270 THE RATE OF GROWTH [ch. 



is not to originate* but to remove: donee ad interitum 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 hmited 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 hfe may be changed, and many a refuge found, before 

 the sentence of unfitness is pronounced and the penalty of exter- 

 mination paid. But there comes a time when "variation," in form, 

 dimensions, or other qualities of the organism, goes further 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 Hmits which, as again 

 Lucretius tells us, natural law has set between what may and what 

 may not be, 



et quid quaeque queant per foedera natural 

 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 is not 

 to create but to destroy — to weed, to prune, to cut down and to 

 cast into the fire J. 



* So said Yves Delage {UherediU, 1903, p. 397): "La selection naturelle est un 

 principe admirable et parfaitement juste. Tout le monde est d'accord sur ce point. 

 Mais ou Ton n'est pas d'accord, c'est sur la limite de sa puissance et sur la question 

 de savoir si elle pent engendrer des formes specifiques nouvelles. II semble bien 

 demontre aujourd'hui qu'elle ne le pent pas.'' 



t Lucret. v, 875, "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. 



X Even after we have so narrowed its scope and sphere, natural selection is 

 still a hard saying ; for the causes of extinction are wellnigh as hard to understand 

 as are those of the origin of species. If we assert (as has been lightly and too 



