Species Concepts, Reticulation, and Human Evolution

Abstract

Hennig differentiated parent‐offspring, or tokogenetic, relationships among organisms within a population, which are network‐like, or reticulate, in their structure, from phylogenetic relationships between species taxa, which are hierarchical. However, some biologists have recently argued that reticulation may occur across taxa at high taxonomic levels, and Jolly, using a papionin analogy for hominin evolution, argued that fossil hominins represent a group of allotaxa that likely exhibited varying degrees of hybridization in zones of ecological overlap. Such potential reticulation among the Hominini has important implications for phylogenetic reconstruction and is likely a significant source of homoplasy in the hominin fossil record. Hybridization between taxa can lead to the merging of taxa, to the reinforcement of behavioral barriers to mating, or even to the emergence of new, hybrid species. Templeton has noted that many mammalian species appear to be grouped into higher‐level, hybridizing taxa called syngameons. Evidence for such syngameons within the Hominini is here explored in light of current species concepts.