the larger ones having withstood certain
violent actions which the smaller ones could not withstand.

Similarly with other assemblages of objects which are alike in their
primary traits but unlike in their secondary traits. When simultaneously
exposed to the same set of actions, some of these actions, rising to a
certain intensity, may be expected to work on particular members of the
assemblage changes which they cannot work in those which are markedly
unlike; while others of the actions will work in all of them similar
changes, because of the uniform relations between these actions and
certain attributes common to all members of the assemblage. Hence it is
inferable that on living organisms, which form an assemblage of this
kind, and are unceasingly exposed in common to the agencies composing
their inorganic environments, there must be wrought two such sets of
effects. There will result a universal likeness among them consequent on
the likeness of their respective relations to the matters and forces
around; and there will result, in some cases, the differences due to the
differential effects of these matters and forces, and in other cases,
the changes which, being life-sustaining or life-destroying, eventuate
in certain natural selections.

I have, above, made a passing reference to the fact that Mr. Darwin did
not fail to take account of some among these effects directly produced
on organisms by surrounding inorganic agencies. Here are extracts from
the sixth edition of the _Origin of Species_ showing this.

"It is very difficult to decide how far changed conditions, such as
of climate, food, &c., have acted in a definite manner. There is
reason to believe that in the course of time the effects have been
greater than can be proved by clear evidence.... Mr. Gould believes
that birds of the same species are more brightly coloured under a
clear atmosphere, than when living near the coast or on islands;
and Wollaston is convinced that residence near the sea affects the
colours of insects. Moquin-Tandon gives a list of plants which,
when growing near the sea-shore, have their leaves in some degree
fleshy, though not elsewhere fleshy" (pp. 106-7). "Some observers
are convinced that a damp climate affects the growth of the hair,
and that with the hair the horns are correlated" (p. 159).

In his subsequent work, _Animals and Plants under Domestication_, Mr.
Darwi