sympatric evolution The development of new taxa from the ancestral taxon, within the same geographic range (i.e. it is geographically possible for interbreeding to occur between the potential new taxa, but for some reason this does not happen). Because of the difficulty of envisaging what the reasons might be, few authorities until recently accepted the reality of sympatric evolution, except for certain special kinds of organisms; but recent studies have shown that chromosomal mutation can set up a partial barrier to interbreeding sufficient to permit speciation (stasipatric speciation); and the restricted interbreeding between ecological races of a species could promote separation. Centrifugal speciation appears to be so common in some groups of animals (e.g. mammals) that some sympatric mechanism must be occurring.

sympatric evolution The development of new taxa from the ancestral taxon, within the same geographic range. (It is geographically possible for interbreeding to occur between the potential new taxa, but for some reason this does not happen.) Because of the difficulty of envisaging what the reasons might be, few authorities until recently accepted the reality of sympatric evolution, except for certain special kinds of organisms; but recent studies have shown that chromosomal mutation can set up a partial barrier to interbreeding, sufficient to permit sympatric speciation. This requires the development of some form of reproductive isolating mechanism which has arisen by selection within a geographically confined area; it may be structural, physiological, or genetic.

sympatric evolution The development of new taxa from the ancestral taxon, within the same geographic range; it is geographically possible for interbreeding to occur between the potential new taxa, but for some reason this does not happen. Because of the difficulty of envisaging what the reasons might be, until recently few authorities accepted the reality of sympatric evolution, except for certain special kinds of organism; but recent studies have shown that chromosomal mutation can set up a partial barrier to interbreeding, sufficient to permit sympatric speciation.