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VARIATION 183

clear intellectual conscience back to what may have
been. One result is plain, that variation is a very
general fact of life; whenever we settle down to
measure we find that specific diagnoses are averages,
that specific characters require a curve of frequency
for their expression, that a living organism is usually
like a Proteus. There are no doubt long-lived, non-
plastic, conservative types, such as Lingula, where no
visible variability can be detected (even in untold
ages if we consider the hard parts preservable as
fossils), but to judge from these as to the rate of
evolutionary change is like estimating the rush of a
river from the eddies of a sheltered pool. Another
result is that it becomes possible to distinguish
between continuous variations, which are just like
stages in continuous growth, in which the descendant
has a little more or a little less of a given character
than its parents had, and discontinuous variations in
which a new combination appears suddenly without
gradational stages, and with no small degree of per-
fection. Although there is truth in Lamarck's
dictum that "Nature is never brusque/' although
Jack-in-the-box phenomena are rare, the evidence,
e.g. of Bateson and De Vries, as to the frequent
occurrence of discontinuous variations appears con-
clusive. Such words as "freaks" and "sports"
express a truth, suggested by Mr Galton's phrase
^££ transilient variations," that organisms may pass with
seeming abruptness from one form of equilibrium to
another, There is evidence that these sudden and
discontinuous variations—** mutations " many of them
are called—are often very heritable, that when
they appear they come to stay ; and it seems likely,



	VARIATION 183 clear intellectual conscience back to what may have been. One result is plain, that variation is a very general fact of life; whenever we settle down to measure we find that specific diagnoses are averages, that specific characters require a curve of frequency for their expression, that a living organism is usually like a Proteus. There are no doubt long-lived, non- plastic, conservative types, such as Lingula, where no visible variability can be detected (even in untold ages if we consider the hard parts preservable as fossils), but to judge from these as to the rate of evolutionary change is like estimating the rush of a river from the eddies of a sheltered pool. Another result is that it becomes possible to distinguish between continuous variations, which are just like stages in continuous growth, in which the descendant has a little more or a little less of a given character than its parents had, and discontinuous variations in which a new combination appears suddenly without gradational stages, and with no small degree of per- fection. Although there is truth in Lamarck's dictum that "Nature is never brusque/' although Jack-in-the-box phenomena are rare, the evidence, e.g. of Bateson and De Vries, as to the frequent occurrence of discontinuous variations appears con- clusive. Such words as "freaks" and "sports" express a truth, suggested by Mr Galton's phrase ^££ transilient variations," that organisms may pass with seeming abruptness from one form of equilibrium to another, There is evidence that these sudden and discontinuous variations—** mutations " many of them are called—are often very heritable, that when they appear they come to stay ; and it seems likely,