The Solutrean Hypothesis Meets Mainstream Science: A False Response to a Real Problem vs. A Real Response to a False Problem
World Archaeology 46, no. 5 (2014): 752-774. DOI: 10.1080/00438243.2014.966273
Solutrean Hypothesis: Genetics, the Mammoth in the Room
Stephen Oppenheimer, Bruce Bradley, and Dennis Stanford.
The Solutrean hypothesis for the origin of the Clovis archaeological culture contends that people came from south-western Europe to North America during the Last Glacial Maximum. This hypothesis has received numerous critiques, but little objective testing, either of cultural or genetic evidence. We contest the assertion that there is NO genetic evidence to support this hypothesis, and detail the published evidence, consistent with a pre-Columbian western Eurasian origin for some founding genetic markers, specifically mtDNA X2a, and some autosomal influence, found in ancient and modern Native American populations. The possibility that the inferred pre-Columbian western autosomal influence came more directly than through Siberia is not even considered in such studies. 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.
The emergence in the past 15 years of the Solutrean hypothesis for the origin of Clovis is somewhat an oddity. Advocated by two well institutionalized archaeologists, Dennis Stanford and Bruce Bradley, it shares the belief in the recent (either Clovis-First-recent or just-a-few-thousand-years-pre-Clovis-recent) extra-American origin of New World populations with its intellectual adversary, the mainstream Bering Strait tradition. But it argues that the earliest pan-American archaeological signature, namely the Clovis-like foliate points, was of West European, and specifically Solutrean, origin. This contention based on formal similarities between Clovis and Solutrean points is accompanied by a scenario whereby the bearers of Solutrean technologies did not walk across Eurasia but instead ventured “directly” across the Atlantic Ocean. A theory postulating a migration by land from West Eurasia to America would have been a sufficient challenge to the academic mainstream but Stanford and Bradley had to throw in a maritime Atlantic route for this migration to make sure a major controversy ensues.
After having presented in a number of publications, most importantly in the monograph entitled Across Atlantic Ice (2013), the archaeological evidence for the Solutrean hypothesis, Stanford and Bradley now discuss genetic evidence for the Solutrean migration. Their goal is to rally against the dismissive attitude shown to the Solutrean hypothesis by population geneticists. Being archaeologists and not geneticists, they co-opted into their team a popular interpreter of population-genetic evidence and a guru of coastal and maritime colonization models, Stephen Oppenheimer. Once a proponent of an ill-supported “beachcomber” migration out of Africa, Oppenheimer has now re-emerged as an advocate for a major trans-Atlantic migration from Europe to North America.
What we learn from these academic dissenters is that
“The Solutrean hypothesis (SH) currently offers an archaeological explanation for the origins of the majority of pre-Clovis cultural assemblages and their in situ evolution into Clovis; no such credible cultural-evolutionary sequence has been offered for Palaeolithic East Eurasia as their cultural source.”
What this means is that there is no archaeological evidence for an East Eurasian origin of Amerindians. And this revelation comes some 100 years after archaeologists have convinced everybody (and most recently population geneticists) that they have overwhelming evidence that Amerindians derive from East Asia.
But then Oppenheimer, Bradley and Stanford (2014, 758) accept geneticists’ conclusion that the 4 out of 5 founding New World mtDNA lineages (A, B, C and D) have a “clear” East Eurasian origin and are not found in West Eurasia. (Those are the geneticists who initially accepted archaeologists’ claim that Amerindians came from East Asia – a claim that Stanford and Bradley believe does not really have the material evidence behind it.)
But while 4 out of 5 pan-American mtDNA clades are apparently derived from Asia, the earliest pan-American lithic tradition is not, according to Oppenheimer, Bradley and Stanford (2014). It is derived from the fifth, low-frequency lineage, namely mtDNA X2, which is restricted to North America. So, the Solutrean hypothesis paints a picture in which the vast majority of Amerindian mtDNA lineages stem from a founding population that left no “credible cultural-evolutionary sequence” between land-linked East Asia and America, while a small minority of North Amerindian mtDNA lineages derive from a founding population that easily maintained technological continuity with its source lithic tradition in southwestern Europe despite all the vicissitudes of a trans-Atlantic crossing and, in the New World, spawned a lithic signature that’s recognizably the same from the Mesa Complex in Alaska to the so-called “fish-tail” points in South America. In any other part of the world, such an adventurous, non-parsimonious and ad hoc hypothesis would not even have emerged among judicious academics, but the prehistory of the New World is a special case! Stanford and Bradley are grappling with and thus putting under a microscope a real problem ignored by mainstream science, so it does not really matter that their solution is a false and hopeless one.
