"MISSING LINKS" — MILLER 415 



tion to generation through internal and external factors " (to borrow 

 the words of Dr. David Starr Jordan), a process which has been 

 going on since the beginning of life "On the earth. As this process 

 has continued it has led to the production of ever new kinds of 

 plants and animals, which, on the whole, have tended to become more 

 complicated in structure and more perfectly fitted to use the world 

 around them. It follows that at any period of the world's history 

 all the kinds of plants and animals then living are to be regarded 

 as the product of those which lived at earlier periods and that, if 

 all the creatures which ever lived could be passed in review, it would 

 be seen that the distinctions which now separate the different kinds 

 would gradually disappear as we looked farther and farther into the 

 past. This concept has been illustrated by comparison with a flat- 

 topped tree. If we looked at the top only (representing the j)res- 

 ent) , we should be able to see nothing more than a great number of 

 apparently unconnected twigs, but if we examined the lower parts 

 of the tree (representing the past), we should find that the twigs 

 went down and converged into a much smaller number of branches 

 and that these branches in their turn converged into a trunk, which 

 joined all parts into one organic whole. But while we can easily 

 study an actual tree and learn the true relationship of its terminal 

 twigs to each other and to the main trunk, the most that we can do 

 in tracing the genealogy of an animal is to attempt to fit together a 

 few fragments of the tree preserved as fossils. By fitting together 

 these fragments we are able to obtain some indication of the course 

 by which the present-day twigs have grown away from the older 

 branches and these, in their turn, from the main trunk. Men and 

 apes, according to this theory of evolution, are terminal twigs of a 

 single branch, and the " missing links " which we are trying to find 

 are fragments from the lower parts of these twigs near the point 

 where they forked away from the older stem. Human missing links 

 might therefore be creatures of three different kinds — (a) races of 

 men which had not lost all their ape-like peculiarities, (b) races of 

 apes which had begun to take on human characteristics, or (c) races 

 which were neither exactly men nor exactly apes but which combined 

 the characteristics of both. 



If a human " missing link " is to be found at all, it must be sought 

 among the fossil remains of mammals long ago extinct, since there 

 is no living animal known which possesses the required peculiarities. 

 Investigators know this, and they have long been diligently search- 

 ing in rocks and caves, in gravel pits, and stream beds. As the re- 

 sult of 70 years of effort these tireless workers have made exactly 

 two " finds " — no more — which are of such a nature that they can 

 be seriously regarded as furnishing the looked-for direct evidence 



