Saturday, July 14, 2007

Long-term Continuity Supported in South America

I remember when mtDNA and Y Chromosome studies became hot in anthropology. Studies were being done faster than anyone new what to do with the data, especially the indigenous people who were being studied. Scientists and molecular anthropologists began claiming that they could tell affiliation between present-day indigenous groups and those of the ancient past. How? By looking at what are called allele frequencies in the present-day population and that of the past. Now, this process was, and continues to be, replete with problems (population size is number one often). I wrote an article on it that most molecular anthropologists didn't like. It was eventually published in the AnthroGlobe Journal.

Then I was hired to do some work for an indigenous research company. They were interested in finding out just how far these types of studies had gone. Boy were they surprised. Scientists and molecular anthropologists were making all sorts of claims, mostly focused on migration of indigenous peoples in the past or current biological affiliation between tribes (some even made the error of claiming they could determine cultural affiliation; last I knew, one's culture and their affiliation to it had little to do with genetics). I eventually wrote a book, and it has had mixed reviews. Again, those doing the studies didn't like it. Those who were being studied found it very useful. I foolishly gave it the long title of American Indian mtDNA, Y Chromosome Genetic Data, and the Peopling of North America.

So, where is this post going? Well, in the latest issue of Latin American Antiquity, one of the premiere journals for archaeologists working in South America, an article came out that claims to link ancient DNA to present-day South American indigenous peoples. Here is the title and abstract:

Ancient DNA and Genetic Continuity in the South Central Andes

Alternative models of residential mobility have been proposed to explain the development and spread of Tiwanaku influence across the south central Andes. Within the Osmore drainage, the rich Moquegua Valley has been hypothesized as the site of a significant colonization event (or events) whereby both the natural and human landscape was transformed and integrated into the expansive Tiwanaku state. In this research, the impact of altiplano colonization is inferred from temporal and spatial patterns of genetic variation within and among native groups. Mitochondrial DNA haplogroup frequencies are used as the measure of genetic variation. The haplogroup data are determined for Moquequa Valley archaeological samples (Chen Chen site; A.D. 785-1000) and are compared to published data from 58 other ancient and contemporary native groups. The results support temporal and spatial genetic continuity in the south central Andes for the last 1,000 years. Contemporary Aymara speaking groups are exceptions to this pattern, perhaps because of recent population decline. While the altiplano colonization hypothesis is not rejected, moderate gene flow and relatively large population sizes likely characterized much of south central Andean prehistory regardless of the contribution from Tiwanaku colonization events.

So, what does this confusing abstract really mean? It means that in the south central Andes the populations in prehistory were large enough to mitigate any genetic impacts from migrating newcomers. That is, because the people of the south central Andes had enough resources in their area, they could live there for thousands of years, and that other groups that migrated in (or that even just shared relations with people of the south central Andes) were absorbed into the overall population, at least genetically.

How fine grained is this study and its conclusions. Like many genetic studies that infer something or other about the past and present-day indigenous peoples, one has to look at what the inference is based on. In this case, not much, but more than the older studies. The authors provide us with their "n" (number of individuals whose genetic frequencies were studied and compared). The largest sample used to define a population is 172 Aymara individuals. The smallest consists of only 8 Toba individuals. Most of the other 57 populations range between 15 and 40 individuals per population group. Pretty small number of individuals to define a population! Likewise, because this study, like all academic studies, is built off of citing other works, the researchers of this study actually did very little in terms of procuring their own samples. Rather, they got most of their "data" from previously published studies, some dating back to the nascent period of molecular genetics (the early 1990s).

Indigenous peoples around the world should be aware of just what is going on here. Biological affiliation is being determined across space and time by simple looking at a handful of individuals. Let me illustrate. Say I was a present-day indigenous person. If my mother (and only my mother since the researchers were using mtDNA, which is only transferred via the mother), or my grandmother, or my great great grandmother was not part of the original handful of people used to define the ancient "population", it is very likely that I would be considered biologically unaffiliated! This gets even further complicated because of the use of previously published data (common in academic circles). So if the first study published results, and those results happened to be skewed because of sample size, early techniques that are now considered faulty, mis-categorization of the sample individuals (i.e., claiming that they are Ticuna when really they are Wayuu or something similar), or the like, then future studies are going to be off.

