246 HEREDITY AND EUGENICS 



comparable with present conditions in France and 

 Germany, this would lead to a figure of 320 millions, 

 to which would be added 1 1 millions supported on 

 the grazing lands and forests. A total of 331 millions 

 would thus be the maximum conceivable under any- 

 thing like the present conditions of living. Long 

 before any such density of population is reached, 

 the younger countries would have ceased to be food- 

 exporting, and each country would have to be self- 

 supporting in this regard. But it is ver}^ doubtful 

 if the American population will ever reach such a 

 figure. These problems of racial movements and 

 population increase are, however, beyond our present 

 purview, and can only be touched upon here. 



Population and Quality 



Among primitive races natural selection and 

 differential fertility act so as to tend to preserve 

 existing types, rather than to bring about further 

 evolution. The same appears to be true of wild 

 species in nature generally. Under fixed conditions 

 they tend to remain stable, any unfavourable aberrant 

 types being cut off as they appear. But any kind of 

 change in the conditions initiates readjustments in 

 which selection may favour a different type, and 

 various processes of modification may be set in 

 motion. This must apply, at any rate, to the de- 

 velopment of adaptations, though it apparently does 

 not apply to many mutations. 



As regards the history of man's peculiarly human 

 qualities, it may be the case that progress in intel- 

 lectual capacity came largely before progress in skill. 

 But this evolutionary chapter of man's intellectual 

 development remains mostly to be written. Granted 

 the striking facts of the large cranial capacity of early 

 human races and species, the reasons for this develop- 



