MUTATIONS AND EVOLUTION. 305 



in the southern birds instead of more uniformly oAer the sur- 

 face, as in nortliern birds, can hardly be held to represent the 

 slightest advantage one way or another. Whether the shell is 

 pitted or smooth may possibly be thought to influence the respira- 

 tion of the chick within, but not the slightest evidence of this is 

 forthcoming. The northern and the southern races are equally 

 successful, and no differences in the number or strength of the 

 chicks at hatching are observable. The distinctive skin colours 

 of the two are only conspicuous at the nuptial period, and in 

 comparison with the strong plumage contrasts in the ostrich can 

 certainly not be held to possess any adaptive significance. Whether 

 regarded as specific or varietal, the characters seem to have 

 arisen independently in separate continental areas, and are quite 

 apart from any considerations connected with the welfare of the 

 bird. Appearing in an established race, the necessary germinal 

 changes must have recurred as often as there are individuals con- 

 cerned, for. having no selection value, the new characters could 

 not otherwise have replaced the original characters. The mutual 

 fertility of the two races indicates that physiological isolation can 

 have had no influence : geographical isolation has been main- 

 tained as far as concerns the more extreme parts of the continent, 

 yet has had no influence in bringing about the changes, but only 

 in preventing intermingling. 



For a dominant repetition of similar mutations to occur it 

 is manifest that the germinal changes involved must be removed 

 from the realm of occurrences which are altogether fortuitous or 

 incidental. They must be the result of some intrinsic condition 

 common to the germ plasm of the one race as compared with that 

 of the other, or of some uniform influence acting upon it. That 

 germinal changes are ever of a regular recurrent nature is. how- 

 ever, a view wholly averse from that of mutationists of the pre- 

 sent day. As indicated by the introductory quotation from Prof. 

 Bateson, mutations everywhere seem to be regarded as fortuitous 

 and isolated, dependent upon irregularities in the mitotic pro- 

 cesses which occur between one generation and the next. Yet 

 there appears no escape from the conclusion that the recurrent 

 process must have been largely concerned in the establishment 

 of specific characters generally, if we are to accept the view 

 that most new characters are intrinsic in their origin, are rarely 

 concerned with the welfare of the organism, and are the concern 

 of natural selection only as regards elimination, conclusions which 

 seem to find full confirmation in the ostrich. 



In a paper entitled " The Form of Evolutionary Theory that 

 Modern Genetical Research seems to favour," Dr. C. B. Daven- 

 port* develops the idea, already expressed by Hagedoorn, Lotsy 

 and Bateson, that mutative changes are largely the result of the 

 fractionation of highly complex molecules into simpler, deriving 

 support for it from palceontolog}'^ and experimental breeding, and, 



* "Amer. Nat.," vol. L, Aug., 1916. 

 c 



