328 HUMAN BIOLOGY 



moderately warm, although probably not tropical. One of 

 the chief arguments for this viewpoint is that the optimum 

 chmate for tropical races, as we have seen, is almost the same 

 as for others. Thus it seems probable that all races, if 

 obhged to Hve with little or no clothing and with unwarmed 

 shelters, would find their optimum where the average tem- 

 perature for the summer does not run much above 75°, and 

 that of winter not much below ^^°, or let us say an extreme 

 range from 80° in the hottest summer month to 50° in the 

 coldest winter month. If such a chmate were blessed with 

 frequent but not too extreme variations of temperature, 

 it would be well-nigh ideal for almost any race which did not 

 have our modern means of protecting itself against the cold. 

 The seacoasts of southern Palestine and northern Florida 

 come close to having such temperatures. But if conditions 

 of this kind really come so near to being the optimum for 

 all races in the primitive state, we are perhaps justified in 

 assuming that they may not be very different from those 

 of the climate in which man originated and in which he 

 became stamped with a climatic relationship which he has 

 never been able to eliminate. 



From some such region then we may suppose that man has 

 spread into regions as hot as the southern end of the Red Sea, 

 as warm and moist as the Amazon Basin, as windy as 

 Tierra del Fuego, as cold and snowy as Greenland, and as 

 mild and even as Hawaii. In each of these places he has 

 become sufficiently acclimated to survive even if he cannot 

 prosper, and yet in each of them he is still far from being 

 perfectly acclimated, for nowhere does he find the perfect 

 optimum. 



This gives us a clue to white acclimatization in the 

 tropics. If mankind is derived from one original stock and 

 yet can live comfortably in so great a variety of climates, 

 there is every reason to believe that the white man might 

 become acclimated in the tropics, provided he subject 

 himself to a sufficiently rigid process of selection. 



The secret of the matter seems to lie in selection. Today 

 the white people who live permanently in tropical countries 

 and especially those who bring up children there are an 

 extremely highly selected group. They themselves may not 



