CAIN: CENTER OF ORIGIN * 145 



stock of genes of the species as a whole. When a species is divided into geo- 

 graphic subspecies and ecotypes, these conditions probably apply to them also, 

 but less obviously. No species is completely panmictic. 



On a basis of the Law of Tolerance (Good, 1931), it is concluded that each 

 individual organism can live only within the inherent limits of its tolerances for 

 the environment, and the tolerances of a species is the sum of the tolerances 

 of the component individuals of the species population. Now it seems to me 

 that this summation of Good's can have no real meaning for an individual. No 

 individual can contain (inherit) all the genie variability of the population, al- 

 though in a panmictic population any individual might theoretically contain 

 any possible pair of allelomorphic genes. In many cases it is an observed fact 

 that morphological polymorphism decreases away from the center of area of a 

 species or subspecies. Although it is more difficult to demonstrate, it is reason- 

 able to assume that individual members of a species differ as much physiolog- 

 ically as they do morphologically. In fact, it seems entirely likely that adapta- 

 tion and ecological amplitude reside more in unseen features than in the char- 

 acters of the type usually employed in systematic studies. Both, of course, ul- 

 timately result from the genie constitution of the individuals, and may be linked. 

 In this connection Hiesey, Clausen and Keck (1942) say, "Within popula- 

 tions, hereditary variants occur, some of which may possess physiological qual- 

 ities that give them the potential capacity to survive in different kinds of places. 

 Other variations seem to have no significance for survival, representing ran- 

 dom differences that are not incompatible with the main requirements of exist- 

 ence in their population." Just as individuals vary within a population, so may 

 populations show a statistical difference, which may or may not be adaptive 

 and favor survival. It would seem to follow, then, that when polymorphism is 

 greater near the center of area than at its periphery, it is entirely likely that 

 there will be less dependence upon a restricted habitat at the center of area. This 

 should not lead to the assumption that any one individual has a wider tolerance 

 and a lesser dependence upon a restricted habitat because it happens to live 

 near the center of area. 



If primitive members of a group have a wider tolerance than more ad- 

 vanced ones, and if primitive members are more likely to be found near the 

 center of origin, there should be a lesser dependence upon a restricted habitat 

 at the center. The wide ecological tolerance that primitive species are supposed 

 to have is sometimes based on the paleontological evidence of large areas which 

 species of modern genera are known to have had in Cretaceous or Tertiary 

 times. This is frequently a spurious argument because many of these species 

 are known not to have had these wide areas synchronously, and furthermore, 

 little is known of ecological subdivisions of the species. Finally, there are no 

 physiological studies, so far as I know, which indicate that primitive species 



