An Introduction to a Biology 



total possible number of combinations occurs when the first 

 crosses are mated together and in no other way. Suppose 

 the cross between the Black Hamburgh and the White Le^r- 

 horn had been made with a view to get a black fowl with a 

 single comb, nothing could have been more disappointing 

 than the first cross — a white fowl with a rose-comb, a fowl 

 which exhibits neither of the characters it was wished to 

 combine. What the breeder would probably do under such 

 circumstances would be to mate the hybrid back with one 

 of the parents " to put in some more of the required blood." 

 The last thing he would have dreamt of doing would be to 

 mate together his two first crosses, which showed neither 

 of the two characters he wished to combine. Yet this is 

 the only mating which would give him the desired combina- 

 tion — black plumage with single comb. The reason that 

 he would not think of mating together the two first crosses 

 is that he was under the influence of the old error of regard- 

 ing the visible bodily characters of an individual as an indi- 

 cation of its breeding properties. And the reason why he 

 would mate the first cross back with one of the parent forms 

 would be the same. But the fact is that, especially in the 

 case of hybrids, the appearance of the animal gives no clue 

 whatsoever as to what it is likely to produce. And matters 

 are often much worse than in the case of poultry which we 

 have described. The hybrid very often, as is well known, 

 does not, as in the case just described, exhibit the characters 

 of either of the parents, but of some supposed remote wild 

 ancestor. Nothing could be more disappointing than the 

 production of such a scarecrow by crossing two valuable 

 animals of two dillerent sorts ; and nothing is more certain 

 than that the breeder would not breed more of them in order 

 to obtain a male and a female to mate together. Never- 

 theless, this is what, according to the Mendelian doctrine, 

 he ought most unquestionably to do. Indeed, I would even 

 go so far as to suggest this possibility, that the less the first 

 cross approximates to the result which the breeder expected 



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