VI 
DIFFICULTIES AND OBJECTIONS 
143 
it as one of the difficulties which can alone he overcome by his 
theory of physiological selection. He urges, that the same 
variation does not occur simultaneously in a number of 
individuals inhabiting the same area, and that it is mere 
assumption to say it does; while he admits that “ if the 
assumption were granted there would be an end of the present 
difficulty; for if a sufficient number of individuals were thus 
simultaneously and similarly modified, there need be no longer 
any danger of the variety becoming swamped by intercrossing.” 
I must again refer my readers to my third chapter for the 
proof that such simultaneous variability is not an assumption 
but a fact; but, even admitting this to be proved, the problem 
is not altogether solved, and there is so much misconception 
regarding variation, and the actual process of the origin of 
new species is so obscure, that some further discussion and 
elucidation of the subject are desirable. 
In one of the preliminary chapters of Mr. Seebohm’s recent 
work on the Charadriidce, he discusses the differentiation of 
species ; and he expresses a rather widespread view among 
naturalists when, speaking of the swamping effects of inter¬ 
crossing, he adds: “ This is unquestionably a very grave 
difficulty, to my mind an absolutely fatal one, to the theory of 
accidental variation.” And in another passage he says : “ The 
simultaneous appearance, and its repetition in successive genera¬ 
tions, of a beneficial variation, in a large number of individuals in 
the same locality, cannot possibly be ascribed to chance.” These 
remarks appear to me to exhibit an entire misconception of the 
facts of variation as they actually occur, and as they have been 
utilised by natural selection in the modification of species. I 
have already shown that every part of the organism, in common 
species, does vary to a very considerable amount, in a large 
number of individuals, and in the same locality ; the only point 
that remains to be discussed is, whether any or most of these 
variations are “beneficial.” But every one of these variations 
consists either in increase or diminution of size or power of the 
organ or faculty that varies; they can all be divided into a 
more effective and a less effective group—that is, into one that 
is more beneficial or less beneficial. If less size of body would 
be beneficial, then, as half the variations in size are above and 
half below the mean or existing standard of the species, there 
