388 GENERAL SUMMARY Part II. 
fications, especially through the study of monstrosities : 
hence the labours of experimentalists, such as those of 
M. Camille Dareste, are full of promise for the future. 
In the greater number of cases we can only say that the 
cause of each slight variation and of each monstrosity 
lies much more in the nature or constitution of the 
organism, than in the nature of the surrounding con- 
ditions ; though new and changed conditions certainly 
play an important part in exciting organic changes of 
all kinds. 
Through the means just specified, aided perhaps by 
others as yet undiscovered, man has been raised to his 
present state. But since he attained to the rank of 
manhood, he has diverged into distinct races, or as they 
may he more appropriately called sub-specios. Some 
of these, for instance the Negro and European, are so 
distinct that, if specimens had been brought to a natu- 
ralist without any further information, they would un- 
doubtedly have been considered by him as good and 
true species. Nevertheless all the races agree in so 
many unimportant details of structure and in so many 
mental peculiarities, that these can be accounted for 
only through inheritance from a common progenitor ; 
and a progenitor thus characterised would probably 
nave deserved to rank as man. 
It must not be supposed that the divergence of 
each race from the other races, and of all the races 
from a common stock, can be traced back to any one 
pair of progenitors. On the contrary, at every stage 
in the process of modification, all the individuals which 
were in any way best fitted for their conditions of life, 
though in different degrees, would have survived in 
greater numbers than the less well fitted. The pro- 
cess would have been like that followed by man, when 
he does not intentionally select particular individuals* 
