512 Edward Livingston Youmans. 



in 1859 in the Medico-Chirurgical Review, it was in the 

 autumn of 1851, during a country ramble with Mr. George 

 Henry Lewes, that the germinal idea of that essay was 

 reached. This idea, that the forms of organisms, in re- 

 spect of the different kinds of their symmetry and asym- 

 metry, are caused by their different relations to surround- 

 ing incident forces, implies a general recognition of the 

 doctrine of Evolution, a further extension of the doctrine 

 of adaptation, and a foreshadowing of the theory of life 

 as a correspondence between inner and outer actions. 



In 1852 Mr. Spencer published in the Westminster 

 Review the Theory of Population deduced from the Gen- 

 eral Law of Animal Fertility, setting forth an important 

 principle which he says that he had entertained as far back 

 as 1847. Here also the general belief in Evolution was 

 tacitly expressed ; the theory being that, in proportion 

 as the power of maintaining individual life is small, the 

 power of multiplication is great ; that along with increased 

 evolution of the individual there goes decreased power of 

 reproduction ; that the one change is the cause of the 

 other ; that in man, as in all other creatures, the advance 

 toward a higher type will be accompanied by a decrease of 

 fertility ; and that there will be eventually reached an ap- 

 proximate equilibrium between the rate of mortality and 

 the rate of multiplication. Toward the close of this argu- 

 ment there is a clear recognition of the important fact that 

 excessive multiplication and the consequent struggle for 

 existence cause this advance to a higher type. It is there 

 argued that " only those who do advance under it even- 

 tually survive" and that these " must be the select of their 

 generation." That which, as he subsequently stated in the 

 Principles of Biology, Mr. Spencer failed to recognize at 

 this time (1852) was the effect of these influences in pro- 

 ducing the diwrsities of living forms ; that is, he did not then 

 perceive the co-operation of these actions of the struggle 



