VARIED RESULTS OF CROSSING 387 



species " are rare is erroneous ; for, apart from the familiar mules, 

 fertile pairing is known between lion and tiger, dog and jackal, 

 wild and domestic cat, brown bear and polar bear, American 

 bison and European wild ox, horse and zebra, hare and rabbit, 

 duck and goose, canary and finch, thrush and blackbird, caper- 

 caillie and blackcock, carrion crow and hooded crow, pheasant 

 and fowl, and the list soon becomes very long if we include 

 backboneless animals and plants (see Evolution of Sex, revised 

 ed., 1901, p. 163). 



The popular impression that fertile crosses between "distinct 

 species " result invariably in sterile offspring is also erroneous ; 

 for the hybrids of American bison and European wild ox, of 

 Indian humped cattle and domesticated ox, of common goose 

 and Chinese goose, of common duck and pintail duck, of different 

 kinds of pheasants, and many more are certainly fertile. 



At the same time, the general statement may be safely made 

 that successful crossing and the fertility of the hybrid offspring 

 is in inverse proportion to the distinctness of the species crossed. 

 It seems also safe to say that the characters of species-hybrids 

 do not conform to any general formula. They may be a blend 

 of the parental characters, they may be exclusive or particulate, 

 they maybe reversionary — i.e. allowing expression of long-latent 

 ancestral characters — or they may be novel and peculiar. 



On the whole, the crossing of distinct species, while it may 

 be interesting physiologically, does not seem to have much 

 interest for the evolutionist. It does now and then occur in 

 nature, but it seems to be a mere by-play of little phylogenetic 

 importance — unless perhaps in very early days, of which we 

 know nothing. 



Diverse Results of Hybridising. — An inheritance is such a.. 

 complex integrate of items that no one can hope to predict 

 the result of mingling two more or less distinct inheritances. 

 We have two organisms, A and B, which can be crossed and 

 produce offspring : but, before the germ-cells of A and B are 



