Archaeological Fantasies and the genetic history of the Americas

The excellent podcast Archaeological Fantasies recently had me on as a guest for a wide ranging discussion on genetics. We covered everything from the genetic prehistory of the Americas to issues surrounding ancestry testing companies. Here’s a link to the episode (apologies for the fact that I kept cutting in and out–apparently our university wireless connection isn’t very good).

Since so much of our discussion focused on haplogroup X2a and models for ancient American prehistory, I decided to break from the normal tradition here at VM and actually re-publish a post to make it easier for people to get answers to any questions they might have. And if you have specific questions about content from the podcast, please feel free to leave them in the comments on this post.

This post was originally published last year to address some questions that Deborah Bolnick and I were getting about our paper “Does Mitochondrial Haplogroup X Indicate Ancient Trans-Atlantic Migration to the Americas? A Critical Re-Evaluation.”  I’ve edited it slightly to reflect the fact that the paper itself is now open access, and you should be able to download it here or at my academia.edu page. (I’m actually really shocked at the number of downloads it’s gotten…apparently this is a topic that a lot of people find interesting!).

As soon as my syllabi for the upcoming semester are finished, I will try to write up another post that summarizes recent findings in North American anthropological genetics, and what they mean for our understanding of the initial peopling of the Americas. In the meantime, if you’re interested in ancient DNA I highly recommend you get up to speed on some of the methods by reading this post.

 

Responses to some questions about our recently published paper on haplogroup X and North American prehistory

 

What is the paper about?

We reviewed existing genetic data to answer the question: Could mitochondrial haplogroup X2a have been brought to the Americas by an ancient trans-Atlantic migration? This is a rather old question from the perspective of anthropological geneticists, but we’ve seen it appear in both academic publications and documentaries rather frequently. We thought it was worth revisiting in light of recent genetic publications.

Quite simply, we found that mitochondrial and genomic data do not support this migration hypothesis as the most plausible explanation for X2a’s presence in North America. Instead, the most parsimonious interpretation of the genetic data continues to be that haplogroup X2a had the same migration history and ancestry as the other founder Native American mitochondrial lineages (i.e., from Siberia). Based on the current evidence, we feel that there is no need to invoke a distinct origin for individuals bearing this lineage.

If you’d like another summary of the paper, Andy White wrote a very good blog post about it here.

How can you say that this proves once and for all that all Native Americans have exclusively Beringian ancestry when you haven’t sequenced all of them? Isn’t that unscientific?

We don’t say that. This work presents our best interpretation of all the genetic evidence currently available that are relevant to this question. In fact, we end the paper saying:

It is of course possible that genetic evidence of an ancient trans-Atlantic migration event simply has not been found yet. Should credible evidence of direct gene flow from an ancient Solutrean (or Middle Eastern) population be found within ancient Native American genomes, it would require the field to reassess the “Beringian only” model of prehistoric Native American migration. However, no such evidence has been found, and the Beringian migration model remains the best interpretation of the genetic, archaeological, and paleoclimate data to date.

We don’t think it’s likely that new evidence will suddenly crop up showing another source of ancestry for Native Americans, but it remains a formal, albeit remote, possibility. Should such evidence be found, it will require us to reexamine our models. But we can’t incorporate hypothetical results into our interpretations. That would be unscientific.

Doesn’t skeletal data contradict the Beringian hypothesis? What about the very early Paleoindians whose skulls look physically different from later and contemporary Native Americans? Aren’t they proof that Native Americans have European ancestry?

The skeletal data show changes over time in the cranial morphology of ancient Native American populations. It’s true that comparisons of skull shapes were, for a very long time, how anthropologists studied genetic relationships between populations. However, over the last few decades, we’ve developed the technology to assess biological relationships between individuals and populations by comparing genomes. It’s generally acknowledged that this is a more precise, direct means of assessing ancestry than morphology, which can be influenced by environmental, developmental, and cultural factors.

Furthermore, the genomes of several of the Paleoindians with differently shaped crania have been examined, and they show no evidence of different ancestry than later or contemporary Native Americans. For example, Kennewick Man, who we discuss in the paper, exhibited what some have described as “Caucasoid” cranial features. However, his overall genetic affinities group him with Siberians/East Asians, not Europeans. And his mitochondrial haplogroup is the most basal lineage of X2a so far observed. This result shows that X2a—and this Paleoindian cranial morphology—are compatible with Siberian ancestry.

