Cretecesms of Theory of Natural Selection. 343 
of natural selection in any case depends upon a variety 
of highly complex conditions; and, therefore, that the 
fact of all those conditions having been satisfied in 
one instance is no reason for concluding that they 
must also have been satisfied in otherinstances. Take, 
for example, the case of monkeys passing into men. 
The wonder to me appears to be that this improve- 
ment should have taken place in even one line of 
descent ; not that, having taken place in one line, 
it should not also have taken place in other lines. 
For how enormously complex must have been the 
conditions—physical, anatomical, physiological, psy- 
chological, sociological—which by their happy con- 
junction first began to raise the inarticulate cries of 
an ape into the rational speech of aman. Therefore, 
the more that we appreciate the superiority of a man 
to an ape, the less ought we to countenance this 
supposed objection to Darwin’s theory—namely, that 
natural selection has not effected the change in more 
than one line of descent. 
Even in the case of two races of mankind where 
one has risen higher in the scale of civilization 
than another, it is now generally impossible to assign 
the particular causes of the difference; much more, 
then, must this be impossible in the case of still more 
remote conditions which have led to the divergence 
of species. The requisite variations may not have 
arisen in the one line of descent which did arise in 
the other; or if they did arise in both, some 
counterbalancing disadvantages may have attended 
their initial development in the one case which 
did not obtain in the other. In short, where 
so exceedingly complex a play of conditions are 