Don't get me wrong, I think this study did an excellent job based on the data it used, and I think their inferences are fairly accurate based on the paradigm they were set. But these sort of studies should be closely examined. Indigenous peoples need to know that their history is currently being rewritten (again, archaeologists already did it once). There are thousands of samples of blood in freezers around the world that can be used in these sorts of studies. In all molecular anthropological studies, caution needs to be heeded. Proclamations of biological affiliation can have long-term consequences for indigenous peoples, consequences that are often not anticipated by the researchers. I just hope that we can educate the public about these studies and what they really evidence before another mixup in biological versus cultural affiliation takes place.

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4 comments:

Victor said...

I haven't read your article (yet), but I can see from your post why the genetic research concerns you. Actually, the mdDNA situation is even worse than what you stated, because it's inherited STRICTLY along the female line, meaning you've inherited your mother's mtDNA, her mother's mtDNA, and her mother's mother's mtDNA. But NOT your father's, nor his father's, NOR YOUR FATHER'S MOTHER'S -- NOR YOUR MOTHER'S FATHER'S, NOR YOUR MOTHER'S MOTHER'S FATHER'S. In other words, any mtDNA profile of any individual is going to have a great many holes, and the farther back you go the more holes there will be. And if you add a Y Chromosome profile, that will only fill in some of the gaps. You'll get your father's Y, but not your father's mother's. In fact there is no way to get to your father's mother or your mother's father via either method. And nuclear DNA is even worse in that respect, since, as I understand (I'm far from being an expert), it's based on teasing statistics from large populations and not applicable to individuals at all (I could be wrong but that's been my impression).

What the above tells us is that it would be a huge mistake to infer any individual's ancestry using any of these methods. That's not what the most sophisticated researchers are interested in anyhow. They're looking at whole populations, not individuals.

The genetic research is not going to go away. It's the most promising and in fact exciting development in anthropology for a long time, possibly ever. While there are certainly some serious flaws, contradictions, sampling problems, etc., the field will only be improving with time, working out its flaws and contradictions and expanding its samples.

Where your concern lies is in this research being misused, and there I fully agree. (There's an irony here, however, since it's the indigenous groups themselves who have tended to give so much importance to the determination of "blood lines.") The answer to the problem, IMO, is to make the public aware, not of the deficiences of genetic science (because those will diminish over time I assure you) but its sheer irrelevance to the question of INDIVIDUAL genetic inheritence.

Peter N. Jones said...

Victor,

I couldn't agree with you more. It is not the science per se that is a problem, but simply how it is being used to create misunderstandings that affect real people's lives. I published another article related to this topic here that may be of interest.

Anonymous said...

The paper that you are discussing champions some of the things you are saying as a critique. The paper discusses how previous studies may have oversimplified genetic data, and shows how there are multiple potential histories that can fit the data. For example, look at how the paper discusses the potential complex role of the Aymara language in prehistory. That seems to be the right way of doing of things. Also, the paper thanks a local Peruvian museum for permission to collect and study their samples.

Peter N. Jones said...

Anonymous,

Good critiques, although I don't know if you got the jist of the post. Sure, it is great that the scientists thanked the local Peruvian museum for the samples, but that is still just "convenience sampling". The individuals whose blood the museum "gave permission" for did not. I doubt they even knew it was being used for this kind of investigation. I do agree, the paper points out the flaws of some previous studies and how it builds on those, this is standard scientific practice. However, it does not point out the ethical issues that actually effect the indigenous peoples of the Andes, namely that they are rewriting a groups history (potentially) without letting that group know (while still using their blood).

Also, I agree, bringing in language into the study is smart, but what about archaeology, trichology, or perhaps most importantly, the indigenous oral traditions. I bet if one looked, the oral traditions would tell a very revealing story that more than likely would jive with the genetic data.

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