March 17, 2010

Abstracts from AAPA 2010

Some abstracts from the upcoming (April 14-17) meeting of the American Association of Physical Anthropologists.

Why are pygmies small? An anthropometrical and anthropogenetical question
Pygmy populations from central Africa have the shortest stature worldwide. The name “pygmy” indeed comes from the Greek “pugmaios” that is a measure of length. This reduced stature has been the subject of numerous endocrinological studies and many evolutionary hypotheses have suggested that this phenotype was an adaptation to the rainforest (hot, humid and dense environment), to alimentation or due to life history trade-offs (high mortality). We have anthropometrical data for a sample of more than 1000 individuals from 7 pygmy populations and 3 neighbouring farmer populations from Gabon, Cameroon and Central African Republic. DNA samples are also available for a large number of individuals. The analysis of anthropometrical data shows that all pygmy groups have a male mean stature under 160 cm (this was used in the definition settled by Cavalli-Sforza in1986) and that a high variability exists between various pygmy populations. Verdu et al. (2009) published a genetic analysis based on neutral microsatellites on the same populations and found that pygmies present a variable admixture proportion with nonpygmies. Comparing this data with our anthropometrical data at the individual level we find a strong correlation between level of admixture and stature, thus strongly supporting the existence of a genetic component in pygmy short stature. We developed a candidate-gene approach to search for such genetic factor and will present current results on various genes located in the GH-IGF1 axis.
New evidence on headshaping from the Early Byzantine Maroneia in Thrace, Greece.

The first case of headshaping from Early Byzantine Greece was identified in 2006 at the cemetery of Maroneia (5th-6th c. A.D.). Biocultural evidence suggested the presence of a female individual culturally linked to Hunic traditions. This paper analyzes the second case of headshaping on a female skeleton uncovered in 2009 and allows for the wider discussion of the presence of a larger group related to the Huns in the city of Maroneia. The skull was examined by combining macroscopic observation and x-ray. Points of pressure are recorded in the frontal, post-coronal and occipital regions resulting in an undulation of diploic bone. Possible bilateral pressure on the frontal bone has produced an artificially narrowed frontal. The skull extends posterosuperiorly. These features suggest the application of bandaging producing circular modification. Both headshaped skulls exhibit the same type of modification. Similarly, both women were buried in a supine position, without offerings, just like the remaining 36 deceased individuals in the cemetery of Maroneia. Headshaping was unknown among Byzantine customs. On the contrary, the Huns who attacked the Balkans twice and who unsuccessfully threatened Maroneia in 411 practiced a pronounced form of circular headshaping. Consequently, biocultural evidence strongly supports the hypothesis that a group linked to the Huns was installed at the city and was assimilated into this Early Byzantine society. Future biogeochemical analysis needs to be undertaken in order to investigate migration patterns. However, headshaping reflects the cosmopolitan character of Maroneia, an important urban center in a province of the Byzantine Empire.

The genetic legacy of indigenous Caribbean peoples: Evidence from autosomal and mitochondrial data.

Archeological evidence suggests that autochthonous peoples began to migrate into the eastern island chain in the Caribbean, known as the Lesser Antilles, as early as 7200 years BP. Upon the arrival of Europeans, an estimated 2-4 million people lived on these islands. Within 32 years of contact, the native populations had virtually disappeared from the region due to European-introduced disease, abuse, and genocide. This lead many scholars to conclude that indigenous Caribbean people had become extinct. However, small pockets of indigenous communities have survived and are present today on several Lesser Antillean islands. Furthermore, ethnohistoric data suggests that gene flow occurred between autochthonous peoples and enslaved Africans beginning in the colonial period. In this study, we examine the genetic legacy of autochthonous Caribbean peoples from the Lesser Antilles in contemporary African- Caribbean populations as evidenced from mitochondrial data and novel autosomal data. A total of 516 individuals from eight Caribbean islands were typed for 109 ancestry informative markers and a subset of individuals were also typed for their mitochondrial haplogroup. Mitochondrial haplogroups indicate that 5% of the sample has indigenous ancestry while admixture estimates from autosomal markers show 4% indigenous ancestry. Both lines of data suggest that despite the dramatic postcontact decline in population size, indigenous Caribbean people have made notable genetic contributions to contemporary African-Caribbean populations. Furthermore, these genetic contributions vary according to the genetic system typed and across the islands.
Chuvash origins: Evidence frommtDNA Markers.
ORION M. GRAF et al.

