Reconciling Species Concepts: An Ecological Perspective.

Species concepts remain contentious, both in paleoanthropology and in modern taxonomy. The lineage-based concept emphasizing evolutionary independence is most fundamental, but in practice is generally represented by proxy evidence of morphological or genetic divergence. This has resulted in a troubling proliferation of species names in the hominin fossil record. Pseudo-extinctions where lineages persisted under a new species name need to be distinguished from cases where lineages ended terminally-the implications for ecological adaptability are diametrically opposed. Furthermore, the ecological criterion for species coexistence is widely overlooked. The competitive exclusion principle holds that species sharing closely similar niches cannot continue to coexist in the same place at the same time. Notably, the largely vegetarian Paranthropus lineage remained distinct from the diverging, more versatile Homo lineage until fading from the fossil record during the later Pleistocene. Claims that additional hominin species existed are ecologically suspect unless supported by evidence of adequate niche separation. Modern examples where there has been equivocation in lineage recognition are illustrated for bovids, giraffids, baboons, and elephants. Furthermore, the mechanisms that resulted in the displacement of Neanderthals by modern humans are reappraised from an ecological perspective. Representations of evolutionary divergence as a bushy tree need to be superseded by the emerging paradigm of reticulate lineages diverging and coalescing through time and space.