LATENCY AND RETROGRESSION 113 



important adaptation. But before discussing this matter it will 

 be well to inquire more closely into the exact nature of progressive 

 and retrogressive variations on which all racial change depends. 



185. We have seen that, since the child recapitulates, with varia- 

 tions, the development of the parent, he must necessarily recapitu- 

 late, with inaccuracies, with additions and subtractions, the life- 

 history of the race. Whence it follows that a progressive variation 

 implies a complete recapitulation (as regards the character affected) 

 of the life-history as presented by the parent, plus an addition ; 

 whereas a retrogressive variation implies an incomplete recapitulation 

 of the parental development, and therefore a reversion to the stage of 

 development reached by some progenitor more remote than the 

 parent. There is really no escape from these conclusions ; for grant- 

 ing the undisputed fact that the child recapitulates the development 

 of the parent, other conclusions are actually, literally, unthinkable. 



1 86. The reader, however, must be very careful not to confuse 

 latency with retrogression. Latency implies, not the loss of a 

 capacity to develop in this or that direction, but only its inactivity. 

 We shall see later 1 that it occurs when two rival hereditary tend- 

 encies are present in the germ-plasm, one of which becomes 

 dormant while the other directs the development of the individual. 

 Thus colour-blindness and haemophilia, which are commonly 

 restricted to males, tend to be transmitted in a latent condition 

 through daughters to grandsons. All the sexual characters, 

 primary and secondary, are latent in individuals of the opposite 

 sex. Thus the daughters of heavily bearded men tend to have 

 heavily bearded sons. Male aphides are absent during the summer 

 months, and reproduction, therefore, is parthenogenetic, but at the 

 end of the warm season males are produced, which fertilize the 

 winter eggs. Amongst honey bees also the reproduction of drones 

 is parthenogenetic. Male characters, therefore, are latent in the 

 germ-plasm of the females. " It is well known that a large number 

 of female birds, such as fowls, various pheasants, partridges, 

 pea-hens, ducks, etc., when old or diseased or when operated on, 

 assume many or all of the secondary male characters of their 

 species. In the case of the hen pheasant this has been observed 

 to occur far more frequently during certain years than during 

 others. A duck ten years old has been known to assume both the 

 perfect winter and summer plumage of the drake. Waterton gives 

 a curious case of a hen which had ceased laying, and had assumed 

 the plumage, voice, spurs, and warlike disposition of the cock ; 



1 See chapter vii. 

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