A sample of 96 unrelated individuals from Chuvashia, Russia was sequenced for hypervariable region-I (HVR-I) of the mtDNA molecule. The Chuvash speak a Turkic language that is not mutually intelligible to other extant Turkish groups, and their genetics are distinct from Turkic-speaking Altaic groups. Some scholars have suggested that they are remnants of the Golden Horde, while others have advocated that they are the products of admixture between Turkic and Finno-Ugric speakers who came into contact during the 13th century. Earlier genetic research using autosomal DNA markers suggested a Finno-Ugric origin for the Chuvash. This study examines non-recombining DNA markers to better elucidate their origins. The majority of individuals in this sample exhibit haplogroups H (31%), U (22%), and K (11%), all representative of western and northern Europeans, but absent in Altaic or Mongolian populations. Multidimensional scaling (MDS) was used to examine distances between the Chuvash and 8 reference populations compiled from the literature. Mismatch analysis showed a unimodal distribution. Along with neutrality tests (Tajima’s D (-1.43365) p less than 0.05, Fu’s FS (-25.50518) p less than 0.001), the mismatch distribution is suggestive of an expanding population. These tests suggest that the Chuvash are not related to the Altai and Mongolia along their maternal line but supports the “Elite” hypothesis that their language was imposed by a conquering group-- leaving Chuvash mtDNA largely of Eurasian origin with a small amount of Central Asian gene flow. Their maternal markers appear to most closely resemble Finno-Ugric speakers rather than fellow Turkic speakers.
Population history and substructure of Anatolia and Turkey as evidenced by craniofacial diversity.

Anatolia, the Asian segment of Turkey, is an area of evolutionary importance for human groups who used this corridor as a bridge for migration between the Caucasus, Western Asia and Europe since Lower Paleolithic times. Historically, Anatolia has been occupied by diverse civilizations, including the Byzantine and Ottoman Empires. This study is an attempt to understand Turkish population substructure and history by examining craniofacial diversity through several temporal periods framed within a population genetic model. If the region of Anatolia has been used as a migratory corridor for peoples spanning disparate geographic areas (Balkans, Central Asia, and East Asia), then gradual craniofacial change is expected due to these migrations coupled with extensive admixture. Studies using mtDNA indicate a pre-Neolithic expansion resulting in extensive migration, while Y chromosome studies reveal haplogroup clustering and gene flow from the Caucus with less admixture from Central and East Asia. Overall, our results indicate minimal Turkish population substructure. When crania were separated into sex, our results are consistent with uniparental marker population history. Female crania show a distinctness with modern groups and are actually more similar to Neolithic European and Near Eastern populations. This would indicate a relatively stable female population in Anatolia since Neolithic times. Male crania are more heterogeneous and cluster within a larger geographic zone of Eurasia and the Near East consistent with greater male migration. There is little support for admixture from Central or East Asian groups. These results support the hypothesis for a Turkic language displacement with insignificant genetic exchange.
Genetic analyses reveal a history of serial founder effects, admixture between longseparated founding populations in Oceania, and interbreeding with archaic humans.

Genetic anthropologists continue to debate whether human neutral genetic variation primarily reflects a continuum of demes connected by local gene flow or colonization and serial founder effects. A second unresolved issue concerns the genetic contribution of archaic species to the modern human gene pool. Some studies suggest that this contribution was substantial and that it played an important role in human adaptation. These issues remain unresolved because of inadequacies and biases in datasets, problems in statistical methodology, and the failure to recognize that different evolutionary processes may produce similar outcomes. This study redresses these limitations by analyzing gene identity within and between populations in a dataset comprised of 614 STRs assayed in 1,983 people from 99 widespread populations. Our strategy is to fit hierarchical models to these data and examine residual deviations from the models. Each model involves nesting smaller units such as populations into larger units such as continental regions. It is possible to restate many of these models as either expansions or reductions of each other and thereby identify aspects of population structure that have had a major impact on the overall pattern of diversity. The strong fit of a model estimated using the Neighbor Joining algorithm indicates that human genetic diversity primarily reflects a history of successive founder effects associated with our exodus from Africa, not a continuum of demes connected by gene flow. Residual deviations from the model suggest: 1) the genomes of Oceanic peoples are the product of two independent waves of migration to the region and admixture, and 2) genetic exchange occurred between archaic and modern humans after their initial divergence.
Correlations between genetic ancestry and superficial traits indicate substantial admixture stratification in Brazil.

