192 Crossing the North and South African Ostrich 



just as the loss of the first, second and fifth toes has for long conferred 

 a mechanical advantage by transferring practically the whole of the leg 

 movements directly to the big middle toe. If however the degenerative 

 forces are so relentless as they appear to be and should next begin to 

 attack the big toe there could then be no question of the ultimate 

 influence of the genetic changes upon the well-being of the bird, for 

 with the loss of all its toes it is inconceivable that the extinction of the 

 ostrich would not be imminent. While the losses of the scales in the 

 case of the single break on the middle toe and the still rarer double 

 break are deemed to be the first steps in this direction, it is conceivable 

 that they are for the time being advantageous in the flexions and ex- 

 tensions of the toe. 



On the whole then no evidence is forthcoming that the differences 

 between the northern and the southern ostrich have arisen because of 

 any direct utilitarian consideration; and the same can be said of the 

 retrogressive changes common to both. Having appeared, they may 

 come to have an adaptive value ; but even for this there is no support 

 except perhaps as regards the loss of the toes. On the other hand there 

 is much to indicate that, if the degenerative losses continue in the various 

 directions already initiated, we may look forward in the dim future to 

 the sad spectacle of a wingless, legless and featherless ostrich, if ex- 

 tinction does not supervene. 



As already remarked it is impossible to resist the conviction that we 

 have in the ostrich some intrinsic influence, slow but continuous in its 

 action, which is bringing about the gradual loss in piecemeal fashion of 

 the various parts of the wing and the legs as well as of the plumage, 

 wholly irrespective of external influences or adaptive considerations. 

 The losses are separate mutative changes so far as the individual is con- 

 cerned, yet the result for the race is continuous, determinate degeneration 

 along several directions. If, as seems to be the case, the losses hitherto 

 have no adaptive value, then natural selection is in no ways concerned 

 with them, though it will become operative when degeneration has 

 proceeded so far as to interfere with the ordinary activities of the bird. 

 Some adaptive value may be ascribed to the loss of the three toes from 

 the foot, and also to that of the fourth which is in progress, yet it could 

 hardly be conceded when, the same degenerative tendency continuing, 

 the only remaining toe is attacked. It is manifest that an evolutionary 

 change may be advantageous up to a certain point but disastrous when 

 continued beyond. 



The Nagelian idea that evolutionary changes have taken place as 



