Examples of Recent Human Evolution

The Seeds Article that I mentioned in my last post, about the basics of evolution, talks at length about the idea that natural selection is an ongoing process in modern human populations. Their information primarily comes from a publication in PNAS (Proceedings of the National Academy of Science) written by John Hawks, Eric T. Wang, Gregory M. Cochran, Henry C. Harpending, and Robert K. Moyzis. Their article, “Recent acceleration of human adaptive evolution” argues that the rate of evolution has accelerated in modern humans because a larger population is capable of producing a greater number of random gene mutations. Hawks and colleagues suggest that between 7 and 10% of the human genome is currently evolving at the maximum rate. They argue that natural selection is still an active factor in human evolution because trends of change visible in HapMap (a massive survey of the genetic differences between selected populations from around the world) seems too consistent from person to person to be the result of genetic drift. You might say, “Yeah, that’s just common sense.” However, the idea that human evolution is still active is contradictory to the popular scientific thought of the past several decades that argued that the development of culture got rid of the need for evolution to adapt to our environments. Many scientists today are still arguing for this approach to human evolution. So where can we find evidence to support the newer theory that evolution is still active in modern humans? I can think of two relatively recent examples off-hand: the development of the ability for adult humans to digest milk and the development of the CCR5 gene variant that protects against HIV infection.

The first is probably the most well known to the general public just because of it’s prevalence in our daily lives. How often do you reach for a glass of milk with dinner, or pour milk over your cereal in the morning without thinking twice about it? The ability to drink milk without feeling sick as an adult doesn’t apply to everyone in the world. There’s an interesting table originally published in an article by Robert McCracken that shows the percentages lactose intolerant adults in different ethnic groups. According to McCracken, Sweden, at 4%, has the overall lowest percentage of lactose intolerant adults while Native Americans and Asian Americans have some of the highest percentages of lactose intolerant adults with 95% and 95-100% respectively. The National Digestive Disease Information Clearinghouse reports similar numbers with up to 80% or African Americans, 80-100% of Native Americans, and 90-100% of Asian Americans being lactose intolerant. The general trend overall is that European adults can drink milk while most adults in the rest of the world can’t. Why is this? Looking at the question from an evolutionary perspective we would probably immediately make a hypothesis that the ability to drink milk is the result of a genetic mutation in the past for certain human groups.

Scientists believe that before the domestication of cattle and other milk-producing herds all human adults were incapable of drinking milk because there was no need to drink milk. Children stopped drinking their mother’s milk after their first few years of life and in hunter-gatherer or foraging societies before herd domestication people didn’t have access to milk as a food source. Once nutrient-rich non-human milk became available to humans in pastoralist societies, adults with a genetic mutation that allowed them to consume milk had an additional food source, and thus a survival advantage over adults without the mutation in pastoralist societies. This mutation would then have been selected for because it provided a fitness advantage. Over time, probably the past 3,000-6,000 years, the percentages of adults with the ability to drink milk became what it is today. Two other, more technical hypotheses for why the ability to drink milk as an adult spread so successfully throughout many European societies are discussed in an article by Clare Holden and Ruth Mace.

A second interesting example is the CCR5 gene variant which might protect carriers against HIV. It is probably a much more recent mutation. Scientists believe today that this genetic mutation initially developed and was selected for in Europe during the time of the Black Death or bubonic plague. In their article, “Evaluating plague and smallpox as historical selective pressures for the CCR5-Δ32 HIV-resistance allele,” by Alison P. Galvani and Montgomery Slatkin provide a great discussion about this gene mutation and what scientists are discovering about its development and implication. Both of these mutations have developed and been selected for in recent human history, well after the development of culture. This suggests that using culture to adapt to our environments, technology, and modern medicine alone are not enough to stop evolution in its tracks. Perhaps Hawks and his colleagues are even correct in arguing that evolution is speeding up in humans today because our population size has gotten so big. We can look eagerly to seeing what scientists have to say about this hot topic in the coming future!


Here are some additional resources that I found helpful! -


Robert McCracken’s Article that I mentioned can be found here:

Robert D. McCracken, "Lactase Deficiency: An Example of Dietary Evolution,"
Current Anthropology 12 (Oct.-Dec. 1971, pp. 479-517) and Norman Kretchner, "Lactose
and Lactase," Scientific American 277 (Oct. 1972, pp. 71-78).

