286 THE EVOLUTION OF SEX. 



is a process of disintegration, and is thus essentially opposed to that process 

 of integration which is one element of individual evolution. The matter 

 and energ}^ supplied for the young organism represent so much loss for 

 the parent ; while, conversely, the larger the amount of matter and energy 

 consumed by the functional actions of the parent, the less must be the 

 amount remaining for those of the offspring. The disintegration which 

 constitutes genesis may be complete or partial, and in the latter case the 

 parent, ha\"ing reached considerable bulk and complexity before reproduc- 

 tion sets in, may sur\-ive the process. In the same way, individual evolution 

 may be expressed in bulk, in structure, in amount or variety of action, or in 

 combinations of these ; yet, in any case, this progress of each individuality 

 must correspondingly retard the establishment of the new ones. 



While in the first portion of the argument, then, it was shown that a 

 species cannot be maintained unless self-preservative and reproductive 

 power vary inversel}', it is now evident that, irrespective of an end to be 

 subserved; these powers cannot do other than vary inversely, and the one 

 a priori principle is thus seen to be the obverse of the other. And if we 

 group under the term individuation all those race-preser\-ative processes by 

 which individual life is completed and maintained, and extend the term 

 genesis to include all those processes aiding the formation and perfecting of 

 new individuals, the result of the whole argument may be tersely expressed 

 in the formula, — Individuation and Genesis vaiy inversely. And from this 

 conception important corollaries open ; thus, other things equal, advancing 

 evolution must be accompanied by declining fertility ; again, if the diffi- 

 culties of self-preservation permanently diminish, there will be a permanent 

 increase in the rate of multiplication, and conversely. 



In attempting the inductive verification of these a priori inferences, 

 practical difiiculties arise, owing to the high complexity of each of our two 

 sets of factors and the independent variability of their details, and thus the 

 total cost of individuation and of genesis alike is hard of estimation and 

 comparison. For this purpose, however, there are successively to be in- 

 vestigated, — (i) the antagonism between growth and genesis, sexual and 

 asexual ; (2) that between development and genesis ; (3) that between ex- 

 penditure and genesis ; and (4) the coincidence between high nutrition and 

 genesis. It is impossible to summarise the wealth of evidence drawn from 

 a wide survey of the animal and vegetable world contained in the chapters 

 devoted to those various heads, but attention may be called to the last and 

 most obscure of these. It is indeed evident a priori that, if the cost of 

 individuation be once provided for, a higher nutrition will render possible 

 a greater propagation, sexual or asexual, and this may be abundantly veri- 

 fied by obser.-ation and experiment. "Witness the case of aphides, in which 

 the rate of parthenogenetic reproduction is found to be directly proportional 

 to temperature and food-supply; or, again, that of domestic animals, such as 

 the sheep, whose fertility is in direct relation to richness of pasture and 

 warmth of climate ; or, finally, and most obviously of all, that of field or 

 fruit crops, upon which the influence of increased liberality of manuring 

 will not be disputed. Yet it is sometimes maintained, for both plants and 

 animals, that overfeeding checks increase, while lim.ited nutriment stimu- 

 lates it ; and to support this view there are cited such cases as that of the 

 barrenness of a very luxuriant plant, and the fruitfulness which appears on 

 its depletion. But if this objection really held, manuring would in all cases 

 be inexpedient, instead of only in plants where the growth of sexless axes 



