MATTHEW, CLIMATE AND EVOLUTION 211 



In Africa, the region north of the Sahara has been overrun by succes- 

 sively higher types from the east. The great desert was a barrier to 

 southward migration, being pierced only by the narrow strip of the Nile 

 valley, from whose head spread out the successive populations of central 

 and southern Africa. The main trend of migration followed the eastern 

 highlands, the valleys of the iSTiger and Congo being more remote. 



In the East Indies, the succession of great islands to the southeast, 

 perhaps more connected formerly than now, formed stepping stones of 

 miration to the distant continent of Australia. 



The lowest and most primitive races of men are to be found in Aus- 

 tralasia, in the remoter districts of southern India and Ceylon, in the 

 Andaman Islands, in southwest and west central Africa and, as far as the 

 New World is concerned, in northern Brazil. These are the regions most 

 remote, so far as practicable travel-routes are concerned, from Central 

 Asia. A century ago, the present habitat of primitive races was taken to 

 be approximately the primeval home of man. With our present under- 

 standing of the conditions and causes of migration, a theory more in ac- 

 cord with tradition and history is generally accepted, and the dispersal 

 center of man is regarded as situated in central or southern Asia. The 

 influence of the old opinion is perhaps seen in the tendency to place this 

 region south of the great Himalayan ridge and in tropical or semi-trop- 

 ical climate. 



This last assumption — that man is primarily adapted to a tropical cli- 

 mate — is, I think, only partly true at best. Its general acceptance is 

 perhaps due, among other reasons, to the supposed relation between loss 

 of hair on the body and the wearing of clothes, the first being regarded as 

 an earlier specialization in an environment of tropical forests, the second 

 as a secondary adaptation resulting from migration to a cold climate. 

 But here, it seems to me, we are putting the cart before the horse. We 

 may more reasonably regard the loss of hair in the human species as a 

 result of wearing clothes and conditioned by this habit, rather than attrib- 

 ute it to any climatic conditions. This view is supported by several points 

 in which the loss of hair in man is differentiated from the partial or com- 

 plete loss of hair common in tropical animals, the following two being 

 most clearly significant. 



1) It is accompanied by an exceptional and progressive delicacy of skin, 

 quite unsuited to travel in tropical forests. 1 do not know of any thin-haired 

 or hairless tropical animal whose skin is not more or less thickened for pro- 

 tection against chafing, the attacks of in.sects, etc. 



2) The loss is most complete on the back and abdomen. The arms and the 

 legs and, in the male, the chest, retain hair much more persistently. This is 



