2 THE TREND OF THE RACE 



be transmitted to the next generation, naturally hold that man's 

 inherited traits can be modified through experiences with his 

 social environment. In the writings of Mr. Herbert Spencer, for 

 instance, most of the peculiarly social endowments of human 

 beings are explained as due to the cumulative inherited effects of 

 the experience of men with their fellows. Human nature through 

 such a process came to be moulded into conformity with the needs 

 of social life, and in the course of time the adjustment, it was 

 supposed, would become more and more nearly complete. 



If, however, as most biologists now believe, acquired characters 

 are not transmitted to offspring, the social environment never- 

 theless is able to influence human heredity in many ways. It may 

 determine to a large extent what kinds of variations survive and 

 propagate, and it may also determine, to some degree at least, the 

 nature of the heredity variations which arise in the germ plasm. 

 Whatever forces have been concerned in the evolution of plant 

 and animal life doubtless continue to operate in the human species. 

 Much still remains to be learned, however, in regard to the factors 

 of evolution in the organic world. The subject is still steeped in 

 controversy. Opinion among biologists remains undecided as to 

 the potency of natural selection, the Lamarckian factor, ortho- 

 genesis, isolation and mutation as causes of evolution. And he 

 who would throw the most light on the problems of human 

 biological evolution would perhaps labor most effectively by 

 directing his attention to the lower organisms where it is possible 

 to apply rigidly controlled experimental methods. 



But greatly as problems of human evolution would be illumi- 

 nated by a knowledge of the way in which evolution has been 

 brought about in organisms below man, there would remain a 

 multitude of specifically human evolutionary problems which can 

 be solved only by the study of human data. The development of 

 civilization has brought mankind under influences which have 

 never before come into play. In addition to the natural forces to 

 which lower organisms are exposed, man has come to live in a 

 social milieu which constitutes a very large part of what may be 

 called his effective environment. From this circumstance have 



