If you're interested in how, when, and from where people first entered the Americas, you should be aware of a new paper by Jennifer Raff and Deborah Bolnick titled "Does Mitochondrial Haplogroup X Indicate Ancient Trans-Atlantic Migration to the Americas? A Critical Re-Evaluation" (PaleoAmerica 1(4):297-304). It is a concise, clear, and largely non-technical essay discussing what the presence of mitochondrial Haplogroup X2a in Native Americans might be telling us about the pre-Columbian migration of populations across the Atlantic. 

The answer is . . . (drumroll): not much.

Haplogroups are genetic populations that share a common ancestor.  The common ancestry of mitochondrial haplogroups is defined by differences and similarities in mitochondrial DNA, a kind of DNA that is contained in the mitochondria of cells.

Haplogroup X is found in living populations in Europe, west Asia, and northern North America.  Studies in the late 1990s began to ask whether the geographic distribution of Haplogroup X among living populations was telling us something about the origin of at least some New World peoples. A widely-read 1998 popular article titled "Genes May Link Ancient Eurasians, Native Americans" (Science 280(5363):520) helped popularize the idea that peoples from the Near East or Europe contibuted to Native American ancestry.  This idea was very popular among Mormons looking for evidence of a migration of Near Eastern peoples to the New World several thousand years ago (it is regarded with less enthusiasm now, especially after the publication of genetic data from Kennewick Man: see this blog post, for example).  

The distribution of Haplogroup X has also been proffered as evidence by proponents of the Solutrean Hypothesis (the idea that Paleolithic peoples from Europe migrated to eastern North America around 20,000 years ago). In a 2014 paper ("Solutrean Hypothesis: Genetics, the Mammoth in the Room," World Archaeology 46(5):752-774), Stephen Oppenheimer, Bruce Bradley, and Dennis Stanford argued that

"The mtDNA X2a evidence is more consistent with the Atlantic route and dates suggested by the Solutrean hypothesis and is more parsimonious than the assumption of a single Beringian entry, that assumes retrograde extinction of X in East Eurasia." (from the abstract)

Raff and Bolnick's essay strongly challenges that interpretation, concluding the following (page 301):

"We remain unconvinced by the arguments advanced thus far in favor of a trans-Atlantic migration prior to 1500 cal yr BP or so. As we have discussed, X2a has not been found anywhere in Eurasia, and phylogeography gives us no compelling reason to think it is more likely to come from Europe than from Siberia. Furthermore, analysis of the complete genome of Kennewick Man, who belongs to the most basal lineage of X2a yet identified, gives no indication of recent European ancestry and moves the location of the deepest branch of X2a to the West Coast, consistent with X2a belonging to the same ancestral population as the other founder mitochondrial haplogroups. Nor have any high-resolution studies of genome-wide data from Native American populations yielded any evidence of Pleistocene European ancestry or trans-Atlantic gene flow."

This is an interesting case where, I think, interpretations based initially solely on genetic information from living populations are and will continue to be refined as data are added from prehistoric remains.  Genetic data from living populations are great for formulating hypotheses, but they don't actually provide direct evidence about the past -- that has to come materials and skeletons that are actually from the past.  Whatever story is "true" has to be consistent with all lines of evidence.  Raff and Bolnick (page 301) mention that there are currently no genetic data from Solutrean skeletal material -- I hope someone pursues that in the near future.

As a final aside: it's a bummer that every single paper I discuss in this post is behind a paywall. I can get to them through my university library access, but the public generally can't.  A lot of people out there who are not professional academics are interested in these issues and it's a shame we can't make our work more openly available to them.  The Raff and Bolnick paper is a great example, I think, of an essay on a technical issue that is written in such a way as to be palatable to a non-technical audience (and when it comes to genetics, I include myself in that audience).  I hope that their paper can somehow be made open access so anyone and everyone can read it.​

Update (11/7/2015):  A copy of Raff and Bolnick's paper can be downloaded from Jennifer Raff's Academia.edu page.

The purported pre-Clovis assemblage from Topper is entirely stone, consisting of items described as cores, blades, flakes, gravers, spokeshaves, scrapers, etc. Bifaces are absent, which, I think, is one of the aspects of the assemblage that gives many North American archaeologists pause. You can see images of some of the pre-Clovis material here and in Doug Sain's dissertation (discussed more below). You can also read Goodyear's 2009 update on work at the site here.

