GERMINAL SELECTION 455 



struggle between rival organisations and rival institutions, and 

 no one doubts the reality of an intrasocietary selection. This, 

 again, is more complex than the ordinary personal or individual 

 selection. 



" Personal " Selection. — Of personal or individual struggle 

 there are many forms and phases, notably (a) the competition 

 between fellows of the same kin for food and foothold, which 

 is not self-regarding only, but for the sake of mates and family 

 as well ; (b) the opposition between foes of quite different kin — 

 e.g. between birds of prey and small mammals ; and (c) the 

 struggle between organisms and the changeful inanimate en : 

 vironment. Besides these three main forms there are many 

 special cases, such as the battles between males of the same 

 species for the possession of females, as in the case of seals and 

 stags, and the sometimes serious disagreements between mates, 

 so quaintly illustrated in some spiders. Corresponding to these 

 different forms of struggle there are different modes of selection 

 and elimination. 



Intra- organismal Selection. — In 1881 Roux introduced the 

 idea of a struggle of parts within the organism. He pointed out 

 that functional stimulus tends to strengthen an organ, that 

 there is a " quantitative self-regulation of an organ according 

 to the strength of the stimulus supplied to it." It may be 

 over-compensated for its expenses, and grow, just as the opposite 

 conditions may lead to atrophy. It is well known that if all 

 the work of renal excretion be thrown on one kidney, that 

 organ increases greatly in size, and that if the nerve to a muscle 

 or gland be cut, that muscle or gland begins to degenerate. If 

 we pursue this line of thought we begin to realise what is meant 

 by a struggle of parts within the organism, r and by intra-organ- 

 ismal selection. Some change occurs in the conditions of nutri- 

 tive and other stimuli ; there are limitations affecting the 

 nutritive supply, the amount of available space, and so on ; 

 and there has to be an internal give and take, a mutual re- 



