, and especially if it increases the variability of both, plasticity will be increased. Professor Cope’s ‘‘ Doctrine of the Unspecialized”’ (Origin of the Fittest, pp. 232-235) rests on the fact that the most highly specialized types, as well as individuals, are most likely to be exterminated by extraordinary changes in the environment; and Mr. Hyatt’s ‘‘Tera- tology”’ (Proceedings American Association, vol. XxxxII, pp. 349-360) teaches that types that are being slowly exterminated usually assume forms resembling those produced by old age and disease in the indi- vidual. These and other laws in the growth and decay of types and individuals are of great interest, as they afford organic condi- tions under which the factors of transformation must act. ee INDEPENDENT TRANSFORMATION DIVERGENT. IgI 4. The Transformation of Freely Intergenerating Organisms Never Permanently Divergent. I mention these eight principles of transformation, not with the purpose of entering upon a full discussion of the same, but simply to point out the relation in which they all stand to divergent, or poly- typic, evolution. It is evident that, whether acting separately or together, they can never be the cause of divergent evolution in organ- isms that are freely intergenerating; for in such a group of organisms whatever modifies one part of the group in characters that are inheritable will, ere many generations, modify the whole. If the group is exposed to a variety of inharmonious conditions, which, with independent generation would produce divergent character, with free intergeneration, the only result will be variation. Without indepen- dent generation (or isolation) there can be no permanent divergence. 5. Independent Transformation Always Divergent. If any species is divided into two or more sections that do not inter- generate and that are severally subject to highly complex transform- ing influences, it may only be by a series of coincidences which the reason refuses to receive as in the slightest degree probable that any two sections will be modified in exactly the same way. This high degree of probability, amounting to a certainty, that when causes of transformation codperate with causes producing isolation the result in successive generations will be increasing degrees of segregation and of divergence, is what I call the law of intensive segregation. The different forms of this principle, resting on the certainty that the codperation of any one of the principles of transformation with any one of the principles of independent generation will produce increas- ing segregation with increasing divergence, are the following: (1) Assimilational intension, or segregation and divergence through independent assimilation. (2) Stimulational intension, or segregation and divergence through independent stimulation. (3) Suetudinal intension, or segregation and divergence through independent suetude. (4) Emotional intension, or segregation and divergence through independent emotional transformation. (5) Selectional intension, or segregation and divergence through independent selection. (6) Eliminational intension, or segregation and divergence through independent and indiscriminate elimination. 192 APPENDIX II—INTENSIVE SEGREGATION. (7) Amalgamational intension, or segregation and divergence through independent amalgamation. (8) Fecundal intension, or segregation and divergence through independent fecundal transformation. In groups that do not intergenerate, divergent forces reveal them- selves whenever transformation is introduced. If it were possible to believe that the effects of independent selection or of independent suetude had been completely parallel, it would still be impossible to believe that both of these, together with the remaining six principles of transformation, would ever so combine as to produce completely parallel transformation in isolated sections of a species, even if all were surrounded by the same environment. This principle is not inconsistent with the introduction of what Professor Hyatt calls ‘‘representative of parallel characteristics’”’ in two or more divergent series of forms. What he points out is that, under the influence of heredity, similar organisms exposed to similar environments undergo similar transformation (Anniversary Memoirs of the Boston Society of Natural History, 1880: ‘‘The Genesis, of the Tertiary Species of Planorbis at Steinheim,” pp. 24-29). In the description of these principles I have used the adjective ‘independent’ to signify that the principle is operating in sections of the species that are prevented from intergenerating. In the term ‘‘independent variation’? Mr. Romanes has already used the adjec- tive ‘‘independent”’ as meaning ‘‘when accompanied with the prevention of intercrossing.”’ 6. The Pervasive Influence oj the Causes of Transformation and the Law of Intension. In my paper on “‘ Divergent Evolution” I made the statement that ‘When separate generation is long continued we have reason to believe it always passes into segregate generation with divergent evolution.”’ The same thought had been expressed in a previous paper by the statement that ‘‘Variation is so strong that all that is necessary to secure divergence of types is to prevent their intermingling.”’* The certainty that independent generation with transformation will never produce parallel, but always more or less divergent evolution is the law of intensive segregation already referredto. Butinaddition to this cer- tainty there is a very strong probability that where independent gen- eration is long continued, transformation of some kind will supervene. If there are any species in which the power of cumulative variation has * See ‘Diversity of Evolution under One Set of External Conditions.” Journ. Linn, Soc., Zodl., vol. XI, p. 499. THE LAW OF INTENSION. 193 been entirely lost, this latter law can not hold in their case; but it is doubtful whether among species that reproduce sexually there are many such. The variability of some species is so small, and the con- ditions of the environment are so constant, that comparatively long periods of independent generation pass before perceptible transfor- mation arises. This seems to be the case with the thirteen and seventeen year races of Cicada septendecim, to which I shall refer when giving examples from nature. From the high probability that long- continued independent generation (7. e., isolation) will be followed by independent transformation, and the certainty that independent transformation will be divergent, there follows the corollary that long-continued independent generation will probably be attended by divergence. In other words, independent generation long continued is almost always attended by independent transformation; and inde- pendent transformation inevitably produces divergence. This double principle I call the law of intenston. his law rests on the ubiquity of transforming influence and on the impossibility that in a species possessing any plasticity the inherited effects in any section indepen- dently generating should be exactly the same asinany other section. This is especially the case when the species is highly plastic and when the isolated section is very small. We can not doubt that when a diversity of powers and suscepti- bilities in the different sections is acted upon by a great variety of influences the responses of the different sections will be unlike, and the result will be increasing segregation and increasing divergence. Now, itis impossible to doubt that in species propagating sexually and possessing some degree of plasticity, these are exactly the con- ditions whenever the species is divided into sections that do not inter- generate. It should be observed that, in accordance with the principle of intension, not only is indiscriminate separate generation when long- continued transformed into more and more strongly segregate gen- eration, but any form of segregate generation, resting on some one principle that causes the division of the species into sections differing in regard to some one form of endowment, will, if it is long continued, be inevitably reinforced and intensified by transformations, which, being independently combined and transmitted, will multiply the number of characteristics in regard to which divergence takes place. If, for example, the pollen of a given variety, when falling upon the stigma of the same variety or race, is prepotent over the pollen of every other variety or race that falls upon the same stigma at the 194 APPENDIX II—INTENSIVE SEGREGATION. same time, or at a somewhat earlier time, what I call prepotential segregation will divide the species into two groups that are prevented for the most part from intergenerating; and these separate groups, gradually coming under the influence of different degrees, forms, and combinations of the transforming principles, will in time become strongly characterized species. It is not, however, necessary that all or any of these forms of transformation should codperate with segre- gation in order to produce a distinct species. The accumulated effects of segregation, unaided by these principles producing intensi- fication, would be sufficient to produce well-defined species; but it is impossible that they should often remain unaided. 7. Utilitarian and Non-U'tilitartian Divergence. The principles of suetude and selection, though they are directly related to the development of utilitarian characters, may produce in the useful innate characters of isolated sections of the same species exposed to the same environment, divergence that is not necessary or advantageous; and the effects of the other six principles are often not only wanting in but opposed to utility. Assimilational transfor- mation includes redundance of growth, which is not always, as well as economy of growth, which is always, utilitarian. Unbalanced elimination, amalgamation, and fecundity may be advantageous, useless, or disadvantageous. We have, therefore, in these six prin- ciples of transformation, abundant cause for the introduction of non-utilitarian characters; and, when accompanied by independent generation, they must be the source of multitudes of non-utilitarian divergences. In the earlier stages of divergent evolution the non- utilitarian distinctions are more abundant; for in the later stages multitudes of them are weeded out by economy of growth, as has been clearly pointed out by Mr. Romanes;* and still others through com- ing under new conditions in the environment or through some new habit of intelligence, become useful endowments, and are brought under the preserving and accumulating influence of natural selection or of suetude. It should, however, be noted that the development of useful specific differences is as much due to independent generation as is the development of useless specific differences. Diversity of suetude or of selection does not produce divergent evolution unless it coéperates with independent generation. * Physiological selection, Journ. Linn. Soc., Zo6l., vol. X1x, p. 383. SELECTIONAL INTENSION. 195 8. Selectional Intension, or Segregation and Divergence Produced by Independent Selection. That we may gain a clear apprehension of the nature and influence of this principle, certain discriminations, which have not always been recognized by writers on the subject, are absolutely necessary; and, for the sake of avoiding misunderstandings, it is desirable that these distinctions should be represented by clearly defined terms. J am fully aware that many will be opposed to the introduction of new terms into the treatment of a subject that has been so long and ably discussed. If these discriminations were not found necessary by the author of the ‘‘Origin of Species,’’ or if the distinctions, so far as recognized by himself and others, have been expressed in the language of ordinary description, why should a more accurate terminology be needed now? In reply it may be said that the freedom from tech- nical language, which is a great advantage ina work which for the first time calls the attention of the world to a vast subject, is a serious defect when the exact relations of the subject come under discussion. In order to secure clear thinking on the subject, I have found it necessary to keep the following distinctions constantly in mind: (1) The selection that results in the transformation of species is not the selection of one species to the exclusion of another. The breeding of the horse to the exclusion of the ass modifies neither the one nor the other. It is the exclusive generation of certain variations of a single intergenerating group that gradually transforms the group. When, therefore, we speak of selection as a cause of transformation, we refer to the selection of the variations that are to interbreed and keep up the race, to the exclusion of other variations. In order to maintain the same distinction in the nomenclature of natural processes, what I call ‘‘selectton’’ is caused by the failure of certain forms of a species to perpetuate their kind as contrasted with the success of other forms. If the failure includes all the forms of a species, I call it the extinction of that species and class it as a cause of transformation in the remain- ing species only so far as it makes a change in their environment. (2) The exclusive generation of certain forms of an intergenerating group does not necessarily result in transformation. Experiments in artificial breeding show that if we select only the typical representa- tives of a race the general character of the race is not changed, though any tendency to fluctuating variation may be gradually diminished and the stability of the type increased. When, however, one form of deviation from the mean is constantly selected without a counterbal- ancing selection of the opposite deviation, the transformation of the 196 APPENDIX II—INTENSIVE SEGREGATION. race is usually the result. In other words, balanced selection produces stability of type,and unbalanced selection produces transformation of type.* In the light of this twofold law we see how there may be stringent selection without transforming effect. In nearly every species there is a constant struggle between the different forms of variation; and as it never happens that all the forms are equally successful, the process of natural selection isalways bearing in full force upon the species. If, then, it could be shown that natural selection, wherever it exists, must necessarily produce transformation, it would be impossible to resist the conclusion that nearly every species is undergoing transformation through this cause. But it is unbalanced rather than balanced selec- tion that produces transformation. We also see that heredity tends’ to make the most successful form the average form, and thus to con- vert unbalanced into balanced selection. From this it follows that in order that selection should produce continuous transformation, cov- ering a wide range, it is necessary that the form of variation selected should from time to time be changed. This may be expressed as the principle of continuous transformation through successive changes in the character of the selection. Though selection produces transformation only when it involves the survival of other than typical forms, it is still very possible that there are only a few species in which completely balanced selection prevails for very many generations in succession. It is still certain that long-continued independent selection gradually passes into diver- sity of selection producing divergent evolution. (3) Though in more than one passage Darwin maintains that uni- formity of external conditions involves uniformity of natural selec- tion, and that isolation can have no effect in transforming a species if physical conditions and surrounding organisms remain the same, still I think that if the question had been distinctly brought before him he would have admitted that exposure to a new or changed environment was not a necessary condition for change in the char- acter of sexual selection. Now, I think it can be shown that, besides sexual selection, there are several forms of selection that depend upon the relations of the members of one species to each other and that may undergo change without the organism being exposed toa different environment. Selection depending on the relations of the organism to the envi- ronment I call environal selection, of which I find two kinds, namely, * The general law is here stated, without any attempt to explain why selection, securing the exclusion of those falling below a certain standard, is necessary for the preservation of that standard in the case of many characters (see par. (6) below). DIVERSITY OF SELECTION THROUGH DIVERSITY OF USE. 197 active and passive selection, and under passive selection I place natural and artificial selection. Selection depending on the relations of the members of a species to each other I call reflexive selection, the chief forms of which I call conjunctional, dominational, impregna- tional, and institutional selection.* (4) It must be carefully noted that diversity of selection depending on diversity in the relations of the organism to the environment does not necessarily involve the exposure of the organism to different environments. In other words, change in even environal selection does not necessarily involve either change in the environment or the entrance of the species into a new district. Darwin's teaching seems, at times, to be in conflict with this statement, but there are passages in his writings which distinctly state that variations in instinct may lead to different habits of sustentation, and it is evident that this would naturally lead to a difference in the congenital qualities that win success in the different sections and so to difference in the envi- ronal selection. It should be remembered, however, that the meaning of anyone’s statements on this subject will depend on his definitions of the words used. What is meant by environment, external conditions, and other similar terms? Until we define we shall only beat the air, how- ever exact our statements may seem tobe. I therefore repeat what I have elsewhere stated, that, according to my definition, change in the environment is always change in activities that lie outside of the species, or of the segregated group, of individuals that is under consideration. In Darwin’s usage the phrase ‘‘change in external conditions’’ seems to carry the same meaning; but in some cases this can hardly be the case. Diversity in the uses to which isolated sections of one species put their powers, when appropriating resources from the same environ- ment, must produce diversity in the forms of variation that are most successful in the different sections. This I call active selection as con- trasted with passive selection, which varies according to differences in the environments.t All diversities of environal selection that do not vary according to differences in the environments must be classed as diversities of active selection, for they must have originated in some variation in the powers of the organism or in the diversity of uses to which it has put its powers. Diversity in the successful use of the powers of the species in dealing with the environment, whether * To these I now add prudential selection. + For ‘‘active” and ‘‘passive’’ selection, I often substitute ‘‘endonomic’”’ and ‘‘heteronomic’”’ selection. 198 APPENDIX II—INTENSIVE SEGREGATION. initiated by diversity in the action of the species in its different sec- tions or by diversity in the nature of the different environments, necessarily introduces diversity of environal selection. This principle may be expressed as the dependence of diversity of environal selection on diversity in the relations of the powers of the organism to conditions in the environment. (5) Diversity of innate powers in the different sections of a species can not be maintained and accumulated without some degree of segre- gation between the different sections, for within one intergenerating group every initial divergence is speedily merged in the general char- acter of the group. This law may be briefly defined as the depend- ence of increasing divergence of racial characters on the continuance of isolation. As was shown in my paper on ‘Divergent Evolution,” without the aid of causes preventing intercrossing, the selection of other than average forms will produce transformation but never diver- gence—will produce monotypic but never polytypic evolution. (6) Diversity in the character of the selection may be introduced, not only by the intervention of new forms, but also by the cessation of old forms of selection. We shall find that important differences of this kind may arise, resulting in considerable transformation before any new form of selection has come into action. A good illustra- tion of the cessation oj selection is found in the increasing frequency with which human mothers, notwithstanding their failure to give suck, succeed in raising their children. The power to give suck is through this process being diminished in the more civilized races, though there is no reason to believe that those who do not give suck have, on the whole, any advantage over those who do. The new result is, therefore, being produced not by the introduction of a new form of filio-parental selection, but by the cessation, or the weaken- ing, of the old form. Romanes has pointed out the effects that must often be produced by the cessation of natural selection,* but he has not considered the cessation of other forms of selection. In subse- quent paragraphs of this section relating to social and filio-parental selection are given a number of examples of the influence of accom- modation in causing certain forms of selection to cease and in certain cases introducing new forms of selection that are the reverse of the older forms. (7) It is often convenient to distinguish between selection resulting from rational devices and that resulting from the superior success of * See an article on ‘‘The Factors of Organic Evolution,” in Nature, vol. XXXVI, pp. 402-404, in which reference is made to previous papers in which the cessation of natural selection is discussed. FORMS OF SELECTION. 199 organisms better adapted than their rivals of the same intergenerant to the natural laws and conditions of the environment, or to the nat- ural constitution of the species to which they belong. The former I call rational selection and the latter adaptational selection. Under the former I place artificial [prudential] and institutional selection, and under the latter I place processes as unlike as natural selection and sexual selection. This classification does not, however, seem to me so important or so fundamental and clearly definable as that which rests on the fact that some forms of selection depend on the relations in which organisms stand to the environment, while others depend on the relations in which the members of the same species stand to each other. It may here be noted that artificial selection is the exclusive generation of those that are better fitted to the rational environment, through the failure to propagate of those that are less fitted. The effect is the same whether the failure to propagate is through lack of adaptation to human purposes or through lack of adaptation to the unreasoning environment. The following table of the forms of selection will, I think, be a help in maintaining these and other distinctions. FORMS OF SELECTION. ADAPTATIONAI, SELECTION. | RATIONAL SELECTION. Active (or endonomic) selection. . Heteronomic selection. 2 < itso ee 4S) o aS a ae = ae a Zz =I Habitudinal selection. z & Artificial selection. agd Aptitudinal selection. ors , 25 S Aptitudinal selection aS Ceremone. 6a § ies , “af , } o aie Y Cs ; % AQ Passive or heteronomic selection. 9 WinconsiGus: z Natural selection. wy Conjunctional selection. Institutional selection. Sexual selection. Ecclesiastical selection Social selection. Military selection. Filio-parental selection. Sanitary selection. : : : Penal selection. Dominational selection. Prepotential domination. Sustentational domination. Protectional domination. Nidificational domination. Nuptial domination. Prudential selection. REFLEXIVE SELECTION. Impregnational selection. Dimensional selection. Structural selection. Potential selection. Fecundal selection. Balanced and unbalanced. 200 APPENDIX II—INTENSIVE SEGREGATION. (9) Environal selectton.—As environal selection involves not only the superior propagation of the better fitted, but the inferior propa- gation of the less fitted and the non-propagation of the least fitted, it may be described as the exclusive propagation of those better fitted to the environment through the failure to propagate of the less fitted. Transformation by means of environal selection depends on the vary- ing degrees of adaptation to the environment in creatures that are in- tergenerating, the higher degrees being possessed by other than aver- age forms. Divergence is produced by environal selection only when to the above conditions producing transformation are added causes that prevent intercrossing between the sections that are being inde- pendently transformed. In other words, independent environal selec- tion produces divergence. (10) Sexual selection is the exclusive propagation of those better fitted to the sexual instincts of the species through the failure to propagate of the less fitted. In the words of Darwin, ‘‘It depends on the advantage which certain individuals have over others of the same sex and species solely in respect of reproduction.’’* It is the form of reflexive selections which has received Darwin’s attention, and is consequently familiar to all. There are, however, certain points that need to be emphasized. This is the principle in accordance with which correspondence is secured between the external characters and the sexual instincts of a species, and also between the instincts of the two sexes, in so far as they relate to reproduction. This result is secured partly by the failure to propagate of those whose powers of attraction and conquest do not reach the standard demanded by the instincts of the other sex and partly by the failure of those whose instincts diverge too widely from the typical characteristics of the other sex. For example, on the highlands of North China I have observed a species of creeping cricket of the genus Bradyphorus, the male of which calls the female by a sharp stridulation, to which the female responds by approaching the male and finally climbing uponits back. Now, we can well under- stand that the call of the male has been brought to its present shrill, penetrating perfection through the failure to attract mates in the case of males that were but feebly endowed, but it is equally certain tha~ those females whose sluggish instincts have been capable of respond- ing only to an unusually intense call have for the most part failed of leaving offspring, and, if any have been so unreasonable as to wait for the male to seek them out, they have, doubtless, perished without per- * “Descent of Man,” p. 3 of Chap. VIII. ENVIRONAL AND SEXUAL SELECTION. 