GENETIC ADAPTATIONS TO THE ENVIRONMENT 



Figure XI — 1 —DISTRIBUTION OF THE YANOMAMA INDIANS IN SOUTH AMERICA 



proven, require some adaptiv: 

 ferences in the skin-color genotypes 

 in various environments to explain 

 them. The physiological basis of 

 this selection has not been demon- 

 strated, but there is still no other 

 reasonable explanation in genetic 

 theory for these differences. The 

 fact that skin color seemed to be a 

 climatic adaptation may have given 

 rise to the idea that there must be 

 many more climatic adaptations in 

 man. At first it was hypothesized 

 that gross structural differences may 

 exist; but studies have shown that 

 the number of eccrine sweat glands 

 as well as the number of melanocytes 

 are about the same, and their dis- 

 tribution on the body is also the same 

 in all groups of men. 



The small map shows the general location of the Yanomama Indians. The large 

 map shows the detailed location of their villages. Two villages located near the 

 Venezuelan-Brazilian border are those from which blood samples for the cytogenetic 

 studies were obtained. 



Although human structures and 

 basic responses to climatic stresses 

 are about the same everywhere, many 

 physiological studies have shown dif- 



Figure XI-2 — CYTOGENETIC FINDINGS IN 49 YANOMAMA INDIANS FROM TWO VILLAGES IN VENEZUELA 



The table shows cytogenetic differences between some Yanomama Indians and 

 several control populations. The data are compatible, since the same culture 

 methods were used except that the Japanese control cultures were not delayed in 

 the initiation of the 72-hour cultures. Complex cells include those with multiple, 

 exchange-type aberrations. 



375 



