Ill] GEOWTH AND CATALYTIC ACTION 137 



all but sudden appearance on the earth of such exaggerated and 

 almost monstrous forms as those of the great secondary reptiles 

 and the great tertiary mammals*. We begin to see that it is in 

 order to account, not for the appearance, but for the disappearance 

 of such forms as these that natural selection must be invoked. 

 And we then, I think, draw near to the conclusion that what is 

 true of these is universally true, and that the great function of 

 natural selection is not to originate, but to remove : donee ad 

 inter itum genus id natura redegitf. 



The world of things living, like the world of things inanimate, 

 grows of itself, and pursues its ceaseless course of creative evolution. 

 It has room, wide but not unbounded, for variety of living form 

 and structure, as these tend towards their seemingly endless, but 

 yet strictly limited, possibilities of permutation and degree : it 

 has room for the great and for the small, room for the weak and 

 for the strong; Environment and circumstance do not always 

 make a prison, wherein perforce the organism must either live 

 or die ; for the ways of life may be changed, and many a refuge 

 found, before the sentence of unfitness is pronounced and the 

 penalty of extermination paid. But there comes a time when 

 "variation," in form, dimensions, or other qualities of the organism, 

 goes farther than is compatible with all the means at hand of 

 health and welfare for the individual and the stock ; when, under 

 the active and creative stimulus of forces from within and from 

 without, the active and creative energies of growth pass the 

 bounds of physical and physiological equilibrium : and so reach 

 the limits which, as again Lucretius tells us, natural law has set 

 between what may and what may not be, 



"et quid quaeque queant per foedera naturai 

 quid porro nequeant." 

 Then, at last, we are entitled to use the customary metaphor, 

 and to see in natural selection an inexorable force, whose function 



* Cf. Dendy, Evolutionary Biology, 1912, p. 408; Brit. Ass. Report (Portsmouth), 

 1911, p. 278. 



I Lucret. v, 877. "Lucretius nowhere seems to recognise the possibility of 

 improvement or change of species by 'natural selection'; the animals remain as 

 they were at the first, except that the weaker and more useless kinds have been 

 crushed out. Hence he stands in marked contrast with modern evolutionists." 

 Kelsey's note, ad loc. 



