IX.] RETROGRESSIVE DEVELOPMENT IN NATURE. 21 



ever, entirely disposed of by a fact which admits of no dispute 

 and cannot be explained away, viz. the fact tJiat the worker's of 

 ants are infertile^ and do not propagate their species. Consequently, 

 it is impossible that the degeneration caused by disuse during 

 individual lives should be handed down, and the elimination of 

 the wings is only explicable on the other theory, which ascribes 

 it to the cessation of the operation of natural selection which 

 ensued when the wings became useless and of no importance. 

 It may certainly be objected that the disappearance of the wings 

 might have taken place before the workers became infertile; 

 but such a supposition cannot be accepted, for reasons which I 

 need not enter upon here. The infertility of workers may also 

 be regarded as a difficulty from my point of view, but it must 

 be remembered that the principle of the ehmination of the un- 

 fittest does not act directly on the workers, but on their parents, 

 the propagators of the species. In other words, natural selec- 

 tion does not affect the workers themselves, but the parents, 

 and determines their survival according as they produce perfect 

 or imperfect workers. 



The process by which the degeneration of superfluous organs 

 takes place may fittingly be called 'universal crossing' (Pan- 

 mixia), because it implies that not those individuals only in 

 which any particular organ is best developed survive and 

 propagate their species, but that survival is quite independent 

 of the efficiency or non-efficiency of the organ. This process 

 of Panmixia must have had, and must have still great influence 

 on the development of the organic world. The changes 

 wrought by evolution have been and are innumerable, and 

 they by no means always occur in an upward direction, but 

 often — as shown in the case of the parasites — in a downward 

 one, or perhaps most frequently in both directions at once, the 

 change being retrogressive in one part and progressive in 

 another. And very often the former change may actually lead 

 to the latter. We ourselves could hardly have attained so high 

 a degree of intellectual development, had we not forfeited a 

 considerable share of the physical advantages possessed by our 

 remote ancestors. The savage tribes which depend upon the 

 chase, are gifted with a much keener sense of hearing, smell, 

 and sight than we are, and this is not merely the result of 

 constant training, but is also due to the inheritance of more 



