THE EVIDENCE FOR ORGANIC EVOLUTION 519 



In the case of man, for example, one might ask " Where are the 

 forms that Hnk man with the apes?" The foregoing discussion 

 of fossil records shows that missing links, or synthetic types, as 

 they are called scientifically, are not to be looked for among exist- 

 ing animals, but among fossils, since the connecting links are the 

 common ancestors in the past. Thus the Hnks between modern 

 horses, zebras, and wild asses are members of the horse family that 

 were ancestral to these types. The connecting links between the 

 Asiatic and Indian elephants, and between existing camels and 

 guanacos (cf. Fig. 280) are likewise extinct. The connecting 

 links between men and apes are the extinct pre-human races 

 (cf. Figs. 289 to 292). 



Connecting links between larger groups are not wanting, as 

 in fossils showing structures that are transitional between amphib- 

 ians and reptiles, or between reptiles and birds, or reptiles and 

 mammals, although no one animal shows all the transitions in 

 these instances. The most spectacular examples, perhaps, are 

 the primitive birds that show reptiUan features, notably Archccop- 

 teryx (Fig. 279). In this instance there are teeth, clawed digits 

 on the fore limbs, and an elongated tail with feathers on either side, 

 while various features of the skeleton are distinctly reptilian. We 

 have seen in our study of development (cf. p. 424) that birds 

 closely resemble reptiles. It is also true that their adult anatomy 

 is far more like that of reptiles than would be supposed from casual 

 examination. As Huxley put it, birds are " glorified reptiles." 

 Archceopteryx is perhaps as nearly a " connecting link " as one could 

 hope to find in view of the imperfections of the fossil record. Here, 

 as elsewhere, the facts of Anatomy, Embryology, and Paleontology 

 tell the same story of evolution. 



Many other examples of the geologic succession of fossils could 

 be cited. The most important feature of all this evidence from 

 Paleontology, as of the e\'idence from Anatomy and Embryology, 

 is its cumulative nature. The facts in many lines tell a consistent 

 story when interpreted as evidences of evolution. 



Geographical Distribution. — The study of geological distribu- 

 tion includes both the lateral distribution of fossils, which indicates 

 past distribution over the surface of the earth, and their vertical 

 distribution, which indicates relative age. For example, study 

 of the horse and elephant families includes the distribution of 

 species over the various continents and their order of appearance m 



