August 28, 1914] 



SCIENCE 



295 



The appearance of contemporary vari- 

 ability proves to be an illusion. Variation 

 from step to step in the series must occur 

 either by the addition or by the loss of a 

 factor. Now, of the origin of new forms 

 hy loss there seems to me to be fairly clear 

 evidence, but of the contemporary acquisi- 

 tion of any new factor I see no satisfactory 

 proof, though I admit there are rare ex- 

 amples which may be so interpreted. We 

 are left with a picture of variation utterly 

 different from that which we saw at first. 

 Variation now stands out as a definite 

 physiological event. We have done with 

 the notion that Darwin came latterly to 

 favor, that large differences can arise by 

 accumulation of small differences. Such 

 small differences are often mere ephemeral 

 effects of conditions of life, and as such 

 are not transmissible ; but even small differ- 

 ences, when truly genetic, are factorial like 

 the larger ones, and there is not the slight- 

 est reason for supposing that they are 

 capable of summation. As to the origin or 

 source of these positive separable factors, 

 we 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 composi- 

 tion of the living creature so that when 

 present they are treated in cell-division as 

 constituents of the germs, we can not con- 

 jecture. 



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 hankiva, the 

 Indian jungle-fowl. So we are taught ; but 

 try to reconstruct the steps in their evolu- 

 tion and you realize your hopeless ignor- 

 ance. 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 re- 

 spects. 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 White 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-ele- 

 ments, but to the action of something which 

 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. .1 might thus 

 go through the list of domesticated animals 

 and plants of ancient origin and again and 

 again we should be driven to this sugges- 

 tion, that many of their distinctive char- 

 acters must have been derived from some 

 wild original now lost. Indeed, to this un- 

 satisfying conclusion almost every careful 

 writer on such subjects is now reduced. 

 If we turn to modem evidence the case 

 looks even worse. The new breeds of do- 

 mestic animals made in recent times are the 

 carefully selected products of recombina- 

 tion of preexisting breeds. Most of the new 

 varieties of cultivated plants are the out- 

 come of deliberate crossing. There is gen- 



