xxiv. ii. GROWTH OF POPULATIONS 641 



developed late and were therefore better behaved, in early years 

 because of immaturity, and later by the great development of the 

 'inhibitory' or balancing functions made possible by growth of the 

 frontal lobes (p. 633). Families composed of such slow-developing and 

 restrained individuals would therefore survive and the genetic factors 

 involving delay of maturity be selected. 



10. Growth of human populations 



This increase of the post-natal developmental period may well be 

 connected with the appearance of the fourth outstanding feature of 

 man noted by Schultz (p. 633), the great population increase in 

 recent times. No exact figures are available, but it is probable that a 

 first increase occurred when the Neolithic agricultural civilization 

 developed, perhaps 10,000 years ago. This development presumably 

 depended on factors making for orderly and restrained behaviour, 

 such as we have been discussing; it is no accident that family customs 

 are closely linked with those of tribes and nations in all stages of 

 society. A further great increase of human population, probably at 

 least a doubling, has occurred during the past 200 years, and we may 

 associate this with the further extension of habits of thought and 

 restraint in the conduct of affairs, making possible the development 

 of logic and science and their application to human productivity. 



1 1 . Time of development of the Hominidae 



Thus there are seen to be profound differences between man and 

 the existing apes, and it must be remembered that we have considered 

 mainly skeletal features and hardly touched on the details of the inner 

 life of the animals, or their powers of communication or social organi- 

 zation. The most significant difference between man and all other 

 animals is in the size of the brain (Fig. 382) and the difference of life 

 and behaviour that goes with this. In studying the documents of our 

 history, however, we can discover only little of the brains and less of 

 the behaviour of our ancestors; we must rely mainly on study of the 

 skeleton. 



No undoubted human remains are found before the beginning of 

 the Pleistocene, less than 1-5 million years ago. They are not common 

 until 500,000 years later, but their total absence from the Pliocene, 

 Miocene, and Oligocene epochs must certainly be considered sus- 

 picious. During those periods we have admittedly only few remains of 

 apes, but they do occur and men do not; there is therefore a prima 

 facie case for considering that men have evolved from the same 