The questions about the Topper pre-Clovis assemblage boil down to two main issues:

• Is the material cultural?
• Is it really that old?

Both of those issues are much simpler to raise then they are to answer.  

Is It Cultural?

The "is it cultural" question is Question Number 1: if it's not cultural, then it doesn't really matter how old it is. Some archaeologists (such as Michael Collins in this Popular Archaeology article and this CNN story)  have stated that the the pre-Clovis materials from Topper are the result of some natural process rather than the products of human behavior (i.e., they're "geofacts" rather than artifacts). If the Topper pre-Clovis "artifacts" are just a bunch of rocks, the rest of the story doesn't really matter.

Yesterday I looked at some of the material from Topper that is displayed at USC's Salkehatchie campus. I wasn't doing a systematic analysis, and I didn't actually handle the material (I was just looking through the glass like everybody else), so I'm not yet ready to offer a strong opinion of my own.  I will say, however, that at least some of the objects displayed surely looked like good candidates for human-made stone tools and cores to me. There were several pieces that appeared to have fairly clear unifacial retouch, one flake with a very clear bulb of percussion, large "cores" that appeared to have multiple flake removals, etc.

In my opinion, several of the pieces from the Topper pre-Clovis assemblage that I saw (the only ones I've looked at recently) show characteristics that appear to be consistent with human manufacture. Does that mean they couldn't have been produced by some sort of natural process? Good question. Doug Sain's recent (2015) dissertation on the pre-Clovis assemblage from Topper attempted to address that issue by developing several lines of analysis (experimental archaeology, attribute analysis, refitting, etc.).  Sain concluded (on page 567) that:    

"Evidence from this study supports King’s (2011) findings and demonstrates a human origin for the pre Clovis conchoidal flake assemblage at the site. However, this assemblage likely resulted from flake core and flake tool manufacture as opposed to biface manufacture and furthermore does not reflect bioturbation as an agent responsible for deposition. The assemblage is at minimum 14,000 BP and possibly much older. The bend break assemblage from the Lower Pleistocene Sands and Upper Pleistocene Terrace at Topper are also considered products of human agency based on the presence of specific technological attributes (compression rings, lips), retouch modification, and lack of differentially weathered scars." 

I confess that I have only skimmed through Sain's dissertation at this point (it is 2400 pages).  It's clear, however, that he's done a lot more than simply look at some pieces of stone and say "yup, looks like an artifact" or "nope, doesn't look like an artifact." He has looked more closely at the material than (I would guess) anyone else at this point.  Thus his conclusions are an important data point suggesting that we shouldn't be so quick to dismiss the materials from Topper just because they are difficult to reconcile with the "knowns" of North American prehistory.

Is It Really That Old?

If the pre-Clovis materials from Topper are legitimate products of human behavior, can they really be 50,000 years old?

It looks to me like there is little question that the sediments (writ large) from which the Topper materials were excavated really do date to several tens of thousands of years ago.  This (2009) paper by Michael Waters et al. discusses the geoarchaeology and dating of the Topper sediments, if you want to wade into the particulars.

Even if the general sediment stratigraphy is understood and well-dated, however, it is fair to ask if younger artifacts might have been introduced into older sediments through some sort of natural process - tree roots? animal tunnels? cracks in the earth?  I wasn't present at any of the Topper excavations, so I can't really add anything about the possible role bioturbation might have played in moving artifacts around. Again, there is discussion in Sain's dissertation about whether some kind of bioturbation could explain how much younger (i.e., Clovis age) artifacts were introduced into such old sediment.

What If?

Healthy skepticism is an important part of doing good science. I'm as skeptical as the next person, and I think the extraordinary nature of the claims being made about Topper warrant significant scrutiny.  What I (and many others, I think) are anticipating is the definitive publication by Goodyear that lays out the evidence and the argument in a succinct, clear way.  That will let us evaluate the totality of the claim and find a path forward for future inquiry.  The Topper site is still there, and new excavations could be conducted to target questions that develop from analysis of what has been done so far.

But take off the skeptic's hat for a minute and put on the "what if" hat: how cool would it be if there was an archaeologically-recognizable occupation of eastern North America pre-dating the Last Glacial Maximum? Where did those people come from? What were their societies like? What happened to them? Humor me for a minute here.

