Apr 28 2017

Shaky Evidence for Humans In Americas 130,000 Years Ago

mastodon bonesScientists like to be really sure. That is pretty much what the scientific method is all about – systematically controlling for all possibilities, all confounding factors, all variables and all alternative interpretations. We feel more confident when multiple lines of evidence converge on one explanation, and when rigorous attempts to disprove that explanation fail.

I like seeing that process in action over specific claims, especially when the claim itself is interesting.

One such interesting question is, what was the earliest human presence in the Americas? Any question about first or earliest is always tentative in paleontology. It simply refers to our current evidence, but it is statistically unlikely that we will have found the literal earliest example of a species or an occupation. So conclusions about “earliest” are always changing, moving back as more evidence is found.

There is solid archaeological evidence for human occupation near the  Bering Strait 14,000 years ago. There is strong but not universally accepted evidence for this occupation going back 24,000 years. So that is the current range of possible dates for the earliest presence of humans in North America.

Solid evidence of human occupation is human bones with reliable dating. Obviously if there are human remains in North America, then humans were in North America. The only question then is about dating. Human bones are considered direct unequivocal evidence.

But there are lots of types of indirect evidence. The next step down the evidence ladder in terms of reliability are unequivocal human artifacts, such as stone tools. Tools that have been extensively shaped in such a way that only human action could have done so is also great evidence that humans were present. The tools themselves cannot be dated, but the substrate in which they are found sometimes can be (depending on local conditions).

We can also find evidence of human occupation. For example, the Monte Verde site in Chile has evidence of wooden structures, hearths, and stone tools. The site dates to 12,500 years ago, within the accepted time frame of human occupation.

As we go further down the evidence pyramid we get to equivocal and disputed indirect evidence. This is evidence that suggests human occupation, but archaeologists are generally unwilling to accept this evidence as definitive, especially if it moves back the date of first occupation. The two main types of such equivocal evidence are possible artifacts and possible evidence of activity, such as processing bones.

The evidence for human occupation in Alaska at 24,000 years ago is based entirely on marks on bones that are consistent with stone tool marks. This came from an exhaustive survey of thousands of bones in the Bluefish caves, with 14 showing evidence of stone tool marks. This evidence is interesting, but not universally accepted.

There is also the Topper site, which some archaeologists (most notably Goodyear) claim contains human artifacts from 50,000 years ago. The “human artifacts”, however, are possible “rudimentary” stone tools – in other words, they are rocks.  Such evidence is generally considered unconvincing.

New Evidence for 130,000 Years

Researchers are now claiming evidence for human occupation in North America dating to 130,000 years ago. The evidence is not human remains, and not unequivocal artifacts. It is possible stone artifacts and possible evidence of working bone – the weakest form of evidence for occupation. As the BBC reports:

Thomas Deméré, Steven Holen and colleagues examined material from the Cerutti Mastodon site near San Diego. The site was originally uncovered in 1992, during highway construction work. Possible stone tools were discovered alongside the smashed up remains of a mastodon (Mammut americanum) – an extinct relative of mammoths and living elephants.

“Possible stone tools” means rocks. They are unworked – they haven’t been reshaped for use. The evidence that they are tools comes from wear marks on the rocks.

The evidence that the  Mastodon bones were broken deliberately by smashing them with rocks is due to the pattern of breaks. The spiral pattern is consistent with being broken up while fresh. The researchers also reproduced breaking up elephant bones with large rocks and the resulting pattern of breaks was similar to the fossil finds.

The BBC did a good job of reporting this item. They did what science reporters are supposed to do – they spoke with experts in the field who are not the researchers making the claims. They found general skepticism among those experts. The consensus is that this evidence is “provocative” but extremely thin and unconvincing.

Skepticism is higher because of the nature of the claims. Moving back first occupation to 130,000 years is a huge change. That could mean they were not even modern humans, but Neanderthals. There is nothing impossible about this, but that is a massive claim based on a thin reed of evidence.

I think it is reasonable for paleoarchaeologists to be conservative in this regard. Human remains and unequivocal human artifacts are solid evidence of human occupation. The lesser forms of indirect evidence are suspect. As some of the scientists pointed out, there are lots of ways for stones to be worn and bones to be broken, and many of those could look like human activity.

This type of evidence relies heavily on an argument from ignorance – not knowing another way that the bones could have been marked or broken the way that they were. That is a far cry, however, from proving that there was no other possible way for the observed breaks to have occurred.

This type of reasoning is common in science, which is why we prefer direct or corroborating evidence. Inference to the best conclusion is fine, but always a weak and tentative conclusion without direct evidence to back it up. In this case I think that the skepticism of the scientific community is fully warranted.

