Affinities and Role of Nazlet Khater Man

January 31, 2010

Afrocentrists have a particular interest in considering Nazlet Khater man, an Early Upper Paleolithic skeleton from Northeast Africa, racially Negroid and believing it to represent the ancestors of Egyptians and several Out-of-Africa migrants. But as with Mesolithic Nubians, this seems highly unlikely. Though Thoma (1984) describes Nazlet Khater as "suggestive of Negroid morphology", and Pinhasi and Semal (2000) find that it clusters with Middle Stone Age Sub-Saharan Africans, anthropologists have often misclassified as Negroid various archaic traits, especially in the mandible (see above link on Mesolithic Nubia). And Nazlet Khater certainly fits this familiar pattern, according to Vermeersch et al. (1984):

The Nazlet Khater 4 site (Nile Valley, Upper Egypt) is located on one of the small wadi-interfluves in the lower desert near the steep cliffs bordering the western Nile Valley edge.... The 1982 excavation reported here confirms that Nazlet Khater 4 is a chert mining site with a complex extraction strategy, going back 33,000 yr. A nearby grave contained a skeleton of a man in the extended position. We show that the cranial morphology is anatomically modern with archaic characteristics such as a very robust mandible. There is evidence that the skeleton has a similar age to that of the mining site.

It's so archaic, in fact, that Trinkaus (2007) expresses doubts about whether or not it's fully modern and representative of Out-of-Africa humans:

The only other directly relevant specimen is Nazlet Khater 2, from ≈42 ka B.P. in Egypt. Approximately contemporaneous with the earliest EEMHs [European early modern humans], it may represent the morphology of modern humans dispersing out of Africa after ≈50 ka B.P. However, in some features it is more archaic than the MPMHs [Middle Paleolithic modern humans], which raises questions as to the degree to which its ancestry was purely from the MPMHs and therefore whether it represents the ancestral modern human morphology.

[...]

The role of the Nazlet Khater 2 skeleton is also debatable; it has two plesiomorphic mandible features absent in the MPMHs, suggesting that its post-MPMH ancestors may have experienced admixture with regional late archaic humans.

Even the Afrocentrists' own sources comment on its robust and archaic morphology. From Pinhasi and Semal, who reference Thoma:

Thoma's analysis of the postcranial features further suggests that the specimen is altogether modern and extremely robust. Thoma therefore classified the Nazlet Khater specimen as an anatomically modern Homo sapiens with some archaic morphological features.

They also suggest that the clustering pattern is based on robusticity and not racial affinity, as Nazlet Khater also has affinities with robust prehistoric North Africans but not with modern Sub-Saharan Africans:

The post-Neolithic Northwest African populations have small mandibles and are generally gracile in their morphology, while the Epipalaeolithic and Neolithic Northwest African specimens are robust. The PC1 score of Nazlet Khater is rather high (PC1=2•18) but well within the range of some sub-Saharan and Epipalaeolithic North African specimens.

[...]

The position of mean measurements of the protohistoric and modern South African populations indicate that, in its mandibular dimensions, the Nazlet Khater is not closely related to modern Negro and Khoisan populations.

[...]

Lahr (1996) observed that morphological variability among sub-Saharan African populations was at its peak during the Late Pleistocene–early Holocene period. However, this is partially due to the fact that during this period many of the sub-Saharan and North African populations display levels of robusticity which are largely lost in present African populations.

And finally, based on its potential Sub-Saharan affinities, they (logically) propose a migration of the population it belonged to in the direction opposite that hoped for by Afrocentrists:

Both hypotheses are compatible with the hypothesis proposed by Brothwell (1963) of an East African proto-Khoisan Negro stock which migrated southwards and westwards at some time during the Upper Pleistocene, and replaced most of the local populations of South Africa. Under such circumstances, it is possible that the Nazlet Khater specimen is part of a relict population of this proto-Khoisan Negro stock which extended as far north as Nazlet Khater at least until the late part of the Late Pleistocene.

So even if we accept that Nazlet Khater is ancestral to morphologically Negroid populations, these are not to be found in Egypt or Nubia, let alone anywhere outside of Africa. They're restricted to Sub-Saharan Africa.

Natufians NOT Source of European Neolithic

January 26, 2010

There's a theory that the migrations that spread agriculture from West Asia to Europe during the Neolithic period had their source in the Natufians, a Mesolithic Levantine population. Afrocentrists have latched on to this theory (and often cite it as fact) because some anthropologists believe that Natufians traced their origins to Africa and had Negroid affinities. That's a separate issue that's more or less rendered moot by the craniometric evidence against the above theory.

