Favorite Things Redux: Beringian DNA

Map of gene-flow in and out of Beringia, from 25,000 years ago to present

Scientists have long believed that the first humans made it to the Americas by crossing from now-Russia to now-Alaska. When and how they did it–by boat or by foot–remain matters of contentious debate. Did people move quickly through Alaska and into the rest of North America, or did they hover–as the “Bering standstill” hypothesis suggests–in Beringia (or the Aleutian Islands) for thousands of years?

Archaeologists working at the Upward Sun River site (approximately in the middle of Alaska) recently uncovered the burials of three children: a cremated three year old, and beneath it, a 6-12 week old infant and a 30 week, possibly premature or stillborn fetus. The three year old has been dubbed “Upward Sun River Mouth Child,” and the 6 week old “Sun-Rise Girl Child.” Since these aren’t really names, I’m going to dub them Sunny (3 yrs old), Rosy (6 weeks), and Hope (fetus).

They died around 11,500 years ago, making them the oldest burials so far from northern North America. Rosy and Hope were probably girls; cremation rendered Sunny’s gender a mystery. Rosy and Hope were covered in red ocher and buried together, accompanied by four decorated antler rods, two dart points and two stone axes. (Here’s an illustration of their burial.) The site where the children were buried was abandoned soon after Sunny’s death–perhaps their parents were too sad to stay, or perhaps the location was just too harsh.

Rosy and Hope were well enough preserved to yield DNA.

Surprisingly, they weren’t sisters. Rosy’s mother’s mtDNA hailed from haplogroup C1b, which is found only in the Americas (though its ancestral clade, haplogroup C, is found throughout Siberia.) Hope’s mtDNA is from haplogroup B2, which is also only found in the Americas. Oddly, B2’s parent clade, (B), isn’t common in Siberia–it’s much more common in places like Vietnam, Laos, the Philippines, and Saipan. It’s not entirely absent from Siberia, but it got to Alaska without leaving a larger trail remains a mystery.

Since they are found in the Americans but not Asia, we know these lineages most likely evolved over here; the main questions are when and where. If the Bering Standstill hypothesis is correct and the Indians spent 10-20,000 years stranded in Beringia, they would have had plenty of time to evolve new lineages while still in Alaska. By contrast, if they crossed relatively quickly and then dispersed, these new lineages would have had much less time to emerge, and we would expect them to show up as people moved south.

Source: Ancient Beringians: A Discovery Changing Early Native American Hisotry

Or there could have been multiple migration waves, with different haplogroups arriving in different waves. (There were multiple migration waves, but the others occurred well after Sunny and the others were buried.)

In fact, there are five mtDNA lineages found only in the Americas (A2, B2, C1, D1, and X2a.) With Hope and Rosy, we have now identified all five mtDNA lineages in North American burials over 8,000 years old, lending support to the Beringian Standstill hypothesis.

But were the Upward Sun River children’s families ancestral to today’s Native Americans? Not quite.

It looks like Sunny’s tribe split off from the rest of the Beringians (or perhaps the others split off from them) around 22-18,000 years ago. Most of the others headed south, while Sunny’s people stayed in Alaska and disappeared (perhaps because all of their children died.) So Sunny’s tribe was less “grandparent” to today’s Indians and more “great aunt and uncle,” but they still hailed from the same, even older ancestors who first set out from Siberia.

I have previously favored the Aleutian or at least a much more rapid Beringian route, but it looks like I was wrong. I find the idea of the Bering Standstill difficult to believe, but that may just be my own biases. Perhaps people really did get stuck there for thousands of years, waiting for the ice to clear. What amazing people they must have been to survive for so long in so harsh an environment.

Recent Exciting Developments: 130kya American Hominins?

