The Western Stemmed Tradition, Clovis and mtDNA 9-bp Deletion

The Western Stemmed Tradition, Clovis and mtDNA 9-bp Deletion

Science 13 July 2012: Vol. 337 no. 6091 pp. 223-228 DOI: 10.1126/science.1218443

Clovis Age Western Stemmed Projectile Points and Human Coprolites at the Paisley Caves

Jenkins, Dennis L. et al.

The Paisley Caves in Oregon record the oldest directly dated human remains (DNA) in the Western Hemisphere. More than 100 high-precision radiocarbon dates show that deposits containing artifacts and coprolites ranging in age from 12,450 to 2295 14C years ago are well stratified. Western Stemmed projectile points were recovered in deposits dated to 11,070 to 11,340 14C years ago, a time contemporaneous with or preceding the Clovis technology. There is no evidence of diagnostic Clovis technology at the site. These two distinct technologies were parallel developments, not the product of a unilinear technological evolution. “Blind testing” analysis of coprolites by an independent laboratory confirms the presence of human DNA in specimens of pre-Clovis age. The colonization of the Americas involved multiple technologically divergent, and possibly genetically divergent, founding groups.

Link

An important paper that continues the business of debunking the Clovis-I model of the the origins of American Indians. Paisley Caves are located in south-central Oregon, hence the name “Western Stemmed Tradition.” The University of Oregon has been conducting excavations at the site since the 1930s but it’s only in 2002 that these excavations became thorough and consistent. 190 conventional and AMS radiocarbon dates were obtained from coprolites, sedimented urine, artifacts, bones and sagebrush twigs. The assemblage and the human coprolites were dated at 11,070 and 11,340 radiocarbon YBP. confirming that the site is either contemporaneous with or older than Clovis. There were no Clovis-type points found on the site:

“There are no classic Clovis technology prismatic blades, overshot flake terminations, overshot flake scars on exceptionally large bifaces, fluting flakes or flute repair flakes in the Paisley assemblage. Rather, the assemblage is dominated by small flake debris reflecting simple core reduction and finish-tool-shaping or rejuvenation by pressure flaking. (Jenkins et al. 2012, Suppl. Mat., 34).

Technologically, the Western stemmed projectile points are different from Clovis points in the following ways (Jenkins et al. 2012, 224):

“Western Stemmed projectile points are generally narrow bifaces with sloping shoulders, and many have relatively thick contracting bases. They were commonly made on flakes by broad collateral, midline, percussion flaking and finished by pressure flaking. In this, they are morphologically and technologically distinct from the generally broader, concave-based, fluted Clovis points made on large bifacial preforms often thinned by overshot flake technology. Prismatic blades—long, narrow flakes with triangular cross sections driven from specially prepared cores—are common to Clovis sites outside of western North America and are less common to WST assemblages.”

Regarding Siberian affinities of the Western Stemmed Tradition, Jenkins et al (2012, 223-224) note,

“Stemmed points were present earlier in East Asia and Siberia, and the basic form could have arrived in the Americas before Clovis developed. Like Clovis, the WST is a New World development sharing basic morphological and technological characteristics with Old World forms.”

Two flake-based projectile point traditions coexisted in Late Pleistocene North America, neither of them have immediate antecedents in Siberia but both of them have generic Old World associations. Importantly, just like with Clovis sites, there is no evidence of microblades at Paisley Caves. Microblades are widely present in Siberia since 20,000 BP and are found in Alaska and along the Pacific Northwest all the way down to the Vancouver Island. But they don’t penetrate any further south suggesting that the areas south of the ice shields were occupied by populations with “New World technological developments,” and not descendants of Siberian migrants. Regarding Clovis, it’s also becoming increasingly apparent that Clovis has a southern origin in North America (the Buttermilk Complex in Texas) and spread north into Alaska and, possibly, Northeast Asia with the retreat of the glaciers. Time will show if the Western Stemmed Tradition, too, expanded up north along the Pacific Coast. For now, Jenkins et al (2012, 227) suggest that the Western Stemmed Tradition was an “indigenous development in the far western United States, whereas Clovis may have developed independently in the Plains and Southeast.

Of special interest is mtDNA obtained from 26 Paisley Caves coprolites. It’s the oldest DNA in the Western Hemisphere (the upper bound is 12,265 ± 25 radiocarbon YBP) and it furnished a surprising finding (see Table S12 in the Supplement):

“Twenty-one specimens belonged to mitochondrial founder haplogroup A, screened for the presence of the A – G SNP at nucleotide position (np) 663 (all positions given with reference to the revised Cambridge Reference Sequence). Five belonged to haplogroup B, characterized by a 9 base-pair (bp) deletion following np 8281, also present in eight of the coprolites assigned to haplogroup A. The presence of this 9bp deletion after nucleotide 8281 has been previously reported for haplogroup A, but it has also been reported for haplogroups C and D.”

PhyloTree assigns these 9-bp deletion-carrying A lineages to hg A2d1 (see below, partial view) and it’s possible that the Paisley Caves samples are A2d1.

As I reported earlier, 9-bp deletion has a wider distribution globally than just hg B. Geneticists tend to interpret the pervasiveness of this mutation as a sign that it emerged multiple times in human history but this explanation is not particularly compelling. First, methodologically, this may be true in some cases but it doesn’t mean that every time we encounter this deletion on a different haplotypic background, it must be homoplastic. In some cases, it’s the haplogroups that may not have been properly defined. For instance, PhyloTree postulates that the 9-bp deletion emerged independently on hg B6 (supposedly related to hg R11 with no deletion) and B4’5 but it’s just as likely that B6, B4 and B5 form hg B4′B5′B6 to the exclusion of hg R11. Second, the well-established hg B4′B5 is defined as a monophyletic cluster by a combination of 8281-8289d and 16189C but this pair of mutations is found in Africa on L0a2 lineages, in West Asia on T2f lineages and in America on A2d1. In the latter case, A2d1 and B4′B5 are part of macrohaplogroup N. Third, the global presence of 9-bp deletion may indicate great antiquity, and we need to seriously consider the possibility that this mutation dates back to the time prior to the formation of the respective haplogroups. The fact that at Paisley Caves there are more hg A samples with the deletion than hg B samples suggests that A lineages with 8281-8289d may have been rather common in the past.

Distributional evidence supports the antiquity of 8281-8289d or of the 8281-8289d + 16189C combination: it’s rare to non-existent in Siberia but it penetrates deep into South America. If hg B2 was brought to America as a separate, later migration, then we would have found it in Siberia and not likely in South America. The distributional pattern of 9-bp deletion, namely its presence in South America and Sub-Saharan Africa but not in Siberia is not unique. HTVL virus shows the same puzzling geography.