EVOLUTION OF PHYSICAL CHARACTERS 383 



mentation is taking place. Attempts to establish this correlation 

 have, however, failed. It is of particular interest to notice that 

 no correlations have been found between physical and mental 

 characters ; this is so even as regards intellect and size of head. 



8. A survey of the facts regarding the bodily evolution of man, 

 and of the conditions under which it has taken place, shows that 

 there is at least no more difficulty in understanding how it has 

 come about than in understanding how the varieties of any other 

 species have come into existence. Given mutations, the action of 

 selection and of differential fertility provides an explanation which 

 is in general satisfactory, though we may be a very long way 

 from understanding how any one particular change came about. 

 There are in fact greater difficulties met with from time to time 

 in trying to reach a satisfactory explanation of evolution among 

 other animals than when dealing with man. The evolution along 

 particular lines of organization, the evolution of teeth and horns 

 among mammals, for instance, raises a difficulty which seems in 

 the present state of our knowledge perhaps to require the assump- 

 tion that at times there is a tendency for the continual occurrence 

 of mutations in the same direction. Such a difficulty does not 

 occur in the case of human bodily evolution. 



It has been suggested that the facts regarding the course which 

 the evolution of living organisms has taken requires the assumption 

 that large mutations have occurred from time to time and have 

 estabhshed themselves as varieties. There is no doubt that large 

 mutations do occur and have established themselves in the course 

 of the evolution of the varieties of animal types known to us, and 

 they may have done so in the case of man. There is, however, 

 no reason to imagine that the origin of any particular change in 

 man was due to a large mutation. It has been stated that the 

 number of chromosomes is different in the white man and in the 

 negro, and upon the basis of this statement it has been suggested 

 that one variety had arisen as a mutation from the other. This 

 statement, however, was apparently based upon erroneous 

 observation. Again, it has been suggested that the Pj^gmy type 

 arose as a mutation. But it has been observed that some Ba Twa 

 pygmies of the Congo who three generations ago left their forests, 

 settled near the Bushongo, and took to agriculture have become 

 markedly taller. Inter-marriage is said to be out of the question 

 and therefore we are led to suppose in the new environment 



