Species by John S. Wilkins

Author:John S. Wilkins
Language: eng
Format: epub
Tags: The Evolution of the Idea
Published: 2018-01-31T10:15:20+00:00

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. Nägeli’s [1898] 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.

186

Species

An example of this is the vestigial hind limbs in the Greenland whale.119 So

Weismann was not exactly the panadaptationist he is sometimes made out to be,120

and he also allowed for the existence of neutral characters. However, he rejected

outright the views of those who thought that isolation was a precondition to new spe-

cies and that the characters that formed them were in any way neutral. In discussing

variation, he notes that

… there are very variable species and very constant species, and it is obvious that

colonies which are founded by a very variable species can hardly ever remain exactly

identical with the ancestral species; and that several of them will turn out differently,

even granting that the conditions of life be exactly the same, for no colony will contain

all the variants of the species in the same proportion, but at most only a few of them,

and the result of mingling these must ultimately result in the development of a some-

what different form in each colonial area.121

This is in some ways an early forerunner of the “founder effect” conception of

the origin of new species proposed by Mayr and developed further by Hampton

Carson.122 What is most striking about this is that Weismann is effectively ascrib-ing speciation in this case to stochastic sampling. This is something that, as the

strict selectionist Romanes held him to be, he should not have adopted. Weismann

opposed, though, an exclusivist position such as that of Wagner’s that all species had to be formed in this way.

BIBLIOGRAPHY

Amundson, Ron. 2005. The Changing Role of the Embryo in Evolutionary Biology: Structure

And Synthesis, Cambridge Studies in Philosophy and Biology. New York: Cambridge

University Press.

Barlow, Nora, ed. 1967. Darwin and Henslow: The Growth of an Idea; Letters, 1831–1860.

London: Murray for Bentham-Moxon Trust.

Beatty, John. 1985. Speaking of species: Darwin’s strategy. In The Darwinian Heritage, edited by David Kohn. Princeton PA: Princeton, University Press.

Bernardi, G. et al.

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