Global Genetic History of Homo sapiens is the title of a new special issue of Current Biology (volume 20, issue 4, dated 23 February 2010), with eight papers available free online.

The first article is a guest editorial by Colin Renfrew, a British archaeologist who has worked for decades in the Middle East. His books often focus on the emergence of civilization, the emergence of Indo-European languages, and a relatively new subdiscipline in archaeology called archaeogenetics. Renfrew has defined archaeogenetics as research at the confluence of archaeology, linguistics, and genetics. Archaeogenetics, therefore, uses molecular genetics to expand archaeological data about early human populations. This is particularly useful in reconstructions—or models—of early human migrations and the populating of the globe.

Renfrew’s editorial, “Archaeogenetic—Towards a ‘New Synthesis’?” sets up the other articles in this special issue. The next six papers address human migration in specific geographic areas: Africa, Europe, South Asia, East Asia, Oceania, and the Americas. Each provides considerable detail and summarizes genetic, linguistic, and archaeological data for the region.

Renfrew closes his introductory editorial with these observations:

Perhaps the most important general point that can be drawn from the reviews assembled in this special issue might be that we have not yet learnt how to interpret the data very effectively. A number of contributors have commented upon the need for simulation studies, based upon explicit models which might allow the testing of specific scenarios…, and this is likely to be one of the most important future research directions. Above all, the pace of research is now so fast that new insights are soon likely to become available. These are early days in the field of archaeogenetic research, and I predict that over the next twenty years or so a more coherent synthesis of the data from genetics, archaeology and linguistics is likely to emerge than we can yet envisage. [page R165]

Figure 1* from O’Rourke and Raff’s article.

As an example of the geographically defined articles, consider the one on the Americas, “The Human Genetic History of the Americas: The Final Frontier” by Dennis H. O’Rourke and Jennifer A. Raff. O’Rourke and Raff marshal mitochondrial DNA data (which is passed down through the maternal line) that shows five major genetic groups among New World peoples. They conclude that these data, along with other genetic data, suggest New World peoples coalesced “just prior to or immediately after the LGM”—the Late Glacial Maximum. The LGM refers to the last time ice sheets extended far south/north from the Earth’s poles, when mid-latitude locales were cooler and drier than today. As the ice formed, it lowered sea levels, when the ice captured sea water. Thus, more land was exposed on the margins of continents, and the Bering Sea land bridge could have provided a “highway” for Asian peoples traveling eastward, either on land or in small boats following the coast. Given the very early dates for human occupations from southern South America, O’Rourke and Raff note:

…the archaeological data in the Americas continue to raise questions regarding the timing and mode of colonization. The resolution afforded by the newer molecular data assists in evaluating alternative migration scenarios. [page R202]

Yet, even with all the data they bring together, O’Rourke and Raff conclude, as do many researchers regarding a wide variety of topics, that “more work is needed.” They write:

“Complete agreement between mtDNA, Y-chromosomal DNA and autosomal genetic systems has not yet been realized with respect to colonization models….” [page R206]

This is consistent with observations in the final article, “The Genetics of Human Adaptation: Hard Sweeps, Soft Sweeps, and Polygenic Adaptation” by Jonathan K. Pritchard, Joseph K. Pickrell, and Graham Coop. They agree with the last quote above:

Ultimately, a comprehensive model of the nature of selection would tell us how much adaptation occurs by any of a variety of different models and mechanisms. … To make real progress on these problems will require much greater integration of selection studies with biological information. [page R213]

These articles that summarize the current understanding of human archaeogenetics are insightful and informative, although some of the data they discuss is rather technical. Perhaps after you take a look at one or two of them, you will have some comments you’d like to note here—please login and do so!

The link to the special issue is here; you can download any of the eight papers individually.

* The original figure title reads: “Hypothesized routes for original migration into the Americas. The Beringian and Pacific coastal routes (blue and yellow, respectively) may have been roughly contemporaneous following the Last Glacial Maximum (LGM), although contemporaneity is not certain. The more hypothetical northern migration path (red) implies a pre-LGM population movement. These migration paths need not be considered mutually exclusive.”

Illustration by Barry Roal Carlsen, provided by University of Wisconsin—Madison.

Did people kill off Pleistocene megafauna in North America, or were those species done in by climate shifts? Or…?

This question is still not answered unambiguously.

However, research by Jacquelyn Gill of the University of Wisconsin—Madison shows that neither scenarios is probable based on fossil pollen, charcoal and dung fungus spores that date to just after the ice retreated. Neither the mass extinction model, based on heavy hunting, nor simple climate and thus habitat change matches the data she and colleagues Stephen T. Jackson (University of Wyoming), Katherine B. Lininger (University of Wisconsin—Madison), and Guy S. Robinson (Fordham University) have marshalled.

