THE REPRODUCTIVE FACTOR IN EVOLUTION.' 3rT 



prevision of future advantage in remaining clubbed together in 

 co-operation, nor indeed credited with much primitive altruism 

 in so doing. None the less is it clear, that this greatest of 

 morphological steps was directly due, not to any struggle, 

 but rather to an organic sociality, or at any rate to a process 

 which is not interpretable in terms of individual advantage. 



No structure is more emphatically nutritive in its adult 

 result than the gut-cavity of the embryonic gastrula. It is 

 worth inquiring whether this important step in differentiation 

 was attained in history in response to nutritive needs. The 

 usual supposition is certainly that the gastrula cavity, by what- 

 ever peculiarities of growth it may have arisen, justified itself 

 from the first in an additional nutritive advantage. But 

 Salensky, in his studies on the primitive form of the Metazoa, 

 has given strong arguments in favour of the theory that the 

 primitive cavity, arising in a volvox-like form, was originally a 

 brood-cavity or "genitoccel," and that it only secondarilyacquired 

 nutritive significance. It would be indeed striking if this 

 important morphological step in the establishment of the 

 nutritive system was reached along the road of reproductive 

 modification ; for if this most fundamental of nutritive and 

 self-maintaining advantages, the belly itself, be but a secondary 

 resultant of an originally reproductive and species-regarding 

 progress, that lower Utilitarianism, which has so long been 

 arguing from economics to biology and back again, is evidently 

 a step nearer exposure. 



Or again, that increase of reproductive sacrifice, which at 

 once makes the mammal and marks its essential stages of 

 further progress through oviparous monotreme, prematurely- 

 bearing marsupial, and various grades of placental ; that 

 increase of parental care ; that frequent appearance of sociality 

 or co-operation, which even in its rudest forms so surely 

 secures the success of the species attaining it, be it mammal or 

 bird, insect or even worm, — all these phenomena of survival of 

 the truly fittest, through love, sacrifice, and co-operation, 

 need far other prominence than they could possibly receive on 

 the hypothesis of the essential progress of the species through 

 internecine struggle of its individuals at the margin of subsist- 

 ence. Each of the greater steps of progress is in fact associated 

 with an increased measure of subordination of individual com- 

 petition to reproductive or social ends, and of interspecific 

 competition to co-operative association. 