Brazil is one of the most admixed countries in the world. How this admixture affected the distribution of genetic ancestry across Brazilian ethnic (“Color”) groups is a fundamental question which to date has only received minimal attention. In an effort to systematically study variation in genetic ancestry in Brazil, we collected DNA and various phenotypic measures from 596 volunteers in Brasilia, Brazil. Participants were asked to provide their self-described “Color” as defined by the Brazilian census (Preta/Black, Parda/Brown, Branca/White, Indigena/Indigenous, Amarela/Yellow). Phenotype data was collected from each subject including hair texture, highresolution eye photographs, skin and hair color by reflectometry, and three-dimensional facial photographs. To estimate genomic ancestry, DNA from each participant was genotyped using 176 ancestry informative markers (AIMs), autosomal SNPs with large frequency differences between parental populations known to contribute to Brazilian admixture (West African, East Asian, European and Indigenous American). Although genomic ancestry shows significant overlap across “Color” groups, there are highly significant differences in average proportional ancestry. Additionally, analyses comparing trait values and genetic ancestry show significant correlations consistent with expectations of populations stratified with respect to genetic ancestry. Ethnographic research indicates that designations of “Color” are fluid and largely based on physical traits as opposed to known ancestry. This likely contributes to the observed ancestry overlap between ethnic groups and the strong association between phenotype and group. This study emphasizes the importance of genetic marker based estimates of ancestry as well as objective assessment of superficial traits in understanding the admixture process.
Geographic structure of genetic variation in North America: Population fissions and European admixture.

A satisfactory understanding of how modern Native North America populations are biologically related to each other requires increased sampling of populations and/or genetic markers and testing of the fit of different models of population structure. To this end, we combine new autosomal microsatellite data from Native North American populations with previously published data. Using J.C. Long’s Generalized Hierarchical Modeling software, we evaluate the fit of different trees to the data. Although we observe a correlation between population pairwise genetic and geographic distances, as expected with a long-term process of isolation by distance, we show that this correlation likely results from geographically-structured population fissions. This pattern could result from the initial peopling of North America or from a later process. The magnitude of European ancestry in the sampled populations, as estimated with the software structure, varies drastically among geographic regions, and may limit our ability to use modern genetic variation to investigate Native North American prehistory.This study was funded by the Wenner-Gren Foundation for Anthropological Research, grant number 7580 to K.B. Schroeder and D.G. Smith, and by the National Science Foundation, grant BCS- 0422144 to R.S. Malhi, B.M. Kemp, and D.G. Smith.
Coalescent modeling of Yakut origins points to small founding population based on mtDNA variation.

Based on archaeological and ethnohistorical evidence, the Yakut people of northeastern Siberia are considered to be descendants of ancient Turkic-speaking populations once living in the distant Altai- Sayan region on the Russian- Mongolian border. The results of phylogeographic studies on Siberian mtDNA variation have been generally concordant with a southern Yakut origin, although the timing of the northern migration, the size of the founder group and the degree of genetic admixture with non-Turkic Siberian populations are less apparent. In an effort to better understand Yakut origins, we modeled 25 demographic scenarios, including parameters such as effective population size, growth rate and gene flow, and tested by coalescent simulation whether any are consistent with the patterns of mtDNA diversity observed in present-day Yakuts. The models consist of either two simulated demes that represent Yakuts and a South Siberian ancestral population, or three demes that also include a regional Northeast Siberian population that served as a source of localized gene flow into the Yakut deme. The model that produced the best fit to the observed data defined a founder group with an effective female population size of only 150 individuals, migrating northwards approximately 1,000 years BP and undergoing significant admixture with neighboring populations in Northeastern Siberia. These simulation results indicate a pronounced founder effect that was primarily kin-structured and reconcile reported discrepancies between Yakut mtDNA and Y chromosome diversity levels.
The role of selection-nominated candidate genes in determining Indigenous American skin pigmentation.
World-wide variability in skin pigmentation has been a subject of anthropological inquiry from the beginning of our discipline. Recent genomic studies indicate that skin pigmentation is one of the most rapidly evolving phenotypes in many human populations and that genes underlying skin pigmentation have been subject to some of the most extreme selective pressures of any genes in the human genome. Unlike previous research, this study both identifies pigmentation genes that have undergone selection in Indigenous American populations and tests the influences of these genes on skin color in admixed individuals. 906,600 single nucleotide polymorphisms (SNPs) were surveyed for signatures of selection in indigenous populations from Central and South America. Evidence of selection was identified by comparison to HapMap Phase I populations using reduction in heterozygosity (lnRH), Locus- Specific Branch Length (LSBL), Tajima’s D, and haplotype block structure. In the 12 pigmentation candidate genes that show the strongest evidence of selection (ADAM17, POMC, AP3B1, OPRM1, SILV, OCA2/HERC, PLDN, MYO5A, RAB27A, CYP1A2, ATRN, and ASIP), 48 SNPs selected to represent the overall variation in the selection nominated candidate genes were genotyped in individuals of admixed Indigenous American and European ancestry. These SNPs show substantial allele frequency differences between the parental populations. Using admixture based regression model analyses, genes contributing to darker skin pigmentation in Indigenous Americans were found. This study not only identified skin pigmentation genes contributing to skin color variation in previously understudied Indigenous American populations, it validated the usefulness of using population genetic tests of selection to identify functional genes. This study was generously funded by the National Science Foundation Dissertation Improvement Grant 0925976


terryt said...

