Species

Darwin and the Darwinians 185

We see, therefore, that the idea of species is fully justified in a certain sense; we find

indeed at certain times a breaking up of the fixed specific type, the species becomes

variable, but soon the medley of forms clears up again, and a new constant form arises—

a new species, which remains the same for a long series of generations, until ultimately

it too begins to waver, and is transformed once more. But if we were to place side by

side the cross-sections of this genealogical tree at different levels, we should only see

several well-defined species between which no intermediate forms could be recog-

nized; these would only be found in the intermediate strata.^113

... the species is essentially a complex of adaptations, of modern adaptations which

have been recently acquired, and of inherited adaptations handed down from long ago—

a complex which might well have been other than it is, and indeed must have been dif-

ferent if it had originated under the influence of other conditions of life.^114

In contradiction to Karl von Nägeli (Swiss, 1817–1891), who thinks of species as
“a vital crystallization” (in Weismann’s words^115 ), Weismann denies that there is an
evolutionary force that impels species to evolve, and defends natural selection as the
entirety of evolutionary mechanism. Since the major features of evolutionary groups
are adaptive in their origin, Weismann says^116

... if the step from one species to the next succeeding one does not depend on adap-

tation, then the greater steps to genera, families, and orders cannot be referred to it

either, since these can only be thought of as depending upon a long-continued splitting

up of species.

Weismann appears to think that entire species transmute and are changed into

new species after a period of fragmentation of forms. However, he realizes that spe-

cies are variable:

But of course species are not exclusively complicated systems of adaptations, for they

are at the same time ‘variation complexes,’ the individual components of which are

not all adaptive, since they do not all reach the limits of the useful or the injurious.^117

He recognizes that selection applies to sub-organismic “vital units,” and that there

are “indifferent characters,” or non-adaptive characters, which result as by-products,

as it were, of selection for “a harmonious whole.” Selection in the “germ plasm” may

... give rise to correlative variations in determinants next to them or related to them in

any way, and that these may possess the same stability as the primary variation. This

seems to me sufficient reason why biologically unimportant characters may become

constant characters of the species.^118

(^113) Op. cit., vol. II, 305.
(^114) Op. cit., vol. II, 307.
(^115) Mazumdar 1995 gives details of Nägeli and Schleiden’s views on species. Nä gel i’s [189 8] account of
species relied upon there being a mechanical “idioplasm” or reproductive plasm.
(^116) Op. cit., vol. II, 306.
(^117) Op. cit., vol. II, 307.
(^118) Op. cit., vol. II, 308.