201 petuating their perverted instincts. If my view is correct, the change producing divergent sexual characteristics may be either in the instinct or in the characters with which the instinct is correlated. It seems probable that in the vast majority of cases the more strongly divergent forms have been reached by a multitude of deviations alter- nating between the psychical and the physiological and morphological characters of the species, the chief, indispensable condition being the prevention of interbreeding between the diverging sections of the species. Sexual selection is sometimes referred toas if it were the influence of sexual instincts in giving character to the organs of a given sex, first by the instincts of the given sex rousing the individuals of that sex to successful activity in securing propagation, the degree of suc- cess depending on the degree of adaptation of the organsof the indi- vidual to the purpose of the activity (as in the case of barnyard cocks winning partners by the use of their spurs), and, second, by the in- stincts of the opposite sex being roused to successful action according as the endowments of the given sex are fitted to the end (as in the case of peacocks winning partners by the display of ornamentation). Starting, however, with this conception of the nature of sexual selec- tion, we shall find great difficulty in obtaining from the principle any explanation of the origin of species or of divergent evolution of any kind. If divergent instincts are the causes of divergent forms, colors and qualities, what are the causes of the transformation of the instincts in lines that are persistently divergent? The problems of transformation and divergence are as far from solution after the appli- cation of the theory as before. If, on the other hand, we recognize sexual selection as the har- monizing of the forms, colors, and qualities of a species with its sexual instincts and of the sexual instincts with its forms, colors, and quali- ties, we shall not claim that either set of characters is directly and continuously the cause of transformation in the other; but rather that the two sets play upon each other in such a way as to produce a state of unstable equilibrium in both sets, the result of which is indefi- nite transformation in the secondary sexual characters of each section of a species that constitutes a separate intergenerant, and that the independent transformation inevitably results in divergence. In Darwin’s presentation of the principle of sexual selection, the chief endeavor is to show that differences in voige and ornamentation between males and females of the same species are probably, ina large degree, due to diversity in the action of sexual selection upon the different sexes; but this is a very different result from differences in 202 APPENDIX II—INTENSIVE SEGREGATION. the same respects between those of the same sex in closely allied varie- ties and species, and no clear understanding of the subject will ever be reached till those who study and discuss the subject discriminate between these two classes of phenomena. The formation of differ- ences of the former kind is simple transformation without divergence, while the entrance of differences of the latter kind is divergent evolu- tion tending to the production of separate species. If a species deficient in secondary sexual distinctions, after being divided into segregated sections, attains a high development of such distinctions, it is easy to believe that they will be developed in differ- ent ways in the different sections, and that thus they will become specific distinctions; but it is not so easy to see why a species in which sexual distinctions have already been fully developed should undergo divergent changes in the different sections into which it may be divided. It isin such cases that we discover the important influence of what I have called unstable equilibrium. It seems probable that in some cases small differences originating through indefinite variation in only a few isolated individuals are seized upon by the exaggerating fancies of the other sex, and are thus first preserved through isolation and then exaggerated by sexual selection. In other words, zndepen- dent sexual selection produces segregation and divergence. (11) Social selection is the exclusive breeding of those better fitted to the social constitution and instincts of the race through the failure to breed of those less fitted. Social organization has reference chiefly to codperation in securing sustentation and defense. If for each species there were but one possible form of social organization through which sustentation could be secured, there would be no need of considering social selection, for the form of social organization would be rigorously determined by natural selection, and the success of the individual through conformity to that organization would be sufficiently explained by the principle of natural selection. But dif- ferent forms of social organization are often exhibited by the same or closely allied species; and we find that, in such cases as elsewhere, the prosperity of the individual is largely dependent on his conformity to the social organism to which he belongs. Social selection must, there- fore, in some cases, have been an important factor in maintaining a correspondence between the capacities and the social organization of a race orspecies. Whenaspecies or asection of aspecies is undergoing a change of social habits, there will be individuals that fail through reverting to the old instincts and methods which put them out of accord with the rest of the community. But through the failure of these the_inherited instincts of the race are brought into increasing SOCIAL AND FILIO-PARENTAL SELECTION. 203 accord with the new habits till, in the case of most species, there are but few individuals that fail through lack of appropriate social in- stincts. Nevertheless, in the branches of the human species that have attained the highest civilization the process is still far from complete, for the instincts of many individuals are in conflict with civilized habits. We find that the natural faculties that are best fitted to secure indi- vidual success, and a numerous and long-continued descent, are different under different forms of civilization. Social habits in a great measure determine the food and clothing of a community and thus deeply affect the qualities of the race. The degree of exposure to which the young are habitually subjected is also largely determined by social custom, and so the quality of the constitution that is per- mitted to survive. In other words, the form of parental selection that prevails in any community is often determined by social selec- tion, as the form of social selection is sometimes determined by nat- ural selection. Many matters which, amongst irrational animals, are determined by instincts guiding the individual directly to the needed resources, and showing what provision must be made, are, with man, determined by social instincts, leading the individual to follow the general experience or traditional habits of his clan. As in countries where there are no beasts of prey the gregarious in- stinct of cattle ceases to be a necessity for the preservation of life, it is no longer maintained by natural selection, but it may be preserved by social selection; for though occasional stragglers appear, they are, through lack of adaptation to the social organization, specially liable to fail of finding mates, and, therefore, to fail of propagating their kind. Between the capacities of a community and its social organization there is a constant action and reaction which tends with more or less rapidity toward transformation; and this tendency is increased when a small community, during a long separation from other communities, gradually increases in strength, independently constructing a civili- zation of its own. In other words, independent social selection tends toward divergent evolution of capacities and oj social organization. (12) Filio-parental selection is the exclusive breeding of those better adapted to the relations in which parents and offspring stand to each other, through the failure to live and propagate of those less adapted. How the power of giving suck and the corresponding instinct for sucking were first developed it may be impossible to tell; but it is evident that having once been established as the method of sustenta- tion for the young of mammals, any young lacking the instinct would perish without leaving descent. There is every reason to believe that, 204 APPENDIX II—INTENSIVE SEGREGATION. with the exception of a few of mankind, and still fewer of domestic animals, it may be truly said of every individual mammal that all its ancestry, through all generations since they became fairly mammalian, have had this instinctin full force; and yet it sometimes fails and the line of descentis cut short with the individual that fails. Till compara- tively recent times the same was true of man; but we now find some cases in which the young survive in spite of their inability to suck, and the constancy of this mammalian characteristic is being gradually impaired. There is also in some races an increasing tendency to shorter periods of lactation, or to the entire suppression of the func- tion; so that it seems not improbable that there may yet arise a variety of the human species in which the power will be comparatively obsolete. Under such conditions the instinct for sucking would cease to be of any advantage, while special advantage would accrue to those best able to thrive on the artificial food habitually provided by the parents. In some countries this would be the milk of ruminating animals, while in other countries it would be some vegetable prepara- tion. Through this diversity in the food provided by the parents for their infants and small children, there is even now a constant diversity in the parental selection prevailing in different countries. Diversity in the forms of parental selection is also produced by diversity in the clothing and artificial heat provided by parents; in the protection, on the one hand, of children from the wind and rain and direct rays of the sun, and on theother hand, their exposure to the same with shaven heads or naked bodies; and inthe methods of binding, cramping, and mutilating the head, feet, waist, and other parts of the body. From this point of view we see how largely the form of parental selection is determined by social custom, and how it is sometimes enforced by social selection, which excludes from the benefits of the caste or tribe all who have not passed through the ordeal. As filio-parental selection is due to different degrees of adaptation between the parent and offspring, it may be characterized not only by fatal departures in offspring from the characters required in their rela- tions to their parents, but by fatal departures in parents from the char- acters required in parents in their relations to their offspring. Asan example of the former, we may refer to the death at birth of children with excessively large heads; and as an example of the latter, to the death at birth of all the children of a mother with a contracted pelvis. (13) Dominational selection.—Variations that are equally fitted to cope with the environment may be divided into two classes—those better able and those less able to cope with other members of the species in the appropriation of resources. Increase of population and DOMINATIONAL SELECTION. 205 the consequent competition between members of the same species condemns the latter to premature death, or at least to failure in prop- agating, unless they find new resources by migrating or by changing their habits. Competition between kindred for the possession of identical resources we find directly connected with two quite distinct principles of evolution: (1) With the principle of dominational selec- tion tending to discriminate between those equally adapted to the environment, through the success and consequent propagation of those only that are best able to cope with their kindred in appro- priating advantages; (2) with the principle of competitive disruption, tending to break up old relations and old habits, and so preparing the way for the formation of new habits producing segregation and divergence. The latter of these principles was referred to at the end of Section III of my paper on ‘‘Divergent Evolution through Cumulative Segregation.’’ ‘The first I now briefly describe, without attempting to show its important influence on the transformation and divergence of species. Dominational selection is the exclusive breeding of those better able to appropriate natural resources or mates, or the provision made by parents of society, not through being better fitted to the environment or to the organized methods of codperation and assistance, but through being better able to overcome or outdo their rivals of the same species. It results from the contest or rivalry with each other of members of the same species that are equally fitted to the environment and to the con- stitution of the species and the consequent failure of all that are not able to cope with their kindred. ‘‘Thelawof battle” isa form of dom- inational selection which Darwin emphasizes as having great influence in determining what males shall have the best success in procuring mates. But there is a similar law determining what individuals shall obtain the resources furnished by nature or elaborated by parents and society. We may have dominational selection relating to susten- tation, protection, and nidification, as well as to the possession of females. And in gaining a single end there may be a great variety of dominating methods. Combat between males for the possession of females is not found in the vegetable kingdom; but the prepotence of the pollen of certain flowers over that of other flowers of the same race may play a similar réle. This we may call prepotential domination. Dominational selection differs from natural selection in that it does not depend on degrees of adaptation to the environment, and from other forms of reflexive selection in that it depends on a special form of the relationship in which members of the same species stand to each other. It seems desirable that this form of selection, which depends 206 APPENDIX II—INTENSIVE SEGREGATION. on adaptation for overcoming, outdoing, or supplanting others of the same species, should be clearly distinguished and named. We further note that there can be no doubt that dominational selection acting for many generations on sections of a species that are prevented from intercrossing will in all probability follow somewhat different lines. In other words, independent dominational selection will produce diver- gent evolution. (14) *Impregnational selection—The codrdination between the pollen of a given species and the stigma and ovules of the same species must be kept up by a process of selection, resulting from the failure to propagate of the individuals whose pollen is least potent, and of those whose ovules are most difficult to fertilize. This we may appropriately call potential selection; and it will be convenient to class it with forms of selection securing other codrdinations necessary for success- ful impregnation. These other forms are: dimensional selection, of which we have an example in the codrdination between the length of the pollen tubes and of the pistils; also fecundal selection, illustrated by the different degrees of survival secured by variation in the number of the ovules and in the quantity and methods of distribution of the pollen grains; and, as illustrated, in many species of insects, structural selection, due to the success gained through superior coérdi- nation of the organs by which males and females clasp each other. Impregnational selection is an important form of reflexive selection. I wish here to call especial attention to the importance of fecundal selection. (15) Fecundal selection produces intensive segregation with diver- gence through independent jfecundal intension, in isolated sections of a species. Itis the form of selection that results from propagation according to degrees of fertility. Asit involves not only the superior propagation of the more fertile, but the inferior propagation of the less fertile and the non-propagation of the least fertile, it may be described as the exclusive propagation of the more fertile through the failure to propagate of the less fertile. It would avail nothing in determining the form that is to prevail in succeeding generations if it did not in some degree preclude the crossing of the less fertile with the more fertile; but, as it is evident that, so long as increased fertility is not a disadvantage, the more fertile half of the species will leave a larger number of offspring than the less fertile half, it follows that when the off- spring have come to maturity a larger portion of the fertile will consort with the fertile than in the previous generation; and so the fertility of the following generation will be still further increased. The chief check to this law of cumulative fertility is found in the correlative law of cumulative adaptation through adaptational selection. The combined action of these two laws results in the triumphant development of the most fertile of the best fitted or the best fitted of the most fertile. *As this paragraph does not occur in the original paper it is printed in different form. FECUNDAL AND INSTITUTIONAL SELECTION. 207 Another result from the combined action of these two laws is that, in specres well adjusted to the environment, the typical, that is the average, form of the species is not only the best adapted, but it is the most fertile; and this correlation between fertility and adaptation in the average form of the species or race is a strongly conservative principle, tending to prevent the rapid transformation of the race or species. Giants, dwarfs, and extreme departures from the type of other kinds are more likely to be sterile than the typical form of the species; and therefore if, through change in the environment or in the social conditions, some extreme form has an advantage in gaining subsistence, it will usually fail of propagating its kind with the relative rapidity of the less-favored averageform. Thisisat present true of highly intellectual variations of civilized man. Those of moderate capacities are more prolific and accordingly persist, though less successful in other respects than the intellectual. But so long asthe most successful individuals are those surpassing the average in intellectual endowment, so long will the aver- age endowment be more or less steadily advancing; for, of intellectual families, those that are fairly fertile will leave more impress on succeed- ing generations than those that are sterile; and of fertile families, those that are above the average in intellect will have the advantage in leav- ing descendants to inherit their endowments. (16) Institutional selection is a form of exclusive breeding closely re- lated to social selection, but differing from it very much as artificial selection differs from natural selection. Institutional selection is the influence of institutions, customs, and laws in determining what classes of individuals have an opportunity to raise children. In most civilized countries criminals convicted of important offenses are usually so confined as to prevent their adding tothe population of the community during the time of their confinement. This is a method of improving the race that might be carried farther than it has been. In some countries the insane, the imbecile, and lepers are confined in asylums and not allowed to marry, and in other countries eccle- siastical and military restrictions prevent certain portions of the community from raising families. (17) * Prudential selection is due to the delay of marriage and other methods of limiting the number of children for prudential reasons. (18) Result of the foregoing survey of selectional intenston.— The analy- sis we have now completed shows us that certain changes in the form of selection are due to changes in the environment and that others are * As section (17) does not occur in the original paper, it is printed in different form. 208 APPENDIX II—INTENSIVE SEGREGATION. due to changes in the organism. We find: First, that all the forms of reflexive selection are due to the relations of members of the same species to each other, and are liable to change without any change in the environments; second, that active selection is due to change in the successful use of the powers of the organism in dealing with the environment and is not dependent on change in the environment; third, that passive selection, which is due to the exposure of the or- ganism toa different environment, is often produced by the organism’s entering a new environment without there being any change in either the new or the old environment; fourth, that though passive selec- tion is produced by change in the environment, the more effective forms of selection do not appear till the organism has so multiplied as to produce what I call ‘‘dominational selection” through intense com- petition between rival individuals of the same species in gaining pos- session of limited resources; and fifth, that passive selection, which depends on change in the environment, also depends on variations in the adaptations of the organism. (19) *In this enumeration of the different forms of selection I have introduced certain divisions that are not given in the paper as read before the Linnean Society in 1889. These are structural, dimensional, and potential selection (which I have grouped with fecundal selection as forms of impregnational selec- tion), and prudential selection, which stands by itself; fecundal selection was discussed in the paper as originally published, under the term ‘‘fecundal inten- sion.’ As having an influence on survival, I now recognize it as belonging among the forms of selection. The active principle may appropriately be called fecundal selection, and the effect it produces on an organic group may be called fecundal intension. In preparing my table of the forms of selection I have found difficulty in decid- ing where natural selection should be placed, and how wide a definition should be given toit. Some biologists use it as including sexual selection, while others agree with Darwin in considering sexual selection as belonging to a very different sphere, seeing that changes in sexual selection depend on changes in the activities of the organism and not on changes in the environment. But appeal to Darwin’s writings does not remove all difficulty; for, if we decide that Darwin does not include sexual selection under natural selection, it still seems certain that he considered certain forms of what I have called dominational selection as forms of natural selection. But dominational selection is as decidedly reflexive in its action as is sexual selection. If, then, sexual selection is separated from natural selection, should not dominational selection also be considered as distinct? As Darwin has in several places stated that natural selectionis subject to change only when external conditions change, I have classed it as that form of environal * As section (19) does not occur in the original paper, it is printed in different form. + See Origin of Species, in the two chapters on geographical distribution, ed. 6, especially on page 355, where Darwin discusses the divergence of closely allied species on islands within sight of each other. INDISCRIMINATE ELIMINATION. 209 selection which is controlled by activities belonging to nature outside of the species. It is, therefore, clearly distinguished from active (or endonomic) selec- tion, which is controlled by differences of aptitudes or of habitudes in the different groups for dealing with the environment, and not by exposure of the different groups to different environments. 9. Indiscriminate Eliminational Intension. Eliminational intension is segregation and divergence produced by the indiscriminate destruction or failure to propagate of a part of the individuals of an intergenerating section of a species. Though indis- criminate destruction can not be classed asa form of natural selection, it may nevertheless be the cause of transformation; and when a species is distributed in sections that are prevented from intergenerating, divergent evolution will often be hastened by the indiscriminate destruction of part of the members of one or more sections. Ifaspecies inhabiting a large island is divided by geological subsidence into two large sections, there may be a very close resemblance in the average character of the two sections; but if a subsequent eruption of hot ashes destroys a large portion of the individuals of one section, or of both, the probability of a close correspondence in the average character of the two sections will be very much less than before the eruption. Again, when the area occupied by a species is divided into two or more large districts, the occupants of which can have little or no opportunity for crossing, divergent evolution will arise in the different districts unless there is some constantly operating cause that insures that all the varieties surviving and propagating in any one district shall survive and propagate in all the districts. No such cause has ever been pointed out, but, on the contrary, it can easily be shown that the prob- ability is very small that such a correspondence would occur, even if at the time of the division of the areas every individual in each district was represented by a completely similar individual in each of the other districts. Let us suppose a case: (1) Suppose the creatures under consideration to be a species of mollusk, the sexual instincts of which act without any segregative tendency between the varieties of the same species, there being no aversion or other impediment that interferes with the free crossing of all the variations occurring within the limits of one district. (2) Suppose that the number of individuals in each district is 10,000,000. (3) Suppose that one in a thousand of these has a tongue strong enough to feed on the bark of the tree the leaves of which are the ordi- nary food of the species, and that one in a thousand is capable of 210 APPENDIX II—INTENSIVE SEGREGATION. digesting the same, so that, in each district alike, one in a million could survive in this way though the crop of leaves should fail. (4) Suppose that there are, through diversity of adaptations of this kind to products of the environment, ten different kinds of accessible forms of food, on each kind of which one in a million of the individuals of each district might feed if driven by necessity. (5) Now suppose the same necessity should occur in each district through the destruction of the leaves on which they habitually feed, and that there are accordingly in each district a hundred survivors able to maintain themselves on other kinds of food. Under such circumstances (the correspondences of which we have in our supposition made much more exact than the actual deviations from a mean ever present), even under such circumstances of completely parallel variation, what is the probability that in each of the separate districts the few that would meet with other individuals and have an opportunity to propagate the species would be similarly endowed and similarly related to the environment? In order to still further simplify the problem, let us assume that in the case of each kind in each district the probability that it will suc- ceed in propagating 1s exactly balanced by the probability that it will fail. The probability, then, that any given number, a, of the ten kinds in a given district will succeed is found by estimating the number of ways in which a things can be taken out of 10 things, and dividing this number by the tenth power of 2, that is, by 1024. This is com- pletely parallel to the number of ways in which ten pennies can be arranged as to head and tail, each penny representing one form of varia- tion, anditslying head-up indicating success in propagating. . In 1024 experiments the probability is— That o will succeed........ rtime | That 6 will succeed.........210 times That 1 will succeed........ 10 times That 7, wall succeed! Se aan save 120 times That 2 will succeed ........ 45 times | That 8 will succeed......... 45 times That 3 will succeed........ 120 times | That 9 will succeed........ 10 times That 4 will suceeed........ 210 times | That 10 will succeed........ 1 time That 5 will succeed........ 252 times | These figures are found in the eleventh line of what is knownas the ‘Table of the Binomial Coefficients,”’ or the ‘‘ Arithmetical Triangle.’’* And so in the case of any number of objects, the number of combina- tions that may be made with n objects is found in the n + 1th line of the arithmetical triangle classified according as there are 0, I, 2, 3, or more objects in each combination. The whole number of combina- tions may also be found by calculating the nth power of 2. * See ‘‘ Principles of Science,’ by W S. Jevons. AMALGAMATIONAL INTENSION. 211 The possible combinations of the ten varieties in question, any one of which is as likely to occur as is any other, are 1,024, which is equal to 2 raised to the roth power; the probability, therefore, that the com- bination or set of varieties that succeeds in one district is ;)j, or 1 in 1,024; while the probability that those that succeed in the one district will not be all the same as in the other will be }), or 1,023 in 1,024, which is more than a thousand times greater than the reverse prob- ability. These 1,024 different results, any one of which may occur in one section, are calculated on the supposition that all the representatives of the species in one section that succeed in propagating will in time coalesce by intercrossing; as we shall presently see, the number of divergences in the two sections may be vastly increased by the diver- sity of ways in which the same varieties may be combined through the greater or less influence of minor segregations within the bounds of each district. 10. Amalgamational Intension. In my paper on ‘‘Divergent Evolution through Cumulative Segre- gation,” I have referred to the fact that the vast majority of diver- gent forms produced by segregation, after existing for a time, are interfused with competing forms of the same species. Now, it is evident that when a permanent segregation arises, if in the separate sections there is a diversity of amalgamations between the slightly divergent forms produced by partial segregations, the results will be divergent in these separate sections. That there will be diversity in this respect, we may argue, first, from the improbability that all the varieties in any one section will occur in each of the other sections; second, from the improbability that if the same varieties occur in each section they will occur in the same proportions; and, third, from the improbability that if they are the same and in the same proportions, they will break over the barriers and breed with each other in precisely the same way in each section. Amalgamational intension relates only to the last point. The other two points have been dis- cussed under the principle that separation always involves more or less segregation (see the third paragraph on the first page of this paper), and under indiscriminate elimination, which we have just been considering. Taking up, again, the supposed case considered under eliminational intension, if the different kinds of new food were so situated as to make it more or less difficult for those feeding on one kind to cross with those feeding on other kinds, the representatives of the species in each of the completely separated districts would be divided into minor 7-37. APPENDIX II—INTENSIVE SEGREGATION. segregations of a partial kind; and the different degrees of intercross- ing between the minor segregations in the separate districts would be an additional cause of divergence, which we may appropriately class as a form of amalgamational intension. Occasional interchange of stations by the varieties in one district would produce a degree of homogeneity in the forms of one district that would not be found when comparing those of different districts; but as the degrees of inter- crossing between any two or more identical varieties that might happen to be preserved in both districts would, in all probability, differ in different districts, the correspondence that at first existed between certain portions of the two sections would gradually disappear. 11. Combined Influence of these Principles. We have not at present sufficient knowledge of the influence of each of the principles of transformation to enable us to estimate their com- parative importance; but we know enough of their combined action to anticipate with confidence that wherever separate or segregate generation arises, producing more or less divergence, there these prin- ciples will in time intensify the result. The transformations and divergences of nature are produced by the interplay of numerous factors most intimately combined, and though for the purpose of com- prehending the process we are compelled to study each principle by itself, we must remember that in nature they not only combine, but combine in a vast variety of ways. ‘There is, however, reason to be- lieve that species sometimes become so devoid of plasticity that nearly all transformation is precluded, and, if the environment is greatly changed, even in the most gradual manner, extinction is the result. II. DIVERGENCE IN MOLLUSKS. 1. Divergent Evolution in the Land Mollusks of Oahu. Oahu is one of the Sandwich Islands, or Hawaiian Islands, as they are now usually called. Itis of volcanic origin, but the two mountain ranges, which lie one on the northeast and the other on the southwest side of the island, show no signs of recent volcanic action. Unlike the mountains of Hawaii and East Maui, their sides are very deeply fur- rowed by the action of water, and their forests are not broken by flows of lava. The forests of the islands cover these two ranges, form- ing two disconnected strips, the one about 36 and the other about 18 miles in length. In these forests are found many hundred varieties, representing over 200 species, belonging to 8 genera, of the Achati- nellide. LAND MOLLUSKS OF OAHU. 213 Two of these genera, Amastra and Leptachatina, are, for the most part, found under the dead leaves of trees in damp places; and one, Laminella, is found chiefly on low shrubs, while the remaining five genera are always found on trees or shrubs. Now, it must be remem- bered that the climate is tropical, and that the rainfall is so distributed through the year that in the shady groves there is nothing to drive the arboreal species from their haunts on the leaves or branches of the trees. Still further, as this family, unlike most other land mollusks, produces its young, not from eggs, but in a living, active form, there is no occasion in its life history that requires it to leave the tree in which it lives from generation to generation. In the distribution and diver- gence of these varieties and species we learn the following lessons: (1) Varieties are incipient species, and species are strongly pronounced varieties. A full collection of the varieties and species of any poly- morphic genus produces an oppressive sense of confusion on the mind of anyone who examines it for the first time. This is preeminently true of a full collection of the Achatinellide of the island of Oahu. Hight genera are represented by a multitude of varieties and species which, within the limits of each genus, are, for the most part, com- pletely intergraded with each other. As natural selection has not removed the intermediate forms, it is impossible to say where a species begins and where it ends. Having selected a given form as the type of a given arboreal species, we soon find that it inhabits perhaps only one or two valleys, say half a mile in width, and only one, two, or three miles in length. Beyond these limits it is represented by varie- ties that become more divergent as the distance from the home of the type increases; and, in the case of the Achatinella and Bulimella, this difference is so great that in districts eight or ten miles apart every one will admit that the forms all belong to different species. Indeed, in many cases, though the same vegetation is present, the habits of feeding have changed, while in other cases the form and color have changed while the habits remain essentially the same. Though it is easy to find degrees of divergence which most natu- ralists will agree in calling specific, but which in a full collection are shown to be completely intergraded, yet if a full collection of the dif- ferent forms should be submitted in succession to a hundred different naturalists to classify, it would be found that no two would agree as to the number of species, and a still greater diversity of opinion would be revealed as to where the limits of the different species should be placed. This is exactly what we might expect if varieties are incipient species, and species are simply strongly developed varieties. Such being the case, it is folly to ask that the nomenclature should 214 APPENDIX II—INTENSIVE SEGREGATION. be based on some fundamental distinction between species and varieties.* The best nomenclature is the one in which the specific distinctions correspond in degree with those that are recognized as specific in other families, and in which a degree of divergence that is considered specific in one part of a genus is considered specific in every part. If the dis- tinctions on which Reeve, Pfeiffer, and Newcomb have founded the species in Makiki and Manoa are received as specific distinctions, then similar distinctions occurring in the forms of other valleys must be recognized as belonging to different species. I by no means contend that these differences should be regarded as specific; but having re- ceived the three or four forms of Achatinella found in Manoa as good species, it will not do to say that the forms of Achatinella found in Waialei, differing from each other in the same manner and degree, are but one species. Notwithstanding the diversity of opinion that will always exist as to how many species should be made of the forms occurring in any one valley, every one will agree that the forms of Bulimella and Achati- nella found in any one valley are quite distinct species from those found in valleys that are ten or twenty miles distant. The lessons we are drawing from the divergence in this family are, therefore, not dependent on any special views concerning the number of species that ought to be received. As examples of intergrading species, examine first the types of Achatinella producta, A. adusta, and A. buddw from Makiki; then all the forms of these and the other species of Achatinella found in Ma- kiki, and then the forms found in the successive valleys of the whole mountain range. If freedom from intergrading is received as the necessary and suf- ficient test of good species, then a multitude of forms that are only varieties may be turned into good species by burning the forests in alternate valleys on either side of this mountain range. Moreover, if this is the true test of species, the species-maker who throws intergrade forms into the fire is quite consistent, even if not quite frank. Whether we call these divergent forms species or varieties, the pro- cess by which the divergence has been produced is a matter of equal interest. Indeed, some evolutionists maintain that one of the chief desiderata in the theory of evolution is an explanation of the origin of varieties.| Variations are deviations from the average, but varieties *So far as the necessary material can be obtained the statistical method of testing species is under such conditions the best. + See ‘‘ Evolution and its Relations to Religious Thought,’’ by Joseph Le Conte, published by Appleton & Co., p. 252 DARWIN AND SPENCER ON CAUSES OF DIVERGENCE. 2T5 are groups of individuals in which the averages differ, and in which the inheritable characters differ. Still further, it is usually admitted that the divergences presented by varieties are not always essential to the well-being of the forms that possess them, and that in many cases the forms that are confined to separate localities might exchange posi tions without suffering disadvantage. Divergence in these initial stages has seemed to many to be an obscurer problem than the ad- vancing usefulness which sometimes entirely remodels an organ. [For as Professor Le Conte has said, ‘‘ Natural selection does not make an organ useful, but only more useful.”’ I believe the theory of divergent evolution, presented in this and the preceding paper, is applicable to the formation of divergences during the stage when some of the differences, if not all, bring neither advantage nor disadvantage to those that possess them. Whatever we call these divergent forms, can we give any explanation of the causes that have produced them? (2) Divergent evolution does not necessarily depend on diverse envi- ronments. In other words, it does not necessarily depend on change in the conditions surrounding the organism, or on the organism being brought into a district presenting a different set of conditions. Darwin maintains that isolation (by which he designates geo- graphical separation), without any differences in the surrounding organisms or in the physical conditions, presents no occasion for divergence of character. He says, ‘‘If a number of species, after having long competed with each other in their old home, were to migrate in a body into a new and afterwards isolated country, they would be little liable to modification.’”’ (Origin of Species, 6th ed., P- 319.) Spencer expresses the same idea by saying that ‘‘Vital actions remain constant so long as the external actions to which they corre- spond remain constant.’’* There must be maintained a tolerably uniform species so long as there continues a tolerably uniform set of conditions in which it may exist.’’ (See Spencer’s Principles of Biology, sections 91, 156, 169, 170.) In other words, divergence of character in the descendants of one stock occupying different districts does not arise except as it is preceded by difference in the physical conditions, or in the surrounding organisms, of the different districts. After molding this thought in many forms, Spencer makes it the funda- mental principle on which he builds not a small portion of his philos- * Though apparently opposed to his theory of ‘‘the production of certain local forms by amixia,’”’ this same idea is found in Weismann’s “Studies in the Theory of Descent,”’ pp. 109-115 (English edition). 216 APPENDIX II—INTENSIVE SEGREGATION. ophy. Darwin is more guarded in his statements; still, as we have already shown, he sometimes seems to reason from an assumption quite in accord with what Spencer would have us receive as essential to the very idea of causation in vital processes. For example, his explanation of the fact that on the different islands of the Galapagos Archipelago one genus is, in many cases, represented by several closely allied species which are undoubtedly modified forms of one continental species, seems to rest on the assumption that if every species that gained access to any island had at the same time gained access to the other islands of the archipelago, there would then have been no occa- sion or opportunity for the divergences we now find. (See Origin of Species, 6th ed., p. 355.) It seems to me that the divergences presented by the varieties and species of the family Achatinellide are at variance with this assump- tion. Not only are islands in sight of each other occupied by diver- gent species, but different parts of the same mountain range exposed to the same winds and rains and clothed with the same vegetation are the homes of divergent forms. Turning to the map of the island of Oahu, we find a mountain range extending 36 miles from northwest to southeast, nearly parallel with the northeast coast. The northeast side of this range is exposed to the trade-winds fresh from the ocean, and accordingly receives a heavier rainfall than the other side; but there is not much difference in the amount of rain received by the different valleys on one side of the mountain. In nearly all these valleys on either side of the range are found shady groves of what the natives call the ‘‘kukui’’ (Aleu- rites triloba). Many species of the genera Achatinella and Bulimella have their haunts in these groves, some species clinging to the leaves and young branches, and others to the trunks and the larger branches. Most of the species thrive only where the shade is dense and the atmos- phere laden with dampness a large portion of each month. The student who starts with the assumption that divergent varie- ties and species arise only through exposure to different environments will expect that these groves, at least those on the same side of the mountain range, will be occupied by the same species. Having found one set of species in a given valley, when he comes to a valley ten miles distant, possessing the same conditions of soil, rainfall, vegeta- tion, and shade, where the birds, reptiles, and insects are the same, where the mice and ants, their only known enemies,* are the same, he naturally looks on the leaves and branches of the familiar trees for * The species that molest the snails were not known on these islands till com- paratively recent times. DIVERGENCE NOT ALWAYS ADVANTAGEOUS. 217 the snails he has found in similar stations not far distant; but what is his surprise to find only different species, all allied to, but quite dis- tinct from, those he has previously known! ‘Twenty miles from the first valley he renews his investigations, finding the forms of all the different groups still more divergent, though all the conditions of the environment are, so far as he can observe, the same. He finally perceives that he must give up the theory that the cause of this divergence is exposure to different environments. (3) When the environment is the same in two districts occupied by allied spectes or vartetves, vt 1s evident that the differences that distinguish the latter can not be advantageous, even though their differences include strongly contrasted habits. For in order that these differences should be advantageous, it is necessary not only that they should relate to the performance of vital functions, and, therefore, be differences of adaptation, but it is necessary that these differences of adaptation should relate to differences in the environment, so that the forms would be at some disadvantage if they should exchange districts. Advantageous differences are always adaptational; but adaptational differences are not always advantageous, and in such cases the diver- gence can not be primarily attributed to diversity in the action of natural selection in the different districts. Under the protection of isolation, diversity of selection may arise which helps in producing divergence; but when the environments are the same, the divergence is in no sense advantageous; for, if a given combination of characters is an advantage in one district, so would it also be in the other dis- trict, and the difference or divergence is no advantage. A familiar example will perhaps put the distinction between the causes of survival and transformation and the causes of divergent sur- vival and transformation in a clearer light. The forms of language are growths that are governed by the laws of utility as fully as the forms of varieties and species. Each language and each part of a language exists and persists only asitisfound tobeofuse. The ‘‘sur- vival of the fittest’? is alaw that is perhaps as conspicuous in the domain of language asin the organic world. Again, every language, like every organic species, is in many respects determined by the environment. A language, for example, developed in Java will pre- sent names for many plants and animals that will not be represented in a language developed in Greenland. But, granting all this, does it follow that linguistic differences are necessarily advantageous? The Polynesian system of counting by fours, and the Eskimo system that proceeds by scores, are undoubtedly useful systems; but is there any- thing advantageous in the difference? I think not, for each system is 218 APPENDIX II—INTENSIVE SEGREGATION. as well adapted to the environment of the other as to its own envi- ronment. We may look uponthe moreimportant parts of alanguage as persisting through their usefulness, the survival of the fittest being the law; but the divergent evolution which brings several languages out of one seems to be principally due to other principles which are closely akin to the principles that produce divergence in the organic world. The fundamental condition in both organic and linguistic diver- gence ts isolation; and, this being secured, diversity of habits, bring- ing diversity of aptitudes and diversity in the forms of survival, ts sure to arise even when the environment ts the same. (4) Specific differences are not always differences of adaptation to the environment, and those that are not should not be attributed to the action of natural selection. It is admitted by every one that a distinction relating to a character that is of no use in the economy of the organism can not have arisen under the influence of natural selection. Those who maintain that all specific distinctions are due to natural selection maintain at the same time that these distinctions are adaptational and advantageous. There are naturalists who maintain that the very essence of the Darwinian theory is ‘‘that specific differences must be advantageous,’’* and, therefore, adaptational, while they do not claim the same for generic, family, and ordinate distinctions, or, indeed, for varietal distinctions, if I rightly understand. I have never seen any attempt to explain this supposed exception in the midst of the taxonomic series; and it seems to me that the break in the continuity of nature which this interpretation of the Darwinian theory supposes should‘lead us to a very careful investigation of the facts before we accept it as a true interpretation of nature. I shall content myself with pointing out one distinction, occasion- ally occurring between allied species, for which no use has ever been, or is likely to be, found. I refer to the distinction between what are known as dextral and sinistral forms. This distinction relates to the form of the twisting of the animal and its shell. Itis most easily recognized by holding the shell with the aperture toward you with the apex turned upward, and observing whether the aperture lies on the right side of the central columella of the shell or on the left. In the first case it is described as dextral, in the second as sinistral. In most familiesand genera of water mollusks the sinistral form occurs only as a sport (as in man the heart is sometimes found on the right side), and even among air-breathing mollusks the dextral form vastly predominates. Of the Achatinellide, Amastra and Leptachatina, * See letter from Mr. W. T. Thiselton Dyer, in Nature, vol. XXxIx, p. 8 NATURAL SELECTION NOT ALWAYS THE CAUSE. 219 which are genera of terrestrial habits, are (with but few exceptions) dextral in form; while the other genera, which are plant feeders and constantly hanging to branches or leaves, present many species that are constantly sinistral, and many others that are both dextral and sinis- tral. Why should Achatinella adustain Pauoa and Makiki be constantly sinistral when the most nearly allied A. producta found in the same valleys is both dextral and sinistral? Why should A. bacca and A. abbreviata in Palolo and Waialae be constantly dextral when other species of Achatinella in the same valleys are for the most part sinistral ? Is there any adaptation to the environment possessed by a dextral form which would be lost if the form was reversed? If not, natural selection could not have anything to do with that part of its char- acter. Sulimella rosea is sinistral, while B. bulimoidesisdextral. If in this respect they should exchange forms, would any disadvantage beexperienced by either species? It is impossible to conceive of any disadvantage that would follow, and, therefore, I can not believe that this difference in the two species was in the first place due to natural, sexual, or any other form of selection. There are many other specific distinctions presented in this family which seem to be of no advantage, though they are not so far removed from all suggestion of the possibility of use as the character we have just been considering. The brilliant colors and varied patterns pre- sented by many of the arboreal species would be of advantage to them- selves if they served as warning of nauseous qualities to creatures that are liable to prey upon them; but no such conditions exist. The birds of the forest region are for the most part fruit and nectar feeding; and the ants and mice which in recent years have made sad havoc with the mountain snails unfortunately do not spare the highly colored species. There can be no doubt that when representatives of different genera occupy the same trees they remain segregated through the influence of sexual instincts, which must be associated with some means of rec- ognizing those of their own group; but it is not at all probable that the colors and patterns of any species are recognized by their mates, or have been developed under the influence of sexual selection. There is, therefore, strong reason to doubt whether selection of any kind has been concerned in the production of the beautiful colors and patterns of these species, unless possibly correspondences in color within the limits of a genus are, in some cases, due to the inheritance of tendencies produced by selection when conditions were very differ- ent from what we now find. But the divergences in color and pattern in the species of one genus can not be thus explained. 