ASPECTS OF KINETIC EVOLUTION 355 



environmental experiences, but the inadequacy of this con- 

 jecture is made plain by the fact that the greatest of these intra- 

 specific divergencies, those of sexes, castes and alternating 

 generations are obviously not subject to such an explanation. 

 Protoplasmic arrangement, and the specializations of the organs 

 and processes of reproductive cells, were not, of themselves, 

 effective for the problems of advancing organization. There 

 had to be differences, vital tensions, as it were, between the 

 protoplasms, if organic progress were to be maintained, and con- 

 jugation were to become adequate for the building up of large, 

 complex and long-lived organisms. 



As fission suffices for the reproduction of only the simplest 

 types, and haplogamy, apaulogamy and finally paragamy, 

 have proved necessary to continue the propagation of organisms 

 of successively higher degrees of complexity, so, for the very 

 highest, sexual diversity and continuously maintained symbasis 

 are requisite. The effect of prolonging the process of con- 

 jugation is to double in each organism the threads of the vital 

 network. The separation of a species into sexes is a still more 

 advanced category of specialized descent, since it doubles the 

 whole specific network, permits accumulation of two sets of 

 variations, and insures that each individual be descended from 

 two diverse parents. 



But even this provision of interbreeding does not suffice to 

 maintain the perfection of organic excellence found in man 

 himself, where the requirement of diverse descent is so acute as 

 to forbid, on pain of degenerate offspring, the union of indi- 

 viduals separated by less than four or five generations, or by 

 two or three strains of alien blood. Human descent is so 

 difficult and precarious a fabric that the double network cannot 

 be held in place merely by the joining of adjacent knots. 

 The structure is likely to totter or fall if the lines of descent 

 which join in the building of each new individual are not well 

 braced by meeting each other at broad angles. Neighboring 

 parallel or only slightly divergent lines do not afford the neces- 

 sary stability of contrast, the vital tension which enables the con- 

 jugate cells to build a well-knit body. The intricacies of rela- 

 tionships which fascinate the genealogist are not gratuitous or 



