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Evolutionary theory should ideally specify the necessary and sufficient determinants of the convergent and divergent patterns that have evolved in subterranean mammals (i.e. mammals that have radiated over space and time into the subterranean ecological zone). These include fossorial species that spend most of their lives in sealed burrows and come to the surface only incidentally (Table 1). The physical and biotic uniqueness of subterranean ecology provides an excellent evolutionary theater where adaptive conver gent evolution molds populations, species, and communities in similar but geographically distinct environments throughout the world on all levels of organization: genetic, biochemical, physiological, anatomical, behavioral, populational, life-historical, and speciational. The objective of this paper is to compare and contrast the evolutionary patterns and adaptive strategies of completely subterranean mammals and to suggest a theory specifying the selective forces operating in this unique environment. Which mammals radiated underground? Three of the 19 orders of mam mals have completely subterranean representatives: the rodents, the insec tivores, and the marsupials. Distribution patterns, geographical and paleontological, are given in the Table and Figures. The taxonomic distribution of subterranean mammals is extensive: 10 of 132 mammali an families (�7.5%), comprising some 35 of 1004 mammalian genera (�3.5%), and 144 of 4060 mammalian species (�3.5%), based on classical taxonomy (2). The new discoveries of widespread chromosomal sibling species in mammals may increase manyfold the number of subterranean
Eviatar Nevo (Thu,) studied this question.