190 Crossing the North and South African Ostrich 



descended from a common parent, it might be expected that they would 

 occasionally vary in an analogous manner." All the parts of the germ 

 plasm may be held to be the same for any " pure " species ; some parts 

 are changed and give us the distinctions between species ; other parts 

 diflfer in producing generic separations, and still more fundamental parts 

 in giving ordinal, class and phylar distinctions; but corresponding 

 changes may take place in the germ plasm which remains common to 

 phylum, class, order or genus and so give rise to parallel mutations, the 

 Analogous Evolution of Prof. H. F. Osborn^, while divergent changes in 

 the common germ plasm would produce Polyphyletic Evolution. In the 

 ostrich specific changes have taken place, and others embracing the 

 genus are in progress. 



Adaptive Value of Changes. We may briefly consider whether the 

 changes set up in the germ plasm, and expressing themselves in the soma, 

 have any adaptive significance in the life of the ostrich. Following 

 largely the teachings of Bateson and Morgan, few writers now are pre- 

 pared to admit that germinal changes are a response to external environ- 

 mental influences, or have appeared in response to some need of the 

 organism, or have necessarily some selection value; rather it is held 

 that they are dependent upon some intrinsic cause which may vary in 

 different cases. Though we may not know much as to the conditions 

 under which the changes are brought about till oncie effected and 

 manifested in the body, we may discuss the question of their utility or 

 otherwise to the individual and their influence on the evolution of the 

 race. 



The bald head patch on the northern ostrich is probably as neutral 

 in its effect on the bird as it is possible for any character to be ; it is 

 impossible to think of it as exerting any beneficial or harmful influence 

 compared with the feathered condition in the southern bird. Both races 

 are equally successful. It should probably be regarded as the first step 

 in the loss of the head covering, thus introducing plumage degeneration 

 to this region of the bird, following upon losses which have already been 

 effected over the legs, wings and body and which are presumably still 

 in progress. In this case the baldness raises the whole question of the 

 adaptive significance of the loss of plumage going on in the ostrich, only 

 the bare facts of which can now be noticed. In chicks the outer surface 

 of the leg, from the knee joint to the ankle, is well covered with feathers 

 which practically all drop out before maturity is reached. The under 



1 H. F. Osborn, The Age of Mammals, Macmillan and Co., 1910, pp. 29—34. 



