Species concepts and speciation: Facts and fantasies

The identification of the punctuated mode of evolution, an alternative to gradualism, has required renewed focus on the nature of species. A species is an evolutionary lineage and may be recognized by having fixed (absolute) heritable differences from other species. Among the various modes of speciation which have been proposed, allopatric speciation is the best authenticated; it can be divided into dichopatric and peripatric. Other modes are parapatric, sympatric, stasipatric, and, one which has recently assumed a considerable importance, speciation by hybridization. All these must be considered when thinking about how the various species identified in the hominin fossil record originated.