io8 RETROGRESSION 



magnitude, but which are now shrunken to mere vestiges. Thus 

 in the ostrich the wings are no longer capable of sustaining the 

 animal in flight. In the apteryx they are quite functionless and 

 so rudimentary as to be hidden in the feathers of the body. In 

 the extinct dinornis they had, apparently, disappeared altogether. 

 In most snakes no traces remain of limbs, but in the python the 

 hinder pair are still represented by vestiges. In some species of 

 whales, also, the hinder pair have disappeared ; in others the small 

 remains of them are buried in the body. Man has numerous 

 vestiges of structures which formerly were functional, for example, 

 the hairy covering of his body. 



175. Lamarckians have attributed the retrogression of useless 

 parts to the transmitted effects of disuse. But man, for example, 

 never 'used' the hair of his head more than that of his body; 

 nevertheless the former persists, whereas the latter has become 

 vestigial. However, it is unnecessary to discuss the Lamarckian 

 doctrine here. The reasons which caused us to reject it as an 

 interpretation of progression are valid against it as an interpreta- 

 tion of retrogression. 



176. At first Darwinians attributed retrogression to reversed 

 selection, " the selection which effects not increase of an organ, but 

 decrease of it." They argued that useless structures are worse 

 than useless, they are burdensome ; therefore nature secures their 

 disappearance by eliminating the most burdened individuals. But 

 the evidence is very ample that selection is a cause of racial change 

 only when it is stringent, and a hairy man is not really burdened 

 to an appreciable extent as compared with less hairy men ; at any 

 rate, not to such an extent as to diminish his chances of survival. 

 Again, pythons and whales, which have vestiges of hind limbs, 

 and the apteryx, which has vestiges of fore limbs, are hardly at a 

 disadvantage as compared to species in which retrogression has 

 been complete. A fortiori, individuals of the same species which 

 have vestiges a trifle smaller than their fellows, have on that 

 account no greater chance of survival. Osborn was very right 

 when he declared in reference to this question, " If acquired 

 variations are transmitted, there is some unknown principle in 

 heredity ; if they are not transmitted, there must be some unknown 

 factor in evolution." 



177. Next, Darwinians argued that the struggle for nutriment 

 is very severe, and that useless structures absorbed nutriment and 

 so increased elimination. But useless structures, being inert, 

 especially when composed of a stable tissue like bone, absorb 



