414 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 192 8 



are fairly unanimously accepted by the genuine scientific world as 

 undoubtedly such links? Around these questions as a center the 

 controversy revolves, with no present indication that it is likely soon 

 to come to rest. To some persons the existence of human missing 

 links appears to be more than unlikely ; to others it appears to be not 

 only likely but definitely established. Between these two extremes 

 stand those who believe that the links probably existed but that they 

 certainly have not yet been found. 



From these points of view writers are tirelessly putting forward 

 their rival opinons. What I wish to undertake here is to summarize 

 these opinions and to set forth the facts which underlie them in such 

 form that the reader may be enabled to come to some conclusion 

 for himself. But before examining any actual fossils it will be 

 necessary to have a clear understanding of the nature and conditions 

 of our problem. I shall therefore begin by explaining what a true 

 missing link is understood to be. Then I shall quote some typical 

 examples of opinions which show how variously the subject can be 

 regarded when the links are supposed to have formed part of a chain 

 binding man's history to that of other mammals. After this a very 

 brief account will be given of the main features which distinguish 

 the skeleton of man from that of the mammals which most nearly 

 resemble him. We shall then be in position to look intelligently at 

 the fossils and at the opinions of the experts who have studied them. 



WHAT IS A MISSING LINK ? 



About the meaning of the term " missing link " there is much popu- 

 lar misunderstanding. Many persons suppose that such a link must 

 have been something in the nature of a hybrid, a monster, or a 

 freak. Nothing could be more incorrect. Whether, as some author- 

 ities believe, evolution moves onward by the gradual changing of 

 whole populations of creatures, or whether, as others consider more 

 likely, it moves by a less uniform process in which individual pe- 

 culiarities play an important part, a missing link can never be any- 

 thing else than perfectly normal. At the time when it lived there 

 must have been many individuals like it ; and the reason why some of 

 the links which have been found in groups of animals not related 

 to man are represented by only one specimen is that fossils, on the 

 whole, are rare. 



The idea of the existence of " missing links " arose partly from 

 the discovery of connecting fossils and partly from the commonly 

 accepted theory of organic evolution. According to this the different 

 kinds of living animals and plants have not always existed in the 

 forms that we now see. On the contrary, they have all come to be 

 what they are by a process of " modification of traits from genera* 



