

CHAPTER FIFTY-ONE 



THE EVOLUTION OF MAN 



1. IT is impossible for any of us, unless we happen to our igno- 

 be kings or their kindred, to trace our ancestry back rance of 



J human 



many generations. In any group of Americans gathered ancestry 

 together, it will be found that few know the family 

 names of their grandmothers, and almost none those of 

 their great grandmothers. We all know, of course, that 

 the stream of life has been continuous, that one family 

 is not any older than another, that all are of incalcu- 

 lable antiquity. If it is thus difficult or impossible to 

 trace our human ancestry, how can we expect to succeed 

 with -the prehuman, and recover traces of those beings 

 whose existence millions of years ago was necessary in 

 order that we should be here today ? 



2. No biologist supposes that it will ever be possible Deveiop- 

 1 to ascertain all the details of human evolution. Yet the ment . of j< 



man indi- 



general outline of the process is recognizable. First of cates the 

 all, the human individual, in his development, appears of^s^ 

 to repeat more or less the history of animal life, to evolution 

 climb, as Huxley said, his own family tree. Thus all 

 animals, including man, begin as a single cell, agreeing 

 in its general features with the lowest forms of life 

 known, the permanently one-celled organisms called 

 Protozoa and Protophyta. All many-celled creatures 

 can be traced back to the one-celled condition at the 

 beginning of their existence, and we can hardly doubt 

 that the evolutionary process began in a similar manner. 

 Thus the first stage of human evolution may be de- 

 scribed as protozoan. 



3. Development proceeds through segmentation. Early stages 

 Numerous cells are formed, which, instead of separating oi ^t*i~ 

 and becoming isolated individuals, as in the Protozoa, evolution 



429 



