EXTERNAL FACTORS 195

When formulating his views on the classification of the
sciences and his reasons for dissenting from the philosophy
of Comte, Spencer pointed out that all the concrete sciences
under their most general aspects give accounts of the redistri-
butions of matter and motion; and he asked the question,
What is the universal trait of all such redistributions ? His
answer was that" increasing integration of matter necessitates
a concomitant dissipation of motion, and that increasing
amount of motion implies a concomitant disintegration of
matter/* Thus Evolution and Dissolution appeared " under
their primordial aspects/' and differentiations, with resulting
increase of heterogeneity, were seen to be secondary not
primary traits of evolution. So he arrived at his famous
definition of evolution : —Evolution is an Integration of matter
and concomitant dissipation of motion, during which the matter
passes from an indefinite, incoherent homogeneity to a definite,
coherent heterogeneity ; and during *which the retained motion
undergoes a parallel transformation " [First Principles, p. 396).

Having illustrated the evolution of the evolution-
theory in Spencer's mind, we pass to his final state-
ment of the factors of organic evolution.

(l) External Factors.—He begins by pointing out
that living creatures are in the grip of a complex
environment, which acts on them and to which they
react. And whether we think of the seasons or the
climate, the soil or the sea, we find that this environ-
ment is intricately variable. Every kind of plant and
animal may be regarded as for ever passing into a
new environment, and with increasing fullness of life
there is additional complexity in the incidence of
external forces. Every increase of locomotive power,
for instance, increases the multiplicity and multiformity
of action and reaction between organism and environ-
ment. There are chemical, mechanical, dynamic,
and animate influences which modify organisms, and
as the actions of these several orders of factors are terms, as an