The time period between about 60,000 and 30,000 years ago (i.e., the time period that is claimed for some of the pre-Clovis materials from Topper) saw the movements of human groups into several previously-unoccupied parts of the world, including northern Asia, Japan, and Australia. What if an early wave of colonizers reached the New World? What if the 33,000 year-old remains from Monte Verde (Chile) were left behind by people in this first wave? What if the 48,000-32,000 year-old remains from Pedra Furada (Brazil) were also left by those early settlers? What if the stone tool technologies of these early settlers, like those of many Paleolithic groups in the Old World, were not based heavily on bifaces? What if a lack of formal bifaces in these early pre-Clovis technologies means that the lithic tools and debris left behind by these early settlers is "hiding in plain site," the nondescript assemblages of pre-Clovis flakes and unifacial tools blending in with the lithics left by much later peoples?  What if that earliest occupation was ultimately unsuccessful, leaving behind no survivors and presenting no evidence for a historical connection between the technologies of its people and those of the people who followed?

That's a lot of "what ifs," but I think that's okay.  "What ifs" are free.

If the pre-Clovis lithics from the Topper site were really produced by a very early human occupation of eastern North America, there is quite a story that remains to be told in this part of the world. And if that story is true, maybe Topper won't even be the site that can tell it the best. If there were people in the Southeast 50,000 years ago, it will ultimately be possible to find other examples of sites that they produced.  Perhaps a systematic look at buried deposits predating the LGM will help produce some information (positive or negative) that can help us understand what Topper means.  After visiting Topper and having a cursory look at some of the materials myself, I'm looking forward to watching the debate play out and seeing what happens next. Who knows -- I may get in on the action myself someday.  

After having set computer modeling aside (out of necessity) for the past year, I'm ready to start getting back to that component of my research.  I'm hoping to get things ramped back up this semester and be doing some fairly hardcore computational work by next semester.  I've got some technical and logistical issues to address, and I'll surely  have to spend some time getting back up to speed with Java and Repast.  But it shouldn't be too bad

One of the things I'd like to do when I get up and running again is take another look at how the children's labor might affect the dependency ratio and household-level calculations about family size, etc. (see this paper for my first attempt to address the issue). In the models I'm currently using (e.g., the ForagerNet series), I represent a child as either a "producer" or a "non-producer" by comparing the child's age to the value of a parameter that specifies the age at which children become producers. Clearly that's a significant simplification of reality: children do not magically become "producers" overnight on their 8th birthdays or their 12th birthdays, etc.

I was watching my two boys (ages 4.7 years and 2.2 years) shell beans at the kitchen counter over the weekend, and it got me wondering what kind (if any) quantitative data are available about age-based changes in the proficiency of children in doing various kinds of productive tasks. Watching my two kids, there was a huge difference in the proficiency (and interest level) of the older and younger boys.  The older one stuck with the task until we ran out of beans and, while not as fast as an adult, was really pretty good.  Despite an equal contribution of energy (at least in the beginning), the productivity of the younger one was much lower.  Part of that had to do with the desire to do a victory dance for each single bean that he managed to pull from a pod. 

What would the age-based "proficiency curve" of bean processing look like?  A linear progression? A rapid increase in proficiency between ages 2 and 6?  At what age do individuals reach "full proficiency" in processing beans?  

​Are there ethnographic data available that would allow me to understand how proficiency at processing various kinds of plant foods changes with age? How about tasks related to gathering?  Or planting?

There has been an increase in interest in the lives of children in hunting-gathering societies (see this paper by Nurit Bird-David), and I'm hoping that some quantitative data are available from recent ethnographic studies (e.g., see this 1994 paper by Blurton Jones et al., this 2004 paper by Raymond Hames and Patricia Draper, this 2009 volume edited by Barry Hewlett and Michael Lamb).  I'm less familiar with possible sources for quantitative data relevant to modeling age-based changes in children's work proficiency in agricultural societies.  Maybe there are government agencies or NGOs that monitor that sort of thing (the site of the International Labour Organization discusses children's domestic work, for example).

Anyway, this blog post is just a placeholder. I'm interested in tracking down some data if they're available (if you know of any, please let me know!).  

If there are not suitable data already out there, I might have to generate some of my own through some controlled experimentation.  Let me know if you like beans.  We may soon be producing a surplus at my house. And I may soon ask to borrow the participation of children of various ages.
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