18 The Recapitulation Theory and Human Infancy 



of adaptation would be eliminated at one stroke. Adaptation 

 would effect embryonic and larval structures, as he clearly 

 points out, but presumably its principal effect would be to 

 extend the ontogeny in a linear way corresponding to a similar 

 linear extension of the phylogeny through geological time. 

 However this may be, one misses in the accounts of Haeckel 

 the detailed consideration of the effects of heredity, variation, 

 and adaptation in the life-histories of succeeding generations, 

 so noticeable in the treatment of Darwin and Miiller. This, 

 perhaps, is what reasonably might have happened from a pre- 

 occupation with the parallelism he presupposed. The upshot 

 of the matter is that Haeckel greatly overestimated the con- 

 serving force of heredity operating through descent. This 

 renders intelligible his concluding formula: "Phylogeny is the 

 mechanical cause of ontogeny," a true statement when the par- 

 ents and immediate ancestors are considered, only true with 

 respect to the remote ancestors in a phylogeny on the assump- 

 tion that the force of heredity has been fairly constant through- 

 out. 



It would, however, be unfair to Haeckel to rest an inter- 

 pretation of his biogenetic law upon his formal summaries alone. 

 A consideration of the actual use to which the law was put 

 in elaborating phylogenies presents a somewhat different aspect. 

 For instance, in developing the phylogeny of man the argument 

 invariably proceeds from a comparison of embryonic resem- 

 blances to a discovery of the palingenetic, or racially older, fea- 

 tures by an elimination of the cenogenic, or more recent ad- 

 ditions. Once these older features are determined the bio- 

 genetic law is invoked and the ancestral reference made. In 

 the earlier stages the ancestral reference is to hypothetical 

 ancestral adult forms, as from the gastrula to the Gastraea, 

 or from the coelomula to the hypothetical Coelomaea, and a 

 sequence of such forms results, in keeping with recapitulation 

 in the ordinary sense of a chronological series. But in the 

 later and higher stages the ancestral reference is not to specific 

 ancestral adult characters, but to ancestors having an embry- 

 ogeny with similar features. This last may be illustrated 

 "We see," he says, "that man entirely resembles the higher 

 Mammals, and most of all the apes, in embryonic development 

 as well as in anatomic structure. And if we seek to understand 



