The origin and evolution of Homo sapiens

Abstract

not [24,25] (see also [26]). Moreover, I have argued that this species represents the most reasonable LCA for the neanderthalensis and sapiens lineages, with their common origin placed at about 400 ka based on the estimated mtDNA coalescence date of the two lineages [25,27]. A new study using geometric morphometrics of various crania to virtually reconstruct the LCA of Neanderthals and modern humans also found that an Afro-European species (H. heidelbergensis s.l.) most closely approached the hypothetically reconstructed LCA, with the added suggestion that the LCA most likely lived in Africa [28]. An alternative model has a much older proposed LCA for the neanderthalensis and sapiens lineages, based on the ‘modern’ maxillary conformation of the ATD6-69 H. antecessor face from Gran Dolina, Atapuerca, dated approximately 850 ka [29]. Such a model would imply that this facial morphology was retained in the descendant sapiens lineage, but was lost in that of the Neanderthals. New data are emerging that are relevant to these models concerning the ultimate ancestry of H. sapiens and H. neanderthalensis (and thus also of the Denisovans), and I will return to this issue in §5. A fourth question follows from the previous ones. Once the Neanderthal and modern human lineages began to evolve, did more ancient (and perhaps ‘ancestral’) morphologies in Eurasia and Africa soon die away, or could they have persisted alongside their ‘descendants’ for a considerable time? And if the latter, might the contemporaneous lineages have exchanged genes? While such a question poses serious issues for any simple cladistic, phylogenetic or taxonomic schemes, there is growing evidence of the survival of what could be considered as earlier middle Pleistocene morphologies (cf. H. heidelbergensis or H. rhodesiensis) into at least the later middle Pleistocene of Europe and Africa [8,25]. In addition, recent evidence of late Pleistocene episodes of introgression between different human lineages in Eurasia [30] and perhaps also in Africa [31] shows us that comparable genetic exchanges could also have been occurring in the middle Pleistocene.