The Ascent of Man 177 



any people. For the human sense of race is so strong that it con- 

 vinces us of reality even when scientific definition is impossible. 

 It was this the British sailor expressed in his answer to the ques- 

 tion "What is a Dago?" "Dagoes," he replied, "is anything wot 

 isn't our sort of chaps." 



Steps in Human Evolution 



Real men arose, we believe, by variational uplifts of consid- 

 erable magnitude which led to big and complex brains and to the 

 power of reasoned discourse. In some other lines of mammalian 

 evolution there were from time to time great advances in the size 

 and complexity of the brain, as is clear, for instance, in the case 

 of horses and elephants. The same is true of birds as compared 

 with reptiles, and everyone recognises the high level of excellence 

 that has been attained by their vocal powers. How these great 

 cerebral advances came about we do not know, but it has been one 

 of the main trends of animal evolution to improve the nervous 

 system. Two suggestions may be made. First, the prolongation 

 of the period of ante-natal life, in intimate physiological partner- 

 ship with the mother, may have made it practicable to start the 

 higher mammal with a much better brain than in the lower orders, 

 like Insectivores and Rodents, and still more Marsupials, where 

 the period before birth (gestation) is short. Second, we know 

 that the individual development of the brain is profoundly in- 

 fluenced by the internal secretions of certain ductless glands not- 

 ably the thyroid. When this organ is not functioning properly 

 the child's brain development is arrested. It may be that in- 

 creased production of certain hormones itself, of course, to be 

 accounted for may have stimulated brain development in man's 

 remote ancestors. 



Given variability along the line of better brains and given 

 a process of discriminate sifting which would consistently offer 

 rewards to alertness and foresight, to kin-sympathy and parental 

 care, there seems no great difficulty in imagining how Man would 



VOL. I 12 