Why the skulls of the earliest inhabitants of the Americas look different from the later indigenous inhabitants is a very interesting question. We suspect it has to do with evolutionary forces like selection or drift acting on morphology over millennia. Current genomic research just doesn’t show evidence that they had different ancestry from later Native American groups.

Isn’t it pretty well proven that Clovis technologies are descended from Solutrean technologies?

No. The majority of archaeologists think that the similarities between the Clovis and Solutrean points are either spurious or coincidental. Very, very few archaeologists interpret the data as supporting the Solutrean hypothesis. We don’t see the genetic evidence as supporting the Solutrean hypothesis either.

Archaeologists were wrong about the “Clovis First” hypothesis, so doesn’t that mean that you’re wrong too?

Why? These are two separate models. The model of Beringian genetic ancestry of Native Americans is not dependent on the Clovis First hypothesis; in fact, the same evidence from which the “Beringian Pause” model was developed—early coalescence dates of mitochondrial lineages and ancient DNA data—was an important component in overturning the Clovis First model.

In science, any hypothesis is falsifiable, and any model is provisional pending contradictory data. The overturning of the Clovis First model is a great example of the process working as it should.

Isn’t it unfair to critique the Solutrean hypothesis before it’s been fully “fleshed out?” There’s bound to be more data supporting it soon!

Any hypothesis is open to testing, otherwise it’s not scientific. And there’s no “waiting period” to protect a hypothesis until it’s gathered enough data to make it immune to criticism. This argument is a species of special pleading—no other idea in archaeology is treated this way.

What about the signal of “West Eurasian” ancestry seen in Native American genomes? Does it support a trans-Atlantic migration?

This finding has led to a lot of confusion among non-geneticists, and we address it in some detail in the paper. To summarize: Raghavan et al. (2014) and Rasmussen et al. (2014) studied the genomes of the Siberian Mal’ta individual and the Anzick-1 individual, respectively, and they found that a portion of their ancestry (between 14-38%) was derived from a population that also contributed alleles to the contemporary inhabitants of West Eurasia. Notably, the contemporary European gene pool appears to have emerged quite recently—within the last 8,000 years—as a result of significant migration and admixture events. We don’t know what the genomes of Solutrean peoples looked like, since none have been sequenced yet, but from these findings we predict that they would more closely resemble pre-Neolithic hunter-gatherers than contemporary Europeans [see Allentoft et al. 2015, Haak et al. 2015, and Lazaridis et al. 2014]. Importantly, based on the pre-Neolithic genomes that have been studied, it appears that these early European hunter-gatherers did not exhibit close genetic affinities to Native Americans.

Several studies have also formally tested the evolutionary relationships between Native American genomes and genomes from ancient and contemporary populations worldwide (see Rasmussen et al. 2015, Raghavan et al. 2015, and Lazardis et al. 2014). These studies have consistently showed that the model which best fits the current genetic data did not match the predictions of the Solutrean hypothesis. We discussed this in the paper, noting that the most supported model:

was one in which the population ancestral to Native Americans was derived from ancient North Eurasian and East Asian sources, while contemporary Europeans were derived from ancient North Eurasian and West Eurasian sources. In other words, gene flow was from the ancestral North Eurasian population into both the ancestral Native American and ancestral European populations. Lazaridis et al. (2014) did not find any evidence of Pleistocene gene flow directly from West Eurasians into Native Americans. Their model is also consistent with other studies, which have shown that 62-86% of Native American ancestry derives from East Asia.

 

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9 thoughts on “Archaeological Fantasies and the genetic history of the Americas

  1. ArchyFantasies August 19, 2016 / 11:38 am

    Reblogged this on Archaeology Fantasies and commented:

    We recently had Jennifer Raff on the Podcast (it went live Monday). This is a repost from her excellent blog where she talks about her paper that we mentioned in the show.

  2. Employee Performance August 30, 2016 / 10:56 am

    Hi Jennifer,

    Thanks for sharing your discussion on haplogroup X2a and models for ancient American prehistory. Really fascinating info.

    Dennis

  3. E.P. Grondine September 8, 2016 / 9:14 am

    Hi Jennifer –

    My current working hypothesis is X mt DNA evolved along the Black Sea before it flooded following the rise in sea levels following the Holocene Start Impact Events. See my current working notes here:

    http://archaeologica.boardbot.com/viewtopic.php?f=9&t=3656
    http://archaeologica.boardbot.com/viewtopic.php?f=9&t=3668

    This flooding leads to a maritime people expanding through the Mediterranean Sea area, and finally to the Atlantic. At which point we have Canadian Red Paint evolving into Canadian Red Ochre evolving into Old Copper Culture evolving into Adena.

