148 
DARWINISM 
CHAP. 
another on the same side an equal distance apart. In a very 
lengthy paper, presented to the Linnean Society last year, on 
“Divergent Evolution through Cumulative Segregation,” Mr. 
Gulick endeavours to work out his views into a complete 
theory, the main point of which may perhaps he indicated by 
the following passage : “ No two portions of a species possess 
exactly the same average character, and the initial differences 
are for ever reacting on the environment and on each other 
in such a way as to ensure increasing divergence in each 
successive generation as long as the individuals of the two 
groups are kept from intercrossing.” 1 
It need hardly be said that the views of Mr. Darwin and 
myself are inconsistent with the notion that, if the environment 
were absolutely similar for the two isolated portions of the 
species, any such necessary and constant divergence would 
take place. It is an error to assume that what seem to 
us identical conditions are really identical to such small 
and delicate organisms as these land molluscs, of whose 
needs and difficulties at each successive stage of their existence, 
from the freshly-laid egg up to the adult animal, we are so 
profoundly ignorant. The exact proportions of the various 
species of plants, the numbers of each kind of insect or of 
bird, the peculiarities of more or less exposure to sunshine 
or to wind at certain critical epochs, and other slight 
differences which to us are absolutely immaterial and un¬ 
recognisable, may be of the highest significance to these 
humble creatures, and be quite sufficient to require some 
slight adjustments of size, form, or colour, which natural 
selection will bring about. All we know of the facts of 
variation leads us to believe that, without this action of 
natural selection, there would be produced over the whole area 
a series of inconstant varieties mingled together, not a distinct 
segregation of forms each confined to its own limited area. 
Mr. Darwin has shown that, in the distribution and 
modification of species, the biological is of more importance 
than the physical environment, the struggle with other 
organisms being often more severe than that with the forces 
of nature. This is particularly evident in the case of plants, 
many of which, when protected from competition, thrive in a 
1 Journal of the Linnean Society, Zoology, vol. xx. p. 215. 