"1) the genomes of Oceanic peoples are the product of two independent waves of migration to the region and admixture"

We seem to have come to some sort of agreement at your earlier post on the subject. It seems basically one from the north (Northern China), and one from the west (India).

"2) genetic exchange occurred between archaic and modern humans after their initial divergence".

I'm sure there will be many doubters regarding that statement. However, again, I have long suspected it to be so.

Mongols said...

"Northern China"? you mean, the areas of yellow river?

Andrew Oh-Willeke said...

The statement of two waves of Oceanic peoples is not very controversial if they include New Guinea in Oceanic peoples and are suggesting an Austronesian wave and a prior Papuan wave.

"genetic exchange occurred between archaic and modern humans after their initial divergence"

I'd be interested in seeing the evidence behind that. The abstract doesn't provide much insight. Are they saying that Javanese show something in their genes that links them to Homo Erectus, or that there is evidence of Hobbit-modern human admixture on Flores?

Conventional wisdom is that Australians and Papuans moved into virgin territory, and that areas that they didn't reach were not inhabited by humans or human ancestors until the Austronesians came along. Which populations are they finding the signal in?

Andrew Oh-Willeke said...

More on old Flores archeology here.

terryt said...

"'Northern China'? you mean, the areas of yellow river?"

Possibly. But somewhere north of SE Asia.

"The statement of two waves of Oceanic peoples is not very controversial if they include New Guinea in Oceanic peoples and are suggesting an Austronesian wave and a prior Papuan wave".

It's more than just a little ambiguous in that regard. I suspect they're talking two migrations in the Australian/Papuan period. The two regions are remarkably separate in their haplogroups, and even their physical appearance.

"I'd be interested in seeing the evidence behind that. The abstract doesn't provide much insight".

None at all actually. It would certainly be interesting to follow the article up.

"Are they saying that Javanese show something in their genes that links them to Homo Erectus"

That's the way I read it, although I could be totally wrong.

"Conventional wisdom is that Australians and Papuans moved into virgin territory, and that areas that they didn't reach were not inhabited by humans or human ancestors until the Austronesians came along".

And almost certainly basically correct. Although the Australians and Papuans must have moved through some islands later occupied by Austronesians, which implies the islands had become uninhabited by the Austronesian expansion. A conclusion Maju is very much opposed to.

"Which populations are they finding the signal in?"

That's what I'd like to know as well. Promises to be controversial anyway.

terryt said...

"More on old Flores archeology here".

Thanks. From the link: 'A date of 880,000 years ago for human occupation made for a convenient explanation of faunal turnover on the island, which happened around that time. The turnover included the extinction of the small pygmy stegodont species Stegodon sondaari, which was replaced in later faunal assemblages by the Java-derived Stegodon florensis".

A 'faunal turnover' argues agains a sea crossing. So argues against necessary human possession of boats so early.

Cĕvĕlti said...

It's a shame ORION M. GRAF et al. made a careless observation on the history of my people and only claim my ancestors - Chuvash - to be descendants of Golden Horde, who arrived in the 13th century. It's a ridiculous 19th century non-scientific view. Chuvash (Volga Bulgaria) were actually conquered by Mongols and Tatars (Golden Horde). Thorough historic and ethnographic studies proved over and over that the Chuvash-speaking people settled in the present region from 7th to 9th century, after the defeat of Bulgaria Magna, and later Khazaria. After the Mongolian conquest of 13th century the population split, with Chuvash preserving the original and unique to the Turkic language family Bulgaro-Turkic language, and the other part later forming into Kazan Khanate, inheriting Volga Bulgarian Islam with renewed influences from Central Asia - modern Tatar people. Tatar language is made from mixing of Chuvash, nomad Turkic (original Tatar), and literate Chagatay.

It is also duely observed in todays genetic studies: Tatars show mostly the same results as Chuvash but also significantly more of Turkic nomadic ancestry than the Chuvash (mostly North and Central European). In both populations the Asian component plays a small role, because the Volga Bulgarian region has been of settled agriculturalists. Nomad (original Tatar, Bashkir) and hunter (Finno-Ugrian) populations couldn't compete in number.

It is absolutely apalling that ORION M. GRAF et al. suggests the Chuvash were the Golden Horde founders, when in fact we were the nation who for centuries struggling against it and even helped Ivan the Terrible for better or worse to destroy the Kazan Khanate.