368 ANNUAL KEPOET SMITHSONIAN INSTITUTION, 1915. 



lation of small differences. Such small differences are often mere 

 ephemeral effects of conditions of life, and as such are not trans- 

 missible ; but even small differences, when truly genetic, are factorial 

 like the larger ones, and there is not the slightest reason for supposing 

 that they are capable of summation. As to the origin or source of 

 these positive separable factors, v>^e are without any indication or 

 surmise. By their effects we know them to be definite, as definite, say, 

 as the organisms which produce diseases; but how they arise and how 

 they come to take part in the composition of the living creature so 

 that when present they are treated in cell-division as constituents of 

 the germs, we can not conjecture. 



It was a commonplace of evolutionary theory that at least the 

 domestic animals have been developed from a few wild types. Their 

 origin was supposed to present no difficulty. The various races of 

 fowl, for instance, all came from Gallus hanhiva^ the Indian jungle 

 fowl. So we are taught; but try to reconstruct the steps in their 

 evolution and you realize your hopeless ignorance. To be sure there 

 are breeds, such as Black-red Game and Brown Leghorns, which have 

 the colors of the jungle fowl, though they differ in shape and other 

 respects. As we know so little as yet of the genetics of shape, let us 

 assume that those transitions could be got over. Suppose, further, as 

 is probable, that the absence of the maternal instinct in the Leghorn 

 is due to loss of one factor which the jungle fowl possesses. So far 

 we are on fairly safe ground. But how about AVhite Leghorns? 

 Their origin may seem easy to imagine, since white varieties have 

 often arisen in well-authenticated cases. But the white of White 

 Leghorns is not, as white in nature often is, due to the loss of the 

 color elements, but to the action of something wdiich inhibits their 

 expression. Whence did that something come? The same question 

 may be asked respecting the heavy breeds, such as Malays or Indian 

 Game. Each of these is a separate introduction from the East. To 

 suppose that these, with their peculiar combs and close feathering, 

 could have been developed from preexisting European breeds is very 

 difficult. On the other hand, there is no wild species now living any 

 more like them. We may, of course, postulate that there was once 

 such a species, now lost. That is quite conceivable, though the sug- 

 gestion is purely speculative. I might thus go through the list of 

 domesticated animals and plants of ancient origin and again and 

 again we should be driven to this suggestion, that many of their 

 distinctive characters must have been derived from some wild origi- 

 nal now lost. Indeed, to this unsatisfying conclusion almost every 

 careful writer on such subjects is now reduced. If we turn to modern 

 evidence the case looks even worse. The new breeds of domestic 

 animals made in recent times are the carefully selected products of 

 recombination of preexisting breeds. Most of the new varieties of 