Indeed, mainstream science has no good explanation for mtDNA hg X2, which is found in West Asia, North Africa and all over western and central Europe at low frequencies, and then again in North America at somewhat higher frequencies that reach 30% in Algonquin-speaking Ojibwe. Oppenheimer, Bradley and Stanford (2014, 765) criticize mainstream science for not providing any evidence for the presence of hg X in East Eurasia and for finding comfort in the belief that it was simply lost there.
“In spite of such theoretical claims, long-distance uniparental lineage migration nearly always leaves, not only a trail, but progressive, geographically-defined mutational branch markers. One of the best examples of such trail-persistence, can be found in the progression of B4a1a from SE Asia through the Melanesian islands to Eastern Polynesia in the Pacific. In spite of serial founding
effects and drift a progressive genetic trail can be traced along the island chain evolving through B4a1a1, to B4a1a1a to B4a1a1a1. In spite of evident drift, nowhere is the trail actually lost en route (Fig. S1 in Soares et al. 2011). If a phylogeographically specific genetic trail can be left across the Pacific Islands in spite of serial founder effects, it is more likely, than not, to be left somewhere in the landmass of East Eurasia or at least have left specific traces.”
In their passionate critique of mainstream inertia Oppenheimer, Bradley and Stanford, however, forget that the Solutrean hypothesis can offer neither a “progressive genetic trail” that runs across the Atlantic, not even the “islands” to hop over. It does not offer a better solution to the X2 puzzle; it only makes the conundrum starker. Moreover, they conveniently ignore the fact that hg B shares with hg X the pattern of not being found among Siberian populations, and hg B is not a West Eurasian lineage.
Recent whole-genome and ancient DNA studies have affirmed the reality of a West Eurasian-Amerindian connection (to the exclusion of East Eurasians) but Oppenheimer, Bradley and Stanford (2014), who are clearly enamored with mtDNA hg X2, are strangely taciturn about them. Their treatment of “autosomal evidence for pre-Columbian West Eurasian admixture” is just 1.5 pages long! This reticence to delve deep into what has emerged as the strongest genetic evidence for non-East Eurasian affinities of New World populations can be explained by the mere novelty of the whole-genome data and the complex statistics behind it. But most likely Oppenheimer, Bradley and Stanford (2014) glanced over the growing body of studies simply because they know that they disprove the sexiest parts of the Solutrean hypothesis, namely the trans-Atlantic crossing and the unique link between southwest Europe and North America.
The two ancient DNA samples pose the strongest challenge and provide the germs of the strongest alternative to the Solutrean hypothesis. These samples are Mal’ta (24,000 YBP) and Anzick (11,500 YBP). As Fig. 1 (from Raghavan et al. 2013) and Fig. 3 (from Rasmussen et al. 2014) (see below) show, Mal’ta and Anzick show a very similar pattern of shared genetic drift with other human populations. Anzick (right) is just more divergent from Old World populations than Mal’ta (left), which displays medium-strong affinities with Northern Europeans.
Mal’ta DNA comes from an archaeological site located in South Siberia (and not in Western Europe) – a region that many mainstream science publications postulated as a likely ultimate source for New World populations. But its link to modern Amerindians is surprisingly strong considering the pre-LGM date. A somewhat weaker Amerindian signal is showed by Paleolithic central (Kostenki), Mesolithic southeastern (La Brana) and modern northern Europeans. Importantly, Mal’ta DNA, while located within the putative geographic source area for Amerindians, does not show any East Eurasian influence whatsoever, to the dismay of mainstream science. But it does not belong to mtDNA hg X either. Its mtDNA falls under hg U, which is a likely signature of Upper Paleolithic West Eurasians and it is not found among Amerindians. It’s rather closely related to Amerindian hg B, which, as Oppenheimer, Bradley and Stanford agree, has East Eurasian affinities.
