ASPECTS OF KINETIC EVOLUTION 269 



inable proportion with differences of conditions, habits or selec- 

 tive requirements. Hundreds of species, genera, families, and 

 even orders, have been differentiated notwithstanding complete 

 and long-standing adjustment to the same kind of existence. 



The multiplication of species under such circumstances has 

 little reference to environment or to natural selection, and the 

 characters by which the groups differ are not explainable on the 

 basis of utility. The diplopod fauna of tropical Africa changes 

 almost completely every thousand miles, but the tropical forest 

 conditions under which a large proportion of the species live 

 are, for their purposes, practically identical the world over. 

 But with these wingless, slow-moving creatures unable to bear 

 exposure to daylight and dry atmosphere, the opportunities for 

 segregation are greater than those for dissemination. The 

 environment allows a wide freedom of choice, and evolution 

 by means of useless changes has far outrun the natural selection 

 of advantageous differences. As far as their external charac- 

 ters are concerned, these animals appear to have been quite as 

 well adapted to their environment in the carboniferous age as 

 they are to-day, but they have not ceased to differentiate species, 

 although preserving much more than in some groups the same 

 general form. Indeed, the wealth of definite structural differ- 

 ences is, if anything, greater than among the higher insects, 

 where the progress in adaptive structural changes would seem 

 to have removed the necessity of accentuating the inconse- 

 quential differences which the diplopoda have utilized as 

 means of evolutionary motion. 



DIFFERENCES OF NEW VARIATIONS (NEISM). 



Much of the heterism or normal individual diversity of the 

 members of a species can be described as resulting from differ- 

 ent combinations and proportions of what have been called the 

 unit characters of the species. The interweaving of the lines 

 of individual descent brings, as we know, an infinite diversity 

 of form and features, and with these differences accentuated by 

 environmental influences there is almost an infinity of possibili- 

 ties of diversified characters in the same species. Nevertheless, 

 the making of all possible permutations of the characters which 



