Various Opinions on Heredity. 101 



the characters of either grandparent often reappear, 

 either perfectly or by segments, in the progeny. It is 

 (in error to suppose that the male transmits certain charac- 

 ters and the female other characters." 



I think a little examination will show clearly the im- 

 p >ssibility of proving this statement from the phenome- 

 na of crossing. In order to breed together animals must 

 bo closely related; they must belong to the same species 

 or to two closely allied species. Since the individuals 

 which belong to two closely related species are the de- 

 scendants of a common, and not very remote, ancestral 

 species, it is clear that almost the whole course of their 

 evolution has been shared by them in common; all their 

 generic characteristics being inherited from this ances- 

 tor. Only the slight differences in minor points, which 

 distinguish one species of a genus from another, have 

 been acquired since the two diverged, and not even all 

 of these slight differences, for a difference between two 

 allied species may be due to the fact that while one has 

 been modified the other has retained, unmodified, cer- 

 tain resemblances to their common ancestor. We know 

 that the duration of even the most persistent species is 

 only an infinitesimal part of the whole history of their 

 evolution, and it is clear that the common characteris- 

 tics of two allied species must outnumber, thousands 

 of times, the differences between them. It follows that 

 the parents of any possible hybrid must be alike in 

 thousands of features for one in which they differ. It 

 is therefore out of the question to attempt to prove, 

 from the phenomena of crossing, that each parent can 

 transmit to the child all its characteristics. Crossing 

 simply results in the formation of a germ by the union 

 of a male and a female element derived from two essen- 

 tially similar parents, with at most only a few secondary 