There has been SO MUCH EXCITING NEWS out of paleoanthropology/genetics lately, it’s been a little tricky keeping up with it all. I’ve been holding off on commenting on some of the recent developments to give myself time to think them over, but here goes:

  1. Ancient hominins in the US?
  2. Homo naledi
  3. Homo flores
  4. Humans evolved in Europe?
  5. In two days, first H Sap was pushed back to 260,000 years,
  6. then to 300,000 years!
  7. Bell beaker paper

1. Back in May (2017,) Holen et al published an article discussing A 130,000-year-old archaeological site in southern California, USA, in Nature:

Here we describe the Cerutti Mastodon (CM) site, an archaeological site from the early late Pleistocene epoch, where in situ hammerstones and stone anvils occur in spatio-temporal association with fragmentary remains of a single mastodon (Mammut americanum). The CM site contains spiral-fractured bone and molar fragments, indicating that breakage occured while fresh. Several of these fragments also preserve evidence of percussion. The occurrence and distribution of bone, molar and stone refits suggest that breakage occurred at the site of burial. Five large cobbles (hammerstones and anvils) in the CM bone bed display use-wear and impact marks, and are hydraulically anomalous relative to the low-energy context of the enclosing sandy silt stratum. 230Th/U radiometric analysis of multiple bone specimens using diffusion–adsorption–decay dating models indicates a burial date of 130.7 ± 9.4 thousand years ago. These findings confirm the presence of an unidentified species of Homo at the CM site during the last interglacial period (MIS 5e; early late Pleistocene), indicating that humans with manual dexterity and the experiential knowledge to use hammerstones and anvils processed mastodon limb bones for marrow extraction and/or raw material for tool production.

Reconstruction of a Homo erectus woman, Smithsonian

Note that “Homo” here is probably not H. sapiens, but a related or ancestral species, like Denisovans or Homo erectus, because as far as we know, H. sapiens was still living in Africa at the time.

This is obviously a highly controversial claim. Heck, “earliest human presence in the Americas” was already controversial, with some folks firmly camped at 15,000 years ago and others camped around 40,000 yeas ago. 130,000 years ago wasn’t even on the table.

Unfortunately, the article is paywalled, so I can’t read the whole thing and answer simple questions like, “Did they test the thickness of mineral accumulation on the bones to see if the breaks/scratches are the same age as the bones themselves?” That is, minerals build up on the surfaces of old bones over time. If the breaks and scratches were made before the bones were buried, they’ll have the same amount of buildup as the rest of the bone surfaces. If the breaks are more recent–say, the result of a bulldozer accidentally backing over the bones–they won’t.

They did get an actual elephant skeleton and smacked it with rocks to see if it would break in the same ways as the mammoth skeleton. A truck rolling over a rib and a rock striking it at an angle are bound to produce different kinds and patterns of breakage (the truck is likely to do more crushing, the rock to leave percussive impacts.) I’d also like to know if they compared the overall butchering pattern to known stone-tool-butchered elephants or mammoths, although I don’t know how easy it would be to find one.

Oldowan tool, about 2 million years old

They also looked at the pattern of impacts and shapes of the “hammerstones.” A rock which has been modified by humans hitting it with another rock will typically have certain shapes and patterns on its surface that can tell you things like which angle the rock was struck from during crafting. I’ve found a few arrowheads, and they are pretty distinct from other rocks.

Here’s a picture of an Oldowan stone chopper, about 2 million years old, which is therefore far older than these potential 130,000 year old tools. Homo sapiens didn’t exist 2 million years ago; this pointy rock was probably wielded by species such as Australopithecus garhi, H. habilis, or H. ergaster. Note that one side of this chopper is rounded, intended for holding comfortably in your hand, while the other side has had several chunks of rock smacked off, resulting in convex surfaces. Often you can tel exactly where the stone tool was struck to remove a flake, based on the shape and angle of the surface and the pattern of concentric, circular lines radiating out from the impact spot.

Homo erectus, who lived after the Oldowan tool makers and had a fancier, more complicated lithic technology, did make it out of Africa and spread across southeast Asia, up into China. This is, as far as I know, the first case of a hominin species using tools to significantly expand its range, but we have no evidence of erectus ever expanding into places that get significantly cold in the winter, and boat-building is a pretty advanced skill. We don’t even think erectus made it to Madagascar, which makes it sailing to the Americans rather doubtful.

I dislike passing judgment on the paper without reading it, but my basic instinct is skepticism. While I think the peopling of the Americas will ultimately turn out to be a longer, more complex, and interesting process than the 15,000 years camp, 130,000 years is just too interesting a claim to believe without further evidence (like the bones of said hominins.)

Still, I keep an open mind and await new findings.

(We’ll continue with part 2 next week.)