Anthropology.net

Earlier this year, I wrote a massive summary on the genetics of pigmentation for one of my graduate courses. I wasn’t particularly keen on the topic before but it has since grown on me and I’m now a big fan. So to read from Yann, Dienekes, and Razib that one of the key pigmentation genes, SLC45A2 is involved in hair color among Polish people, I was both excited and, well, frankly not very surprised.

Before I drag you into a review of the paper let me first introduce the gene and its function. SLC45A2 stands for solute carrier family 45, member 2. It is found on the short arm of chromosome 5. Not very informational, but the protein it ultimately encodes for is known as membrane-associated transporter protein (MATP). As the name implies, this protein is thought to regulate traffic melanosomal proteins into melanosomes, organelles within pigmentation cells (melanocytes) where melanin is produced. Melanin functions as a protective agent. It is dark in color and accumulates in cells in reaction to sunlight, absorbing light and protecting the nuclear genome from mutations caused by the ionizing radiation from UV rays. Thus, making MATP and the genetics of SLC45A2 an important part of the skin pigmentation pathway.

Recent studies have shown that certain variants of MATP affect pigmentation, such as Cook et al., 2008 and Graf et al., 2007. In the latest piece that everyone is buzzing about, “Association of the SLC45A2 gene with physiological human hair colour variation,” the authors were able to make an significant association between one of two non-synonymous polymorphisms in SLC45A2 and the hair color phenotype of a Polish population.

Inspired by Razib's example: Marzena Cieslik, Miss Poland 2006

The two SNPs are rs26722 and rs16891982. Both are missense mutations that encode for a different amino acids. The first SNP, rs26722, is a change from a guanine base to an adenine at position 907 of the mRNA transcript. This swap to an adenine affects the resultant the codon, creating a lysine on position 272 of the amino acid sequence instead of a glutamic acid residue (annotated as E373K). Similarly, rs16891982, is also a switch of a guanine but for a cytosine base on a different position of the transcript, 1214. The leucine residue on position 374 is thus changed to a phenylalanine (annotated as L374F).

Biochemistry aside, these two end products, MATP-E272K and MATP-L374F, have distinct population frequency distributions, especially MATP-L374F. Among the Polish sample of 392 individuals of varying skin, hair, and eye color, the rare allele is L374… Found in only 2.3% of the population. The MATP-374F allele is represented in 97.7% of the Polish sample. Curiously, all people who carried the rare allele had dark hair. The authors calculated the odds the L374 genotype increased the likelihood a person would have dark hair by 7 times.

Razib linked up an awesome resource, called ALFRED, the allele frequency database which shows the distribution of rs16891982 world wide. You can see that in northern Europe, 374F is the prevalent allele. Only when you get to Italy, Spain, Turkey, do you begin to see more of the L374 allele (the dark hair allele).

Worldwide Distribution of the rs16891982 SLC45A2 Allele

This all makes sense, people who carry a cytosine on position 1214 of the SLC45A2 mRNA have lighter color hair than those who carry a guanine (L374). A similar distribution frequency was observed a German and Japanese sample by Nakayama et al., 2002 & Yuasa et al., 2004 & Yuasa et al., 2006. 96.5% of Germans had the lighter 374F allele. 100% of Japanese had the darker L374.

But why?

I returned to one of the previous studies I mentioned earlier, the Cook et al. paper, “Analysis of Cultured Human Melanocytes Based on Polymorphisms within the SLC45A2/MATP, SLC24A5/NCKX5, and OCA2/P Loci.” The authors of this paper grew primary melanocytic cells with specific mutations and tried to see the effects they had on melanin content and tyrosinase activity. In their array, one of their comparisons included the impacts of the MATP-L374 variant to the MATP-374F variant. They found that MATP-L374 cells expressed significantly lower MATP transcript levels compared to MATP-374F ones.

I’ve spent a lot of time thinking about this and quite frankly, I’m very confused. Correct me if I’m wrong, but lower levels of MATP transcript means less transport proteins translated and available to bring melanosomal proteins into the cells. Less building blocks equals less melanin. And less melanin should equal lighter pigmentation. So why do people who have dark hair have the less productive allele?