Pinhasi and Pluciennik (2004) analyzed the crania of Mesolithic and Neolithic populations and found no biological relationship between the Natufians and the later West Asian groups who spread farming to Europe:

Analysis of morphological variability in the Near East and Europe suggests that the Epipalaeolithic populations from the Natufian Levant were noticeably different to the Mesolithic populations described from the Danube Gorge, the western Mediterranean, and central Europe. No close similarities were observed between Early Neolithic and Mesolithic European groups in any of the regions studied, with the possible exception of Mediterranean Europe. However, neither were clear affinities observed between Epipalaeolithic Near Eastern groups [Natufians] and any other Neolithic or Mesolithic groups. These results support a third scenario — that the Epipalaeolithic population from which the first Anatolian farmers descended has yet to be discovered.... There is therefore no unequivocal evidence from biological morphometrics for local continuity between Natufian specimens and any of those from the Anatolian or Levantine PPN [Pre-Pottery Neolithic] cultures. Statistical analysis of the Levantine populations indicates no obvious biological continuity between Natufian groups and their successors — either the first Neolithic cultures of the PPNA or subsequently between the PPNA and the PPNB.

Pinhasi and von Cramon-Taubadel (2009) confirm the previous findings, and as a result don't involve the Natufians at all in any of the possible dispersal models of migration from West Asia to Europe:


Figure 1. Map showing geographic distribution of all OTUs. Dispersal models involving the active migration of people from SW Asia take two basic forms. Once-off single dispersals from either Anatolia (brown arrow) or the Levant (orange arrows), or continuous dispersal models whereby active population migration continued from southeastern Europe into central Europe (blue arrows). CD = Continuous dispersal, IBD = Isolation-by-distance (null), LGF = Limited gene flow.
Figure 3 plots the first two principal co-ordinates of the craniometric distance matrix. The OTUs [operational taxonomic units] do not group according to any particular geographic or temporal pattern on the first or second principal co-ordinates. However, the first principal co-ordinate separates the archaeologically defined Neolithic OTUs from OTUs designated as Mesolithic plus the Natufian. Therefore, the principal co-ordinate analysis suggests that Neolithic and Mesolithic populations are biologically differentiated.


Figure 3. Plot of the first two principal co-ordinates illustrating OTU affinity patterns based on craniometric data. The major axis of variation (horizontal axis, 34.9% variance) shows a clear distinction between all archaeologically defined Neolithic OTUs (green, brown and black circle symbols) and all Mesolithic OTUs (purple and red symbols) plus the Natufian (black triangle). Second axis = 18.7% variance.

Extent of Black Admixture in the Mediterranean

January 20, 2010

González-Pérez et al. (2010) have analyzed populations from the northern and southern shores of the Mediterranean, with Central Europeans and West Africans as external references. They estimate Sub-Saharan African admixture using two methods that yield vastly disparate results. In the Discussion section, they admit that the inflated "Alu/STR estimate might be artefactual" and favor the estimate based on the Alu loci set alone because it's consistent with previous mtDNA, Y-chromosome and 500,000-SNP structure data.

According to the more accurate latter method, Sub-Saharan African admixture is ~13% in North Africa and "imperceptible" (~0.01%) in Southern Europe:


Here are the locations of the sampled populations and an MDS plot showing their genetic distances, again based on the preferred method:


Northern Mediterraneans are almost equidistant from both Central Europe (0.0526 ± 0.015) and Southern Mediterraneans (0.049 ± 0.025), showing distances very close to those between the latter two population groups (0.042 ± 0.013). MDS representation of the genetic distances (see Fig. 2) based on autosomal Alu data stresses the main differentiation of sub-Saharans, the clustering of Mediterraneans in two different groups corresponding to northern and southern populations, and the distant position of the Egyptian Siwa and the Spanish Pas Valley samples from their corresponding population clusters.


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González-Pérez et al. "Population relationships in the Mediterranean revealed by autosomal genetic data (Alu and Alu/STR compound systems)". Am J Phys Anthropol, 2010.

Mesolithic Nubians Probably Weren't Negroid

January 14, 2010

Afrocentrists like to believe that Mesolithic Nubia was populated by Negroids because of its strategic location near Egypt and on the Out-of-Africa route, and the time frame coinciding with the dispersals of haplogroup E3b. And they've found support in some research. For example, Groves and Thorne (1999) say that "Sudanese Nubia is Negroid", referring to Mesolithic Jebel Sahaba and Tushka crania, and Irish (1998) groups Mesolithic Nubians with Sub-Saharan Africans based on dental traits.