220 APPENDIX II—INTENSIVE SEGREGATION. (5) The average radius of distribution for species of the same value in allied genera varies in the different genera directly as the average power and opportunity for migrating, and inversely as the plasticity and vari- ability of each genus. Comparing the distribution of the Helices of Europe with that of the Achatinellide of Oahu, the most striking con- trast is found in the size of the areas occupied by the different species. Helix pomatia is distributed from England to Turkey, over an area 2,000 miles in length, while of the eight genera of Achatinellide on Oahu I know of but one species that seems to be distributed over the whole 36 miles of the main mountain range, and thisoneis rep- resented by three varieties belonging to different parts of the range and perhaps worthy to be regarded as different species. The species to which I refer is A urtculella auricula (Fer.), the typical forms of which are found on the eastern half of the mountain range. On the other half of the range we find the closely allied forms to which I have given the manuscript names solida and pellucida. This great contrast in the size of the areas occupied must be due either to the greater plasticity of the Achatinellide or to their having inferior opportunities for migrating, or to both causes. As I become better acquainted with the great difference in the habits and circumstances of the contrasted species, I give increasing weight to the difference in the opportunities for migrating. With the continental species, floods must be one great means of distribution; but in the case of the insular species, the floods would carry floating individuals upon the grassland or into the sea, in either case to perish. Again, the habit of traveling upon the ground, which belongs to most of the Helices of Europe and America, gives incalculable opportunities for migration which are not enjoyed by species that are strictly arboreal, as are many of the Hawaiian species. Most of the Hawaiian snails are still further restricted in their oppor- tunities by their inability to resist a dry atmosphere or exposure to the sun, which renders it necessary that they should remain in the isolated areas that are favored with shade in the different valleys. The habits of the different genera occupying Oahu are also instruc- tive as throwing light upon the relative areas occupied by the species of the different genera. Achatinella and Bulimella seem to be the most restricted in their opportunities for migrating; first, because they are entirely arboreal in their habits, clinging to the trunks and branches of trees through their whole life history; and, second, because, for the most part, they occupy the shady and damp thickets and groves, the shade in each valley being separated from similar shades in adjoin- ing valleys by lofty and sparsely wooded mountain ridges at each side of the valley and by open grassland at the mouth of the valley. On AVERAGE RADIUS OF DISTRIBUTION. 221 the other hand, Apex, which for the most part occupies trees and shrubs on the ridges which are connected with each other through the central ridge of the mountain range, and Amastra and Leptachatina, which are for the most part found on the ground under dead and de- caying leaves, seem to possess better opportunities for migration than either the Achatinella or Bulimella. Corresponding with these facts we find the species of Achatinella and Bulimella especially limited in the areas they occupy, while the species of Apex, Amastra, and Lep- tachatina are less so. For example, the area occupied by Amastra turritella, A. tristis, and A. ventulus includes the areas occupied by many species of Achatinella and Bulimella; and Apex loratus and A. pallidus, occupying the mountain ridges, range from Makiki to Halawa, exceeding the range attained by any arboreal species occupy- ing the valleys of the same region. (6) When a group of divergent forms that are fertile with each other is being developed through the influence of local or geographical isolation, other conditions remaining constant, the number of forms that will be pro- duced within a given area will vary inversely as the square of the average radius of distribution for the different jorms. As this average radius of distribution may be taken as the measure of the power and opportu- nities for migration, we may say that, other powers and opportunities remaining constant, the number of species developed within a given area will vary inversely as the square of the average power and opportunities for migration. Though migration is in one sense a cause of isolation, it is evident that the number of isolated groups of individuals of a given form within a given area does not increase with the increase of migration. Isolation 1s produced by the great contrast between ordinary and extraor- dinary combinations of opportunities for migration; and this contrast is liable to be as great in the case of species that have limited powers and opportunities as in the case of those that have very great powers and opportunities. The number of isolations thus produced that can exist within the limits of a given area must vary inversely as the square of the power and opportunity for migration. The facts of distribution we have been considering seem to corre- spond to this law. (7) Forms that are most nearly related, and are, therefore, the least subject to sexual and impregnational rsolation, are distributed in such a manner that their divergence is directly porportional to their distance from each other, which ts also the measure of the tome and degree of thewr geographical isolation; while those most manifestly held apart by sexual instincts and impregnational incompatibilities do not follow this law. tO ty to APPENDIX II—INTENSIVE SEGREGATION. Bulimella is represented by two groups of species, one of ovate form, the other elongated and with the outlines of the spire less rounded. The widest divergence between these groups is presented by species occupying the same districts and valleys, but the widest divergences in the species of either of these groups are found in valleys widely sepa- rated. Inthelatter case, the degree of geographical separation is prob- ably anapproximate measure of the time and degree of isolation, and, therefore, the measure of the degree of divergence; while, in the former case, the isolation is probably as complete between forms occupying the same valley as between those of widely separated valleys. Thereis reason to believe that in the eastern part of the island these two groups are not fully held apart by sexual isolation or segregate fecundity and vigor, for there is complete intergrading, and the divergence between the groups in any one valley is much less than is found in the northwest portion of the island, where sexual incompatibility seems to be complete. Achatinella bacca and A. abbreviata completely intergrade with each other, but they are associated with a number of other species of Acha- tinella with which they do not intergrade, prevented, it seems to me, by mutual incompatibility. We have, therefore, in the eastern valleys two groups of Achatinella completely segregated from each other, though occupying the same districts and in some measure the same stations; while in the other valleys the two groups coalesce, the different species occupying any one valley being only partially isolated by divergent habits of feeding. The different genera and subgenera, which are undoubtedly segre- gated by divergent sexual instincts, as well as by physiological incom- patibilities, are equally divergent, whether we compare forms from the same or from distant valleys. (8) The distribution of the varieties, species, and genera of Achati- nella on this island 1s gust such as would be produced by divergent evolu- tion which depends on isolation as a necessary condition, even when the environments are difjerent, and which always follows long-continued isolation, even when the environment surrounding the different sections as the same. It may be safely said of the multitude of varieties which inhabit the island of Oahu that every one is more or less segregated from all other varieties; and I believe this will be found true concerning varieties in every part of the world. This fundamental fact would probably never have been denied, except for the delusive idea that the advan- tage of divergence would lead to the accumulation of divergence even if segregation were entirely wanting. What could be a greater DIVERGENCE DEPENDS ON ISOLATION. 223 mistake for the breeder of animals than to imagine that by selecting extreme variations and breeding them together he would in time secure well-marked races? It must be equally at variance with fact to suppose that any advantage secured by divergent variations can be preserved and accumulated while the different forms are freely intergenerating. ; In the family we are considering, the chief forms of isolation are probably what I have called local, geographical, industrial, and sexual isolation, strengthened in many cases by segregate fecundity and vigor. As illustrating local isolation I would mention varieties and species of Apex, for the most part occupying mountain ridges which are all connected with each other, without the intervention of geographical barriers. Geographical isolation is illustrated in the forms of Achati- nella and Bulimella, which for the most part occupy the deep valleys, the ridges forming barriers that are very rarely surmounted. Indus- trial isolation is illustrated by the closely allied varieties of one group of species that occupy one valley, but are prevented from crossing by different habits of feeding. It is probable that sexual or seasonal iso- lation prevents the pairing of Achatinella with Bulimella when both occupy the same trees. Moreover, cross sterility would undoubtedly prevent the multiplication of the hybrids, if cross-unions ever do occur between forms so widely divergent. There can be no doubt that the same principles prevent the strongly marked groups of either genus from intergenerating; as, forexample, in the case of Achatznella bacca and A. abbreviata, which are intergraded with each other, but not with the surrounding species of Achatinella. Again, divergent forms of environal selection do not necessarily depend on exposure to different environments. Industrial isolation is produced by different modes of using the environment found in a single district ; and the same cause will often produce diversity in the forms of environal selection affecting the isolated sections, distrib- uted in different districts, but exposed to the same environment. Cumulative divergence in the methods of using the environment in the different sections of the species depends upon their isolation, and, therefore, increasing divergence in the forms of selection affect- ing the different branches depends upon their isolation. Geograph- ical isolation under the same environment, if it does not of itself produce divergent forms of selection, opens the way for change in the habits of feeding, with diversity of selection in the different sections of the species. ‘Take, for example, the species of Achatinella: In Manoa and Makiki they chiefly occupy the kukui (Aleurites triloba) and other trees, while in Kawailoa and that region they neglect the larger trees and take to the lobelia and other shrubs and herbaceous plants. e 224 APPENDIX II—INTENSIVE SEGREGATION. But why should the degree of divergence increase with the contin- uance of the isolation? The answer seems to be that the combined effects of the different principles of transformation in the isolated groups increase with the time of isolation; and, as independent transformation is never parallel, the divergence increases in the same ratio. Diversity of environal selection is undoubtedly one of the prin- ciples producing this divergence, even when the vegetation and physical conditions of the different districts are the same, for when the habits of feeding change, the environal selection must usually change. But there are cases of divergence accompanying isolation in which the habits of feeding seem to have remained unchanged; and in such cases I explain the divergence by the fact that any small fragment of a species is incapable of propagating all the qualities of the species in the exact proportion presented by the average of the species. 2. Similar Facts in Other Regions. Many of the facts embodied in these eight propositions must have been observed wherever naturalists have studied the geographical dis- tribution of the varieties and species of polymorphic genera; but in the distribution of the Achatinellide there are features of peculiar interest arising from the fact that the powers of migration possessed by the species of the surrounding environment are very much greater than those possessed by these molluscan species. Through this circum- stance a comparatively uniform environment is produced in which the effects of independent generation unmodified by the effects of changed environment may be observed. The remarkable facts of distribution which we have on the island of Oahu are found in other parts of the Hawaiian Islands, wherever this family occurs. Iam also fully con- vinced that, in other parts of the world, wherever one genus or family of very low powers of migration is surrounded by a body of plant and animal forms possessing much higher powers of migration, there similar facts will present themselves whenever investigation is made. The distribution of land mollusks belonging to the genus Partula found on the Society Islands present similar features. The island of Reiatea, which is but 14 miles in length and 3 or 4 miles in breadth, is the home of about 30 species and varieties, most of which are confined to areas only a few square miles in extent. Iam not informed as to the distribution of the plants on which these species feed, but there is no reason to suppose they occupy limited districts corresponding to those occupied by the different species of Partula.* * See Bulletin of the Museum of Comparative Zodlogy at Harvard University, vol. Lx, No. 5. DIVERGENCE IN INSECTS. No to wn III. DIvERGENCE IN INSECTs. The dependence of divergence on some form of isolation is most clearly exemplified in insects, and though my studies are but limited in that field, I shall refer to a few cases, which may serve to direct atten tion to a class of facts of the highest interest not only to entomology, but to general biology. 1. Divergence in Erynnis and Thanaos. Erynnis (Pamphila) and Thanaos (Nisoniades).—These two genera of small North American butterflies are worthy of the special atten- tion of those who are studying the problems of divergent evolution, for they furnish strong indications that organisms which are with diffi- culty distinguished from each other by external form or color may, nev- ertheless, be well-established species segregated presumably by sexual instincts corresponding to sexual characters by which those of opposite sexes of the same species readily recognize each other, and probably cut off from the possibility of producing hybrids through incompati- bility of physiological endowments. In the origin of some of these species geographical isolation may have had an important influence; but concerning others there can hardly bea doubt that the segregative influences, holding apart species that occupy the same districts, were, from an early stage, peculiarities of their sexual instincts and constitu- tion. The reason for accepting this view of their origin is found in the fact that, though slightly divergent in other points, the characters by which they are clearly distinguished are found in the forms of the male genitalia ; and in the characters of these organs we find clearly marked species, for the most part free from the intergrading forms which would certainly be presented if the different species were not prevented from crossing by sexual instincts or constitution. A full description of these genera, with observations on the asymmet- rical devolopment of the right and left sides of the genital armature in Thanaos, will be found in Scudder’s Butterflies of New I/ngland. (See also Mem. Boston Soc. Nat. Hist., 1 (1874), and Proceedings of the same Society for April 27, 1870, vol. x11I (1871), p. 282. 2. Divergence in Basilarchia. (1) Basilarchia (Scudder) is an attractive genus of butterflies pecu- liar to North America, where it is represented by four or five species. Three of these are found in New England, and are minutely described in Scudder’s ‘‘ Butterflies of New England,” from which I draw my information (pp. 250-305). 226 APPENDIX II—INTENSIVE SEGREGATION. The distribution of these three species is of great interest, as it illus- trates divergence both with and without local segregation. Basuil- archia archippus ranges over nearly the whole United States and over the southern portion of Canada. JB. astyanax occupies the valley of the Mississippi and eastward to the Atlantic from the Gulf of Mexico on the south to the lakesonthenorth. B.arthemzs is distributed from Newfoundland and Nova Scotia on the east, over New England, Can- ada, the region of the lakes, away to the northwest, toward the con- fines of Alaska. It will be observed that the area of distribution of B. archippus includes the whole of that of B. astyanax anda large portion of that of B. arthemis; while the areas of B. astyanax and B. arthemis overlap along the whole northern border of the territory occupied by B.astyanax. Thisarea of overlapping distributionin which the three species are associated is about 1,000 miles in length and from roo to 250 miles in width. (2) Forms of Isolation that separate Basilarchia archippus from B. astyanax and B. arthemis.—It is evident that, in the present condition of distribution, geographical barriers and territorial separation have nothing to do with the integrity of B. archippus as a separate species. In other words, it is not under the influence of geographical or local isolation. Whatever may have been its past history, these certainly are not the causes that at present prevent it from interfusing with other species of Basilarchia with which it is associated. Again, seasonal isolation seems to have but little influence; for though B. archippus seems to appear 15 or 20 days earlier than the other species, the remainder of the breeding season, which extends over many weeks, is coincident. The habits and feeding instincts of this species must tend to sepa- rate it somewhat from B. arthemis, for this latter species frequents forest regions, especially when elevated and hilly, while B. archtppus is found in the open country in fields and meadows, especially in low levels. The eggs of B. arthemis are chiefly deposited on the species of birch and willow that are found on the highlands; while the eggs of B. archippus are chiefly deposited on the willows and poplars found on the lowlands, though on the White Mountains it occasionally extends its range to as high levels as B. arthemis. ‘There is, therefore, between these species a slight degree of industrial isolation; but this partial segregation does not prevent their being often found in the same fields, and unless held apart by sexual instincts and by partial infer- tility, hybrids, which are now very rare, would be very common. We are, therefore, led to believe that diversity of sexual instincts, accompanied by a considerable degree of cross-sterility, is the chief PARTIAL ISOLATION ILLUSTRATED. 207 cause preserving the independent character of this species. Except for the sexual segregation and segregate fecundity there is every rea- son to believe that this species could never have arisen, or, if it had arisen asa variety in some isolated locality, would have been submerged in the allied forms when its wider distribution was reached. This con- clusion, which has been reached by observing the general relations of the species, is confirmed bya minute examination of the structure of the threespecies. We find that while the male genitalia of B. astyanax and B. arthemvs differ but slightly, those of B. archippus are consider- ably divergent. This isan index of the psychological and physiolog- ical relations of varieties and species of no small importance; for a comparison of many species shows that differences of this kind are usually accompanied by corresponding degrees of segregation in sexual instincts and of cross-sterility. In other words, we find that difference in the male genitalia, which is a form of structural segregation, is an index of sexual segregation and segregate fecundity. (3) The Partial Isolation of B. astyanax and B. arthemis.—In the relation of these two species we find examples of segregative influences differing somewhat from those that have just been found in the case of B.archippus. Regional isolation, with exposure to different climates and adaptations to different food-plants, has undoubtedly had an important influence in the formation of these species; but, in the part of the country where they coexist, their life-histories correspond com- pletely, and cross-unions seem to be frequent. The hybrid form has been described as a separate species, and some entomologists have classed it asa dimorphic form of B. arthemzs; but Scudder gives several reasons for believing that it is the result of cross-unions between these two species. There are, however, several reasons for believing that partial segregate fecundity exists between the two species; for, in the strip of territory where the two are associated they do not completely coalesce, as would be the case if they were completely cross-fertile. In Scudder’s Butterflies of New England, pages 159 and 160, we find mention of two species (Cercyonis alope and C. nephele), in which the cross-sterility must be considerably weaker than between the two spe- cies we are now considering; for, in the intermediate region in which their areas overlap, the intergrade forms are comparatively abundant. Moreover, the difference in the male genitalia of B.astyanax and B. arthemis, though much less than that which appears when either of these is compared with B. archippus, is such as indicates a considerable degree of infertility. In these two species we have, then, a good example of partial isola- tion through distribution over areas which, though overlapping, are 228 APPENDIX II—INTENSIVE SEGREGATION. s for the most part distinct, reinforced by partial segregate fecundity which mayor may not be accompanied by slightly divergent sexual instincts. Thereisalsosome isolation resulting from the fact that the plants on which B.arthemis seeks to deposit its eggs are chiefly the birches and willows of the hilly country, while B. astyanax prefers fruit trees of the Rosacee family and other plants that are found in the more open country. These are, as I have shown in my paper on ‘Divergent Evolution through Cumulative Segregation,”’ exactly the conditions that produce, in successive generations, increasing degrees of segregate fecundity. (4) Cumulative Segregation in the Formation of the above Species.—I judge that in the relations to each other of these three species we have the results of divergent evolution through cumulative segregation very clearly illustrated. In the earlier stages of divergence in this genus, Basilarchia archippus, with its fondness for the open fields, must have become partially separated from the parent form from which both B.astyanax and B.arthemis have since sprung. The separationmay have been in some measure due to the methods of escaping from enemies; for we find that the form that has kept to the open country has through protective selection gained a very close resemblance to the coloring of Anosia plextppus, which is protected by its disagreeable qualities. The other form has probably gained compensative advan- tages by keeping closer to the woodlands. But the partial segrega- tion thus produced would never have resulted in constant specific dif- ferences if segregate fecundity had not arisen between the two forms. We may believe that some form of impregnational segregation (either segregate structure, segregate fecundity, or segregate vigor) was early introduced, and that under the protection of this barrier the specific distinctions of the two forms became fully established, though even now the barrier is not so complete as to entirely preclude hybrids between B. archippus and each of the other species. Examples of both these hybrids are described by Scudder. While this segregation was being completed, one of the two forms thus created must have become subject to a new set of segregative in- fluences arising from wider distribution with diversity of climate and of habits of feeding, reinforced by a slight degree of segregate fecun- dity. B.astyanaxand B.arthemis are the two species resulting from this last segregation, and the process is so far from being complete that wherever the areas of these two species overlap a hybrid form, which has been known as B. proserpina, appears. That it isa hybrid is proved by the fact that it ‘‘varies most toward astyanax where this prevails, and most towards arthemis where that prevails;” that it is DIVERGENCE IN THE PERIODICAL CICADA, 229 found only in the narrow belt where the two species are brought into contact, and that it has been reported from so many points in this nar- row belt that there is reason to believe that it occurs wherever the two species are broughtinto contact. If our exposition of the segregations to which these species have been subjected is correct, they are cumu- lative in two respects: first, because after one segregation has been established another is superimposed, and second, because a partial segregation established in one generation tends to become more com- plete in subsequent generations. The primary causes in the whole process are the activities of the organisms acting upon each other and upon the environments in sucha way as to produce, in the first place, independent generation with some degree of divergence, and then unbalanced selection of different forms producing transformation, which, acting upon sections of the species that are prevented from crossing, result in ever-increasing divergence. 