Come to think of it, there could be many different reasons, actually. Biochemical pathways are hardly ever a 1:1 mechanism. There’s lots of redundancy and sometimes one component isn’t the point man. For example, other parts of the pathway, such as tyrosinase, an enzyme that catalyzes the production of melanin, is higher in darker skin. Other transport proteins, such as SLC24A5/NCKX5 are also part of the melanin and melanosome production network and could have a different impact.

Either way, there are a few curious things to come out of all of this… We now know a definitive allele that affects hair color. Albeit, how is still up in the air, ’cause darker haired people come with less membrane-associated transporter proteins on their melanocytes. But still, there is a distinct structure to the distributions of these haplotypes.

Wojciech Branicki, Urszula Brudnik, Jolanta Draus-Barini, Tomasz Kupiec, Anna Wojas-Pelc (2008). Association of the SLC45A2 gene with physiological human hair colour variation Journal of Human Genetics DOI: 10.1007/s10038-008-0338-3

I mentioned the drawn out process of me trying to download this new paper, “Dynamics of Alliance Formation and the Egalitarian Revolution,” the other day. I’ve read it and although I found it to be a difficult and theoretically dense paper, I believe you should also read the open access piece if you have any interest in understanding how culture evolved and the possible mechanisms of egalitarian behavior early on in human evolutionary history. The paper’s first author is Sergey Gavrilets, a theoretical evolutionary biologist from the University of Tennessee, Knoxville. The other co-authors are also from the same institution.

You may know Gavrilets’ other piece on cultural evolution, the 2006 paper in which he and Aaron Vose built a mathematical model to test out the social brain hypothesis — creating situations where genes control brains which invent and learn strategies that are then used by individuals to gain advantage in competition for mates. He’s continued researching the evolution of social behavior, and in his most recent piece he and his team tackle the dynamics of coalition formation.

The observation that Gavrilets et al. make is that while our closest living evolutionary cousins form alliances and cooperate in groups, their social systems are extremely hierarchical. The most glaring example can be seen in a gorilla troop where a dominant silverback presides over a few adolescent males and a harem of females. The group dynamic is fluid throughout life history, but each member of the system ultimately plays a role in the dominance hierarchy.

But early human societies, such as the quintessential hunter-gatherer society, is generalized as being egalitarian. Prior to the agricultural revolution, hunting and gathering is thought to have been the only subsistence strategy deployed by early human cultures. Studying modern day hunter gatherers, ethnographers have noted that such societies distribute dominance much more equally and thus tend to be non hierarchical. Leaders are comparatively weaker than their subordinates which reverses the pyramid of power.

So why was there such a big behavioral shift during our evolutionary history? We may never know for sure. There are ideas floating around that all seem to suggest the lack of food and realization that cooperation, rather than competition, was more beneficial for overall survival. When food sources became more dependable, as seen after the Neolithic and the dawn of agriculture and pastoralism, is when we’ve seen a return to a traditional hierarchy.

Gavrilets and team created a complex model which ultimately relied on probability to solve problems. They simulated alliance formation among a group of individuals who had different fighting abilities. Their system distinguished between conflicts that existed only between pairs of individuals and conflicts that were composed of more than two individuals. In situations that conflicts existed solely between two individuals, a very structured hierarchy emerged, favoring the ones best able to fight for their interests. In situations that composed of more than two individuals, there was interference or a balance of power, where the hierarchy was biased towards one result over another.

With an increase of group size, Gavrilets et al. were able to see an increase in dyadic conflicts. When members of a group were aware of other conflicts, of which they were not directly related, there was also an increase of dyadic conflicts. Naturally, larger coalitions have a higher probability of winning a conflict and a positive outcome increased affinity between members of the coalition.

Again, this was a rather hard paper to read, and I’ve left out a lot of details. I’m a bit unclear about what was rewarded to drive forward the model, i.e. what were they fighting for? Some of you may write off models as being controversial and reductionist. You’re right. For starters, it is difficult to interpret methods and the data doesn’t seem like it factors in the interactions of so many different variables — some come from evolutionary, ecological, behavioral, and social factors and all acting simultaneously. It is also awkward to evaluate relevant time-scales, aside from generation turnover, and to figure out possible evolutionary dynamics.

