122 Heredity. 



The Offspinng of Hyhrids more variable than the First 



Generation 



There is another aspect of the variability of hyhrids 

 which is very remarkable, and which is in perfect agree- 

 ment with oiir theory of heredity, bnt, so far as I am 

 aware, absolutely inexplicable without it. 



This is the law that although the offspring of the first 

 generation are generally uniform when two species or 

 races are crossed, the subsequent generations of children 

 produced by these hybrids dis])lay an almost infinite di- 

 versity of character. (Darwin, Variation, ii. p. 321.) 



Darwin also refers to this curious law in the Origin of 

 Species, p. 260, and attempts an explanation of it. He 

 says: ** The slight variability of hybrids in the first gen- 

 eration, in contrast with that in the succeeding genera- 

 tions, is a curious fact, and deserves attention. For it 

 bears on the view which I have taken of one of the 

 causes of ordinary variability, namely, that the repro- 

 ductive system from being eminently sensitive to changed 

 conditions of life, fails under these circumstances toper- 

 form its proper function of jiroducing offspring closely 

 similar in all respects to the parent form. Now, hy- 

 brids in the first generation are descended from species 

 (excluding those long cultivated) which have not had 

 their reproductive systems in any way affected, and they 

 are not variable; but hybrids themselves have their re- 

 productive systems seriously affected, and their descend- 

 ants are highly variable." 



According to this view, the variability of the descend- 

 ants of hybrids is a sort of monstrosity, due to the fail- 

 ure of the reproductive organs to perform their proper 

 functions; ordinary variability is not monstrosity, but 

 is perfectly normal, and as the variability of hybrids 



