Lab-meeting about high-altitude adaptation in humans

It is time for a new lab-meeting on Wednesday (September 1), and this time I was thinking that we should discuss a recent Science-paper where the auhtors present evidence for genetic adaptations to high-altitude living in Tibet. The paper can be downloaded here. Interestingly, there is also another recent study on the same topic in PNAS, which can be downloaded here. I suggest we read both of them in preparation for the lab-meeting on Wednesday.

These papers has received quite a lot of attention both in media and in the bloggosphere. I can recommend population geneticist Jerry Coynes blogpost about one of these papers on his excellent blog "Why Evolution is true". Coyne has also a more critical blogpost where he cautions against solely relying on statistical approaches on gene frequency changes to infer selection. Being an experimental evolutionary biologist and ecologist by heart, I could of course not agree more with Coyne.

Time of lab-meeting as usual: 10.15 in "Darwin", Wednesday September 1, 2010. Any fika-volunteer?

Also, do not forget that CAnMove organises a barbecue on the same day in the afternoon at 17.00 at the Biology Department. Contact Sophia Engel for more info.


References and publication details:

Genetic Evidence for High-Altitude Adaptation in TibetTatum S. Simonson, Yingzhong Yang, Chad D. Huff, Haixia Yun, Ga Qin, David J. Witherspoon, Zhenzhong Bai, Felipe R. Lorenzo, Jinchuan Xing, Lynn B. Jorde, Josef T. Prchal, and RiLi Ge Science 2 July 2010 329: 72-75; published online 13 May 201013 May 2010 [DOI: 10.1126/science.1189406] (in Reports)

Natural selection on EPAS1 (HIF2α) associated with low hemoglobin concentration in Tibetan highlanders PNAS 2010 107 (25) 11459-11464; published ahead of print June 7, 2010, doi:10.1073/pnas.1002443107

"Human" vs. "animal" evolution

I thought a recent study from PLoS ONE might be of interest to some of you. In this meta-amalysis, McKellar and Hendry have compared within- and among-population phenotypic levels of variation in humans and animals, for body height and body mass. This study is I think very nice because it is clearly conceptualized, and the results are really straight-forward and well discussed. They also used an estimate of variation called CV, the coefficient of variation that was introduced by Houle in 1992 in a paper published in Genetics and that has in my opinion been a bit neglected by quantitative geneticists. This estimate has the advantage of being scale-free, and therefore allows comparisons between populations or species without bias.

They used an impressive dataset of 99 human populations, 210 animal populations and 848 animal species. Their main conclusions are that within-population variation in body height (but not body mass) is relatively low in humans, whereas among-population variation is more or less similar to what one might measure in animal populations. They interpret it as a sign for strong natural selection on body height in human populations which have become locally adapted.

This paper is, I am sure, probably going to be cited in the media, if it has not already been done, and will probably contribute to the growing success of PLoS ONE. Andrew Hendry has also been working on human influence on evolutionary rates of animals and more in particular human influence on beak size bimodality in finches. He is particularly interested in studying cases of rapid evolution and in the way ecology and evolution interacts on contemporary time scales. I am honored to have him as an opponent for my thesis defense that will take place on the 20th of November, and I can already tell you that Andrew will give a talk on these subjects on Thursday the 19th of November, at 13.00 in Blå Hallen at the Ecology Building.

If you are interested in contemporary evolution, if you have no idea what the term "eco-evolutionary dynamics" really means or simply if this PloS ONE paper has intrigued you, I recommend already now that you mark this date in your calendars, because you will probably don’t want to miss this talk.

Understanding the "Egalitarian Revolution" in human social evolution

Inspired by the previous bloggpost, here is some other news about a recent publication in this research laboratory. In the lastest issue of Trends in Ecology & Evolution I have a so-called Research Update about a recently published model by theoretical evolutionary biologist Sergey Gavrilets and colleagues which deals with the evolution of cooperation in humans. One striking aspect of humans that makes us different from our closest relatives, the great apes, is that our society is less hierarchical and hence more egalitarian, and the evolutionary transition from a great ape society to ours is something that took place during the Pleiostocene and this transition is often called "The Egalitarian Revolution".

