MAMMALS 51 



habitants of the country descended from European colonists 

 the beard has become lank and scanty. 



It does not necessarily follow, because a character such as 

 the beard in man shows great variations in individuals and 

 allied races, that therefore its evolution or origin is suffi- 

 ciently explained by the occurrence of such variations and 

 the process of selection. On the contrary, I believe that 

 such marked variation is often an indication that the 

 character is merely persisting under the influence of 

 heredity alone, the definite stimulation which gave rise to it 

 having ceased to act. This is, in my opinion, the explana- 

 tion of the long-horned and hornless breeds of domesticated 

 cattle, and the great differences in the development of the 

 secondary male characters in breeds of domestic poultry. 



Whatever doubts may arise concerning the origin of the 

 beard and moustache, it seems tolerably certain that the hair 

 of the body in both sexes, and on the face in woman, has 

 become rudimentary since the first differentiation of the 

 human species. In connection with this modification, we 

 have also to consider the fact that children of both sexes are 

 more hairless than adults. 



In seeking the possible causes of the loss of hair, we 

 naturally consider other cases of hairless animals. In the 

 first place, we find nakedness characteristic of certain per- 

 manently aquatic animals, namely, the Cetacea and Sirenia. 

 It is possible that the loss of hair in these is really due to 

 the influence of the water, but this seems to be inconsistent 

 with the fact that seals and otters have such well-developed 

 fur. However, seals and otters are aquatic carnivora, whose 

 near allies have thick fur, and they are not permanently 

 immersed in water, but spend a considerable portion of 

 their time on land. The hippopotamus is hairless, and the 

 elephant and rhinoceros nearly so. The fact that the extinct 

 mammoth and woolly rhinoceros of the glacial epoch were 



