THE ORIGIN OF THE HUMAN BODY 269 



evolutionary explanation. Indeed, the theory of evolution 

 itself stands or falls upon this issue ; for, if structures so strik- 

 ingly similar as the skeletons of a man and an ape, respec- 

 tively, have originated from two distinct ancestral stocks, 

 then in no case at all is the inference of common descent from 

 structural resemblance a legitimate procedure. In other words, 

 if the homologies existent between the human and simian 

 organisms are explicable on some other basis than that 

 of common ancestry, then all organic homologies are so ex- 

 plicable, and the whole evolutionary argument collapses. 



§ 1. Two Theories of Descent 



Two theories have been formulated regarding the alleged 

 bestial origin of the human body: (1) the theory of lineal 

 descent from some known species (living or fossil) of ape or 

 monkey; (2) the theory of collateral descent from a hypo- 

 thetical bestial ancestor common to apes and men. The 

 theory of lineal descent is that to which Darwin himself 

 stands committed. This theory, however, soon fell into dis- 

 repute among scientists, who came to prefer the theory of 

 collateral descent, although signs of a return to the older theory 

 are not wanting in our day. At all events, Darwin came out 

 flatly in favor of the monkey origin of man. This, it is true, 

 has been indignantly denied by loyal partisans anxious to 

 exonerate their idol from the reproach of having advanced 

 a crude and now obsolete theory of human descent. But 

 Darwin's own words speak for themselves: "The Simiadae," 

 he says, "then branched off into two great stems, the New 

 World and Old World monkeys f and from the latter, at a 

 remote period of time, Man, the wonder and glory of the 

 Universe, proceeded." ("Descent of Man," 2nd ed., ch. VI, 

 pp. 220, 221.) Note that he does not say "probably"; his 

 language is not the language of hypothesis, but of categorical 

 affirmation. 



The theory, however, which is most generally favored at the 

 present time holds that, assuming the universality of the evo- 



