THE EFFECT UPON HUMAN EVOLUTION 277 



and offense. Yet no matter how closely he is like them and they 

 like him, he differs and varies, they differ and vary, with a sort 

 of mutual forgiveness, because the amount of resemblance over- 

 tops the degree of variation. In a paper on the "Rediscovery of 

 the Unique," H. G. Wells emphasized the unique quality of the 

 individual, and how, in spite of the cleverest devices of classifica- 

 tion, living things ultimately escaped the classifying net by virtue 

 of their tendency forever to vary. 



The individual is unique. Yet when all is said and done, the 

 fact remains that between individuals there is resemblance, and 

 among them variation. What is the reason for their resemblances 

 and what is the cause of their variation? 



The conception of a particular chemical make-up of the indi- 

 vidual, statable and relatively controllable in terms of the internal 

 secretions, supplies a more rational and satisfactory method of 

 approach to the problem than any so far suggested as far as 

 vertebrates are concerned at any rate. In effect, the differences 

 between individuals may fundamentally thus be grouped among 

 the differences which distinguish other chemical substances. The 

 difference between water, technically known as hydrogen monox- 

 ide, and the antiseptic fluid labeled hydrogen dioxide lies wholly 

 in the possession by the latter of an extra atom of oxygen in its 

 molecules. All the peculiarities and qualities by which hydrogen 

 peroxide is separated from water are referred to that additional 

 quantum of oxygen. So the diversity of constitution and appear- 

 ance of two brothers, alike in that they have inherited the same 

 internal secretion trends, may be traced to the superiority of the 

 pituitary of the one over the other. 



Variation and resemblance are large issues, crucial material 

 of the science of biology upon which much has been thought and 

 written. That the proportion of the endocrines determines varia- 

 tion and resemblance, heredity and evolution is a hypothesis ad- 

 vanced, supported by a large amount of facts, and capable of the 

 most interesting experimental verification and observation. If a 

 child resembles particularly either of its parents, grandparents 

 or relatives, there is good reason for believing that it is because 

 their endocrine formulas are very much alike. When people 

 apparently not blood-related at all resemble one other, the same 

 law must hold. Resemblances may be partial or complete, and 

 the degree will depend upon the amount and ratio of the internal 

 secretions involved. 



The same endocrine constitutions will produce corresponding 



