650 MAN xxiv. 15 



There is much evidence that change of the physical characteristics 

 of human populations has continued during the last 10,000 years. Thus 

 H. sapiens before the Mesolithic period was long-headed (dolicho- 

 cephalic). Short, broad skulls (brachycephalic) first appeared at that 

 time and are now found in more than half the population of the world. 

 Changes in the shape of the jaw and face and reduction of the teeth, 

 which have been going on for a long time, probably continue today. 



Study of the gradual mixing and changing of human populations, 

 besides its personal interest, is of value to a zoologist in calling the 

 process of evolution to our imagination and showing us its complexity 

 and slowness. Without undue difficulty we can have in mind a picture 

 of great populations of human beings, composed of individuals differ- 

 ing slightly in structure and habits, warring and competing with each 

 other, so that one group comes to dominate another, the invader taking 

 over some of the genes and the gods of its victims. We can at least guess 

 how such a process would lead the population of any area to change, 

 either if a set of individuals arises that is more active or in some way 

 more efficient than another, or following a change in conditions that 

 gives preference to a particular set of structures or habits. Though 

 evolution is a slow process it is always going on before us, and the best 

 way to see it is to look at our own species, vastly more familiar and re- 

 vealing than any other. All sheep or shrews look to us much alike, but 

 we can more readily tell what sort of man or woman we are meeting 

 and what they are likely to do in the world. Moreover we can recon- 

 stitute their capacities by the remains of their cultures and recognize 

 clearly how different our ancestors were from ourselves 50,000 years 

 ago and still more so at 500,000 years. In this way we may get some 

 faint picture of the slow and confused changes that constitute evolu- 

 tion. Even with such a slow breeding species as our own the effort of 

 thought is very great. Allowing only so few as four generations per 

 century we may conclude that we are separated from ^Pithecanthropus 

 populations by 40,000 generations. If we ever had an ape-like hairy 

 ancestor it was perhaps our great-grandfather 500,000 times removed, 

 counting back only to the beginning of the Pliocene. Yet men and 

 apes are zoologically much alike. 



Many factors have been suggested to account for the appearance of 

 man's particular characteristics. Disappearance of forests may have 

 favoured a terrestrial bipedal life and use of the hands. The great size 

 of the brain might have followed from this. It has been claimed that 

 this might have resulted from single mutations that increased the 

 number of divisions of the neuroblasts from 31 in apes, giving about 



