Proc. Natl. Acad. Sci. USAVol. 96, pp. 7117–7119, June 1999CommentaryHominids and hybrids: The place of Neanderthals in human evolutionIan Tattersall*†and Jeffrey H. Schwartz‡*Department of Anthropology, American Museum of Natural History, New York, NY 10024; and‡Department of Anthropology, University of Pittsburgh,Pittsburgh, PA 15260As the first extinct human relatives to have become known toscience, the Neanderthals have assumed an almost iconicsignificance in human evolutionary studies: a significance thathas, of course, been greatly enhanced by the very substantialfossil and behavioral record that has accumulated since theoriginal Feldhofer Cave skullcap and partial skeleton wereaccidentally uncovered, on a pre-Darwinian August day in1856, by lime miners working in Germany’s Neander Valley(1–3). Yet even now, 14 long decades later, paleoanthropo-logical attitudes toward the Neanderthals remain profoundlyequivocal. Thus, although many students of human evolutionhave lately begun to look favorably on the view that thesedistinctive hominids merit species recognition in their ownright as Homo neanderthalensis (e.g., refs. 4 and 5), at least asmany still regard them as no more than a strange variant of ourown species, Homo sapiens (6, 7). This difference represents farmore than a simple matter of taxonomic hair-splitting. For, asmembers of a distinct species, of a completely individuatedhistorical entity, the Neanderthals demand that we analyze andunderstand them on their own terms. In contrast, if we seethem as mere subspecific variants of ourselves, we are almostobliged to dismiss the Neanderthals as little more than anevolutionary epiphenomenon, a minor and ephemeral append-age to the history of Homo sapiens.Any new information bearing on this matter is thereforeextremely welcome, and there is no doubt that the claimsadvanced in this issue of the Proceedings by Duarte et al. (8) willbe closely scrutinized by their colleagues. Briefly, Duarte et al.propose that the skeleton of a 4-year-old child, recentlyunearthed at the 24,500-year-old (24.5 kyr-old) site of LagarVelho in Portugal, represents not merely a casual result of aNeanderthal/modern human mating, but rather is the productof several millennia of hybridization among members of theresident Neanderthal population and the invading Homo sa-piens. Species (especially extinct ones) are often tricky toidentify in practice, and speciation, the process (or moreprobably, assortment of processes) by which new species comeabout, is poorly understood. But by anyone’s reckoning, long-term hybridization of this kind would indicate that the twopopulations belonged to the same species. So, if Duarte et al.are right, the case is closed: Neanderthals were indeed no morethan an odd form of Homo sapiens. But is this claim reasonableon the basis of the evidence presented? To clarify this, somebackground follows.‘‘The Neanderthals’’ is the informal designation of a mor-phologically distinctive group of large-brained hominids whoinhabited Europe and western Asia between '200 and lessthan 30 kyr ago (1, 2). They are sharply distinguished frommodern humans by a wide range of cranial and postcranialcharacters (1–2, 4, 9–10), although they do share a number ofderived bony features with other members of the endemicEuropean/western Asian hominid clade that diversified in thispart of the world after '500 kyr ago (10). Subsequent to '150kyr ago, the Neanderthals appear to have been the solesurviving species of this clade. Given the strong degree ofNeanderthal apomorphy (anatomical uniqueness), it is unsur-prising that the remarkable recent sequencing of a short stretchof mtDNA isolated from the Feldhofer individual revealed thisspecimen to be a distant outlier when compared with allmodern human populations (11).The Neanderthals were highly successful over a large regionfor a substantial period of time, but this situation changeddramatically with the arrival in Europe of the first modernhumans, Homo sapiens. Indications are that these ‘‘Cro-Magnons’’ had begun to arrive both in eastern Europe (12) andin the far northeast of the Iberian Peninsula (13) by '40 kyrago; and within little more than 10 kyr, the Neanderthals weregone. The mechanism of their eviction has long been debated,but there are four main possibilities (14). The first and secondof these, that the Neanderthals were eliminated by themoderns in direct conflict or by indirect economic competi-tion, both imply the separate species status of the former, asdoes any combination of the two. The alternatives, that theNeanderthals had simply evolved rapidly into moderns or thatthe genes of the invading moderns simply ‘‘swamped’’ those ofthe Neanderthals, both imply some form of species continuity.Claims for evidence of ‘‘transition’’ between Neanderthalsand moderns, based on supposedly ‘‘intermediate’’ fossilsdating from a short window of time around 40–30 kyr ago (15),have been refuted by the recognition that the fossils concernedare either typically Neanderthal or modern (10) and, in onesignificant case, had been misdated (16). Supporters of thecontinuity argument have thus tended lately to the view thatthe disappearance of Neanderthal morphology was due toextensive interbreeding between the Neanderthals and theincoming Cro-Magnons, who invaded in sufficient numbers todominate the hybrid gene pool and thus the resulting pheno-types (7, 17). The problem has been, though, that nobody hashad any idea what a Neanderthal/modern hybrid might looklike in theory, and few have dared to suggest in practice thatany particular known fossil represents such a hybrid. TheDuarte et al. claim for the Lagar Velho skeleton is the closestanyone has recently come to such a contention, hence theintense interest that it seems sure to arouse.The potential significance of the Lagar Velho claim isenhanced by the burial’s Iberian location, because it seems thatit was in this peninsular extension of Europe that the Nean-derthals lingered longest. Outside Iberia, the latest Neander-thals, and survivals of their ‘‘Mousterian’’ culture, are signif-icantly more than 30 kyr old. At the southern Spanish site ofZafarraya, however, the Mousterian may have lasted to '27kyr ago (18) and is associated with typical Neanderthal remainsat probably not much more than 30 kyr ago. Even more telling,isolated but reasonably diagnostic fossil teeth suggest thatNeanderthals