Ancient Anzick DNA, which is derived from the only available physical specimen associated with Clovis tools, belongs to mtDNA hg D4h3, which Oppenheimer, Bradley and Stanford would agree is an East Eurasian signature in the New World mitochondrial gene pool. And Anzick DNA clustered with Central and South American Indians to the exclusion of North American Indians, which geneticists attributed to “undocumented stream of gene flow” into Northern Amerindians. In order to salvage the Solutrean hypothesis from a barrage of new facts, Oppenheimer, Bradley and Stanford had to appeal to the growing archaeological evidence that there were people in the New World before Clovis. They (2014, 767) found a truly intriguing tension in geneticists’ data:
“Testing the model of ‘undocumented stream of gene flow’, they looked for and found ‘no evidence for Siberian gene flow into the Northern Amerinds’ (Rasmussen et al. 2014, SI Sect. 15.4, 27).”
And they quickly tried to hijack it to bolster the Solutrean hypothesis:
“But, again they did not explore the alternative explanatory possibility of an earlier trans-Atlantic stream of gene flow which, by virtue of geography, would influence the NA in East Canada to a greater extent than the SA populations, in this context.”
But whole-genome data shows that Northern Amerindians are more shifted toward East Asians than are Central and Southern Amerindians. And geneticists’ models have West Eurasian gene flow enter ancestral Amerindians after their separation from East Asians, not before, as Oppenheimer, Bradley and Stanford (2014) would like to have it.
The Solutrean hypothesis is trapped on all sides (technological parallels between Clovis and Solutrean are overstated, a trans-Atlantic crossing is hard to fathom or prove, Clovis mtDNA has East Eurasian affinities, Clovis autosomal DNA has South American affinities, pre-LGM South Siberian DNA has West Eurasian affinities making a “direct” maritime link with North America in post-LGM times theoretically superfluous, etc.) and is doomed to fail. It’s disappointing that the authors demand a “fair hearing” for their ideas from geneticists (“[I]t is presumed in all these analyses that the inferred pre-Columbian west Eurasian admixture into Native Americans arrived via Beringia and there was no mention of the possibility that this pre-Columbian west-Eurasian admixture could, alternatively, have come across the Atlantic. There was nothing in the analysis, which formally or explicitly determined the geographic direction of inferred, shared West Eurasian population ancestry, from Siberia or from the Atlantic”) instead of learning from recent genetic research and adapting their hypothesis to the new realities, which mainstream science, too, cannot explain. Just like mainstream scientists with their shiny “Beringian Standstill,” “Coastal Migration,” “American Indians Came from South Siberia” ideas, Stanford and Bradley seem to be firmly wedded to the fancy and media-worthy side of their thinking (“Solutreans in America,” “trans-Atlantic crossing,” etc.) and not to the analysis of the actual interdisciplinary and multitemporal data that’s now growing exponentially.
Mainstream science is right in dismissing the Solutrean hypothesis on both archaeological and genetic grounds. But, while hopeless, the Solutrean hypothesis will take its mainstream alternatives with it into the grave. Just like there’s no “credible cultural-evolutionary sequence” between Pleistocene East Eurasian technologies and Clovis, Oppenheimer, Bradley and Stanford (2014, 754) confirm that
“there is no established Western Eurasian archaeological trail east of Mal’ta, and into Alaska (as implicit in the archaeo-genetic Upper Palaeolithic route claim in the Mal’ta paper), early enough or archaeologically congruent enough to be ancestral to the older-than-Clovis cultural remains in eastern North America (Collins et al. 2013). The other site mentioned (Afontova Gora) is even further west than Mal’ta and Soviet researchers interpreted that if anything the directionality indicated by Mal’ta to Afontova Gora is to the northwest not toward Beringia.”
The ultimate weakness of the Solutrean hypothesis is not its formal archaeological, geographical or genetic merits but the untested assumptions and false problems it shares with the mainstream models of the “peopling of the Americas” regarding the derived nature of Amerindian culture and genetics and the recent timeframes for the “peopling of the Americas.” The strength of the Solutrean hypothesis is its sober assessment of the actual archaeological content behind the claim of East Eurasian origins of Amerindians (from both an East Asian and Mal’ta-like sources) and its contention that “genetics should not be used, as in the past, to find support for the current most influential archaeological paradigm; rather it should objectively test all testable migration-models” (Oppenheimer, Bradley and Stanford 2014, 755). I can only hope that the out-of-America hypothesis will receive an objective test as well some day.