Fossil evidence for the origin of Homo sapiens

Debates in palaeoanthropology are often quite involved, and they become more arcane the further back we go in time. An modern human jawbone usually elicits a call to the police, but if you find an Upper Paleolithic jawbone, you can write paper upon paper on its anatomical minutiae.

Anthropologists who are intimately familiar with the ancient Homo record are not that many, so it is a pleasure to see a paper which tries to put their feuds and different perspectives into a historical context.

This is not easy reading, but you can skip the impenetrable anthrospeak about bipartite brows and penecontemporaneous specimens and appreciate the story at a higher level.

The paper is basically a polemic against "lumpers" who emphasize the unity of the Homo genus and even go as far as to propose that there is only a single Homo sapiens species that has gradually transformed over two million years.

From the paper:

What is most odd about this history is that anyone actually familiar with even a small portion of the human fossil record would ever even consider embracing Mayr's bizarrely influential assertions about human evolution. For, the signal of that record, even as it existed in the 1950s and 1960s, did not support Mayr's view at all. Nevertheless, most paleoanthropologists not only succumbed to Mayr's dictates but became intellectually constrained by them, apparently for the most part at least as a result of the weight of authority Mayr had gained, along with Dobzhansky and the paleontologist George Simpson, with the triumph of the “hardened” version of the Evolutionary Synthesis. This intellectual victory resulted in the almost complete suppression of competing evolutionary ideas, emanating primarily from Germany and the United Kingdom, that were in many ways much more “synthetic” (Schwartz, 2009a, b; Schwartz, in press) than the Synthesis itself. In the United States, especially, the prominent physical anthropologist S. L. Washburn (Washburn, 1951) was highly influential in publicizing the virtues of replacing old-fashioned “typology” with “population thinking” (e.g., Simpson, 1949). As a result, paleoanthropologists seem not to have noticed that the routine recognition and delineation of three different chronospecies of Homo was becoming ever more artificial and arbitrary as the hominid fossil record expanded.

and:

Among the fossils that most of us were taught were uncontestable early representatives of our species are specimens from Qafzeh and Skhūl. From Qafzeh, the specimen most frequently cited and illustrated is the fairly complete skull Qafzeh 6. Yet this specimen lacks a bipartite brow, possessing instead a superoinferiorly somewhat tall brow that is anteriorly low and mounded, and continuous across an equally tall glabellar, region. Thus, although the neurocranium of Qazeh 6 is rather globular, and relative to it the face is not massive, this specimen conspicuously lacks the one particular apomorphy that would cement its allocation to H. sapiens (Schwartz and Tattersall, 1996b, 2000b) (Fig. 6).

more:

With regard to other specimens that have been identified as “early anatomically modern” H. sapiens, we could confidently detect a glabellar butterfly only in the Liujiang cranium (>67 ka, possibly 101–227 ka) (Fig. 7). In the otherwise distinctive LH 18 (Ngaloba) calotte (108–129 ka) (Fig. 7), there appears to be something resembling this structure, the more robust and superoinferiorly thicker lateral portion forming an antero-obliquely facing plane (Schwartz and Tattersall, 2003). The variably complete crania of Omo Kibish I and II, Singa, and Jebel Irhoud I, and the Klasies River Mouth frontal fragment (Figs. 8 and 9), are broadly contemporaneous with, or older than, the Liujiang and LH 18 specimens and have been suggested as at least representing a precursor to anatomically modern H. sapiens. None of these specimens, however, displays a supraorbital configuration that could be described as bipartite, or as possessing a butterfly-shaped glabellar region.

...

Among chronologically younger specimens that have been considered definitively anatomically modern H. sapiens are the incomplete crania Border Cave 1 and Dar es Soltane II (Fig. 9). Although we have in the past agreed with this interpretation (Schwartz and Tattersall, 2003), our reassessment of these specimens has made us much more tentative now in both cases. Among the variably complete Pleistocene crania that we also viewed as morphological H. sapiens in our 2003 study, we still confidently include in our species the relatively recent specimens from Abri Pataud, Brno, Chancelade, Combe Capelle, Cro-Magnon, Dolni Věstonice, Engis (the adult), Grimaldi, Isturitz, Mladeč, Pavlov, Predmostí, Svitavka, Tuinplaas, Velika Pécina, Vogelherd, Wajak, Zhoukoudian Upper Cave, and Zláty Kůn (Fig. 10). Unaligned with typical H. sapiens on supraorbital conformation are the very recent specimens from Fish Hoek and Boskop (Schwartz and Tattersall, 2003) (Fig. 11). The latest estimate of 6891 ± 37 BP for Fish Hoek (Stynder et al., 2009) makes this atypicality all the more intriguing.

Am J Phys Anthropol. 2010;143 Suppl 51:94-121. doi: 10.1002/ajpa.21443.

Fossil evidence for the origin of Homo sapiens.

Schwartz JH, Tattersall I.

Abstract

Our species Homo sapiens has never received a satisfactory morphological definition. Deriving partly from Linnaeus's exhortation simply to "know thyself," and partly from the insistence by advocates of the Evolutionary Synthesis in the mid-20th Century that species are constantly transforming ephemera that by definition cannot be pinned down by morphology, this unfortunate situation has led to huge uncertainty over which hominid fossils ought to be included in H. sapiens, and even over which of them should be qualified as "archaic" or as "anatomically modern," a debate that is an oddity in the broader context of paleontology. Here, we propose a suite of features that seems to characterize all H. sapiens alive today, and we review the fossil evidence in light of those features, paying particular attention to the bipartite brow and the "chin" as examples of how, given the continuum from developmentally regulated genes to adult morphology, we might consider features preserved in fossil specimens in a comparative analysis that includes extant taxa. We also suggest that this perspective on the origination of novelty, which has gained a substantial foothold in the general field of evolutionary developmental biology, has an intellectual place in paleoanthropology and hominid systematics, including in defining our species, H. sapiens. Beginning solely with the distinctive living species reveals a startling variety in morphologies among late middle and late Pleistocene hominids, none of which can be plausibly attributed to H. sapiens/H. neanderthalensis admixture. Allowing for a slightly greater envelope of variation than exists today, basic "modern" morphology seems to have appeared significantly earlier in time than the first stirrings of the modern symbolic cognitive system.

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