The Recapitulation Theory in Biology 15 



It was noticed, too, that Darwin hesitated to formulate a gen- 

 eralization distinctly in favor of recapitulation, whatever may 

 have been his inclination. It remained for Haeckel to raise 

 M tiller's' second class of cases into very great prominence at the 

 expense of the first, to assume that this represents the more 

 general, and indeed in some fashion a necessary order, and to 

 throw together all the cases of the first class as mere subsidiary 

 disturbances of the order represented by the second. Thus the 

 "law of recapitulation" took the form in which it is best known. 

 It is interesting to consider the consequences if by chance the 

 emphasis had been placed the other way round. Then the 

 "law" would have read somewhat as follows: Ontogeny records 

 the adaptations the life history of descendants has made in its 

 evolution and is indicative of its phylogeny in those cases only 

 in which embryonic or larval deviation has not occurred. 



Haeckel's great popularity as a writer gave his statement 

 very wide currency, in fact, made it dominant. It has happened 

 in consequence that the whole succeeding history of the discus- 

 sion, including its application to mental growth, has turned 

 largely upon either the possible substantiation of his "biogenetic 

 law," or upon its possible refutation. It may be said with 

 justice that much of the mischief that has resulted from a care- 

 less use of his formula has been due to the particular form in 

 which the facts were thus summarized. 



Haeckel was a young man beginning his career at Jena when 

 Darwin's great book appeared. The circumstances of his train- 

 ing had been such as to prepare his mind for the new doctrine and 

 he became its most ardent advocate and disseminator in Ger- 

 many. Haeckel was not content to limit himself to a study of 

 the causes of descent. At once speculative and intrepid, he 

 carried the doctrine in every direction his system-loving mind 

 pointed, and ultimately built a complete natural philosophy 

 upon it. He would not demonstrate the kinships within one 

 class only, as had Fritz Mtiller. Nothing less than a genealogical 

 tree of the entire animal world became his object. Haeckel was 

 particularly interested in the two extremes of descent concerning 

 which Darwin had been less explicit, that of the ancestry com- 

 mon to the great phyla among the lowest forms, and that of 

 man. His original investigations were consequently directed 

 upon the lowest orders and he was able to suggest a succession of 



