Species

Darwin and the Darwinians 171

and subsequently have not varied or come to differ in any degree, or only in a slight

degree, it is not probable that they should vary at the present day. On the other hand,

the points in which species differ from other species of the same genus are called spe-

cific characters; and as these specific characters have varied and come to differ since

the period when the species branched off from a common progenitor, it is probable that

they should still often be in some degree variable,—at least more variable than those

parts of the organisation which have for a very long period remained constant.^59

Asking in effect why the Great Chain of Being principle of lex completio does not

result in no species being seen at all but instead one variable mass, Darwin answers,

I believe that species come to be tolerably well-defined objects, and do not at any one

period present an inextricable chaos of varying and intermediate links”^60

due to

1. The fact that variation and selection take time, and may not have yet
   occurred


2. When smaller isolated populations spread out, selection exterminates the
   older intermediate forms (in modern terms, when in sympatry, allopatric
   variations exclude the less fit older forms)


3. Intermediates are subject to accidental extinction because they are less
   widely spread


4. “Numberless intermediate varieties, linking closely together all the species
   of the same group, must assuredly have existed; but the very process of
   natural selection constantly tends, as has been so often remarked, to exter-
   minate the parent-forms and the intermediate links”^61

When reading the Origin one is struck by Darwin’s repeated locutions “to the
benefit of the species” or “of advantage to the species.” Darwin seems to be mak-
ing the (now) classical blunder of group selectionism. However, as one reads these
examples it becomes clear that Darwin is using it as a circumlocution for “of advan-
tage to the members of the species that carry this trait.” It is clear that he thinks that
selection occurs, in the main, through competition between varieties (and of course
species are just well-marked varieties as he has said above), increasing or decreasing
in relative numbers as they carry beneficial or non-beneficial traits. In this usage,
species is just a way of marking the variety that is subjected to selection, or has been
so subjected and gone to fixation; it is roughly equivalent, therefore, in Darwin’s
mind, to the sum total of what G. C. Williams later called “evolutionary genes”^62 —
those hereditable variations that are selectable.

(^59) Op. cit., 115.
(^60) Op. cit., 127.
(^61) Op. cit., 128.
(^62) Williams 1966.