As a side note – I hope this analogy is not lost of regular readers who have been following the discussion about the historicity of Jesus. (And sorry to beat this horse if it was obvious.) We have a similar situation, in which the conclusion is based upon indirect evidence and reasoning based heavily on an argument from ignorance. Nature has many ways to break bones, and there are many ways for stories to emerge and spread. Not knowing exactly how a story emerged does not mean it was based on a real historical figure. We need corroborating direct evidence, which is lacking.

25 responses so far

25 thoughts on “Shaky Evidence for Humans In Americas 130,000 Years Ago”

  1. Sarah says:

    Humans in the Americas more than an order of magnitude earlier would be a huge deal. Frankly, I would have expected speciation at that rate, because there’s no way we would get free-flowing genes across the frozen land bridge, assuming the then-prominent hominid species could cross it to begin with.

  2. Sarah says:

    We’d need earlier evidence of out of Africa transit, certainly, unless they’re proposing that this is Homo Erectus or some early offshoot.

  3. European Neanderthals go back 160 thousand years, so that is not a problem.
    It is also possible that a population of Neanderthals entered North American, survived for a bit then died out.

  4. Teaser says:

    The paper presenting the evidence has had some quality scrutiny. This article provides some good comments by other experts in the field as wells as link to commentary by an archeologist who reviewed it for Nature.

    Holen himself is professing a sense of sceptism because of what the evidence is indicating.

    Using refined dating methods, the researchers tried again to determine the age of the site. They couldn’t use radiocarbon dating on the mastodon remains because the bones lacked carbon-containing collagen protein. A second method was too imprecise. A third technique, which measures relative levels of radioactive uranium and thorium in bone, suggested that the remains are 130,000 years old. “I’m sure that many of our colleagues are going to be quite sceptical. I would expect that. This is far, far older than most archaeologists expect hominins to be in North America,” says Steven Holen. “I say that even for myself.”

    Alistair Pike, an archaeological scientist at the University of Southampton who specializes in uranium dating, notes that the team’s method relies on simplified models of how uranium seeps from groundwater into bone, but he sees no obvious flaws in the dating work. “At face value, these results are about as good as it can get,” he says.

    From the same article. There is a link to her commentary on the paper in this section.

    Erella Hovers, an archaeologist at the Hebrew University of Jerusalem who reviewed the paper for Nature, says she raised her eyebrows when the manuscript arrived in her inbox: “I was like, ‘Uh, really?’”. But after revisions that elaborated on the dating work and demonstrated that hitting modern elephant bones with large rocks produces damage patterns similar to those seen on the mastodon bones, she is now convinced that hominins created the California site.

    “This is mind-boggling,” says Hovers, who also wrote a commentary accompanying the study. “It leaves a ton of questions because we know nothing else, except that there were some sort of people there at this time.”

    http://www.nature.com/news/controversial-study-claims-humans-reached-americas-100-000-years-earlier-than-thought-1.21886

  5. Sophie says:

    If they did make it to the Americas but didn’t survive that is still fascinating. Are we assuming they traveled the same way the other early humans got here? It’s not by Cross the sea right? But the land/ice bridge?

    Makes me wonder how many other times something like this happened, where a group tried to make it work in a new place but didn’t survive. Assuming this is real, of course.

  6. “It is also possible that a population of Neanderthals entered North American, survived for a bit then died out.”

    Yes, considering how thin the evidence is, at this point, there’s no reason to assume the speculated humans in North America from 130,000 years ago are the ancestors of the indigenous, Pre-Colombian Americans.

  7. Sarah says:

    I’ll admit that I’d be surprised and that I’m doubtful, but I’ll submit that it’s possible. This one study won’t convince me, though.

  8. Sarah says:

    Crossing the sea would be very dubious. We’d expect them to have used the land bridge if at all.

  9. …on the other hand, if they made it all the way to San Diego, you’d think that that was due to the expansion/ radiation of an established population rather than one group came across the land bridge and only stopped to settle down when they reached the southern end of modern California.

    I mean, I hear it’s a beautiful climate, but seriously, there’s lots of nice places to settle down between Alaska and San Diego.

  10. banyan says:

    The Evidence for the History of Jesus – 186 comments
    New Study of The Hobbit – 10 comments
    Jesus Mythicism Revisited – 187 comments

    Seems like Jesus is a horse people love to beat. So to speak.

  11. LittleBoyBrew says:

    Well, banyan, if you want to bring up the historicity of Jesus then we all know the earth is only 6000 years old, so these scientists are wayyyyyyyy wrong.

