Category Archives: race

Clandestine trysts and human evolution

Recent advances in the field of paleogenomics (the study of ancient genomes) have uncovered the story of inter-species mating in those early days out of Africa before dispersal into Eurasia. Prior to these studies we’ve had little evidence supporting either cultural interaction with archaic humans or inter-breeding.

Clandestine trysts or common practice? The draft sequence of the Neanderthal genome published in 2010 revealed that we mated with Neanderthals in the Near East enough to share 1-4% of our DNA with them. On the heels of the draft sequence of the Neandertal genome, the same team published the Denisovan genome using DNA extracted from an exceptionally preserved finger bone from remains found in Denisova Cave in Siberia. The archaeological data at Denisova show a mixed toolkit with elements of Upper- and Middle-Paleolithic industries. Molar morphology indicated Denisovans were distinct from both modern and known archaic humans. The genomic data indicate Denisovans were indeed a new species with unique genomic markers. The power of modern genomics allows us to also find evidence of mating with modern humans, specifically modern Melanesians who share 4-6% of their genomes with Denisovans. Were these matings clandestine trysts or was there more at stake—some flow of genes to modern humans that helped us adapt to the novel environments of Europe and Asia?

Genomic breadcrumbs? Preliminary comparisons between Neandertal and human genes indicate significant differences in aspects of cognition, metabolism, and skeletal and skin morphology. But what about the inherited portion of the genome? Does it have a role in any functional aspect of our biology and physiology? Dr. Green, lead author on the draft sequence of the Neandertal genome described the inherited portion as ‘sparsely distributed across the genome, just a ‘bread crumbs’ clue of what happened in the past’. But two new papers tell a different story, suggesting that inter-breeding may have significantly contributed to successful adaptation to the new environments of Eurasia.

In the summer of 2011, another team identified a Neandertal origin for a unique cluster of co-inherited gene variants (a haplotype) in the non-coding segment of the dystrophin gene on the X-chromosome. This haplotype occurs at a frequency of 9% in all modern non-African human populations and likely first appeared in the genome prior to or very early in the migration out of Africa. The authors of the study posit that either this genetic (and/or cultural) exchange enabled successful modern human adaptations to the novel environments of Eurasia. There is an intriguing possibility that human males left Africa in greater numbers and mated with archaic females: an earlier study on modern human variation found the X-chromosome experienced more than expected genetic drift at the time of human migration out of Africa, a pattern not found in the migrations into East Asia and Europe.The authors of this study conclude that female effective population size was reduced compared to males due to some sex-biased process or natural selection affecting the X-chromosome in non-African populations.

Speculations that inherited genomic material conferred a fitness advantage gained further ground in a study published this summer in Nature. A Stanford University team identified HLA gene variants that are rare in modern Africans but significantly present in West Asians, again suggesting genetic admixture outside Africa prior to Eurasian expansion. HLA class I genes are critical to the immune system because they target and destroy pathogens. The authors of the study argue that inter-breeding restored HLA diversity that was reduced by a population bottleneck in migration out of Africa, citing examples of similar events in the evolutionary genetic history of the peopling of the Americas. Not only was diversity restored to modern humans but new immune variants specifically adapted to local pathogens may have been acquired in the process as well. HLA-A*11 (associated with Epstein-Barr virus protection), for example, has become a dominant form in non-African populations occurring at rates of 64% in East Asia and Oceania (and even more in Papua New Guinea) suggesting strong selection. The high frequency of these gene variants (as compared with other regions of the genome) may be explained by the need for the immune system to be flexible to new pathogens (particularly rapidly evolving viruses), rendering it more susceptible to the forces of natural selection.

The future of the past. If the data from these various studies is supported by future work, we may end up rethinking our relationship to our closest cousins – were we separate species? Even field biologists who have the array of genes, biology, physiology and behavior sometimes have trouble determining whether two groups be classed as separate species or not. For those working in paleoanthropology or paleogenomics, the dataset is even more limited and the creation of new taxa is temporary pending further data but useful as a heuristic tool.

The field of paleogenomics is relatively young and has a tremendous number of methodological and technical challenges to overcome before we can comfortably say that the sequences yielded are authentic and reliably represent the genetic data. A major challenge is verifying and authenticating the endogenous (or local) DNA in a specimen that has been potentially contaminated by microbes and human researchers. The past decade has been punctuated by marvelous advances that have helped us better understand recent human evolution and ourselves. The possibility that our advantage in global colonization derives from early acts of inter-breeding is a fascinating one. With the rapid advancements in technology and increased interest in ancient DNA, the future looks promising for unraveling the story of the immediate past.

  1. Green, R. E. et al., Science 328, 710 (2010).
  2. Reich, D. et al., Nature 468, 1053 (2010).

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Filed under anthropology, Anthropology and Evolution, Denisovan, Neandertal, race, Science, sex

Race and Anthropology in European Origins

In the US, our focus on race is centered on the enslavement of Africans and the consequences of those actions. The past 11 years have been wrought with new aspects of race and race relations. After 9-11, the often ill-treatment of anyone who appeared to be Arabic corresponded to the surge of emotions surrounding the tragedy of that day. Shifts in our demography have also played an increasing major role in our understanding of race: Hispanics are now the largest urban minority and are also responsible for the majority of population growth in the US. The heated Democratic primaries that featured two minority candidates (e.g., non-white and non-male) was a benchmark moment only supplanted by the election of Barak Obama to the presidency. These events are part of the unfolding complexity of race in America, a young nation with a huge immigrant population and varied demography.

