72 THE EVOLUTION OF MAN. 



means of tracing the causes of the Evolution of Forms. It 

 seems to me that it is in this respect that this great naturalist 

 has had such an extraordinary effect on the entire subject of 

 the History of Evolution. 



In glancing, as we must now do, at the last period, but 

 just begun, of ontogenetic research, we enter at the same 

 time into the second division of the History of Evolu- 

 tion, namely, the History of the Descent, or Tribe 

 (Phylogeny). In the first chapter I drew attention to 

 the exceedingly important and intimate causal connec- 

 tion which exists between these two main branches of the 

 History of Evolution, that of the individual, and that of 

 his ancestors. We stated this connection in the funda- 

 mental Law of Biogeny : the brief Ontogeny, or the 

 Evolution of the Individual, is a swift and contracted 

 reproduction, a compressed recapitulation, of the Phylogeny, 

 or the Evolution of the Species. This proposition in reality 

 comprises everything essentially relating to the causes of 

 evolution, and we shall try everywhere, in the course of 

 these chapters, to establish it, and to uphold its truth, 

 by adducing actual facts in proof. The meaning of this 

 fundamental Law of Biogeny, in relation to this causal 

 significance, is perhaps yet better expressed as follows : 

 " The evolution of the species, or tribes (phyla), contains, 

 in the functions of heredity and adaptation, the determin- 

 ing cause of the evolution of individual organisms ; " or, 

 quite briefly : '" Phylogeny is the mechanical cause of 

 Ontogeny." 



It is owing to Darwin that we are now able to trace 

 the causes of individual evolution, which were previously 

 deemed quite unapproachable, and to understand their real 



