. Bulletin of the British Ornithologists' Club. 1. P. meyeri 2. P. senegalus 3. P. crassus 4. P. flavifrons 5. P. rufiventris 6. P. cryptoxanthus 7. P. rueppellii f. V —\ • • • '/. Figure 2. Distribution of the African parrots of the Poicephalus meyeri superspecies. Simpli- fied after Snow (1978). This assemblage of parapatric species was used by Rensch (1928), together with other evidence, to discuss the occurrence of vicariant biospecies. the early 1930s when be became familiar with the new redefinition of mutation as slight genetic variations which could respond to natural selection. In Nor
. Bulletin of the British Ornithologists' Club. 1. P. meyeri 2. P. senegalus 3. P. crassus 4. P. flavifrons 5. P. rufiventris 6. P. cryptoxanthus 7. P. rueppellii f. V —\ • • • '/. Figure 2. Distribution of the African parrots of the Poicephalus meyeri superspecies. Simpli- fied after Snow (1978). This assemblage of parapatric species was used by Rensch (1928), together with other evidence, to discuss the occurrence of vicariant biospecies. the early 1930s when be became familiar with the new redefinition of mutation as slight genetic variations which could respond to natural selection. In North America, the systematic principles of both Hartert and Chapman regarding the ranking of taxa as subspecies and species were increasingly applied in their work by the leading ornithologists of the 1920s and 1930s, J. Chapin, R. C. Murphy, J. L. Peters, L. Griscom and many others who were also influenced by the new concepts of genetics and evolution. Chapin (1932) warned against the hasty lumping of geo- graphic representatives under a binomial name to include groups that may have diverged to a point beyond the possibility of intergradation. He emphasized the genetic basis of slight subspecific differences knowing that "environment selects, rather than directs the variations". Building on the work of Stresemann and of Rensch, Mayr (1942, 1963, 1970) prepared several major critical syntheses of the systematic, genetic and ecological aspects of biological species and an analysis of the speciation process. Thus he established the theoretical biological species concept in all its ramifications, based on which he defined the multi- dimensional species category within taxonomy. Through his contri- butions, the biospecies concept became one of the central tenets of the modern synthetic theory of evolution during the 1940s and 1950s, a fact too well-known to be discussed here in any detail. Lack (1944,1949,1971). Please note that these images are extracted from
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