3. Divergent Evolution in the Periodical Cicada (Cicada septendecim).* In Cicada septendecim we have examples of two quite distinct diver- gences, each depending on its own forms of segregation, which are easily recognized. The life history of this insect covers seventeen yearsand one or two months. The imago appears late in May, and fora little more than a month the males make the woods ring with their shrill stridulations. The eggs, which are deposited in the green twigs of trees, mature dur- ing the latter part of July, and each newly hatched larva, dropping to the ground, takes up a solitary subterranean life, which it follows till its period of seventeen years is nearly complete. It then appears above the ground, passes into its winged stage, and enters on a few weeks of social life which closes its career. This species is widely dis- tributed in that part of the United States that lies between the Atlan- tic shores and the Rocky Mountains, but does not occur in Minne- sota, Northern Michigan, or Northern New England. Itis, however, represented by two races in every respect the same, except that one has a life-history of thirteen and the other of seventeen years. The thirteen-year race prevailsin the Gulf States, butin New England and the Middle States the seventeen-year race is alone found. In Illinois, Missouri, Kansas, and in several of the Southern States the two races occurin the same localities ; but it is evident that even in such localities it is only once in 221 years that there will be any opportunity for cross- ing between them, and we are informed by those who have made * My information is chiefly derived from Bulletin No. 8, Division of Entomology, U.S. Department of Agriculture, by Dr. C. V. Riley. 230 APPENDIX II—INTENSIVE SEGREGATION. a special study of the subject that they do not cross when these opportunities occur; for 14, 15, and 16 year races are not found. These two races are, therefore, prevented from crossing by partial local isolation; by cyclical isolation rendering it impossible that a brood of each occupying the same locality should have opportunity for crossing more than once in seventeen generations of the shorter- lived race, or once in thirteen generations of the longer-lived race; and by sexual isolation that shows itself in diversity of instincts preventing them from pairing when other conditions favor. Whether devices have been tried to induce cross-unions, and whether such unions are unfruitful, I have never heard; but the simple fact that fifteen-year forms do not appear in localities where the two races are found indicates that in nature they do not cross. Several such localities have been reported, but in none of them hasan intermediate form been found. It seems, therefore, that we may safely draw the conclusion that we have here a case of complete sexual segregation be- tween forms which to the human eye are undistinguishable, and which call their mates with stridulations which to the human earare the same. Now, I claim that in such races as these we have the beginning of diver- gent species, a beginning that lies in the segregative influences of con- stitutional and instinctive qualities persistently inherited by the two races, though the naturalist who examines specimens of the two races can not distinguish them. All that is necessary to convert these two races into good species is the transformation of one or both of them while they are thus prevented from crossing; for we may be assured that the results of transformation under such circumstances will never be completely parallel. Each of these races is again subdivided; for accompanying each is a diminutive form, differing somewhat in color, not so early by eight or ten days in its first appearance, producing a quite distinct stridula- tion, and showing no disposition to associate with the larger form. This small form was described in 1851 by Dr. Fisher as a new species under the name Cicada cassinit. Dr. Riley, however, hesitates to receive it as a separate species, because the differences presented by the genitalia are not constant. He says: There are sufficient differences to separate the two forms as distinct; but while the hooks of the large kind (septendecim) are quite constant in their appearances, those of the smaller kind (cassiniz) are variable, and in some few specimens are indistinguishable from those of the large kind. This circumstance, coupled with the fact that the small kind regularly occurs with both the seventeen and thir- teen year broods, would indicate it to be a dimorphic form of the larger, and only entitled to varietal rank.* * Bulletin No. 8, Division of Entomology, U.S. Department of Agriculture, p. 7. BROODS AND RACES OF THE PERIODICAL CICADA. 2 we ~ I consider this case as of equal interest with the previous one; for it is an example of complete isolation between the forms of one specics through diversity in their instincts. Whether these divergent in- stincts are sexual or social may be a matter of question; but in either case they are effectual in preventing crossing. If future investigation shows that the small form is often produced directly from the eggs of the large form, it will have but little claim to be regarded as a separate race; but even then, if the small form breeds only with its own kind, as has been reported by several observers, and if the offspring persistently reproduce the characters of the parents, it will have to be considered something more than a dimorphic form of the large one. It would, in this case, be a dimorphic form that is assuming the character of a species. If the two forms were without segregative sexual and social instincts, then, with cross-fertility, the small form would be rapidly absorbed by the large form, which greatly preponderates in numbers; and with cross-sterility the small form would rapidly become extinct; for, through the comparative scarcity of their numbers, the representatives of the small form would have but little chance of mating with each other. On the other hand, if the sexual and social isolation is complete, it matters but little whether the forms are mutually sterile, for the sep- arate races or species will be protected by the positive segregation produced by the divergent instincts, even if the negative segregation depending on structural incompatibility and lack of physiological adaptation is entirely wanting. It is only when associated with pos- itive segregation that is partial in its.results that negative forms of segregation become important factors in the preservation of diverging forms. In animals that pair, isolation through sexual and social instincts playsa similar role in giving preemptive power to the males of a given species over the females of the same species that is played by poten- tial and prepotential isolation in organisms whose fertilizing elements are distributed by wind and water. In the one case instinctive and in the other potential segregation, arising between varieties of the same species, marks these varieties as being the initial forms of divergent species. This species presents another form of isolation which is of much in- terest, though it has not yet resulted in forms that can be ranked as different races. I refer to the complete cyclical segregation that exists between different broods of a given race appearing in different years. Of the thirteen-year race there are seven broods and of the seven- teen-yearracefourteen. Asan example of different broods occurring 252 APPENDIX II—-INTENSIVE SEGREGATION. in the same region I would mention the two broods in the District of Columbia, one appearing in 1885 and atintervalsof seventeen years thereafter, and one appearing in 1894 and at intervals of seventeen years thereafter. We have no means of testing the sexual or the social instincts of these different broods, for they never appear in the same year. Noonecansay whether if they could be brought together they would be found as indisposed to breed with each other as are the thirteen-year and seventeen-year races. But, be that as it may, the two forms are as completely isolated as they can be, and the oppor- tunity for independent, and, therefore, divergent, transformation, is much the same as that which exists between the thirteen-year and seventeen-year races. Two or threeof the States have but one brood each; but in Ohio there are at least six seventeen-year broods, and in North Carolina one thirteen-year and six seventeen-year broods. I judge, however, from the reports that even in these last-mentioned States, there are but few places, if any, where more than three broods overlap. I have not seen any discussion of the causes that have produced these broods, but if we may believe that they have existed for a thousand generations, a possible if not a probable cause is found in the unsettled conditions of climate that must have attended the breaking-up of the greatice period. During years of diminished cold, colonies may have taken possession of regions which were too cold for their development at the return of the seventeen-year period when the offspring should have appeared; and still some of the benumbed and delayed pupe may have survived, making their appearance one, two, three, or more years later, when conditions were more favorable. The following ob- servation referred to by Dr. Riley, in explanation of the accelerated or retarded appearance of sporadic individuals, throws some light on the origin of the different broods: That circumstances favorable or otherwise may accelerate or retard their devel- opment was accidentally proven in 1868 by Dr. E. 5. Hull, of Alton, Ill., as by con- structing underground flues for the purpose of forcing vegetables, he also caused the Cicadas to issue as early as the 20th of March, and at consecutive periods afterwards till May, though, strange to say, these premature individuals did not sing. They frequently appear in small numbers, and more rarely in large num- bers, the year before or the year after their proper period. This is more especially the case with the thirteen-year broods.* That climate has been an important factor in the development of the thirteen and seventeen year races is indicated by the fact that most of the districts occupied by the seventeen-year race lie north of latitude * Bulletin No. 8, Division of Entomology, U.S. Department of Agriculture, p. 8. SEXUAL AND CYCLICAL ISOLATION. 233 38°, and most of those occupied by the thirteen-year race lie south of that line, though in Illinois there is a thirteen-year brood as far north as latitude 40°. Dr. Riley has not referred to the coincidence, but it seems to mea fact of some interest in this connection that the southern limit of the great ice-cap which covered Canada and the northern part of the United States during the glacial epoch extended along an irreg- ular line between the parallels of latitude 38° and 40°. Lying south of the ice region there was probably a considerable belt of country cov- ered with pines and other conifers not adapted to the breeding of this species, so that both races, if they then existed, must have been crowded into the southern portion of the region now occupied by the thirteen-year race. Instinctive and cyclical forms of isolation, such as cause the inde- pendent generation of the races and broods of this species, are usually associated with clearly developed specific distinctions relating to form, color, and function. This does not, however, prove that the isola- tive divergence was subsequent to the general divergence 1n other re- spects. The number of generations covered by the initial stage in which the different sections are only races is very small compared with those that are likely to be covered by the stages when they are separate speciesand genera. Itisonly, therefore, by rare chance that we find two forms that are still in the earliest stage of palpable divergence and are, at the same time, completely segregated by constitutional differences. Again, segregative endowments are usually developed somewhat grad- ually; and while the segregation is advancing other transformations take place, so that by the time all crossing has come to an end the dif- ferent sections have become well-marked species. Sometimes, as in the three species of butterflies already considered, there is more or less crossing after the sections have become quite distinct species. Such cases, however, asare presented by the thirteen-yearand seventeen-year races and by the different broods of this species of Cicada show that complete segregation may be produced by the psychological and physio- logical constitution of different races, while distinctions of form, color and manner of call are entirely wanting so far as we can observe. This has seemed impossible to some naturalists, especially since Dar- win has admitted that cross-sterility can not be attributed to natural selection, and has, therefore, attributed it to the indirect effects of other qualities which have been produced by natural selection. The great contrast in this respect between the species of Basilarchia and the thirteen-year and seventeen-year races of the periodical cicada may perhaps be partially explained by the fact that the latter spend the greater part of their existence under ground, where the conditions 234 APPENDIX II—INTENSIVE SEGREGATION. have not been seriously changed since the close of the last glacial period. Again, one generation of the seventeen-year race of Cicada covers many generations of the Basilarchia, bringing thirty or forty fluctuations of climate, food, ete.,to the latter, while the former is, for the most part, protected from serious fluctuations. It is of course equally impossible to prove by allinclusive observa- tions either that transformation is never completely parallel in sections of a species that are prevented from crossing or that independent gene- ration long continued is sure to result in independent transformation, and, therefore, in divergence; but it is of no small interest that we find in the thirteen-year and seventeen-year races of this species the strongest proof that there are sometimes divergences which our senses do not perceive. If our senses were a sufficient test, it might be main- tained that between these races a high degree of loeal and cyclical isolation has existed for many generations, without any other form of transformation having arisen to increase the divergence; but if our informants are correct when they tell us that these races do not cross when appearing in the same district and at the same time, we need not hesitate to affirm that there must be some distinguishing character- istics by which those of one race are able to find each other, as well as segregative instincts which lead them to choose each other’s society; and, even if our informants are mistaken in supposing that cross-unions do not occur, there must be some form of incompatibility between the two races, resting on divergent endowments; for other- wise we should find hybrid descendants with periods of more than thirteen and less than seventeen years’ duration. IV. CONCLUDING REMARKS. 1. Outline of the Argument in Support of the Theory of Divergent Evolution through Cumulative Segregation. (1) The invariable experience of mankind in producing domestic races shows that segregation is a controlling factor. The segregation that produces domestic breeds and races is found to be of two kinds: first, that which is produced by men who designedly preserve the different styles of variation presented by one species, while at the same time they prevent them from crossing; and, second, that which commences in the indiscriminate division of the species into sections that are prevented from freely crossing through their being under the care of separate tribes of men, and which is changed into decided segregation through the diversity of selection, or of some other trans- forming principle, to which the different sections are sure to be OUTLINE OF THE ARGUMENT. 235 exposed; for it is found that these principles when brought to bear on separated sections never produce completely parallel effects. (2) The paramount effects of independent generation having been shown in the broad fields of biological experiment presented by the domestication of plants and animals, the question is next raised whether species in a state of nature are subjected to influences divid- ing the individuals of one species into sections that are prevented from crossing; and, if they are, how far this independent generation involves segregate generation. In my paper entitled ‘‘Divergent Evolution through Cumulative Segregation,”’ it was shown that there are many classes of activities by which the individuals of a species are thus divided, and that, in the majority of cases, the very process that separates them assorts them into classes with reference to one or more points of character; thus producing segregation that is similar in its character to the seg- regation that is designedly produced by the pigeon-fancier between his various breeds of pigeons. In the earlier half of the present paper I have shown that the planting of a small colony, resulting from migration or other causes, inevitably involves some segregation; and whenever the transform- ing influences of the other factors of evolution begin to operate in the different sections, this initial segregation is inevitably intensified and the divergence increased; for it isin the last degree improbable that change produced by these principles of transformation in sections that are prevented from crossing should be completely parallel in the different sections, even when exposed to the same environment. (3) The last step is to show, as has been attempted in the latter half of the present paper, that the relations to each other of varieties, species, genera, and the higher groups are such as would necessarily be presented if all such differences were the result of evolution that is always dependent on some form of segregation, but not always on diversity of natural selection, which is produced by exposure to different environments. We have found that persistent differences, whether varietal, specific, or generic, are not all adaptational, for some of them have no relation to utility, and that adaptational differences are not all advantageous, for some of them relate to adaptations that would meet with equal success if the organisms should exchange habitats, but that in every case divergence, whether utilitarian or non-utilitarian, whether advan- tageous or disadvantageous, is not maintained without independent generation. 236 APPENDIX II—INTENSIVE SEGREGATION. 2. Reply to Criticism. In view of the examples of divergence that have been discussed in this paper, I think I may state, as in my previous paper, ‘‘It is, therefore, evident, that the simple fact of divergence in any case is not sufficient ground for assuming that the divergent form has an advantage over the type from which it diverges.’’** Mr. Wallace has criticized this statement, using the following words: It seems to me that throughout his paper Mr. Gulick omits the consideration of the inevitable agency of natural selection, arising from the fact of only a very small proportion of the offspring produced each year possibly surviving. * * #* He omits from all consideration the fact that at each step of the divergence there was necessarily selection of the fit and less fit to survive; and that if, as a fact, the two extremes have survived, and not the intermediate steps that led to one or both of them, it is a proof that both had an advantage over the original less special- ized form. But what if the type from which the new form divergesis surviving at the same time that the newformsurvives? And what if both the forms are surrounded by the same environment which they use in different ways? Where, then, is the proof that the newer form has an advan- tage over theolderform? This was the class of facts I had been consider- ing in the preceding paragraphs, which led to the conclusion criti- cized by Mr. Wallace; and instead of omitting ‘‘the consideration of the inevitable agency of selection,” it was the very thing I was con- sidering. I had pointed out that when a segregated portion ofa species exposed to the same environment changes its habits, learning to appropriate resources that had not been previously used, it be- comes a new intergenerating group ‘‘in which a new and divergent form of selection vs established,’ but that the result of the divergence thus produced is not necessarily advantageous, and may for many generations be somewhat disadvantageous. As I was aware that many naturalists would consider it absurd to suppose that disadvan- tageous or even non-advantageous instincts ever persist and become the occasion of divergent selection, I referred to Darwin’s opinion that such might be the case with sexual instincts, and that the pro- genitors of man were deprived of their hairy coat by sexual selection that was, in its earlier stages, disadvantageous. Jam not aware that Darwin has ever attempted to show how divergent sexual instincts arise and become permanently fixed as distinguishing characters of varieties and species. * Linnean Society’s Journal, Zodlogy, vol. Xx, p. 214. t+ Nature, vol. XXXVIII, p. 491. REPLY TO CRITICISM. 237 ‘“‘The advantage of divergence,” the principle on which he relied to account for divergent habits, producing divergent natural selection, he never attempted to apply here; and, above all, when he believed the newer instincts to be either non-advantageous or disadvantageous as contrasted with the older instincts, he certainly could not have attributed advantage to the resulting divergence. As I have pointed out on previous occasions, Darwin assumed a psychological divergence in the sexual instincts of a species in order to account for the diver- gence in their secondary sexual characters relating to form, color, etc. ; and as there is no reason given why the psychological divergence should take place, or why it should precede the change in form and color, the theory of sexual selection, as presented by Darwin, is in- complete, especially in its relations to divergent evolution. If he had thrown light on the causes of divergence in sexual instincts, he would have found the same or similar principles applicable to the explanation of divergence of all kinds. But my object in referring to his opinion here is to point out that he was free to admit that per- manent divergence in sexual instincts may be non-advantageous, or even somewhat disadvantageous; and if thisis true of sexual instincts, I do not see whyit may not be equally true of industrial instincts. I think there is ample evidence that, when segregation has been estab- lished, divergence which is neither advantageous nor disadvantageous often arises in industrial as well as other instincts, and that these in- stincts may introduce new forms of environal, sexual, or social selec- tion. The relations which exist between habits and their objects are in many species constantly varying in such a way as to constitute a series of experiments; and when independent generation exists be- tween different sections of a species, there is nothing to prevent diver- gence in the results of those experiments in the different sections, even when exposed to the same environment. In Darwin’s ‘‘Posthumous Essay on Instinct,’ published as an appendix to Romanes’s ‘‘ Mental Evolution in Animals,” on pages 378 to 384, mention is made of certain ‘‘imperfections and mistakes of instinct,” and of certain instincts ‘‘that are carried to an injurious excess,” and of others that are ‘‘small and trifling.” Of the last- named he says: I have not rarely felt that small and trifling instincts were a greater difficulty in our theory than those which have so justly excited the wonder of mankind; for an instinct, if really of no considerable importance in the struggle for life, could not be modified or formed through natural selection. After mentioning several which might perhaps be considered tri- fling but are really of great importance to the species, he alludes to a 238 APPENDIX II—INTENSIVE SEGREGATION. few that seem to be ‘‘mere tricks”’ or ‘‘habits without use to the ani- mals.”’ Mr. Romanes, referring to these cases, offers the following explanation on page 275 of the same work (I quote from the New York edition, Appleton & Co., 1884): We have seen abundant evidence that non-adaptive habits occur in individuals, and may be inherited inthe race. Therefore, if from play, affection, curiosity, or even mere caprice, the animal should perform any useless kind of action habitually : and if this habit were to become hereditary in the similarly constituted progeny, we should have a trivial or useless instinct. As an example of a strongly inherited non-adaptive instinct in a wild creature may be mentioned the cackling of the wild hen of India after havinglaidanegg. This habit is referred to by Darwinas one that may be slightly detrimental; but all that is necessary to put it beyond the developing influence of natural selection is that it should fail of bringing advantage to the species; and that it is of no advantage will, I think, be generally admitted. If, then, species differ in regard to instincts that are non-advantageous, they are liable to present non- advantageous differences in form and color, resulting either from the same causes that have produced the divergent instincts, or from divergent forms of environal, sexual, and social selection produced by these instincts; it will, however, be found that segregate intergenera- tion is the necessary condition on which the divergence of innate characters depends. In the present paper and in other places I have mentioned cases, representative of multitudes of others, in which there is divergence between two varieties or species occupying different districts, but surrounded by the same environment. In such cases the differ- ences presented by the separate forms, and the divergence by which the differences have been produced, can not be regarded as advan- tageous; for if the forms should exchange districts, the environment being the same, no disadvantage would be experienced; and this is equally true whether the differences relate to industrial adaptations or to adaptations between the sexual instincts and the secondary sexual characters of the group, or to characters that are absolutely non-utilitarian. Mr. Wallace says that in my previous paper he looks in vain for any proof that cumulative segregation produces cumulative diver- gence; but at the same time he claims that the segregation of which I speak, and which I have illustrated by a supposed case in the breeding of pigeons, is a form of selection which he calls ‘‘selection by separa- tion.’’ Adopting his phrase for the moment, I understand that he fully admits that in domestication ‘‘selection by separation” will CUMULATIVE SEGREGATION AND DIVERGENCE. 239 produce divergence. Does he then doubt that the same process pro- duced by natural causes will result in divergence? Or does he deny that ‘‘selection by separation’’ ever takes place in nature? He will probably grant that wherever natural causes act upon the repre- sentatives of a species in such a way that in each generation those presenting one style of variation are led to breed together and are prevented from breeding with other kinds, there divergence will cer- tainly follow. This is what I call ‘‘segregation.’’ That without it there is no cumulative divergence, and that with it there is always divergence, is amply proved by the universal experience of man in the domestication of plants and animals. All that is lacking is the consistent application of our knowledge to the theory of evolution. Segregation is a process of much deeper significance than indis- criminate isolation, with which he seems to confound it, and one which in nature arises from a wide range of causes, some of which I have pointed out. But isolation without assortment of the forms according to any principle by which those of a kind are brought to- gether is often transformed into segregation by the operation of the principles of transformation in the isolated sections of the species. This change is often brought about by the difference of the environ- ments to which the organism is exposed in the isolated areas. This one form of segregation has been clearly pointed out by Darwin, though he did not recognize segregation as a necessary condition for divergence. There are, however, many other ways in which nature produces a similar result. Some of these are operative when the organism is distributed in isolated districts but surrounded by the same environment, and some of them have to do with the develop- ment of non-adaptative divergences, which can not come under the cumulative influence of natural selection. It thus appears that independent generation codperating with natural selection is one form of the wider principle of segregation which, in its many forms, is the ever-present condition preceding cumulative divergence. Whatever divides the representatives of a species in such a way that those of a kind are made to intergenerate while prevented from intergenerating with other kinds is a cause of segregation. This is my definition of segregation, and my theory is that whatever causes segregation causes divergence, and without segregation there is no cumulative divergence. Now, in order to refute the theory it is necessary to show either that segregation does not take place in nature or that it is not accompanied by divergence, or that diver- gence takes place without segregation. As Mr. Wallace has not at- tempted to prove any one of these counter propositions, I think his 240 APPENDIX II—INTENSIVE SEGREGATION. criticism is aside from the main issue. Even if my paper presents ‘‘a body of theoretical statements” with ‘‘no additional facts,’’ this does not show that the theory is incorrect or the new use of the old facts unimportant in the explanation of divergent evolution. ‘‘The Origin of Species’”’ was filled with new theories applied to old facts. The importance of cumulative divergence through cumulative segre- gation, if a fact, is admitted. Is it a fact? is then the question that needs to be discussed. If, however, segregation is assumed to be the isolation of sections of a species possessing exactly the same average character, the assumption will be contrary to the facts that usually exist, even in cases of indiscriminate isolation. In the Journal of the Royal Microscopical Society, 1889, part I, pages 33-34, will be found an appreciative, though a very brief review of my theory, closing with the suggestion that fuller elucida- tion is needed of the alleged tendency in nature to transform separa- tion, when long continued, into increasing segregation and divergence. Want of space in my first essay made it necessary to postpone the full discussion of this part of the theory, but in the present paper I have sought to point out some of the more manifest principles on which this general law of intension rests. There are undoubtedly other principles of transformation, which, when combined with separate breeding, inevitably produce divergent instead of parallel evolution; but the principles pointed out in this paper are sufficient to establish the general tendency and to show that natural selection is by no means the only principle on which the law rests. If we could obtain sections of a species presenting exactly the same average char- acter, and if we could prevent all the principles of transformation from coming in to aid in the process, separate breeding under such conditions would perhaps never produce divergence; but, as separa- tion never produces exactly equivalent sections, it always tends to introduce transformation, through changed or unbalanced action, and transformation in the separated sections inevitably becomes divergence. We thus gain an explanation of the fact that isolation, even when accompanied by exposure to the same environment, if long continued, always introduces divergent forms of selection. Indepen- dent generation precedes and determines the possibility of the diver- gence, and if it is segregative it also determines in a measure the form of the divergence; but even if it is simply separative, it involves the complete cessation of all forms of reflexive selection maintaining compatibility between the isolated sections, and, therefore, opens the way for the gradual entrance of divergent forms, first of reflexive, and then of environal selection. CONSTRUCTION OF THE PERMUTATIONAL TRIANGLE. 241 3. Construction of the Permutational Triangle. In my paper on ‘‘ Divergent Evolution’’* I referred to the permuta- tional triangle, which I had constructed in order to determine the prob- ability of extinction that would, under certain conditions, result from complete segregate fecundity, when unaided by any form of positive segregation. The first four lines of the table were obtained by direct observation on the permutations of letters arranged to represent the pairing of animals entirely lacking in instincts or qualities that secure the pairing together of those of one kind. For example, Jet A, B, C represent three females of three varieties of pigeons, and a, 6, c three males of the same varieties, all occupying one aviary. Now, supposing they are devoid of segregating instincts, and that they all pair, what are the probabilities concerning the pair- ing of the males with their own kind? These will be clearly shown by arranging the letters representing one of the sexes in one fixed order, placing the letters representing the other sex underneath in every possible permutation oforder. If we make six experiments the proba- bility is that in two cases none, in three cases one, in no case two, and in one case three, will pair with A B C their own kind. These numbers constitute the a b c four terms of the third line. The first, second, a C b | and fourth lines were constructed in thesameway, — c a b but for the construction of the tenth line in this 4 a c way I estimated that several years of constant | 2b c a writing would be required. The remaining lines | c b a here given were, therefore, constructed according to the following rules, which were discovered by studying the first four lines. The discussion of different methods of constructing the permutational triangle, and the interesting properties of the same when constructed, must be deferred; but I may say here that I believe it will be found an important instrument for estimating a large class of probabilities. One method of constructing any line of the permutational triangle from the preceding line.—(1) Of any given line, any desired number, except the first, may be obtained by multiplying the preceding number of the preceding line by the factor of the given line and dividing the result by the figure marking the degree of correspondence of the column of the desired number. (2) The first number of any line is one less or one more than the second number of the same line, according as the factor of the line is an odd or an even number. * Also see pp. 99-100 of this volume. 242 APPENDIX II—INTENSIVE SEGREGATION. A method of constructing the permutational triangle from the arithmet- ical triangle.—Pascal’s arithmetical triangle, which is the same as the table of binomial coefficients, is a series of figures, each line of which may be formed by adding the previous line to itself, as shown in the table below. Now, if we compare this arithmetical triangle with my permutational triangle we find that the first and third diagonal lines in each table are composed of the same numbers arranged in the same way. The fourth diagonal line of the permutational triangle can be obtained by multiplying each number of the arithmetical triangle by 2- 1 1 1 = 1 1 1 1 = 1 ce 1 1 2 1 — 1 3 3 1 1 3} 2 1 1 — 1 4 6 4 1 — Multipliers In short, by using the numbers here indicated as multipliers, each line of the arithmetical triangle may be transformed into the corre- sponding line of the permutational triangle. It may further be noted that these numbers by which we multiply are the occurrents standing in the first column of the permutational triangle; and these are found to be the same as the sub-factorials described by Whitworth in ‘‘Choice and Chance,’’ Chapter IV. 243 THE PERMUTATIONAL TRIANGLE. I te) cr otz 06g ‘1) ggo'rr OSg‘SS ogt ‘zzz sgh ‘Loo 06 Eee 196 ‘PEE ‘11 (Q)) | I re) ge | gl leer Fos | ogz ‘zz ttl ‘99 | LOb ‘ELI | g6t ‘Ce (6). I o | gz cir of9 bor ‘z ob “LZ | 2€g ‘br €fg ‘FI (g) I fe) Iz of Cie tz6 | CSe ‘tr $Og ‘1 (L) I oO ca ob NS) | toz Sgz (Q) I fe) ol Oz SY ad (Gg) 1 fo 9 | 6 (y) aula, plsryn| ay | 1 0 | € c (¢) ‘9uU 47 puloras| ayy | I fo) I (Z) (ama, alsay | aus f f°) (1) Pewee ees aud | ayy | I (or) | () | (@) | (2) | @) | Gs) | &® (€) (Z) (1) (0) = 2. a. i Es Q om | 6 of)sa/pF |) or | ae 8 a ® oO : "SJUIAANIUOD pat ae =008‘gz79‘€ =o1| ss =ogg'zgt =6 | =ozt‘or =g | ce =oto's = | aC =ozl =9 | as =O071 =f | a =z =? | “cs =9 = | ce =Z =Z ( suows ) “1990 > ==1 1p cc eee “S]DIA0JID ‘aPBUDUL [| JDUOYDINUAI ay APPENDIX III. LETTERS PUBLISHED IN NATURE. I. “LIKE To LIKE’’—A FUNDAMENTAL PRINCIPLE IN BIONOMICS.* I follow Professor Lankester in the use of the term bionomics to designate the science treating of the relations of species to species. If the theory of evolution is true, bionomics should treat of the origin not only of species but of genera, and the higher groups in which the organic world now exists. In Professor Lankester’s very suggestive review of ‘‘ Darwinism,”’ by Mr. A. R. Wallace (Nature, October 10, 1889, p. 566), reference is made to “‘his (Mr. Wallace’s) theory of the importance of the principle of ‘like to like’ in the segregation of varieties, and the consequent development of new species.’’ Professor Lankester has here alluded to a principle which I consider more fundamental than natural selection, in that vt not only explains whatever influence natural selection has in the formation of new species, but also indicates combinations of causes that may produce new species without the ard of diversity of natural selection. The form of like to like which Mr. Wallace discusses is ‘‘the constant preference of animals for their like, even in the case of slightly different varieties of the same species,’’ which is considered not as an independ- ent cause of divergence, but as producing isolation which facilitates the action of natural selection. If he had recognized this principle, which he calls selective association, as capable of producing in one phase of its action sexual and social segregation, and in another phase sexual and social selection, he would perhaps have seen thatits power to produce divergence does not depend on its being aided by natural selection. Mr. Wallace’s view is very clearly expressed in the following pass- ages, though I find other passages which lead me to think that the chief reason he does not recognize segregation as the fundamental prin- ciple in divergence is that he has not observed its relations to the prin- ciple of like to like. Hesays: ‘‘A great body of facts on the one hand, and some weighty arguments on the other, alike prove that specific characters have been, and could only have been, developed and fixed by natural selection because of their utility.” (Darwinism, p. 142.) ‘‘Most writers on the subject consider the isolation of a portion of a species a very important factor in the formation of new species, while * Published in Nature, April ro, 1890. 246 APPENDIX III—LETTERS PUBLISHED IN NATURE. others maintain it to be absolutely essential. This latter view has arisen from an exaggerated opinion as to the power of intercrossing to keep down any variety or incipient species and merge it in the parent stock.’’ (Darwinism, p. 144.) I think we shall reach a more consistent and complete apprehension of the subject by starting with the fundamental laws of heredity, and refusing to admit any assumption that is opposed to these principles, till sufficient reasons have been given. Laws which have been estab- lished by thousands of years of experiment in domesticating plants and animals should be, it seems to me, consistently applied to the gen- eral theory of evolution. For example, if in the case of domesticated animals, ‘‘it is only by isolation and pure breeding that any specially desired qualities can be increased by selection’’ (see Darwinism, p. 99), why is not the same condition equally essential in the formation of natural varieties and species? If in our experiments we find that careful selection of divergent variations of one stock does not result in increasingly divergent varieties unless free crossing between the varveties is prevented, why should it be considered an exaggeration to hold that in wild species ‘‘the power of intercrossing to keep down any variety or incipient species, and merge it in the parent stock,”’ is the same that we have found in domestic species. Experience shows that segrega- tion, which rs the bringing of like to like in groups that are prevented from crossing, is the fundamental principle in the divergence of the various forms of a given stock, rather than selection, which 1s like to like through the prevention of certain forms from propagating; and I think we intro- duce confusion, perplexity, and a network of inconsistencies into our exposition of the subject whenever we assume that the latter is the fundamental factor, and especially when we assume that it can produce divergence without the codperation of any cause of segregation divid- ing the forms that propagate into two or more groups of similars, or when we assume that segregation and divergence can not be produced without the aid of diverse forms of selection in the different groups. The theory of divergence through segregation states the principle through which natural selection becomes a factor promoting some- times the stability and sometimes the transformation of types, but never producing divergent transformation except as it codperates with some form of isolation in producing segregation; andit maintains that whenever variations whose ancestors have freely intergenerated are, from any combination of causes, subjected to persistent and cumula- tive forms of segregation, divergence more or less pronounced must be the result. The laws of heredity on which this principle rests may be given in the three following statements. “LIKE TO LIKE’’—A FUNDAMENTAL PRINCIPLE. 247 1. The Laws of Heredity. (1) Unlike to unlike, or the removal of positive segregating influ- ences, is a principle that results either in extinction through failure to propagate or in the breaking down of divergences through free crossing. (2) Like to like, when the individuals of each intergenerating group represent the average character of the group, is a principle through which the stability of existing types is promoted. (3) Like to like, when the individuals of each group represent other than the average character of the group, is a principle through which the transformation of types is effected. 2. Local Segregation often Initiates Divergence, which Social, Sexual, Industrial, and Impregnational Segregation, with Corresponding Forms of Selection, Carry to Completion. In my paper on ‘‘Divergent Evolution’’ I pointed out that sexual and social instincts often conspire to subdivide a species, bringing like to like in groups that do not cross; and that in such cases there will be divergence even when there is no diversity of natural selection in the different groups, as, for example, when the different groups occupy the same area and are guided by the same habits in their use of the environment. There is reason to believe that under such circum- stances divergence often arises somewhat in the following way: Local segregation of a partial nature results in some diversity of color or in some peculiar development of accessory plumes, and through the principle of social segregation which leads animals to prefer to asso- ciate with those whose appearance has become familiar to them, the variation is prevented from being submerged by intercrossing. There next arises a double process of sexual and social selection, whereby both the peculiar external character and the internal instinct that leads those thus characterized to associate together are intensi- fied. The instinct is intensified, because any member of the com- munity that is deficient in the desire to keep with companions of that kind will stray away and fail of breeding with the rest. This process I call social selection. The peculiarity of color or plumage is preserved and accumulated, because any individual,deficient in the character- istic is less likely to succeed in pairing and leaving progeny. This latter process is sexual selection. It can hardly be questioned that both these principles are operative in producing permanent varieties and initial species; and in the circumstances I have supposed I do not see how the process can be attributed to natural selection. Varie- ties thus segregated may often develop divergent habits in their use 248 APPENDIX III—LETTERS PUBLISHED IN NATURE. of the environment, resulting in divergent forms of selection, and pro- ducing additional changes; but so long as the environment and their habits of using the environment remain unchanged, their diver- gences can not be due to environal selection of any kind. Mr. Wallace’s very interesting section on ‘‘Color as a Means of Recognition,’’ taken in connection with the section on ‘‘Selective Association,” already referred to, and another on ‘‘Sexual Characters due to Natural Selection,”’ offers an explanation of ‘‘the curious fact that prominent differences of color often distinguish species other- wise very closely allied to each other” (p. 226). His exposition differs from mine in that he denies the influence of sexual selection, and at- tributes the whole process to natural selection, on the ground that ‘‘means of easy recognition must be of vital importance”’ (p. 217). The reasoning, however, seems to me to be defective, because the general necessity for means of easy recognition is taken as equiva- lent to the necessity for a specialization of recognition marks that shall enable the different varieties to avoid crossing. In the cases I am considering there is, however, no advantage either for the indi- vidual or the species in the separate breeding of the different varieties, and even in cases where there is such an advantage for the species (as there would be if the variety had habits enabling it to escape from competition with the parent stock, but not preventing it from cross- ing with the same), it does not appear how this liability to breed with the original stock can be any hindrance to the success of the individ- ual. The significant part of the process in the development of recog- nition marks must be in the failure of suchindividuals to secure mates, which is sexual selection; or in the unwillingness of the community to tolerate the company of such, which I have called social selection. 3. Permanent Difference in Innate Adaptations not Necessarily Advantageous Difference. It ts often assumed by writers on evolution that permanent differences in the methods in which a life-preserving function is performed are neces- sarily useful differences. That this is not so may be shown by an illustration drawn from the methods of language. ‘The general use- fulness of language is most apparent, and it is certain that some of the laws of linguistic development are determined by a principle which may be called ‘‘the survival of the fittest;’’ but it is equally certain that all the divergences which separate languages are not useful divergences. That one race of men count by tens on their fingers and another by twenties on their fingers and toes, is not determined by differences in the environments of the races, or by any advantage UNSTABLE ADJUSTMENTS AND ISOLATION. 249 derived from the difference in the methods. So, easy recognition of other members of the species is of the highest importance for every species; but difference in ‘‘recognition marks” in sections of the same variety separated in different districts of the same environment is no advantage. Under the same conditions, habits of feeding may become divergent; but, since any new habit that may be found ad- vantageous in one district would be of equal advantage in the other district, the divergence must be attributed to some difference in the activities of the two portions of the species. I have recently observed that, of two closely allied species of flat- fish found on the coasts of Japan, one always has its eyes on the right side and the other always on the left. As either arrangement would be equally useful in the environment of cither species, the divergence can not be considered advantageous. Il. UNSTABLE ADJUSTMENTS AS AFFECTED BY ISOLATION.* In a brief passage in his volume on ‘‘Darwinism,’’ Mr. Wallace refers to a principle which seems to me to be worthy of much wider application than he has given to it. It is a key which requires only a little filing to prepare it for unlocking some difficult problems in divergent evolution. Speaking of the infertility of crosses, he says (p. 184): It appears as if fertility depended on such a delicate adjustment of the male and female elements to each other that unless constantly kept up by the preservation of the most fertile individuals, sterility is always ready to arise. * * * So long as a species remains undivided, and in occupation of a continuous area, its fertility is kept up by natural selection; but the moment it becomes separated, either by geographical or selective isolation or by diversity of station or of habits, then, while each portion must be kept fertile znfer se, there is nothing to prevent infertility arising between the two separated portions. Here is an application of the principle of segregation (or of like to like in groups that do not cross) in which indiscriminate separation is followed by increasing divergence in the different portions, not because they are exposed to different environments, not because there is any advantage in such divergence, not because there is any need that the function should be performed more perfectly in one portion than in the other, but because intergeneration, which is the principle by which correspondence of function is secured, has been suspended for some generations; and, in the absence of intergeneration, neither natural selection, nor any other principle, is capable of preserving complete correspondence. In organisms that reproduce sexually * Published in Nature, May 8, 1890. 250 APPENDIX III—QLETTERS PUBLISHED IN NATURE. the causes of divergence are all causes of segregation; while the causes of unification, whether of functions or of structures, are causes of intergeneration. If the environments which surround the isolated portions are the same, the use of the environment, and, therefore, the forms of selection, may become divergent; if the use continues unchanged, some useless divergence in the method of securing the use may appear; or, if all the relations to the environment, whether useful or useless, remain unchanged, ‘“‘the adjustment of the male and female elements to each other”’ are liable to become slightly diver- gent, producing mutual infertility, or the preference of the sexes for certain shades or arrangements of color in their mates may become slightly different, or, through some slight difference in the hereditary elements distributed in each separated portion at the first, one, or all of these causes of accumulated divergence may be introduced. I think it is evident that we have here a general principle which is as applicable to a wide range of divergences as it is to the divergence that produces mutual infertility and sterility. The context shows that the prominent idea in Mr. Wallace’s mind was divergence in the adjustment of the male and female elements, through correlation with ‘“‘some diversity of form or color,” resulting from divergent forms of natural selection, which had been induced by exposure to ‘‘somewhat different conditions of life.’”’ But if the rea- soning is correct in the sentences I have quoted above it gives an explanation of similar divergences when the separated portions are exposed to the same environment and where there is no possible advantage to be gained by divergence. ‘This is one of the principles I have used in the explanation of the divergences of Sandwich Island land mollusks; and I think that in the earlier stages of the develop- ment of infertility between allied forms it is often the only explana- tion that is applicable. It should, however, be remembered that, for divergence of this kind, it is not always necessary that the isolation should be either complete or very long continued, and that, when the forms that are not fully fertile with each other meet and more or less commingle, there is, through the very laws of propagation, without any aid from natural selection, a constant increase in the ratio of the pure breeds to the mongrels, and an accumulating intensity in the segregative instincts and the physiological incompatibilities. As this point has been fully discussed in my paper on “‘ Divergent Evolu- tion,’ I do not need to enlarge on it here. There is, however, another phase of the subject which is indicated by Mr. Wallace’s suggestion that infertility depends on ‘‘such a delicate adjustment’”’ that it is more easily affected by isolation than A SINGLE PAIR AND THE AVERAGE CHARACTER. 251 some other adjustments. This is, I think, a very interesting point, as it suggests how it is that, in some cases at least, physiological diver- gence of this kind is one of the first forms of divergence that arises. But in some species other adjustments seem to be more delicate than this, and, therefore, more easily disturbed, while in others several sets of adjustments, as colors and other recognition marks with the preferences that correspond, and the habits of feeding and defense, are in a state of equilibrium, the stability or instability of which is about the same as of that which determines the relations of the male and female elements. In this last class of cases several forms of divergence may arise during the same stage of development, and that, too, when the isolated portions are exposed to the same environment. In some species a large number of characters are in a state of unstable adjustment. As Professor Lankester has suggested near the close of his review of Wallace’s book, this cause of divergence seems to be specially operative in the case of human faculties. But variability with plasticity of type is not the only condition that affects the sta- bility of segregated portions of a species. Other things being equal, a single pair of any species is much less likely to represent the average of all the characters of the species than a million pairs. This consid- eration throws light on the comparative lack of divergence between the land animals of England and those of Ireland, which lack has been referred to by Mr. Wallace as an objection to my theory. In this case, many millions of some of the species were probably existing in each district at the time of the separation. As Professor Lankester has pointed out, the representatives of the human species in the two districts have somewhat diverged; and the probability is that, if we were equally acquainted with the other species, we should find other examples of divergence in minor points. If the isolation is made more complete, and is longer continued, I believe the diver- gence will gradually become more apparent. Mr. Wallace has mentioned another class of divergences, which he has explained as due to surplus energy in the species, ready for expen- diture in ways that are not determined by conditions in the environ- ment. I maintain that through unstable adjustment this surplus naturally takes different forms when the species is divided into iso- lated groups; and Wallace is content to attribute the divergence to individual variability, though each group maintains its own type. His words are: The enormously lengthened plumes of the bird of paradise and of the peacock must be rather injurious than beneficial in the bird’s ordinary life. The fact that they have been developed to so great an extent in a few species is an indication 252 APPENDIX III—LETTERS PUBLISHED IN NATURE. of such perfect adaptation to the conditions of existence, such complete success in the battle of life, that there is, in the adult male at all events, a surplus of strength, vitality, and growth power, which ts able to expand itself in this way without injury. That such is the case is shown by the great abundance of most of the species which possess these wonderful superfluities of plumage. . . . Why, im allied species, the development of accessory plumes has taken different forms, we are unable to say, except that it may be due to that individual variability which has served as the starting point for so much that seems to us strange in form, or fantastic in color, both in the animal and vegetable world.* (Darwinism, p. 293.) It is no small gratification to me that Mr. Wallace has found this principle of unstable adjustment worthy of application to two impor- tant classes of divergences; and that, in the case of one of these classes, he has recognized that correspondence in such adjustments can not be continuously maintained between the isolated portions of a species. I trust that when he understands the relation in which instability and isolation stand to each other in my theory he will admit that it throws some light on the remarkable divergences of Sandwich Island land mollusks. The subject was incidentally touched upon in my paper on ‘‘Divergent Evolution through Cumulative Segregation” (see Appendix I), and more fully discussed in the sup- plemental paper on ‘‘Intensive Segregation” (see Appendix II). III. INDISCRIMINATE SEPARATION, UNDER THE SAME ENVIRONMENT, A CAUSE OF DIVERGENCE. f 1. Divergence Resulting from Isolation. I have accumulated a large body of facts indicating that separated fragments of a species, though exposed to the same environment, will in time become divergent. I find that, wherever a species possessing very low powers of migration is for many generations divided into a series of fragments by barriers that do not obstruct the distribution of surrounding species, more or less divergence arises in the separated portions of the species, though, in the same areas, there is no diver- gence in the environing species whose distribution is not obstructed. I still further find that, whenever the distances intervening between the different fragments are an approximate measure of the time and degree of separate breeding (as is frequently the case as long as the divergence does not involve any physiological and psychological segregation), these distances are also an approximate measure of the degree of divergence. The validity of this conclusion is called in question because it is inconsistent with the theory that all divergence is due to diversity of * The italicizing is mine. + Published in Nature, August 14, 1890. DIVERGENCE RESULTING FROM ISOLATION. to wn oS) selection, and that all diversity of selection is due to exposure to different environments. The divergences in the cases above referred to, it is said, are probably due to differences in the environment that are not easily recognized. ‘This was the explanation suggested by Darwin when the facts were reported to him in 1872. The division of a species into isolated portions did not seem to him to furnish any factor that could produce divergence unless it was aided by exposure to different external conditions. The same view is expressed in his ‘Origin of Species,”’ sixth edition, page 319. My reply is twofold. (1) The theory that all divergences in Sand- wich Island land mollusks are due to differences in the environment requires us to believe that there are occult influences increasing in difference with each additional mile of separation, and that these influences control the natural selection of the mollusks, but have no influence on any other species occupying the same areas. A theory that involves so heavy an assumption can not be received when a simpler theory is open to us. (2) I believe I can entirely remove this objection, urged against my conclusion on these purely theoretical grounds, by showing that there are certain causes of divergence, not depending on exposure to different environments, that are necessarily introduced by the division of a species into isolated groups; and that, under the influence of these causes, diversity of habits may arise pro- ducing diversity of selection, even while the fragments are exposed to the same environment. I have elsewhere called attention to the fact that the independent breeding of separated groups, as far as we can judge, always tends to produce divergence; and I have shown that, when a species is indis- criminately broken into independent fragments, the tendency to diver- gence will, on the average, vary in direct proportion to the instability of the species and in inverse proportion to the size of the fragments; for on these factors depends the probable degree of departure of the average character of the fragment from the average character of the species previous to its being broken into fragments, and, therefore, the degree of segregation. I wish now to show that the maintenance of certain classes of char- acters always belonging to an unbroken species is due to a form of selection that can continue only so long, and so far, as free crossing continues. Reflexive selection is aformative principle, depending on the relations in which the members of an intergenerating group of organisms stand to each other, while they continue to intergenerate; but when two portions of an original species have become so divergent as to compete with each other in the same area without crossing, they 254 APPENDIX III—LETTERS PUBLISHED IN NATURE. form incipient species, and each belongs to the environment of the other. While they are members of the same intergenerating group, their mutual influence results in reflexive selection, which maintains the correspondence with each other by which power to cross is preserved ; while they are members of groups that do not cross, their mutual influ- ence results in cumulative segregation; for it inevitably tends toward the preservation of variations that, through greater divergence, best escape from competition. I have elsewhere defined reflexive selection as being the exclusive propagation of those better fitted to the rela- tions in which the members of the same species stand to each other, resulting from the failure to propagate of those less fitted. Among those that are equally fitted to the environment of the species, and, therefore, equally preserved by natural selection, there is often great difference in the degrees of fitness for sustaining such relations to the rest of the species as will secure an opportunity to propagate. To this class of influences belong the different formsof sexual selection through which the sexual instincts and the correlated sexual charac- ters of the different sexes are kept in full codrdination. In like man- ner we must believe that the pollen of any species is kept up to its full degree of potency by the constant selection which results from the failure to propagate of the individuals whose pollen is less potent or whose germs are more difficult to fertilize than the average. We call this potential selection. Again, there is a constant selection of ani- mals that are suitably endowed with the recognition marks and calls by which the different members of the species know each other, and that have the corresponding instincts leading them to associate with their own kind. I have elsewhere called this principle of social coordination ‘‘social selection,’’ and have classed it as a form of reflexive selection. 2. The Cessation of Reflexive Selection between Isolated Sections Causes Divergence as Soon as Heredity Weakens. Independent breeding is in its very nature the suspension, not only of one form, but of all forms of reflexive selection between the separated ‘portions of the species. The importance of the cessation of natural selection in producing the different stages of the degeneration of organs that are disappearing has been fully discussed by Professor Romanes (see Nature, vol. XLI, p. 437, and previous communications there re- ferred to), who points out that, as the power of the special form of heredity by which any organ is produced has been built up by the many generations of natural selection that have acted on the organ, so the gradual weakening of that power follows the cessation of the natu- ral selection. Professor Weismann seems to appeal to the same prin- ARE SPECIFIC CHARACTERS ALWAYS USEFUL? 255 ciple when he attributes the disappearance of ‘‘rudimentary organs”’ to the action of ‘‘panmixia.’’ Now, in the cessation of reflexive selec- tion which follows independent breeding, a similar principle is intro- duced, and the inevitable result must be the weakening of the power of heredity by which the portions of the species were held in corre- spondence with each other before their separation. I have elsewhere shown that separate breeding necessarily disturbs unstable adjust- ments; and we here see that the most stable of the adjustments by which each part of a species is kept in correspondence with every other part gradually becomes unstable under the continued influence of separation. Whenever a species is divided into two portions that do not interbreed, the forms of reflexive selection will cease to act between the two portions, and they will continue in sexual, social, and other forms of harmony with each other only in so far as the force of the old heredity holds them to the old standards. But the power of heredity in these respects will in time fail, and if the sep- arate breeding is long continued, incompatibility in all these respects tends gradually to arise. Moreover, it is manifest that incompatibil- ity of industrial habits involving diversity in the forms of active (or endonomic) selection will in time arise. I therefore maintain that separation, which necessarily includes cessation of reflexive selection between the portions separated, is a cause of segregation and diver- gence; and that this segregation is in time intensified by diversity of environal selection, through diversity in the use of the environment. Unless the separated portions of a species possess exactly the same average character (which we must believe is seldom, if ever, the case), separation must, from the first, be more or less segregative; and even in cases where the portions completely correspond in character (if there are any such cases), the cessation of reflexive selection which rs involved tn the separate breeding must result in divergence as soon as the power of heredity securing the original adjustments begins to weaken; and this 1s in due time followed by other forms of intensive segregation. I therefore conclude that indiscriminate separation may be regarded as a preliminary form of segregation (that is, as demarcational segrega- tion) and that intensive segregation codperating with this produces complete segregation. IV. THe UTILITY OF SPECIFIC CHARACTERS.* I have followed the discussion on the utility of specific characters with great interest; and though I am at such a distance that my thoughts may comea little late, I wish to call attention to a few points. * Published in Nature, April 1, 1897. 256 APPENDIX III—LETTERS PUBLISHED IN NATURE. In Nature for October 22, 1896, page 605, mention is made of a dis- cussion on Neo-Lamarckism at the British Association. In opening the discussion, Prof. Lloyd Morgan referred to the importance of noting the bearing of certain cases that may be considered as crucial, or as nearly crucial as any that we are at present able to obtain, on the process by which specific instincts are built up. As illustrating this class of cases, he refers to the drinking instinct in newly hatched chickens, where the instinctive response begins at the point where the teaching of the parent bird would naturally be inadequate. The question I wish to raise is whether such observations as this can do more than justify the conclusion that life-saving instincts are strengthened and established by natural selection. Are they suff- cient to show that all permanently inheritable specific characters are wholly due to natural selection, or even that natural selection is always one of the factors by whichany and every permanent character hasbeen built up? It seems to me that there are large classes of facts, some of which may be found in almost every species we examine, which throw doubt upon there being any such inseparable connection between natural selection and the inheritance of characters. 1. Right-handedness and Left-handedness. The majority of the human species inherit right-handedness. Does this prove that right-handedness is better for the race than left- handedness? The shells of most snails are coiled in a way that is called dextral; but some groups of species are as constantly sinistral as most groups are dextral; and of the dextral groups there are cer- tain species that are persistently sinistral; others that are nearly equally divided between dextral and sinistral forms. Isit necessary to believe that for each species that is usually either dextral or sinistral there is some vital necessity that would exterminate, or even dimin- ish, the species if the character was reversed? A similar class of cases is found amongst the different species of flatfish. One species persistently lies on the right side, another on the left, and I think it is Mr. Cunningham who has told the readers of Nature that there are some speciesin which bothforms may occur. In each of these classes of cases I am unable to conceive of any advantage gained by the species that would not be equally gained if the character under dis- cussion was reversed. J? the adaptation to the environment of a flat- fish that now les upon the right stde would be equally good in case all the individuals of the species lay upon the left side, then (af I rightly under- stand the meaning of the terms), natural selection can not be the cause of its lying on the right side rather than the left, neither can this character of RIGHT-HANDEDNESS AND LEFT-HANDEDNESS. 25/7 the species be considered a useful character, though wt is persistently inherited, Standing near me is a flower-pot, in which are several stalks of the common calla (I believe the botanical name is Richardia ethiopica) in bloom; and a little inspection shows that each spathe and leaf-bud is twistedinthesameway. If the leaf is held withthe point up and the upper surface toward you, the half of the leaf on your left is the part that formed the inside of the leaf-bud, and the margin of the leaf on your right is the part that formed the outside of the leaf-bud. ‘This character is quite persistent in the specimens of this species found in this city, though I am told that a leaf twisted in the opposite way sometimes appears; while in the distinct species popularly called the black calla I believe the character is reversed. Now, does this persistence prove that the character in question is essential to the welfare of the species? Are we justified in assuming that natural selection is the cause of the persistence of such characteristics? Can anyone throw light on the subject that will make it easier to believe that the adaptation of the species would be in the least impaired if all the leaves and spathes were twisted in the reverse way? The usual method of meeting the natural inference from such cases is based on a double assumption, the first part of which is that natural selection is the only intelligible explanation of the modification of species or the persistence of character that has ever been given, and that if in any case we abandon this explanation, it is equivalent to abandoning all explanation; the second part of the assumption being that it is simply our ignorance of the facts that prevents us from recognizing the life-preserving results that are gained by the char- acteristic in question. This assumption ignores both the fact that species presenting characters of the kind referred to are found on every side, indeed that almost every species that fails to maintain com- plete symmetry of form is an example, and the fact that Darwin him- self pointed out another principle besides natural selection producing persistent characters. This principle of sexual selection he carefully distinguished from natural selection, showing that the results produced by it could never be produced by natural selection, and even maintaining that ‘‘It is not surprising that a slightly injurious character should have been thus acquired.’’ (The Descent of Man, 2d ed., p. 601.) For my part I do not think much progress can be made in dis- covering where natural selection is the chief agent and where it is not the chief agent till we have carefully defined what we mean by utility and natural selection, and then adhere to our definitions. In my 258 APPENDIX III—LETTERS PUBLISHED IN NATURE. papers on ‘‘Divergent Evolution through Cumulative Segregation”’ and ‘‘Intensive Segregation’’ I have endeavored to show that there must be several principles somewhat similar to sexual selection, which I have grouped with it under the names reflexive segregation and reflexive selection. In the former of these papers, pages 212-214, I have pointed out that of freely crossing forms of any species it is only those that are most successful that are perpetuated; while of forms that have by isolation escaped from competition with the original stock and are not crossing with it every variation is perpet- uated that is not fatally deficient in its adaptations to the environ- ment; and this will be the case whether the forms are held apart by reflexive or environal segregation. 2. A Difference in Use that ts not a Useful Difference. “ Let us consider the case of two allied species occupying the same area, and differing from each other in what Dr. Wallace has so appro- priately called their recognition marks, and in the segregating sexual and social instincts correlated with these marks. [If investigation justifies the belief that an early stage of divergence, due, perhaps, to local segregation, resulted not only in sexual and social segregation, but also in what I have called divergent social selection (or what Dr. Wallace prefers to call selective association), then we are warranted in the belief that this segregative and selective principle was sufficient to perpetuate and intensify the new character, although the section of the species possessing the new character had not migrated into any new environment, and had not been exposed to any change in the old environment, and although it had not gained any new adaptation to the common environment of the two sections and, therefore, while both sections of the species were equally subject to identical forms of natural selection. Now, seeing that the individuals of the segregated sections are able to find and keep company with associates, and in the season to pair with suitable mates, as effectually, but no more effectually, than be- fore they were segregated, what shall we say of the usefulness of the distinctive characters that produce the segregation? It is plain that these divergent characters are in constant use; but does that prove that the divergence is a useful divergence? Is it not possible that there should be a difjerence in use which vs not a useful difference? And if nothing has been gained by the difference either in maintaining the con- ditions of individual life, or in propagating the species, how can we call it a useful difference? And how can we attribute the divergence to natural selection, seeing that natural selection is the superior mainte- DIFFERENCE IN USE AND USEFUL DIFFERENCE. 259 nance and propagation of those better adapted to maintain life under the conditions surrounding the species? 3. Divergence through Reflexive Selection often Non-advantageous, I maintain that this reflexive segregation through the sexual and social instincts of the divergent sections of the species is the first ina series of divergent characters which may become a great advantage to both sections of the species by enabling them to become adapted to different kinds of resources, requiring incompatible adaptations; but it can not be claimed that the usefulness to which this segregative character may attain in the future, or may have already attained, was the cause of the divergence which was steadily perpetuated, being in tensified by sexual and social selection, and so completed while as vet this character was of no service to the species. The segregative char- acteris preserved by tts segregativeness, though at the time itarises, and jor many subsequent generations, tt may not be of any advantage to its pos- sessors. In most such cases, I believe, the initial divergence is gained by a local variety in some measure protected by local segregation: but having gained a character which secures segregation, even when commingled with the other section of the original species, it is no longer liable to be swamped by crossing. It seems to me that such cases are examples of divergence, produced by segregate breeding, brought about by sexual and social segregation, reinforced and strengthened by sexual and social selection, and not by diversity in the action of natural selection. 4. Different Methods of Using the Same Resources not Necessarily Advantageous, Another fundamental distinction which needs to be kept in mind is that diversity in the action of environal selection on segregated sec- tions of a species may be due to three classes of causes, which are the real causes of the divergence, which results in the production of dif- ferent species. r (1) Different life-supporting and life-endangering conditions exist- ing in the different districts in which the different sections of the spe- cies are distributed. (2) Different methods of using resources and escaping dangers adopted by the different sections, though occupying the same district. (3) Different methods of using resources and escaping dangers adopted by the different sections of the species occupying isolated districts, whose resources and dangers are alike. If the members of the original species are brought under the influence of the first class of causes, the divergence 1s due to diversity in the en vironments to which migration introduces them; if under the second 260 APPENDIX III—LETTIERS PUBLISHED IN NATURE. class, it is due to diversity in the action of life-preserving habits while at the beginning of the process competing with each other; if under the third class, it is due to diversity in life-preserving habits while not competing with each other. Now, in some of the cases in the second class and in all those of the third class, it is impossible that the differences should be useful. This is most easily shown as regards the third class; for ifin any case a new character attained by one of the sections is an advantage, then the same character would be an advantage for each of the other sections, exposed to the same conditions in other regions, and, therefore, there is no advantage in the difference. If my thought is correct, some of the differences produced by diver- sity in the action of the several forms of reflexive segregation and selec- tion, and all those produced by diversity in the action of environal selection, when that diversity is due to different habits that are not necessitated by any difference in the environment, are non-useful dif- ferences. Therefore, besides the principle of ‘‘correlated variation”’ referred to by Professor Lankester (Nature, vol. Liv, pp. 245, 365), we have other explanations of certain kinds of specific characters that are not useful; but the class of characters of which right-handedness and left-handedness are examples seem to lie beyond the reach of these explanations, and perhaps beyond the reach of the explanation sug- gested by Professor Lankester. 