CAIN: CENTER OF ORIGIN 141 



other locality may be found anything like an equal display of what have l^een 

 considered ancestral characteristics for purely morphological reasons . . . The 

 periphery in general is bounded by highly specialized members of the genus." 



The opposite view concerning the location of primitive species of a group 

 is that the primitive forms are to be found at the periphery of area because 

 they have been crowded from the center by the younger and more aggressive 

 members of the group. The employment of such a criterion as this depends in 

 part upon the validity of taxonomic criteria for the indication of primitive- 

 ness. Many of these criteria (as enunciated for botanists by Bessey, and others) 

 themselves deserve critical analysis. 



One of the most skillful proponents of the view that primitive forms are 

 peripheral is Matthew (1939). The following quotations from "CHmate and 

 Evolution" (pp. 10, 11, 31, 32) reveal his hypothesis which is extensively docu- 

 mented by vertebrate paleontology and phylogenetics, but not universally ac- 

 cepted. 



"Whatever agencies may be assigned as the cause of evolution of a race, it 

 should be at first most progressive at its point of original dispersal, and it will 

 continue this progress at that point in response to whatever stimulus originally 

 caused it and spread out in successive waves of migration, each wave a stage 

 higher than the previous one. At any one time, therefore, the most advanced 

 stages should be nearest the center of dispersal (original), the most conserva- 

 tive stages farthest from it ... to assume that the present habitat of the most 

 generalized members of a group, or the region where it is now most abundant, 

 is the center from which its migrations took place in former times appears to 

 me wholly illogical and, if applied to the higher animals as it has been to fishes 

 and invertebrates, it would lead to results absolutely at variance with the known 

 facts of the geological record , . . The successive steps in the progress must 

 appear first in some comparatively limited region, and from that region the new 

 forms must spread out, displacing the old and driving them before them into 

 more distant regions. Whatever be the causes of evolution, we must expect them 

 to act with maximum force in some one region ; and so long as the evolution is 

 progressing steadily in one direction, we should expect them to continue to act 

 with maximum force in that region. This point will be the center of dispersal 

 of the race. At any period, the most advanced and progressive species of the 

 race will be those inhabiting that region ; the most primitive and unprogressive 

 species will be those remote from this center." 



Cytogenetics is providing a body of information for several groups that 

 points undeniably toward the forms that are primitive in a group. One exam- 

 ple of this type will be sufficient. Anderson ( 1937) says, 'Tn those species which 

 have both diploid and tetraploid races we . . . know that the tetraploids must 

 have originated from the diploids." Tetraploid Tradescantia occidentalis ranges 

 throughout the Great Plains and the eastern Rocky Mountains, and has a small 

 diploid area in central and eastern Texas. Tetraploid T. canaliculata occupies a 

 wide area in the Mississippi Valley, and is diploid in the same territory in 