According to Terry Devitt’s story (19 November 2009) on the University of Wisconsin—Madison website:

The decline of North America’s signature ice age mammals was a gradual process, the Wisconsin researchers explain, taking about 1,000 years. The decline in the huge numbers of ice age animals is preserved in the fossil record when the fungal spores disappear from the record altogether: “About 13.8 thousand years ago, the number of spores drops dramatically. They’re barely in the record anymore,” Gill explains.

Devitt continues:

While both the extinction of North America’s ice age megafauna and the sweeping change to the landscape are well-documented phenomena, there was, until now, no detailed chronology of the events that remade the continent’s biological communities beginning about 14.8 thousand years ago. Establishing that the disappearance of mammoths, giant beavers, ground sloths and other large animals preceded the massive change in plant communities, promises scientists critical new insight into the dynamics of extinction and its pervasive influence on a given landscape.

Archaeologists are often confronted with this situation: how do we get data on human behavior or the human situation, when we don’t have it directly from the archaeological record of human occupations? This research by Gill and her colleagues shows one solution developed to help understand the ecological situation in interior North America early in human occupation of the continent.

Stand by for more data….

Scientists studying ice cores from Antarctica and Greenland conclude that the Earth’s climate changed rapidly about 14,700 years ago. They studied the oxygen isotopes in air bubbles trapped in the ice. About 14,700 years ago, they found changes in the air that came from increases in vegetation levels. These increases happened over about 200 years, which is quite rapidly.

Credit: Zina Deretsky, National Science Foundation

The press release notes:

The ratio of ¹⁸O to ¹⁶O found in an ice core has shown the history of abrupt climate change on Earth. For example, dry spells around 14,700 years ago resulted in the planet being quite arid north of the equator. Monsoons that followed, caused the proliferation of vegetation north of the equator 14,500 years ago.

Combine this with information from the National Science Foundation’s 2009 report “Solving the Puzzle: Researching the Impacts of Climate Change Around the World.” On page 62, the report says:

Earth’s landmasses support critical ecosystems, host Earth’s freshwater environments, and sustain almost all human agricultural activities. Land separates freshwater from the sea, stores nutrients essential for terrestrial and aquatic life, and holds a fossil record of Earth’s climatic past. As the planet warms, the conditions favorable to many plant and animal species are expected to shift toward the poles. Individual species will differ in their ability to make the same shifts. The resulting altered species distributions will likely cause significant disruptions to established ecosystems, as habitats adjust to new species populations.
Land use is inextricably linked to the carbon cycle. Changing land-use patterns, such as clearing forest to create agricultural plots, change the dynamics of the carbon cycle. Livestock such as cattle contribute a net surplus of carbon to the atmosphere in the form of methane, a powerful greenhouse gas.

Past climate change patterns are not predictors of the rate of change we may be experiencing today.

Undisturbed archaeological remains buried in the soil contain all sorts of chemical clues invisible to the human eye. The oxygen isotopes in the air bubbles in the ice are a similar invisible clue. Visible archaeological remains can also reveal clues as to the climate in the past. What invisible chemical information about the climate of the past do you think may be contained in archaeological sediments, artifacts, and features?

Read the full press release on the Science article by clicking here.

Click here to go to the National Science Foundation’s website, where you can download their 2009 report “Solving the Puzzle: Researching the Impacts of Climate Change Around the World.”

Dr. Al Goodyear of the University of South Carolina was the featured speaker at our October 11 meeting at Famous Dave’s Bar-B-Que on Washington Road. Dr. Goodyear gave an update of work at the Topper site and a review of the latest concepts in Paleo Indian studies, including the 11,900 YBP comet theory and the evidence of Redstone points. Dr. Goodyear presented Augusta chapter member Danny Greenway with an award in honor of his contributions and support of Paleo Indian research.

Chris Murphy, Tammy Forehand, and John Whatley attended the SGA board meeting on October 12th.

Jill Nazarete continued her volunteer work at the Savannah River Archaeological Research laboratory.

John Whatley worked with Robert Moon at the Beech Island archaeology day and led a discussion on Georgia projectile points at the University of Georgia’s Rock Eagle facility. John worked with the Ocmulgee chapter of SGA on artifact identification days at the McIntosh house at Indian Springs on October 27th and the Pine Ridge School in Old Clinton on November 17th.

The projectile point handout used for our artifact identification days is being expanded to include pottery types. Our annual holiday party will be held Thursday night December 13th at the home of Audrey and Paul Mahoney.