a7 Darwin, and after Darwin. 
too slight to serve any other purpose, may act as 
“recognition marks,” whereby the opposite sexes are 
enabled at once to distinguish between members of 
their own and of closely resembling species. Of 
course this hypothesis can only apply to the higher 
animals; but the point here is that, supposing it to 
hold for them, Mr. Wallace proceeds to argue thus :— 
Recognition marks “have in all probability been 
acquired in the process of diffcrentiation for the 
purpose of checking the intercrossing of allied forms,” 
because “ one of the first needs of a new species would 
be to keep separate from its nearest allies, and this 
could be more readily done by some easily seen 
external mark!” Now, it is clearly not so much 
as logically possible that these recognition-marks 
(supposing them to be such) can have been acquired 
by natural selection, “for the purpose of checking 
intercrossing of allied forms.” For the theory of 
natural selection, from its own essential nature as a 
theory, is logically exclusive of the supposition that 
survival of the fittest ever provides changes in antici- 
pation of future uses. Or, otherwise stated, it involves 
a contradiction of the theory itself to say that the 
colour-changes in question were originated by natural 
selection, in order to meet ‘one of the firs¢ needs of a 
new species,” or for the purpose of subsequently 
preventing intercrossing with allied forms. If it had 
been said that these colour-differentiations were 
originated by some cause other than natural selection 
(or, if by natural selection, still with regard to some 
previous, instead of prophetic, purpose”), and, when so 
“acquired,” ¢hen began to serve the “ purpose” assigned, 
1 Darwinism, pp. 218 and 229. 