More information on Nutritional Adaptation:

http://anthro.palomar.edu/adapt/adapt_5.htm

Clare Holden and Ruth Mace’s article on the Lactase Gene:

http://findarticles.com/p/articles/mi_qa3659/is_199710/ai_n8778998/pg_1?tag=artBody;col1

Evaluating plague and smallpox as historical selective pressures for the CCR5-Δ32 HIV-resistance allele:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=299980

Scientists see a mysterious similarity in a pair of deadly plagues: http://www.nytimes.com/specials/women/warchive/980526_2007.html

Review of the Archaeology Channels Recently Posted Videos with Regard to Pre-Clovis Evidence.

The Archaeology Channel recently posted two short videos to their website about pre-Clovis evidence that is just now gaining traction and beginning to challenge the long held ‘Clovis First’ theory that has long dominated North American archaeology. This new evidence points to an earlier time frame for the population of the Americas, contrary to the date that has accepted as fact for so long in American archaeology.

The first video, titled Ice Age Discoveries: New Evidence , deals with various theories associated with the population of the Americas. This includes a brief introduction to the Beringia theory (that humans migrated over the land bridge between Russia and Alaska, then spread through modern day Canada or along the coast to populate the lower regions of North America and into South America) and the Solutrean Hypothesis, both of which have holes. It’s argued that the Solutrean theory stands only on similarity found between lithic technologies in mainland Europe and remains found in the eastern regions of Canada. Where this hypothesis is unlikely due to the duration of such a voyage by sea and the harshness of traveling along glaciated ice packs, the Beringia theory lacks the technological continuity that should be found if people really did migrate from Europe though Asia and finally into North America. Pre-Clovis evidence begins with the Topper site in South Carolina is reviewed, for its wealth of Paleo-Indian artifacts (and the fact that it is a chert quarry) including a modest selection of Pre-Clovis stone tools (picture).


The real turning point for a pre-Clovis theory came with the opening of the Cactus Hill site in Virginia. Fortunately two independent expeditions converged on Cactus Hill, one lead by Joseph and Lynn McAvoy and the other headed by Michael Johnson. I say fortunately because these two teams worked independently of each other and were able to verify the others findings through stratigraphy, lithic analysis and absolute dating methods independently of one another. After Johnson’s team hit the Clovis level they stopped digging, because at this point pre-Clovis inhabitation was just a wild hunch. Where Johnson stopped, McAvoy’s team (Cactus Hill, AREA B) continued to dig below the Clovis level and discovered pre-Clovis blades. At which point Johnson’s team mounted another expedition to Cactus Hill in 96’ to continue work and eventually discovered more pre-Clovis artifacts in their original area (Cactus Hill, AREA A). Both teams demonstrated extreme caution in the uncovering and recording of artifacts, taking care to measure and plot every minute detail during the excavation, lending to the integrity of Cactus Hill as a pre-Clovis site.


The beautiful stratigraphy at Cactus Hill lent further credibility to the pre-Clovis supporters. The stratigraphy at Cactus Hill involved a sterile layer (layers containing no artifacts or evidence of human habitation) between the Clovis artifact bed and the pre-Clovis discovery, indicating no disturbance in the layers. This ensured there could be no doubt about whether or not the pre-Clovis artifacts were actually assemblage from another layer that had migrated into lower levels as critics might suggest. It is not unusual for artifacts to move, depending on soil density (dense artifacts can actually ‘sink’ in the earth toward denser soil horizons), vegetation (tree roots), or rodent burrowing.


While Cactus Hill is not the first site to suggest a pre-Clovis human habitation, it is the oldest accepted evidence of pre-Clovis peoples on the East Coast. The first discovery of Pre-Clovis artifacts was at the Meadowcroft rock shelter in Pennsylvania by Dr. Jim Adovasio, but where Meadowcroft was the first evidence of pre-Clovis assemblage, Cactus Hill helped to reinforce the idea that people inhabited the Americas long before 11,000 years ago. The Meadowcroft rock shelter covers a 30,000 year period but the stratigraphy is complex and contains several reversals (a detail not mentioned in the video) which cast some doubt on the credibility of its Pre-Clovis assemblage. Another problem with Meadowcroft is its proximity to a coal seam, and some worry coal dust from the seam has affected radiocarbon dates for the site.


The second video, titled Ice Age Discoveries: the Investigators, deals more with the proponents of the pre-Clovis theory. It also includes more discussion of the theory and evidence itself, rather than focusing on the debate between Clovis First and pre-Clovis. Although it isn't the first thing that comes up in the second video, the lithic technology found at Cactus Hill holds continuity with what a pre-Clovis technology (in this case reflected in spear points) should look like. The basic shape of a pre-Clovis spear point is similar to a Clovis spear point, only shorter, thinner, and less technically sophisticated. Pre-Clovis points do not exhibit the characteristic channel flake from its base (a hallmark of Clovis points) nor is there any evidence of basal grinding. Pre-Clovis tools also tend to be made of poorer quality stone than that used by Clovis peoples. This shift in stone quality may be attributable to people discovering and utilizing new and better stone sources. It makes sense, after all people had thousands of years between the pre-Clovis and Clovis markers to practice making better stone tools with finer stone.