5. Letter by T. D. A. Cockerell, with Suggestions on the Facts Mentioned Above. The following letter in reply to the above appeared in Nature for May 13, 1897: THE UTILITY OF SPECIFIC CHARACTERS. Under the above heading, in your issue of April 1, Mr. J. T. Gulick has an inter- esting communication, in which he asks whether it is possible to explain right- handedness, the dextral or sinistral coil of snail shells, and similar features, as having any utility of which they are certainly characteristic. Can it be due to natural selection that one snail is dextral while another is sinistral ? It is a curious fact, I think, first pointed out by Mr. Call, that in the American fresh-water shells of the genus Campeloma, sinistral shells are more numerous among the young than among the adults. Thus, for example, Mr. H. A. Pilsbry (Nautilus, February, 1897, p. 118), states that Miss Jennie F. Letson examined a lot of Campeloma desisum for him, with the result that out of 681 specimens, mainly adult, but including those from one-fourth grown up, none were sinistral. Out of 410 shells of the uterine young 3 were sinistral, slightly over 0.73 per cent.” He adds: “ Probably all who have collected Campelomas have noticed the greater proportion of sinistral examples among the young shells. This doubtless indi- cates that the reversed condition is an unfavorable one for maturition.”’ So here, at any rate, we have some direct evidence as to selection. I think it will strike anyone that while left-handedness might be as good for the race as DOES ADVANTAGE IN UNIFORMITY EXPLAIN DIVERGENCE? 261 right-handedness, there 7s a distinct advantage in uniformity, and that consideration alone may perhaps suffice to explain Mr. Gulick’s difficulty. Among plants it may seem less obvious, but where seedlings are crowded, uniformity may save space, just as a number of objects of the same shape can usually be packed into less space than those of diverse shapes. More plants can grow in a window-box when all bend to the light than would be possible if half of them bent one way and half another. There also occurs to me a theoretical consideration, perhaps of doubtful value. When a germ has diverse potentialities, so that it is left to germinal or environ- mental selection to decide which course it shall take in development, there must apparently be a certain waste of germinalenergy. Any disadvantage thus arising is ordinarily much more than counterbalanced by the gain due to the adapta- bility of the organism, or in social species to the power of specialization of the in- dividual for social purposes. But it may be that when no such advantage is found, there exists a small disadvantage in deviations, potential or axial, froma common standard. What we really need, in discussing these matters, is the observation of actual facts. The facts above related as toCampeloma are worth more than any amount of theoretical considerations. T. D. A. COCKERELL. MEsILLA, NEw Mexico, U.S. A., April 21, 1897. 6. Reply to Letter of T. D. A. Cockerell. The advantage in uniformity is very manifest in certain cases; and, on pages 68-70 of this volume, I refer to conditions in which it is more manifest than in the cases here suggested by Mr. Cockerell; but the advantage of uniformity does not ‘‘explain the difficulty’? I have raised. For how can the advantage of uniformity explain the introduction of permanent diversity through the sur- vival of a variation that breaks down the former uniformity, and establishes two forms where there was a single form? The disadvantage in deviation from a common standard, if it can be shown to be a fact, is perhaps akin to the fact that variations most widely diverging from the average form are usually less fertile. But how can the advantage of a com- mon standard cause the dividing of a species according to two different standards as in the case of some snails? For any one snail of a dextral group there may be a disadvantage in being of a sinistral form; but does that throw any light on why a species should, under one environment, divide itself into two groups, one being dextral and the other sinistral? and does it show that the process is due to nat- ural selection? The best explanation I can suggest is given on pages 68—7o, J; Ls GurreK, APPENDIX IV. LIST OF PAPERS ON EVOLUTION BY JOHN T. GULICK. An article published in Nature, July 18, 1872, entitled :— The Vartation of Species as related to their Geographical Distribution, illustrated by the Achatinelline. Three papers published in the Linnean Society’s Journal, Zodlogy, vols. Xr, XX, Xxu1I, as follows: ; Diversity of Evolution under One Set of External Conditions, in 1872. Divergent Evolution through Cumulative Segregation, in 1887; reproduced in the Smithsonian Report for 1891; a small portion of the same is also given in Appendix I of this volume. Intensive Segregation, in 1889; reproduced in Appendix II of this volume. Three articles published in the American Journal of Science for January, July, and December, 1890, as follows: Divergent Evolution and the Darwinian Theory. The Inconsistencies of Utulitarvanism as the exclusive Theory of Evolution. The Preservation and Accumulation of Cross-Infertility. Four letters published in Nature, and reproduced in Appendix III of this volume. 262 INDEX. Accommodation, 30, 158, 189. As Acquired Adjustment, 57, 60. Necessary in Case of Sudden Change, 60, 62. Gives Time for ‘‘Coincident Variation,” 61,62. Controls other Influences, 61. Supersedes Natural Selection, 61. In Man Illustrated, 61, 152. May Prevent Coincident Selection, 63. Forms of Accommodation, 153. Acquired Characters: May Influence Racial Characters, 20-22, 45, LSS; Through Different Habits of Feeding, 20. Habit may Control Selection, 21. Often Leads to ‘‘Coincident Variation,” 21. And Segregate Association, 45, 48. Selection and the Inheritance of, 78. Inheritance of, Discussed by Cunningham, 78. By C. B. Davenport, 78. Achatinellide: Illustrating Problems in Evolution, 37-43. Two Hundred Species, 1,000 Varieties, on Oahu, 39. Distribution of the Genera, 37, 40, 42. Adaptation: As Inherited Adjustment, 56. Segregate Adaptation, 87. Adjustment: Acquired by the Individual is Accommoda- tion, 60. When Inherited is Adaptation, 60. Agamic Evolution Defined, 137. Allogamic— Organisms, 79. Evolution Resting on Six Conditions, 79. Evolution Defined, 137. Evolution Controlled by Four Principles, 138. Forms of the Principles of, 138. Amalgamation of Races, 20 151, 188, 211. Anticipatory Action, 29-30, 158. Aptitudes: As Inherited Characters, 47. As Inherited Adaptation, 56, 60. Areas of Distribution: Of Hawaiian Snails, 1-3, 37-43. Of Arboreal Species most Limited, 2. Species a Few Miles Apart do not Intergrade,2 Autogamic— Evolution Defined, 137. Mating used by Karl Pearson, 137. Autonomic— And Heteronomic Influences, 141-144; also Preface. Autonomic—Continued. Influences Include Endonomie and Reflexive, 141. Selection and Isolation, 141. Election and Partition, 142. Demarcation, 142. Partition and Isolation Illustrated, 143-144. Factors, 158. Darwin Recognized One, 158. Baldwin, J. Mark: “Organic Selection,’ 46, 61. Use of the Term ‘‘Selection,” 46. Control of Evolution, 49. ‘Social and Ethical Interpretations,” 46,142. ““Develépment and Evolution,” 30, 50, 53, 61, 189. Bateson,‘ Material for the Study of Variation, '’ 34. Considers Discontinuity of Species as Un- solved, 36. As Inconsistent with Theories of Dar- win and Lamarck, 34. Biometrika, 154. Bionomic Laws, 9-22. Method of Their Investigation, 9-13. Bionomics: Defined, 9. As Taught by Distribution of Species, 10. ‘The Principles Involved in Relations of Spe- cies, 11. “Like to Like,’’ Fundamental in Bionomics, 245-249. Blubber Protects the Eskimo, 62. Broca, ‘‘ Human Hybridity,”’ 166. Brooks, W. K., Variability of Males and of Spe- cies, 190. Bumpus, H.C., on Statistics Proving Selection, 34. Castes, New, being Formed in India, 143, 153. Cats of Aquatic Habits, Illustrating Influence of Habitudes on Aptitudes, 67-68. Cockerell, T. D. A.: On Utility of Specific Characters, 260-261. The Author’s Reply to the Same, 261, Coincident Selection, 61. Coincident Variation, 61, 62. Computation— Of Ratio of Cross-breeds to Pure-breeds, 103-— 106. Compared with Endowment Lessened by Taxation, 103-104. Of Negative and Positive Segregation, Co- operating, 101-111. Of Cumulative Segregation in Plant Species, 108-111. Intensification, Segregation, 263 “ 264 Computation—Continued. Of cumulative segregation, etc.—Continued. Direct, in a Given Case, 109. By Table A in a Given Case, 109. By Table V in a Given Case, 109. Of Ratio of Half-breeds to Pure-breeds, 177— 183. Of Effects of Indiscriminate Elimination, 210. Of Probability of Mismating without Segre- gative Instincts, 99, 241. Of Probability of Mismating given in Permu- tational Triangle, 243. Of Permutational Triangle, 241-242. Conn, Prof. H. W., ‘‘The Method of Evolution,” 36, 145. Cope, E. D.: Retarded and Accelerated Inheritance, 189. ‘‘Origin of the Fittest,’’ 190 Control by the Organism: Of Segregation and Divergence, 37-43, 27. Increases with Stage of Evolution, 156-157. Coéperation, 29, 158. Coulter, John M., ‘‘Plant Structures,” ‘Plant Relations,’’ 89. Cosmic Process: Not, as Huxley says, Opposed to Ethics, 157. Illustrated by the Rising and Setting Sun, 157. Cumulative Adaptation through Survival of the Fittest, 96-98. Cumulative Effects through Repetition in each Generation, 150. Cumulative Integration or Invigoration through Amalgamation, 96-98. Cumulative Multiplication through Predominance of the More Fertile, 96-98. Cumulative Segregation: New Possibilities through Segregation, 96-98. In Plant Species with Computation, 108-111. Producing Divergent Evolution, 159-183, 262. Cunningham, J. T.: “‘Sexual Dimorphism,”’ 78. Inheritance of Functional Characters, 78. Dextral and Sinistral Flatfish. 256. Darwin, Charles, 6, 23, 25, 26, 34, 94, 96, 153, 197, px fe “The Voyage of the Beagle,”’ 3. “The Origin of Species,’’ 3, 10, 26, 167, 215, 253: ‘Variation under Domestication,’’ 167. “‘Cross- and Self-Fertilization,’’ 167. Present Use of Isolation not the Same as His, 185. “Descent of Man,’’ 200. Divergence Due to Environment, 216, 253. Sexual Selection Sometimes Non-utilitarian, 256. Davenport, C. B.: “Texperimental Morphology,” 78. Inheritance of Acquired Characters, 78. Statistical Methods, 154. LiS= INDEX. Degeneration: Through Cessation of Selection, 73-76. Illustrated by the English Cuckoo, 74. Illustrated by the American Cowbird, 74. In Human Eyesight, 74-75. In the Ani and Other American Birds, 75-76. De Vries, Hugo: “Origin of Species’’ in Popular Science, 70. Mutation, 70. “Species and Varieties; Their Origin by Mutation,’’ 77. Dextral and Sinistral Snails, 68-70. Discontinuity of Species, 34—36. Explained by Segregation, 35. Discussed by Professor Conn, 36. Discriminate— And Indiscriminate Modes of Action, 80, 132-136. Success equals Election, 53, 136. Survival equals Selection, 53, 136, 150. And Indiscriminate Isolation, 150. Divergence— ‘That is not Due to Sexual Selection, 3. Nor to Natural Selection, 4-5. Nor in Proportion to Difference in En- vironment, 4. Nor Useful to the Species, 4. But Due to Habits of Feeding, 5. And to Isolation, 7. Due to Independent ‘Transformation, 17-19. Through Isolation and Selection, 17. Through Segregation, 7. e., Discriminate Iso- lation, 17. Independent Transformation always Diver- gent, 18. Through Indiscriminate Destruction under Isolation, 19. a Through Isolation and Variation, 29, 39, : May be Lessened by Selection, 25, 29. ; Increased by Length and Degree of Isolation, Zi. Under the Same Environment, 37-43. Through Methods of Using Resources, 39. Without Advantage, 68-70. Utilitarian and Non-utilitarian, 194, 218. In Land Mollusks, 212-224. In Snails of Oahu, Hawaiian Islands, 212. Without Diverse Environments, 215. In Such Cases Without Advantage, 217. Like Divergence in Systems of Counting, 217. Not Always Adaptive, 218. Must be Advantageous According to Thisel- ton Dyer, 218. In Proportion to Distance of Separation, 221. Depending on Isolation Illustrated, 222. In Land Snails of the Society Islands, 224. In Insects, 225-234. In Butterflies, 225-229. In Periodical Cicada, 229-234. Through Cumulative Segregation, 234-235, 262. Reply to Criticism of this Theory, 236-240. Not Necessarily Advantageous, 248. INDEX. Divergence—Continued. In Use not Necessarily Useful Divergence, 258-260. Through Reflexive Selection not Useful, 259. Not Explained by Advantage of Uniformity, 261. Under One Set of External Conditions, 262. Domestic Races: Reveal the Method of Evolution, 12. The Production of, 13~22. Their Continuance, 13. Their Transformation, 14. Their Divergence, 17. Their Stability, 19. Their Amalgamation, 20. Affected by Acquired Habits, 20-22. Adaptation to the Rational Environment. 13. Dominational Selection and Election, 82, 86-87. Dyer, W. T. Thiselton: Specific Differences Must be Advantageous, 218. Are Dextral and Sinistral Forms tageous, 218. Election: Need of Such a Term, 51. Defined, 53. As Objectionable as Selection, 54. Its Use Must be Decided by Election, 55. Coincident, Illustrated, 66. Reflexive, 81-114. Conjunctional, 82-83. Dominational, 82, 86-87. Institutional, 82, 114. Sexual, 83-84. Social, 83-85. Filio-parental, 83-86. Environal, 115-118. Endonomic, 115-118. Habitudinal, 115-118. Aptitudinal, 115-118. Heteronomic, 115-118. Natural, 115-118. Artificial, 115-118. Always Advan- Environal— Mode of Influence, 80, 115-129. Selection, 115-118. Isolation, 115-128. Election, 115—118. Partition, 115-129. Eskimo, the, Protected by Blubber, 62. Evolution: Of Habitudes, 46, 48. Of Race, 47. Determinate, of Terminology, 50. Controlled by the Organism, 46, 49, 156, 158. Six Conditions for Racial, 79. Six Conditions for Habitudinal, 80. Determinate, of Animals, 158. Divergent, 159-183, 262. Monotypic, of Fight Forms, 187-188. Monotypic and Polytypic, 198. Divergent, and Darwinian Theory, 262. Inconsistencies of Utilitarianism in, 262. 265 Evolution, Papers on, by John I. Gulick, 262. Fecundal Selection, 90-95. In Human Races, 92. Equals Pearsson’s ‘‘ Reproductive Selection,” 92. Filio-parental Selection, 83. And Big Heads, 86. And the Normal Number of Offspring, 91-92. Iree Crossing Within the Group a Condition of Evolution, 79. Formula (1), 181. Formula (2), 181. Used in Constructing Table V, 182. Formula (3), 105. Formula (4), Used in Making ‘fable A, 105. Four Principles of Segregation, The: Analysis of, 79-136. Chief Divisions of, 79-81. The Modes of, 80. Classification of the Forms of, 137-143. Galton, Francis: “Possible Improvement 3reed,’’ 113. Statistical Methods, 154. “Types and Their Inheritance,’’ 186. Giddings, Franklin H., Control of Evolution, 49. Habitudes: As Acquired Characters, 48. As Traditional Forms of Accommodation, 57, 60. Influencing Aptitudes, 57, 67. Hawaiian Snails, Evolution of: Their Distribution, 1-3, 26-29. Small Areas of Distribution, 1, 26. Areas of Arboreal Species Smallest, 2. Divergence in Different Valleys, 2, 26. Diversity of Selection Insufficient Exnlana- tion, 27. Isolation and Variation Essential Factors, 29- Community of Descent Secures Unity, 29. Ten Genera of Achatinellid#, Illustrated, 37-43. Headley. F. W.: “Problems of Evolution,’ 46, 52, 55, 56. Selection Controlled by the Organism, 46. Criticism of Intensive Segregation, 55-56. Heredity: And Tradition, 46, 51, 58. Molding of Heredity and Variation, 60. Aptitudes as Inherited forms of Adaptive Variation, 60. A Condition of Evolution, 79. As Fundamental as Variation, 79. Heteronomic— Influences, 141-142. Selection and Isolation, 141. Election and Partition, 142. Demarcation, Intensification, 142. Factors were Emphasized by Darwin, 158. of the Human Segregation, Huxley, T. H., Ethics Opposed to the Cosmic Process, 157. 266 Hyatt, Alpheus, 192. Methods of Studying Segregation, 154. earlier and Earlier Inheritance, 189. Decline in Individual and in Type, 190. Impregnational Isolation: And Selection, 82, 87-111. Importance of, 95-101. Indisecriminate— . Mode of the Four Principles, 132-136. Survival, 133. Equals Indiscriminate Elimination, 136, 152, 209. Isolation, 133, 150, 152, 186, 252-255. Success, 134, equals Indiscriminate Failure, 136. Partition, 134. Contrast in Discriminate and Indiscrimi- nate Action, 134-136, 150. Table of Discriminate and Indiscriminate Forms, 136. Elimination, Computation Showing Effect of, 210. Individual Variations: Considered of no Effect by Mutationists, 71-77. Importance of, Shown, 73-77. And Degeneracy of Eyesight, 74-75. And Degeneracy in Cuckoo, 75-76. And Degeneracy in Milk Giving, 74. Selection of, Leads to Mutation, 77. Innovation: And Variation, 46, 51, 59. Molding of Innovation and Tradition, 60. Intension: The Law of, 192-194. Selectional, 195—209. Indiscriminate Eliminational, 209-211. Computation of Indiscriminate Elimination, 210. Amalgamational, 211. Equals Intensive Segregation, 185-243, 262. Isolation: In Its Broader Meaning, 6. And Divergent Evolution, 7. Considered by Lamarck and Packard, 7. With Variation Causes Divergence, 29. Importance of, 51. Defined, 53. Coincident, 66-67. Caused bv Partition, 67—68. Structural, 68-70. Reflexive, 81-114. Conjunctional, 82-83. Impregnational, 82, 87-111. Institutional, 82, 114. Sexual, 83-84. Social, 83-85. Family, 86. Dimensional, 87-88. Structural, 87—89. Potential, 87, 89-90, 108-111. INDEX. Tsolation—Continued. Environal, 115, 118-128. Endonomic, 115, 118-122. Industrial, 115, 119-123. Chronal, 115, 123-125. Seasonal, 115, 124-125. Cyclical, 115, 123-124. Migrational, 115, 126-127. Heteronomic, 115, 118, 126, 128. Transportational, 115, 126. yeological, 115, 126. Fertilizaftional, 115, 128. Artificial, 115, 128. Spatial, 125. Geographical, 125. Local, 125. Unbalanced, 149. Usually Somewhat Discriminate, 174. Principles Intensifying Segregation, 174. ‘Use of, and Segregation, 175. As Used by Darwin and as Now Used, 185. Indiscriminate, of a Few Segregative, 186. And Unusual Opportunities for Migra- tion, 221. And Unstable Adjustments, 249-252. Jennings, Herbert S., ‘‘Contributions to the Study of the Behavior of Lower Organisms,’’ 189. Jevons, W. S., ‘‘Principles of Science,”’ 210. Jones, Rev. J. P., The Formation of New Castes in India, 143. ; Jones, Lynds: Accommodation in Birds, 64. Degeneracy in Nesting Habits, 76. Kidd, Benjamin, ‘Principles of Western Civiliza- tion,’’ 30. Lamarck, 7, 34. Lankester, Prof. FE. Ray, 9. On ‘‘Like to Like’’ as a Principle, 245-248. Correlated Variation, 260. Le Conte, Joseph, 215. Marlatt, C. L., On the Periodical Cicada, 124. Mayer, A. G.: Dextral and Sinistral Partula, 70. ““S Study in Variation of Partula,” 155-156. Modes: Of the Four Principles, 80. Environal, of Influence, 80, 115-129. Reflexive Mode of Influence, 80-114. Regressive Mode of the Principles, 129-131. Discriminate 132-136. Morgan, C. Lloyd, 45, 189. “Wabit and Instinct,’’ 21, 61. “Coincident Variation,”’ 61. “Animal Behavior,” 61. Natural Selection of Innate Characters, 256. Morgan, T. H.: “Evolution and Adaptation,” 71, 73. On Mutations, 71-73. Mutation, 70-77. And Varieties, 71. Expounded by ‘T. H. Morgan, 71-73. Theory Loses Sight of Certain Facts, 73-77. and Indiscriminate Modes, ee INDEX. 26 Mutation—Continued. Denies Effect of Individual Variation, 71—77. Reached by Selection of Fluctuating Varia- tions, 77. Natural Species: Evolution of, 23-36, 212-240 Unity and Diversity, 23-29. Unity Through Community of Descent, 23-26. Diversity not Always ‘Through Diversity of Environments, 23-29. Selection May Help Unity or Diversity, 25, 29. May Lose Plasticity and Become Extinct, BD. Varieties are Incipient Species, 213. Illustration of Intergrading Species, Plate TUT, 43. Reference to Intergrading Species, 214. Utility of Specific Characters, 255-261. If All Men were Left-handed no Loss, 256- 25:1 Many Examples of Asymmetry, 257. Cockerell’s Letter on Utility of Specific Char- acters, 260. Osborn, H. F., 45; also Preface. Packard, A. S., ‘‘Lamarck; His Life and Work,’’7. Recognizes Importance of Isolation, 7. Partition: Need of Such a Term, 51. Defined, 53. Industrial, illustrated, 67. Reflexive, 81-114. Conjunctional, 82-83. Institutional, 82, 114. Family 83, 86. Social, 83-85, Environal, 115, 129. Endonomice, 115, 129. Industrial, 115, 129. Migrational, 115, 129. Heteronomic, 115, 129. Transportational, 115, 129. Geological, 115, 129 Artificial, 115, 129. Pearson, Karl: “The Chances of Death,’’ 16, 92-95, 113-114. ““Grammar of Science,’’ 51, 92-94. Statistical Methods, 154. Physiological— Isolation, 95—96. Selection, 96. Plate A, Map of Hawaiian Islands, between 42,43. Plate I, Eight Genera of Achatinellide, 42, 43. Explanation of, 37. Plate B, Map of Oahu, 42, 43. Explanation of, 43. Plate II, Twenty-five Species of Achatinella, 42, 43, Explanation of, 39. Plate III, Variation and Intergrading of Buli- mella, 42, 43. Explanation of, 41. a | Radius of Distribution Varies— Directly as the Power for Migrating, 220. Inversely as the Power for Variation, 220. Rats of Arboreal Habits, as Illustrating Coépera- tion of Positive and Negative Segregation, 101-103. Reflexive— Mode of Influence, 80-114. Selection, 81-114, 151. Isolation, 81-114. lection, 81-114. Partition, 81-114. Regressive Mode of the Four Principles, 80, 129. Selection, 129, 131. Election, 129. Isolation, 130. Partition, 130. Reid, G. A., Increasing Difficulty of Childbirth 86. Riley, C. V., Bul. No. 8, Divis. Entomology, U.S. Department Agriculture, 229-232. Romanes, G. J., 192. “Darwin and After Darwin,’’ 51 52. “Physiological Isolation,’”’ 52. On Cessation of Natural Selection, 198, 254. “Mental Evolution in Animals,’’? 237-238. Scott, William E. D., How Red-winged Blackbird Learned to Crow, 84. Segregate Adaptation, 87, 170. Association, 48; also Preface. , -Segregate Generation, 47; also Preface. A Condition of Allogamic Evolution, 79. Segregate— Survival, 95—96, 108. Union, 95—96. Vigor, 87, 170. Escape from Enemies, 87, 171. Illustrated by Arboreal Rats, 101 103. Fecundity, 87, 170. How Accumulated, 262. Freedom from Competition, 87, 171. Illustrated by Arboreal Rats, 101-103. Segregation: Its Causes and Effects, 6-8. The Fundamental Process in Evolution, 8, 22) 147-15. Through Transformation During Isolation, &. Initial, Through Isolation, 22. Intensive, Through Transformation, The Four Segregative Principles, 45 Industrial, 45. Racial, 45, 47, 151. Social or Habitudinal, 45, 48-49, 151, 153. Without it Differences Would Cease, 47. Interaction of Racial and Social, 49. Four Principles of, 45-145. ; Interaction of the Four Principles, 55-78. Intensive, and Headley’s Criticism, 55-56. Importance of Each of the Principles, 56-58. Impregnational, illustrated, 68-70. Positive, 98-101, 163. Negative. 98-101. 163-164. bat ed N va) 263 ‘ INDEX. Segregation—Continued. Selection—Continued. Negative and Positive, Codperating, 101-111, Defined, 53, 195. 182-183. Coincident, 61, 63, 64, 65, 68. 152. Cumulative, Illustrated in Plant Species, Organic, 61, 62, 152. 108-111. Endonomic, in Cliff Swallows. 63. Intensifying, 151. Autonomic, 151. Control of, 151, 156. Conditions Favoring, 154. Favorable Conditions for, in Partula, 155. Reflexive, 159-183. Conjunctional, 159-163. Social, 160. Sexual, 160-162. Germinal, 162-163. Floral, 162-163. Impregnational, 163-171. Impregnational Alone is Negative, 163. Dimensional, 165. Structural, 165. Potential, 166-170. How Accumulated, 168. Institutional, 171. The Importance of Impregnational, 172- 174. Meaning of Isolation and, 175. Forms of, 176. Computation of, 177-133. Intensive, 175-176. 185-243, 262. Forms of Intensive, 185-212. Forms of, Codperate, 247-248. Divergent Evolution Through Cumulative, 159-183, 262. Selection: Not Always the Cause of Divergence, 3-6. Divergence that is not Due to Sexual, 3. Nor to Natural, 4-5. Of a Species Does Not Change the Species, 14. Of Other Than Average Varieties Produces Change, 15. When Unbalanced Produces Change, 15. Conditioned by Fertility, 15. Of Average Forms Tends to Stability, 16, 195-196. Fecundal, Due to Superior Fertility, 16. May Produce Diversity or Unity, 25, 29. Diversity of, with Isolation Causes Diver- gence, 8, 22. How Far an Explanation of Divergence, 29-34. What it Does Not Explain, 29-31. How Far Determined by Environment, 31-32. Endonomic, One Form of Autonomic, 32. May be Changed Without Change in Envi- ronment, 33. Statistical Proof of Natural, 34. Reflexive, 36, 45. Active and Passive, 45. Headley says, May be Controlled by the Or- ganism, 46. * See under Sexual. | | In Chimney Swift, 64. In Tree Swallow, 64. In House Wren, 64. In Infants, 64. Defined, 65. And Coincident, 65—67. Illustrated by Swimming Cats, 67-68. Structural, 68-70. Reflexive, 82-114, 151, 197. Conjunctional, 32-83, 197. Dominational, 82, 836-87, 197, 203. Impregnational, 82, 87-111, 197, 206. Institutional, 82, 111-112, 153, 197, 207. Prudential, 82, 111-114, 153, 197, 207. By which Man May Control His Own Evolution, 112, 153. Sexual,* 83-84, 200-202. Social, 83-84, 202-203. Filio-parenta!, 83, 86, 203. And Lactation, 204. Dimensional, 87-88, 204-205. Structural, 37-89. Potential, 87, 89. Fecundal, 87, 90 —95, 206. Environal], 115-118, 196, 200 Endonomic, 115-117, 152, 156, 197. Habitudinal, 115-117. Aptitudinal, 115-117. Heteronomic, 115, 117-118, 197. Natural, 115, 117-118. Artificial, 115, 117-118. Forms of, Defined, 139. Conditions Determining the Forms of, 140. Unwarranted Assumption Concerning Nat- ural, 144-145. Unbalanced, 149. Cessation of, 198. Rational and Adaptational, 199. Forms of, Classified. 199. Self-cumulative Endowments, 96-98. Sexual— Election, 83-84. Isolation, 83-84. Selection, 83, 200-202. Darwin says Caused by Divergent In- stincts; what Causes the Latter, 11, 200. Explanation given, 201. Illustrated by Creeping Cricket, 200. Social— Election, 83, 85. Isolation, 83, 85. Partition, 83, 85. Selection, 83-84. Species: Intergrading Between, 40-42. Statistical Test of, 40. 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