172 DOCTRINE OF EVOLUTION 



ment. The human embryo begins its very existence as 

 a single cell, nothing more and nothing less ; in gen- 

 eral structure the human egg, like the eggs of all other 

 many-celled organisms, is just one of the unitary build- 

 ing blocks of the entire organic world. And yet the 

 egg may ultimately become the adult man. Does this 

 mean that man and all the other higher forms have 

 evolved from protozoa in the course of long ages? 

 Science asks if it can mean anything else. When the 

 comparative anatomist bids us look upon the wide and 

 varied series of adult animals lower than man as his 

 relatives, because they display similar structural plans 

 beneath their minor differences, it may be difficult at 

 first to obey him. But in the brief time necessary for 

 the human egg to develop into an adult, the entire 

 range is compassed from the single cell to the highest 

 adult we know. There are no breaks in the series 

 of embryonic stages like those between the diverse 

 adult animals of the comparative array. I do not think 

 we could ask nature for more complete proof that human 

 beings have evolved from one-cell ancestors as simple 

 as modern protozoa beyond the obvious facts of human 

 transformation during development. They at least 

 are real and not the logical deductions of reason ; yet 

 their very reahty and famiharity render us blind to the 

 deeper meaning revealed to us only when science places 

 the facts in intelligible order. 



And now, in the third place, we may look to nature 

 for fossil evidence regarding the ancestry of our species. 

 Much is known about the remains of many kinds of 