The TREE-article comments uponGavrilets et als' new model that aims to explain this evolutionary transition, as well as some recent experimental studies by behavioural economist Ernst Fehr who have done some elegant work on human cooperation and "altruistic punishment". Here is the Abstract for my TREE-article:

"Humans are unique among animals in cooperating in large groups of unrelated individuals, with a high degree of resource sharing. These features challenge traditional evolutionary theories built on kin selection or reciprocity. A recent theoretical model by Gavrilets and colleagues takes a fresh look at the ‘egalitarian revolution’ that separates humans from our closest relatives, the great apes. The model suggests that information from within-group conflicts leads to the emergence of cooperative alliances and social networks."

One of the original articles discussed in this TREE-paper, the model by Sergey Gavrilets et al., was originally published in PLoS ONE, under the title "Dynamics of alliance formation and the Egalitarian Revolution." I had the pleasure of being an academic editor of this highly interesting piece of work. Here is the abstract for that paper:

Background

Arguably the most influential force in human history is the formation of social coalitions and alliances (i.e., long-lasting coalitions) and their impact on individual power. Understanding the dynamics of alliance formation and its consequences for biological, social, and cultural evolution is a formidable theoretical challenge. In most great ape species, coalitions occur at individual and group levels and among both kin and non-kin. Nonetheless, ape societies remain essentially hierarchical, and coalitions rarely weaken social inequality. In contrast, human hunter-gatherers show a remarkable tendency to egalitarianism, and human coalitions and alliances occur not only among individuals and groups, but also among groups of groups. These observations suggest that the evolutionary dynamics of human coalitions can only be understood in the context of social networks and cognitive evolution.

Methodology/Principal Findings

Here, we develop a stochastic model describing the emergence of networks of allies resulting from within-group competition for status or mates between individuals utilizing dyadic information. The model shows that alliances often emerge in a phase transition-like fashion if the group size, awareness, aggressiveness, and persuasiveness of individuals are large and the decay rate of individual affinities is small. With cultural inheritance of social networks, a single leveling alliance including all group members can emerge in several generations.

Conclusions/Significance

We propose a simple and flexible theoretical approach for studying the dynamics of alliance emergence applicable where game-theoretic methods are not practical. Our approach is both scalable and expandable. It is scalable in that it can be generalized to larger groups, or groups of groups. It is expandable in that it allows for inclusion of additional factors such as behavioral, genetic, social, and cultural features. Our results suggest that a rapid transition from a hierarchical society of great apes to an egalitarian society of hunter-gatherers (often referred to as “egalitarian revolution”) could indeed follow an increase in human cognitive abilities. The establishment of stable group-wide egalitarian alliances creates conditions promoting the origin of cultural norms favoring the group interests over those of individuals.

Genetics of pygmy evolution in Africa

Some of you might be interested in a recent study about the evolutionary origins of African human pygmy populations, which is discussed in this bloggpost. A recent study have investigated the molecular genetic history of African pygmy populations and concluded that they are not secondarily derived from the farming populations of the Bantu people. Instead, the different and the isolated pygmy populations in the African rainforests are historical relicts of a greater contiguous population of an ancestral hunter-gather society that was split up in to different fragmented populations when the African Bantu people expanded about 10 000 years ago.

The different pygmy populations in Africa have thus not evolved their short body stature in parallel. Rather their phenotypic traits are traits that they inherited from their ancestors. The pygmy populations and the Bantu people have been separated for at least 60 000 years. The agricultural revolution took place the last 10 000 years, and when the Bantu people brought agriculture to sub-saharan Africa, their population sizes exploded. This is because the carrying capacity of agricultural populations is considerably higher than for hunter-gather societies. which is not very surprising. After all, by using agriculture you can feed a much larger population per unit area than you could by hunting.

The pygmies were thus marginalized by the rapidly expanding Bantu-farmers, and their once large population was split up in to several smaller fragmented populations. The once more widespread pygmies are today more less isolated from each other in the deep African rainforest.

As an aside, this is an interesting example of how population genetics, particularly the use of the population genetic software STRUCTURE, can be fruitfully used to infer population histories and population genetic parameters (see figure above). This is something we are also working on in our laboratory, particularly Anna in her studies of Mediterranean Podarcis-lizards.