EVOLUTION 259 



repeat, we are not sure of the import of these finds in terms of the time- 

 appearance of stocks. Two things must be borne in mind: first, the finds 

 are random and inconclusive because we do not have sufficient numbers 

 to know range of variation; second, the characters commonly diagnostic 

 of stock or race are those of soft parts not preserved in the fossil record. 



If stocks, or sub-species, be of doubtful origin, how about races, or 

 varieties? Here we are more in the dark than ever. We can answer only 

 that Mediterranean-type crania are found well defined by the opening of 

 the Neolithic, about 10,000-15,000 years ago; Nordic-type crania are re- 

 ported in the Swedish Neolithic. The time element in stock and race emer- 

 gence is approximate, nothing more. 



Now that we have considered when they arose, let us take up how they 

 arose. One of the most intriguing theories is that of Sir Arthur Keith,^ 

 who feels that the endocrines may have played a role: "The transforma- 

 tion of man and ape ... is determined by a common growth-controlling 

 mechanism which is residual in a system of small but complex glandular 

 organs." As Keith surveys the role of the pituitary in acromegaly, the 

 thyroid in achondroplasia, the adrenals in pigmentation, the gonads in 

 secondary sex characters, he sees analogies with certain statural, osteologic, 

 cranio-facial, skin conditions in the stocks of mankind; e. g., the big-boned, 

 rugged-skulled Caucasoid shows a possible pituitary dominance; the flat- 

 faced Mongoloid shows a possible thyroid dominance; the dark-skinned 

 Negroid shows a possible adrenal dominance.*^ Keith offers these endocrine 

 associations more as suggestions than as absolute statements. They un- 

 doubtedly exist as factors, but to-day we recognize the endocrines as so 

 complex, so interrelated, that any statement of uniglandular dominance 

 must be taken with tremendous reserve. The exact role of the endocrines 

 in human evolution and in the appearance of stocks and of races is in the 

 realm of conjecture. 



In our present knowledge of human evolution we assume that sometime, 

 somewhere, there existed a generalized proto-human or hominid species 

 that had, potentially at least, all of the morphological characters found 

 to-day in all of mankind. This species must have been genetically fairly 

 homogeneous, though probably inherently variable. 



From this species there arose through mutation, recombination, selec- 

 tion, migration and isolation, the stocks and races as we now recognize 

 them. 



The third "don't" resides in the inadequacy of our knowledge con- 

 cerning heredity in Man. Specifically, we do not know the precise mecha- 

 nism \\hereby traits diagnostic of stock and race are transmitted. 



* A. Keith, "The Differentiation of Mankind into Racial Types," Ann. Rep. 

 Smith. Inst., pp. 443-53. Washington, D.C., 1921. 



5 About 1775 John Hunter concluded that the original skin color of Man was Black, 

 and in 192 1 Keith reaffirmed that statement. 



