An original architect of the neo-Darwinian synthesis, Mayr is best known for his formulation of the biological species concept and for the theory of geographic speciation
. His Animal species and evolution (1963.
A special case of geographic speciation
is seen in ring species (polytypic species demonstrating circular overlap).
Nevertheless, we suggest that the strongest evidence of geographic speciation
mode should result from comparisons of sister species, which have undergone speciation more recently than other sister elements, and had relatively less time for dispersal to obscure the geographic pattern of speciation.
Both were thoroughly familiar with the phenomenon of geographic speciation
, which was to play such an important part in the Evolutionary Synthesis.