But the model did show that the tendency towards egalitarianism is rapid — it consistently happened in the course of several generations. Under situations where all members of a group were a part of one alliance, where not all members were equal, they still remained united. But alliances weren’t permanent. They would phase and out of intensity. Outsiders were also a crucial part of keeping the dynamic alive.

Gavrilets and crew suggest that egalitarianism came along with changes in mating systems and influenced by primate mother-daughter bonding. They also noted that the emergence of language most definitely facilitates the formation of alliances. One last thing, the authors sent out a warning against considering modern day humans under such constraints, because when we join alliances, our decisions are strongly affected by how much we perceive to get out of the alliance versus the costs and risks of being a part of the alliance, which are factors not included in the model.

All aside, this model is informative but it is by no means the way human social behavior evolved. I’ve already outlined some of the caveats to modeling. To further supplement, there are exceptions to the rule that all hunter gatherer societies are/were egalitarian. Non-egalitarian hunter gatherer systems, such as the Haida, have been well documented by ethnographers. I also remember one of my anthropology professors telling me her accounts of living with outcasted Dassenach people. They were forced out of the pastoral lifestyle and into a hunting for crocodiles and fish one. But, they still retained the social structure despite the shift in subsistence.

Sergey Gavrilets, Edgar A. Duenez-Guzman, Michael D. Vose, Erik I. Svensson (2008). Dynamics of Alliance Formation and the Egalitarian Revolution PLoS ONE, 3 (10) DOI: 10.1371/journal.pone.0003293

In World as Laboratory, Rebecca Lemov, an anthropologist, writes for a larger audience.

“I think it’s too bad that a lot of scholarly work never gets read, usually because it’s just plain difficult to read,” she says in an interview with Nicole Merritt of MyShelf.com. “Being difficult is sometimes necessary, but sometimes there’s deliberate obfuscation going on … ‘If you can’t understand what I’m saying, I must be exceptionally smart’.”

David Brooks reviewed it at The New York Times, an honor not always bequeathed to anthropological texts.

The paperback is published by Hill and Wang, rather than an academic press, and the book is written in a humorous, even sarcastic tone, in accessible language that feels like a leisure read full of rich philosophical implications and shocking detail.  The focus of the work is how the laboratory became the locus of power and authority, the fountain of knowledge for social scientists and governments alike, eventually contributing to an extension of the laboratory to world settings – so that the United States, as a colonial power, utilized whole peoples for experiments on the premise that human behavior could be understood, controlled, and even engineered on a massive scale.

Lemov also describes how laboratory science, with its emphasis on objectivity and distance from the subjective – as well as the subject – is built around experiments on animals as the ideal approach to studying human behavior and, yes, even the social.  Yet this practice is built on a puzzling paradox: although humans are assumed to function behaviorally in the same manner as animals, animals as nonhumans (and, in some cases, certain humans considered less than civilized) are permissible subjects of often painful and exceedingly demoralizing experiments.  Furthermore, as Lemov demonstrates, laboratory science itself was generated by personalities, men in fact caught up in a range of personal fears and anxieties – in short, subjectivities.  Yet despite these contradictions, laboratory science built on the assumed subject-object, human-nonhuman distinction is as pervasive as ever, if not more so.

Without proposing any conspiracy theories – in fact, Lemov makes it clear that a lot of these guys were wayward do-gooders and philanthropists who couldn’t possibly know the full ramifications of their brand of science – she points to the lasting effects widespread ideas about the social self have on our lives even today, even in the marketplace, in malls, in everyday politics.

With the laboratory, Lamov writes, scientists “built a stressful world that predicted our own: a world in which stress and its effects can actually be engineered, ratcheted up, and in some sense capitalized upon” (101).

Admittedly, this sounds pretty incendiary for an anthropologist, and Lemov certainly doesn’t pretend to participate in any kind of dalliance with objectivity.  There is something very brave and honest about that.  Lemov is an anthropologist – a person with a PhD – but she clearly isn’t ashamed of her own biases, nor is she interested in putting on a veil with her thinking cap.  Perhaps more importantly, she’s talking about things that sound boring and inaccessible – science studies, subject-object distinctions, intentionalities – in a way that is likely to stimulate more dialogue and participation among a wider range of people than your standard stodgy academic article.

Not that those are unimportant.  It’s just that they, too, are part of the laboratory world.