All in all, the videos present a solid argument for pre-Plovis, the stratigraphy eliminates doubt about the integrity of Cactus Hill. Lithic technology fits into the pre-Clovis construct, moving from less technically proficient (pre-Clovis from Cactus Hill) to more technically proficient (Clovis type points from various areas.) Relative dating puts the pre-Clovis artifacts in the right area, absolute dating indicates pre-Clovis inhabitation and phytolithic concentrations seem to concur with all other lines of evidence that people were in North America before 11,000. All of these are well represented in the second of the two videos. The first video was less informative with regard to the pre-Clovis theory, choosing instead to explain the various theories with North/South American population and giving the viewer a sense of where the Clovis First and pre-Clovis theories with regard to the larger history of man. Although the later half of the video gets back on topic and focuses back in on pre-Clovis theory. Overall, the videos posted on the Archaeology Channel website are very informative, cover their bases with regard to the budding pre-Clovis theory but are blatantly for pre-Clovis. They neglect to mention the heated debate associated with much of the evidence advanced to support pre-Clovis theories.


Also, the music is atrocious.

Link to the Archeology Channels website.

"The Making of Black Harvest" and the Rights of Anthropologists


Recently in my ethnology class here at Luther College, we watched a film trilogy about the Ganiga tribe in Papua New Guinea. This trilogy is a series of documentaries created by the anthropologists Bob Connolly and Robin Anderson, which focus on the introduction of western culture to the indigenous Ganiga tribe. The first film, First Contact, centers on the exploration of inner Papua New Guinea by the Leahy brothers in the 1930s. While there, they encountered a group of indigenous people who had never seen white people before. First Contact tells this story by using actual footage from the 1930s expedition in addition to interviews gathered 50 years later from people who were there when the Leahy brothers arrived. The second film, Joe Leahy’s Neighbors, tells the story about the son of one of the explorers and a Ganiga woman, Joe Leahy, and his interactions with the local people. This film focuses especially on how Joe has assimilated into white culture and the troubles that creates. Black Harvest is the last film in this trilogy and it focuses on a business deal between Joe Leahy and the Ganiga where they enter a cooperative business agreement to co-own a coffee farm. Unfortunately, the coffee prices drop significantly, which produces incredible tension between Joe Leahy and the Ganiga, ultimately, causing him to leave the area by trying to move to Australia.


One of the most striking things about this series, especially in the last two films, is the technique used by anthropologists Bob Connolly and Robin Anderson. Instead of having a script, they let the events naturally unfold and tried to film them whenever possible. As one article puts it, “Their breakthrough observational film is so good that most Australian documentary filmmakers wish they had directed it themselves.” Very rarely do you hear the anthropologists themselves speaking. Instead, there are numerous interviews with Joe Leahy and other Ganiga tribe members in addition to images from their everyday life which tell the story. The final effect is a very moving documentary that lets the images and the people speak for themselves.


Although these films received rave critical reviews, the filmmakers themselves were unsure about whether they had the right to go in and document these people’s lives. A recent book by Bob Connolly, Making Black Harvest, explores the concept more in depth with the help of diaries recorded at the time of filming. In this book Connolly describes the guilt he and Robin Anderson felt in trying to remain objective and wanting things for the good of the movie even when it conflicted with the good of the people. He also writes about how when one of his friends was wounded during a fight, one of the first questions he asked was, “Can we film?” He says that this question still haunts him.


The issue of trying to remain objective while living with and learning about a group of people is something that almost all anthropologists must think about. Where do you draw the line between collecting objective data and becoming an actual member of the community? What gives anthropologists the right to enter these people’s culture and document it? This is still an issue that I myself have trouble with. On one hand, I think that it is important to learn about people of other cultures in order to better understand the world and our own lives. Yet, I think that by becoming part of a community, there are certain responsibilities that conflict with being an objective observer. For instance, I think that it is a breach of friendship and respect to use information you gather to advance your own career, especially when nothing is given back to the people being studied. Oftentimes the people being studied receive little to no benefits and do not even see the final product. Also, being an objective observer can conflict with helping others in need or to put the anthropologist’s needs and wants above that of the people being studied. This can be seen in Making Black Harvest, when Anderson and Connelly wished for the coffee prices to remain low in order to help their movie’s plot. Although Connelly and Anderson later feel guilty for wanting this, it just further illustrates the fine line between being an objective observer and being an active member of the community being studied.