When I teach race and anthropology, I try to help American students understand that the global human experience of race isn’t about physical appearance (even if that is true in the US, among other places). Rather and put simply, race is about defining one’s group against another group. There are reasons this happens: immigrants who might be perceived as a threat to local economic security or regular encounters with a group that is ‘different’. Difference is where the complexity and vagueness lies. Anthropologist Conrad Kottak talks about race relations in Brazil as based on factors such as income, occupation, and residence than skin color. In Japan, the famous treatment of Koreans as second-class citizens has little to do with physical appearance and more to do with point of origin. In some early cities, we see archaeological evidence of ‘racial’ enclaves: the gradual transition from homogenous bands of nomadic hunter-gatherers to sedentary urban conglomerations of people was partially defined by the new proximity of strangers.

But, what about indigenous populations? The US has a long and terrible history to overcome with regard to interactions with Native populations. On the other side of the pond, the immigration to Europe by indigenous populations of former Empires (north Africans in France and West Indians and Indians in the UK)  has created troubled race relations like those we have dealt with in the US for too many years. But, what about the ‘indigenous’ Europeans? Is there a homogenous European identity?

In Japan and China, much archaeology and even bioanthropology is focused on promoting the thesis that there is an independent and unique origin for those cultures that is separate and exclusive from other geographic regions around the world–a sort of racial purity. The genetic homogeneity of populations and prehistorically recent settling of Europe don’t indicate much complexity surrounding origins. Or, do they?

For the past 10 or so years, the peopling of Europe has been heating up in various academic circles and is more interesting that one might think. Without going into the back and forth of the various studies, we can summarize the debate by starting with the demic diffusion model promoted by Cavalli-Sforza that has been reformed and refuted by other scholars along the way. [For a summary of the debate, see the chapters on the peopling of the world in Jobling’s text on evolutionary genetics.]  The central question has been whether Europe was settled by the expansion of Neolithic farmers from a Near East beachhead or from Mesolithic populations surviving in glacial refugia. Or, are they are a blend of both–did the farmers interbreed with locals as they wended their way north into the Balkans or along the Mediterranean coast?

A 2010 study from the University of Leicester asserts a farmer origin:

There has been much debate about whether the westerly spread of agriculture from the Near East was driven by farmers actually migrating, or by the transfer of ideas and technologies to indigenous hunter-gatherers. Now, researchers have studied the genetic diversity of modern populations to throw light on the processes involved in these ancient events.

The new study, funded by the Wellcome Trust, examines the diversity of the Y chromosome, which is passed from father to son. Mark Jobling, who led the research, said: “We focused on the commonest Y-chromosome lineage in Europe, carried by about 110 million men — it follows a gradient from south-east to north-west, reaching almost 100% frequency in Ireland. We looked at how the lineage is distributed, how diverse it is in different parts of Europe, and how old it is.” The results suggested that the lineage spread together with farming from the Near East.

Dr Patricia Balaresque, first author of the study, added: “In total, this means that more than 80% of European Y chromosomes descend from incoming farmers. In contrast, most maternal genetic lineages seem to descend from hunter-gatherers. To us, this suggests a reproductive advantage for farming males over indigenous hunter-gatherer males during the switch from hunting and gathering, to farming — maybe, back then, it was just sexier to be a farmer.”

Another 2010 study argues that hunter-gatherers were thick on the ground and this density slowed the spread of farmers:

The “reaction-diffusion” model explains the archaeological data and the decline in the speed of progress of the Neolithic front. This is based on two mathematical effects relating to the availability of space for the incomers (dispersal of farmers dependent on spatial variation in the population density of hunter-gatherers, and a modified population growth equation).

“The density of hunter-gatherers was higher in northern latitudes, which enables the model to explain the deceleration in the Neolithic transition in Europe,” explains Joaquim Fort, the other author of the study, who is also a physicist at the UdG.

A 2011 study from Oxford asserts the opposite:

Researchers say their work shows that the set of genes chosen to estimate the age of this group of men vary the outcome enormously. They add that the previously reported east-west pattern is not found in their larger and more comprehensive dataset. This, the Oxford-Edinburgh team says, leaves little evidence for a farmer-led dispersal of this major group.

According to Dr Cristian Capelli, the Oxford geneticist who led the research, the study “resets” the debate on the peopling of Europe. He says, “Our works overturns the recent claims of European Y chromosomes being brought into the continent by farmers.”

Co-author, Dr Jim Wilson of the University of Edinburgh’s Centre for Population Health Sciences, adds that the paper shows for the first time that certain properties of the genes studied strongly influence the accuracy of the date estimate.

“Estimating a date at which an ancestral lineage originated is an interesting application of genetics, but unfortunately it is beset with difficulties and it is very difficult to provide good dates. Many people assume that the more genes the more accurate the dates, but this is not the case: some genetic markers are more suited to dating than others.”

The Oxford study seems to have covered new ground with more genes and fine-honed methods and techniques but this will likely not be the last word in the debate. Ultimately, one may wonder what this means to an average European? Well, one is either descended from technologically and culturally progressive farmers from the Fertile Crescent or descended from (at least partly) from technologically and culturally less advanced middle stone aged hunter-gatherers. Clearly, one of these scenarios meshes with European identity more. But, since we now know that non-Africans are partly descended from Neanderthals, maybe the issue of neolithic versus mesolithic origin isn’t so important afterall.

However you look at it, all populations (even ones that seem to have a homogenous and established origin) are interested in roots that make them unique and that mesh with cultural identity. And this is what makes race culturally specific in the details but universal in the need to categorize by origin.

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