Archive for February, 2017


Entrance to Room 33, Pueblo Bonito

A fascinating and important article about Chaco was published last week in Nature Communications, an open-access offshoot of the venerable journal Nature (already a good sign). Since it’s open-access, the full text of the article is available free online here.

The researchers behind the article, based mainly at Penn State and Harvard but also including Steve Plog at the University of Virginia and a couple of people at the American Museum of Natural History, sequenced the mitochondrial genomes of several of the people buried in Room 33 at Pueblo Bonito in an attempt to determine if they were related. This addresses a number of outstanding issues in the interpretation of the Chaco Phenomenon, particularly those revolving around the political economy of Chaco and the degree to which it was a hierarchical society. They also radiocarbon-dated the remains and did some additional genetic analysis to confirm the sexes of the people and try to determine any close genetic relationships among them.

The results were striking. All of the tested remains had identical mitochondrial genomes, indicating that they were all related through the maternal line, which in turn suggests strongly that Chaco was a matrilineal society in which this particular maternal lineage had an enormous amount of power and wealth that led it to have the most elaborate burials in the history of Pueblo societies. The radiocarbon dating suggests in addition that people from this lineage continued to be buried in the special crypt in Room 33 throughout the florescence of Chaco, starting in the early ninth century AD and continuing until the early twelfth century. (What exactly happened then remains obscure.) The DNA sex determinations matched those previously determined through osteological analysis 100% as well.


Old Bonito from Above

These results, which are based on carefully controlled analyses and seem very solid, are not exactly surprising, but they do provide apparent confirmation of certain models of Chaco and apparent falsification of others. Specifically, they support models involving robust social hierarchy and inequality, with some lineages having more authority than others and one at the top. Most recent evidence has pointed in this direction, but this study is a particularly strong support for it. Also, they provide support for the idea that Chacoan society was more like the ethnographic Western Pueblos, which are matrilineal and structured around kin groups known as “clans” that derive their power and status from their control of esoteric religious knowledge, than the Eastern Pueblos, which are patrilineal and structured around non-kin-based groups known as “societies” that derive their power and status from similar bases. (If this distinction seems fairly minor, that’s because it is. But in attempting to reconstruct historic societies it’s important.)

It’s important to note that while these results do provide support for a matrilineal model of Chaco, that’s very different from saying they support a matriarchal one, as some media coverage I’ve seen has either implied or stated explicitly. Reckoning descent through the mother’s line is very different from having women run things with men in a subordinate position. The former is quite common cross-culturally, while I’m not sure if the latter exists at all in the ethnographic record. The fact that several of the people buried in Room 33 appear to have been related maternally doesn’t negate the fact that the two most elaborate burials were both of men, and in general there’s no reason to think that Chacoan society wasn’t strongly patriarchal, and plenty of reason to think it was.

Finally, from a methodological perspective this is a particularly interesting paper. The authors say that it appears to be the first use of genomic analysis to determine family relationships in a prehistoric society (i.e., without the availability of written records to check the results). I’m not completely sure that’s correct, but this has certainly not been a common type of study. In discussing DNA evidence a while back, I mentioned that in the Southwest it had mostly been used so far just for determining mitochondrial haplogroups, which provide some useful information but not nearly as much as can be provided by genomic analysis, which at that time hadn’t really been used at all in the Southwest. This paper marks the first major use of this type of analysis in the region, and it shows how powerful it can be. Now that the precedent has been set, it can be used in other contexts to see where this particular matrilineage shows up elsewhere in Southwestern prehistory both before and after Chaco, as well as to address other issues of kinship and identity within Chaco.
Kennett, D., Plog, S., George, R., Culleton, B., Watson, A., Skoglund, P., Rohland, N., Mallick, S., Stewardson, K., Kistler, L., LeBlanc, S., Whiteley, P., Reich, D., & Perry, G. (2017). Archaeogenomic evidence reveals prehistoric matrilineal dynasty Nature Communications, 8 DOI: 10.1038/ncomms14115

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