But it's not that clear cut. What some anthropologists interpret as Negroid morphology, others view simply as primitive or archaic traits indicative of the generalized morphology of early modern humans. Phillipson (2005) summarizes this debate:

To the south, the harpoon-using fishermen of the central and southern Sahara, the Sudanese Nile Valley and parts of East Africa are represented by a few fragmentary skeletons from Ishango, Lothagam on Lake Turkana, Lowasera, Early Khartoum and elsewhere which are said to show negroid physical features. Similar characteristics occur in skeletons from the Qadan cemetery at Jebel Sahaba in Nubia, where Mechta-Afalou features have also been recognised. These remains may be from a population ancestral to present-day Nilotic negroids. Other authorities, emphasizing the presence of features which are also seen in KhoiSan and Northeast African 'caucasoid' populations, prefer to interpret this material as representing a more generalized 'ancestral African' physical type, which may be regarded as akin to a common ancestor of several more recent populations. This explanation also seems plausible for the varied human remains that have been recovered in association with broadly contemporary and rather later industries from southern Kenya.

Complicating things further is the fact that later era Nubia shows clear Caucasoid affinities, which has forced "Negroid Mesolithic" advocates to postulate a population replacement event during the Holocene (the Afrocentrists gloss over this point). Among the authorities questioning this population discontinuity model are Van Gerven et al. (1973), who believe that changes in morphology can be just as easily explained by adaptation (the study they cite is Greene et al. (1967), which analyzed crania from Wadi Halfa, Sudan):

Although the authors view the Nubian population as having remained stable over the last several thousand years, they propose that the living Nubians are the result of the massive penetration of Negroid Africa by Caucasoid genes during the last 14,000 years. In support of this hypothesis, the skeletal remains of a Nubian Mesolithic population are described as possessing bun-shaped occiputs, massive browridges, sloping foreheads, extreme facial flattening, large teeth and deep mandibles. This and other evidence is proposed to indicate that Africa, north of the Sahara, was originally inhabited by non-Caucasoid populations that can in general be termed Negroid.

There are several points at which this analysis remains essentially typological. Specifically, Greene pointed out in his discussion of racial reconstructions:

If indeed there were adequate models for the presumed Negro race of Africa that existed thousands of years ago, then this approach has validity. However, it can be contended that such models are at present not valid since there is little evidence for reconstructing what the then contemporary African Negroes were like skeletally. One can only extrapolate from modern Negroes who may not at all be like their ancestory since racial groups are not static, but evolve.

In addition, many of the skeletal features listed separately by Burnor and Harris may, in fact, be related functionally and/or epigenetically. Greene and co-workers have suggested that features such as large complex tooth form, glabellar protrusion, gonial eversion and massive mandible are all indicative of heavy masticatory masculature. Such features in the Nubian Mesolithic population are similar to those represented by the Neanderthal remains at the Skuhl site in Israel and also by contemporary aboriginal Australian populations. Such commonality suggests similar adaptation rather than common racial origin and migration.

Once again, the explanation of morphological similarity between two populations in terms of racial origins and affinities is totally inadequate unless the role played by natural selection and possible parallel evolution has been determined and incorporated into the analysis.

More recently, Larsen (1997) revisited the long-running debate and backed the continuity model of Greene, Van Gerven and the others that evolution and adaptation explain the differences between earlier and later Nubians better than population replacement:

Beginning in the nineteenth century, various workers speculated on the origins of human groups occupying the [Nile Valley]. Following Morton's (1844) highly influential study of archaeological crania from Egypt and Nubia, the prevailing notion was that two biologically distinct groups occupied the Nile Valley in temporal succession. In Lower Nubia, Morant (1925) identified an earlier 'Upper Nile type', with predominantly 'Negroid' features, and a later 'Lower Nile type', which lacked 'Negroid' features. The changes were viewed in a diffusionistic paradigm: simply, the disappearance of 'Negroid' features resulted from an invasion and subsequent replacement by alien 'Caucasoid' (Egyptian) peoples from the north.

Recent analyses of crania and dentitions from lower Nubia indicate that the evidence for the diffusionist model of biological change is less than compelling. Independent analyses of skeletal and dental discrete and metric variables and other lines of evidence suggest that the earlier and later Nubian populations represent a biological continuum with no invasion by nonindigenous populations. Therefore, the differences in cranial morphology between earlier and later populations...are best understood in relation to factors not involving population replacement.

