Discrepancy Between Cranial & mtDNA Data Of Early Americans Or Sample Size?

There’s an interesting discussion brewing about on Dienekes’ Anthropology Blog about the ancestral discord between the genetics and craniometric traits of native American populations. I wanted to point it out to all in case you don’t subscribe to Dienekes. The discussion revolves around a rather new PLoS One paper addressing the observation that while native American mtDNA remained relatively static since the Holocene, the cranial morphology of the group has undergone major shifts. The paper is open access and can be found at this link, “Discrepancy between Cranial and DNA Data of Early Americans: Implications for American Peopling.”

Dienekes addresses 3 hypotheses as to why this could be. I generally subscribe to the third hypothesis he mentioned. But in focusing on the paper I have found some concerns about the study sample. Firstly the samples originate only from Argentina. I’m not surprised about this as the researchers are Argentinian scientists, however how can one draw ‘implications for American peopling’ when the sample is confined to 16 individuals from Patagonia and the Pampas? What happened to checking out specimens from Brazil, central America, and the northern territories?

Furthermore, the samples come from a 1,500 year time frame…  starting at 7,800 years ago. We know the earliest migrations to the Americas started 40,000 years ago and people didn’t just make a B-line to Argentina. Populations dispersed. So to make conclusions about Paleoamerican and Amerindian groups based off of 16 skulls from a narrow spatial and temporal window in the peopling of the Americas is flawed, even if these 16 skulls seem to be consistent with morphological and genetic variation patterns interpreted as differences between Paleoamerican and Amerindian groups.

I don’t want this to turn into a time old critique on sample size and distribution analysis. I think we all know that bioarchaeological and paleontological studies also have many reasons to narrow samples. Sometimes it is political, while other times it is based plainly on accessibility to samples as to why a study is narrow. But that doesn’t give anyone an excuse to go ahead and publish it!

    Perez, S., Bernal, V., Gonzalez, P., Sardi, M., & Politis, G. (2009). Discrepancy between Cranial and DNA Data of Early Americans: Implications for American Peopling PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005746

3 thoughts on “Discrepancy Between Cranial & mtDNA Data Of Early Americans Or Sample Size?

  1. Hi. Neither of the hypothesis is correct, IMO, but rather a fourth one:

    Mongoloid traits were part of the variability at the peopling of Eastern Asia and were gradually becoming more and more common on what we can largely consider a random (but maybe also sociological) evolution.

    Many populations anyhow still display non-Mongoloid variability, and this is even more common in Native America, where actually Mongoloid traits are interwined in a complex network of many diverse ones, often non-Mongoloid. You just can’t tell me that, for example the nose of Evo Morales (a very typical Native American nose, specially in the Andes) is “Mongoloid” – it is not. There are many other such non-Mongoloid traits still surviving in Native America and also in parts of East Asia, notably SE Asia.

    And, btw, very good point about the sample being awful. You can’t draw any conclusions based on such minimalistic local sample.

    1. Thanks for the comment Luis. You’re hypothesis is also a valid one which I didn’t fully recognize until your comment. Much appreciated!

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