CREATION BY EVOLUTION 



vertebrates, modifications due to the presence of much yolk, 

 and extraordinary modifications of parasitic larvae. Such 

 modifications indicate that evolutionary changes may occur 

 in embryonic as well as in adult stages — in fact, that they 

 may affect any part of the life history. But this does not 

 disprove the thesis that in general "ontogeny recapitulates 

 phylogeny." The fundamental resemblances or homologies 

 between embryos, larvae, and adults which have been cited 

 above are just as genuine homologies as those between adult 

 structures, and the only natural explanation that has ever 

 been found for such homologies is inheritance from common 

 ancestors. 



The origin of the individual (ontogeny) is not only a key 

 to the conditions and causes of the origin of the race (phy- 

 logeny) but is also an actual evolution — that is, an origin of 

 new forms by transformation from old ones. In the long 

 series of stages which an egg passes through in its transforma- 

 tion into a mature animal one sees not only an actual evolu- 

 tion — the evolution of an individual — but also, more or less 

 obscurely, a repetition of the stages of the long-past evolution 

 of the ancestors of the species. 



Man no less than other mammals develops from a fertil- 

 ized egg, which passes through cleavage, blastula, and gas- 

 trula stages. The human embryo has gill slits and aortic 

 arches, which undergo exactly the same transformations that 

 take place in other mammals. Man's heart is at first like 

 that of a fish, consisting of one auricle and one ventricle. 

 His backbone begins as a notochord, is next a segmented 

 cartilaginous rod, then each segment or vertebra consists of 

 five separate bones, and finally each fuses into a single bone. 

 He has in the course of his development three different pairs 

 of kidneys, first a pronephros (or fore-kidney) , like that of 

 the lower fishes, then a mesonephros (or mid-kidney) , like 



[74] 