  12. sarah_theviper says:

    A good question to ask with this site is how are they dating it. If they are using radiocarbon dating results can easily be messed up if someone touches it or it comes in contact with other organic matter. Also it is good practice to always send more than one sample for testing. One of the professors in my archaeology program told us about a site he was working on where one of the dates came back extremely old, but the other two samples he had had testing were coming back within the normal time frame. He figured that because the site was along a river the older charcoal he had tested had been washed down from further upriver, and was probably the result of a natural fire from like a lightening strike.

  13. bachfiend says:

    Sarah,

    Apparently they were using the uranium-lead method of dating the biological remains, which is very problematic since it relies on models on how uranium traces move through bones (from what I can gather). C14 dating wouldn’t work in any material over 40,000 years old.

    Actually, when I first read the thread my first thought was that perhaps even if the mastodon bones showed evidence of real slaughtering techniques with crude stone tools, there’s no evidence that it was by members of Homo sapiens. Or even Homo erectus.

    Perhaps it was Bigfoot?

    Just joking…

  14. sarah_theviper says:

    Bachfiend

    Admittedly I am unfamiliar with uranium lead dating. It is not something we were utilizing it where I was. Although when I looked it up on Wikipedia it says it is for testing rocks between one million to 4.5 billion years ago.

    https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating

  15. cfeagans says:

    I blogged about this yesterday and a couple of the main problems I had were the cobbles that are alleged to be tools aren’t convincing and there were no butchery marks on the bones. You don’t simply start hammering away at a mastodon leg bone to get a the marrow without first doing something with the meat. Once you start de-fleshing the bone, you leave distinctive cut marks on the bones from the stone tools (worked stone tools, not just ad hoc cobbles). This is almost unavoidable.

    If the argument becomes these were bones that the Neanderthals or Denisovans were scavenging, then where are the scavenger marks from dire wolves, vultures, rodents, or even dermestid beetles. The meat isn’t just going to sit around and rot without the rest of the ecosystem making use of it.

    I suspect the reason there are none of these marks is because the mastodon, along with the other animals in close proximity to it in the same stratum, was caught in the quicksand of a stream or river it was attempting to cross and drowned. The meat was underwater.

    And bones were cracked by other taphonomic processes. Perhaps even the heavy equipment of road construction 130,000 years later.

  16. bachfiend says:

    Sarah,

    I was wrong when I said it was the uranium-lead method. It was apparently the lead-thorium method. PZ Myers had a thread on it several days ago on his blog which I scanned too superficially not really being much interested in it.

    Sorry.

  17. Steve Cross says:

    Interesting … BUT — the “evidence” was discovered 25 freaking years ago, and not one hint of any outside corroboration. At this stage, I think Bigfoot is more likely.

  18. WilliamBreen says:

    Fascinating and provocative find. While I agree with previous posters on the burden of extraordinary claims, and I further agree with Dr. Novella’s speculation on the possibility of an extinct enclave of Neanderthals, I would like to mention a few items. The journal Nature, in it’s coverage, mentioned a few salient points not emphasized elsewhere. According to the authors, the alleged hammerstones and anvils were found in an upward-fining sandy bed, characterized by a very small grain size. As a geology undergrad, with a personal fascination with archaeology, I can say that arrangement is damn unusual. In a fluvial environment, particles of similar grain size typical sort themselves according to size, mass, and stream velocity. So, in other words, boulders tend to cluster, fist-sized cobblestones tend to cluster, gravel tends to cluster, and so forth. To find big, kg-scale pieces in a very fine-grained substrate, with no evidence of the stream velocity or volume increasing, is not outside the realm of possibility, but it is odd, and suggests agency. Further, finding both highly angulated and highly rounded pieces in close proximity, in this depositional environment, is peculiar to the point of being almost unheard of outside of volcanoclastic deposits. The damage patterns were concentrated on the most robust bones, and the most fragile, the ribs, were relatively untouched, suggesting that the butchers were aiming for the most marrow for their buck. The fact that there were no native predators big enough to inflict this much damage also bolsters the authors conclusions. On the other hand, I could not find any mention of the elevation above sea level of the site, nor it’s relation to paleo-shorelines, which might affect depositional energies and the possibility of re-mobilizing 15K y/o remains into partially eroded 130K y/o stratum. Overall, we know that Southern California has been a biological hot-spot for prey animals for millions of years, and we know that Neanderthals, Denisovans and possibly others were in north-east Asia for hundreds of thousands of years previously, and we know from the recent 14K find in NW Canada that the ‘Coastal Sailor’ hypothesis is plausible. It is not outside the realm of possibility that robust hominids migrated along a passable coastline, and once they made the southbound turn, simply followed the food. The elevated presence of Neanderthal and Denisovan DNA within present North American aboriginal populations supplies a tantalizing suggestion of interbreeding.

    Not definitive yet, by any stretch, but compelling.

