44 Evolution and Adaptation 
it was pointed out by Geoffroy Saint-Hilaire that, since the 
conditions of the Egyptian climate are the same to-day as 
they were two thousand years ago, there is no reason to 
expect any change would have taken place. But waiving 
this assumption, we should not forget that the theory of evo- 
lution does not postulate that a change must take place 
in the course of time, but only that it may take place 
sometimes. 
The position that we have here taken in regard to the 
lack of evidence as to the transformation of species is, per- 
haps, extreme, for, as will be shown in some detail in later 
chapters, there is abundant evidence proving that species 
have been seen to change greatly when the conditions sur- 
rounding them have been changed; but never, as has been 
stated, so far, or rather in such a way, that an actual new 
species that is infertile with the original form has been pro- 
duced. Whether, after all, these changes due to a change 
in the environment are of the kind that makes new species, 
is also a question to be discussed later. 
The experimental evidence, in favor of the transformation 
of species, relates almost entirely to domesticated forms, and 
in this case the conscious agency of man seems, in some cases, 
to have played an important part; but here, even with the 
aid of the factor of isolation, it cannot be claimed that a 
single new species has been produced, although great 
changes in form have been effected. It is clear, therefore, 
that we must, at present, rely on other data, less satisfac- 
tory in all respects, to establish the probability of the theory 
of transformation. 
MODERN CRITICISM OF THE THEORY OF EVOLUTION 
Throughout the whole of the nineteenth century a steady 
fire of criticism was directed against the theory of evolution ; 
the names of Cuvier and of Louis Agassiz stand out preémi- 
