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.)

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Amygdalaaas

So, building on last night’s potential revelation, let’s review what we may or may not know about amygdalas.

I had read (summaries of) studies indicating that conservatives have larger amygdalas than liberals. From this I concluded that amygdalas were likely to be involved in some sort of processing that produces more conservative results.

But what does the amygdala do? Articles indicated involvement in the disgust reflex. I concluded that people who are more easily disgusted are just more likely to feel disgust in response to novelty.

But, Frost brings up a good point: has the initial orientation/amygdala data been confounded by researchers failing to control for ethnicity? If researchers have classed, say, Muslims who vote Labour as liberals, then obviously the data is meaningless?

There is an to solve this conundrum: Just find some data that controls for ethnicity and measures liberalness or conservatism, (rather than use self-reported orientation). If no suitable studies exist, do one–go to some rural college, collect an ethnically similar cohort, give them a quiz about their attitudes toward novel foods and other such non-emotionally charged things that seem to correlate with political orientation, and then scan the brains of equal numbers of liberals and conservatives and see what you get. If you find some sort of correlation, repeat the experiment with other ethnicities. If you find nothing, widen your scope to compare whites from different areas, or whites who are further apart in political orientation. If you still find nothing, do a multi-ethnic study and see if the initial results were just ethnic differences in party affiliation.

Recent articles further indicate that my interpretations may have been wrong, or that the picture is more complicated than I realized, eg, Neural and cognitive characteristics of extraordinary altruists, “Functional imaging and behavioral tasks included face-emotion processing paradigms that reliably distinguish psychopathic individuals from controls. Here we show that extraordinary altruists can be distinguished from controls by their enhanced volume in right amygdala and enhanced responsiveness of this structure to fearful facial expressions, an effect that predicts superior perceptual sensitivity to these expressions. These results mirror the reduced amygdala volume and reduced responsiveness to fearful facial expressions observed in psychopathic individuals.”

This does not support my “conservatives have larger disgust reflexes becuz amygdalas,” theory, but would be consistent with a “extremely conservative people were mis-categorized as liberals in other studies,” result.

More research is necessary.