  19. WilliamBreen says:

    Edit: …typically sort themselves according to …

  20. JohnW says:

    Couple more things, Neanderthal and Denisovan admixture is elevated compared to Europeans in east Asians and archaic Siberian populations, who in turn have been found to be ancestral to the Beringian residents who appear to be ancestral all to modern Native Americans (NAs). There is no current genomic evidence of that admixture occurring outside of asia. Also, the complete absence of archaic human tool industries (Acheulian or Mousterian) in North America, despite more than 2 centuries of vigorous paleotological scouring of the North American west in particular, makes it seem highly improbable that somebody was here and the only sign they left behind are a few unworked rocks that homeo habilis might have left. Reading the CM Nature paper, I understand why the authors made their interpretation, but I’ll have to see a few 100kya hand axes found before I buy it. Just too much of an outlier.

  21. WilliamBreen says:

    JohnW raises good points, but “scouring” is a good verb, in that several glaciations would have scoured away the vast majority of any evidence of possible habitation in that time frame. I dug a little deeper, if you will pardon the expression, and noted that the dating and elevation of the site coincides with a shoreline retreat during the transition from the Illinoian glaciation to the Sangamonian interglacial. The elevation just east of the 805, where 54 starts to climb up into the hills, would roughly match up with a paleo-shoreline of 130-125 K, matching the fining upward trend of the grain sizes within the soil column. The local topography and the soil column suggests drainage features. Our hypothetical hunter-gatherers might have been skillful enough to separate a young adult from the group, perhaps down to the river edge for a drink, or to the intertidal zone, if mastodons shared similarities to cows, and sought out salty ‘licks’ for mineral content. I can’t help but speculate that our hypothetical hunters carried off the choice cuts, and their bladed tools (high maintenance), harvested and consumed the marrow on the spot, and left behind the rounded, low maintenance tools. The more I look at the distribution of the recovered pieces, the more unnatural it seems. Small, sharp angular pieces, still lying beside the large, rounded piece that they broke off from, sharp bone shards from large robust bones, all lying there in 2 distinct clusters, on a bed of low energy fluvial sand. Natural river environments don’t organize debris in that fashion.

    It’s an outlier to be sure, but I see features without a natural explanation.

  22. JohnW says:

    Good points William, and consistent with the author’s interpretation. I agree that the images of the debris are odd and provocative. As regards glaciation, seems to me same could be said of Great Britain and Europe and we have no shortage of archaic tools finds in caves and quarry sites there. Granted, any archaic human bands arriving prior to 100 kya in NA may have died out without a trace. But why would that be? That larder was packed! And why break bones for marrow, but not leave other tool marks? Perhaps, as the authors note, focusing more effort on the pre 100kya time horizon may turn up more. We’ll see.

  23. WilliamBreen says:

    John, I share your difficulty in reconciling this possibility with what is currently know, and it is definitely problematic. If you will permit me to heap speculation upon speculation, I tender the following: We are dealing with the anthropological version of Fermi’s paradox. If they were around, then where is everybody? As to where are the remains, I must confess that I am stumped. Perhaps it was only a few small clans that made it across the late Illinoian coastal shelf before the Sangamonian melt flooded, and cut off the possibility of any more travelers. With only a small population, even in a land of plenty, there were too few breeding stock, and inbreeding and a harsh hunter-gatherer lifestyle erased our intrepid band.

    As to the corollary: Where are the rest of the artifacts, I would put my nickel on “In the boxes of presumably Neolithic artifacts in the collections of museums and universities in Southern California.” Many of these pieces would have been collected by amateur spelunkers and prospectors long before the arrival of modern dating techniques, and without professional excavations and recording of provenance and context. If I was one of the authors of the paper, I would send my grad students into the older boxes of bladed tools, pick out the ones that have not been definitively dated, and appear to conserve the most archaic styles, and send them for U-Th dating. If our intrepid band indeed had bladed tools, and used them to chop off and carry away the good mastodon bits, their best tools would have gone with them, back to the home base. If all of the good artifact spots and Neolithic middens in SoCal have been picked over decades ago, it’s natural to group everything under the identity of the most recent occupants.

    And I completely agree with you; we’ll see.

  24. Sylak says:

    That is slim evidence, interesting, but slim. But it would be better if we could LOOK AT THE BONES! lol sorry, it was obvious, but i couldn’t keep myself from doing it. 130 000 is a freaking long time. Maybe some branch of hominides ( huum probably use that term incorrectly I suck at evolutionary biology), some related species. More likely unrelated at all. One part I don’t understand, they can’t date tool? Carbon dating I can see ( although rock could contain carbon?). But there’s no method to date stuff made from rocks?

  25. RickK says:

    Not for this thread, but I would love a discussion about the evidence for the first life on Earth. Current estimates seem too early and too tenuous.

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