    The Adena were tall:

    Now whether this was from a breeding within C mt DNA, as Dragoo hypothesized, or whether it was X mt DNA is an open question, but my hypothesis is that it was X mt DNA.

    • Randy Wright September 12, 2016 / 2:38 pm

      Kennewick Man’s mtDNA haplogroup was shown to X2a, and it arose early in the X2 lineage. Since his remains were shown to 9,000 years old and “related” to all Native Americans studied so far, as well as related to Siberian populations (although more closely related to Native Americans because of the likely “Berengia Standstill” ~15,000 years ago) they clearly predate the events you hypothesize. Moreover, the autosomal DNA (X2a has only been found in this hemisphere) shows a “continuity with Native North Americans over at least the last eight millennia.”

      http://www.nature.com/nature/journal/v523/n7561/full/nature14625.html

      • E.P. Grondine October 11, 2016 / 3:09 pm

        Hi Randy –

        I suppose I’m going to be showing my age here, but

        Take a look t the X mt DNA distribution in the Cambridge World Haplogroup maps.
        Then take a look at Canadian Red Paint sites, the Canadian Red Ochre sites,
        the Old Copper Culture Sites, and then Adena sites.

        Finally, consider these contact era accounts:

        Others in the mainstream are trying to develop their explanations, but in my opinion
        neither the Solutrean nor the X2A hypotheses work to explain the data.

        By the way, I would try to explain to various nuts about red hair in samples from guano caves or the desert, but that would be useless. You want to try to straighten them out?

  4. Solutrean Warrior 14 October 10, 2016 / 10:16 pm

    Typical Bias from PC proponent’s – such as yourself! Simple question how do you explain all the Ancient “Blonde” and Red-Haired” Mummies found in places like South America – years before Columbus or the Vikings? That is a perfect illustration of Ancient Migration from Europe – is it not?

    • RaceRealist December 6, 2016 / 8:20 pm

      That is a perfect illustration of Ancient Migration from Europe – is it not?

      No it’s not. Do you have genetic evidence that this is the case? And what’s funny is that some people use the X2 haplotype to say that there was a Solutrean crossing? See:

      “After several years of multidisciplinary examination, it is now clear that the proposal that Solutrean hunter-gatherers crossed the Atlantic Ocean during the Pleistocene (Stanford and Bradley 2012; see also Bradley and Stanford 2004, 2006; Collins 2012; Stanford and Bradley 2000) is not currently supported in any scientific field (Bamforth 2013; Dulik et al. 2012; Eren et al. 2013, 2014; Eriksson et al. 2012; Fiedel 2012; Goebel et al. 2008; Haynes 2013; Kashani et al. 2012; Lepper 2013a, 2013b; Morrow 2014; O’Brien et al. 2014a, 2014b; O’Rourke and Raff 2010; Raff and Bolnick 2014; Raghavan 2013; Rasmussen et al. 2014; Shott 2005a, 2005b; Straus 2000; Straus et al. 2005; Surovell 2014; Westley and Dix 2008; Whittaker 2013). Moreover,Phillips’ (2014) recent quantitative investigation of an optimal foraging model— which integrates paleoclimatic, paleobiological, and ethnographic factors— suggests that a Solutrean trans-Atlantic expansion during the Pleistocene would not have been possible, even when the model incorporates highly favorable parameters that border on impracticality.

      There are presently no valid data of which we are aware to support assertions that bi-pointed leaf-shaped lithic tools from the Atlantic Seaboard are either “older than Clovis” or that they were brought here by seafaring Solutreans (see also Fiedel 2012; O’Brien et al. 2014; Waguespack and Kelly 2014:48). There is substantial evidence in the archaeological record of eastern North America to conclude that these stone tools are components of tool kits used by indigenous North American populations between the Late Archaic and Early Woodland periods (i.e. the middle Holocene)—periods in which people were exploiting Atlantic maritime resources.

      https://www.researchgate.net/publication/263808760_On_the_Inferred_Age_and_Origin_of_Lithic_Bi-Points_from_the_Eastern_Seaboard_and_Their_Relevance_to_the_Pleistocene_Peopling_of_North_America

      This isn’t from “PC” proponents. Guessing at one’s motivation is ad hominem, good job.

      The Solutrean Hypothesis is a joke.

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