ANCIENT MAN IN AFRICA AND JAVA 271 
Australian native has those intermediate and generalised 
characters needed for such an ancestral form. If we 
agree that the Australian native, or some other primitive 
race, may be accepted as a common ancestor for white 
and black races of mankind, let us ask the following 
question : How long will it take for the evolution of 
two such divergent races as the negro and European 
from such a common stock ? In answering that question 
we have to bear in mind how durable certain modern 
human types are. 
It is when we approach the antiquity of man from this 
point of view that we see that we must postulate a very 
long period of time for the evolution of modern types 
of man. The whole length of the Pleistocene period 
does not seem to me sufficiently long for the purpose. 
Certainly, the common ancestor of modern races must 
have reached a higher stage by the close of the Pliocene 
period than that represented by Pithecanthropus. It is 
for that reason that we must regard the humanoid form 
discovered by Dr Dubois in Java as representing a 
Miocene rather than a Pliocene stage in man's evolution 
(see frontispiece). 