For better understanding of these factors, especially those related to dietary and technological change, Carlson and Van Gerven and their coworkers compared craniofacial morphology in a Nubian-based temporal sequence, including foragers from the Mesolithic (ca. 12,000 BP), initial agriculturalists from the combined A- and C-groups (3400-1200 BC), and intensive agriculturalists from the combined Meroitic, X-group, and Christian horizons (AD 0-1500). These comparisons reveal that Nubian foragers and incipient agriculturalists have flat and elongated vaults with well-developed, protruding supraorbital tori and occipitals. In contrast, later intensive agriculturalists have rounded vaults with small and more posteriorly positioned faces and masticatory muscle attachment site (temporalis and masseter) and reduced temporomandibular joint size.

Carlson and co-workers posit a masticatory-functional hypothesis for explaining craniofacial changes in Nubia. They argue that the primary factor influencing Nubian craniofacial anatomy was the change in subsistence economy, from foraging to food production and the shift to consumption of softer foods. These changes resulted in a reduction in activity of the masticatory muscles and a concomitant decrease in mechanical loading of the craniofacial skeleton. Alteration in masticatory function led to alteration in craniofacial growth in two ways, including (1) decreased stimulation of bone growth, leading to a reduction in facial robusticity; and (2) progressive alteration of the overall growth of the face and vault, resulting in a smaller and more inferoposteriorly oriented face relative to the cranial vault.

[...]

Turner and coworkers reassessed Greene and coworkers' continuity model of Nubian population history. Although lauding the studies of Greene and others for using a nonracial, nontypological approach to Nubian population history, they argue that extra-regional sources of variation have been insufficiently considered, especially sources that may explain temporal shifts in craniofacial morphology in this region. Implicit in the work by Greene and others is the assumption that population continuity extends at least as far back as the late Pleistocene (ca. 12,000 BP). Turner and coworkers contend that continuity can be claimed only if non-Nubian populations are also considered in statistical analyses of dental trait variation in this region.

Turner and coworkers include in their analysis additional Nubian dentitions from the late Pleistocene 'Upper Stone Age', Meroitic, X-group, Christian period, and historic era European samples. Computed MMD values, modified for small samples and tested for significance, reveal few significant differences between Meroitic, X-group and Christian periods, thus confirming Greene's earlier conclusions regarding population continuity. However, significant differences between the Pleistocene and later groups were clearly identified.... Because of the apparent temporal discontinuity between the Pleistocene and later populations, Turner & Markowitz (1990) hypothesize that the ancestry of recent Nubians was not derived from local late Pleistocene populations, and that a population replacement event occurred during the Holocene in Nubia. The origin of these later populations is unclear, but, solely on the basis of dental traits, they argue that populations north of Nubia containing European and Near Eastern traits are the most likely sources.

In an effort to identify other possible sources of variation, Irish & Turner (1990) compared their sample of Nubian dentitions (late Pleistocene to Christian period) to historic-period dentitions from a west African group — the Ashanti. Univariate and MMD statistical treatment of these samples reveal strong similarities between modern west Africans and late Pleistocene Nubians. As with previous studies, later Holocene dentitions were found to be very similar. The late Pleistocene and modern west Africans are strongly divergent from the Meroitic, X-group, and Christian period Nubians. Therefore, the authors argue that there is a population discontinuity between the late Pleistocene and Holocene populations in Nubia, with the former sharing biological affinities with west Africans. Irish & Turner (1990) suggest that the discontinuity can be explained by high rates of violence and decline (or possible extinction) in late Pleistocene (Mesolithic) Nubian forager, which may have left them susceptible to invasion or 'genetic swapping' by other groups from west Africa.

Turner and coworkers' findings are intriguing, but their analyses do not necessarily disprove the continuity model for the Pleistocene to Holocene transition. Especially problematic is the virtual lack of data from the period between the A-group and the Mesolithic, which represents nearly four millennia of occupation of the region. Comparisons of Mesolithic and A-group populations reveal a decrease in craniofacial robusticity and dental complexity. To be sure, the agent of change could have been gene flow from some other region. Additional dental and morphological data, and a more substantial treatment of the archaeological context from regions surrounding Nubia, are required before the discontinuity model can be accepted. Moreover, the west African collection used for identifying dental trait frequencies is largely undocumented. Therefore, although the similarities between late Pleistocene and west African dental traits are interesting, they are not compelling. From the preponderance of evidence from other studies of craniofacial morphology, biological change, and population history, a model of population continuity appears to fit the evidence best.

It's extremely unlikely that Negroids would have penetrated so far north and east that early in time, and even more so considering that the later Nubians were Caucasoid, which requires the equally unlikely explanation of total population replacement after the Pleistocene. The continuity model that a robust, generalized early population evolved into Nubia's modern Caucasoid inhabitants makes a lot more sense.