john hawks weblog

paleoanthropology, genetics and evolution

America

  • Bone of the victim mastodon

    Fri, 2011-10-21 20:37 -- John Hawks

    Michael Waters and colleagues [1] report on the date of a mastodon kill site from Manis, Washington. At 13,800 years old, it's not the earliest evidence of New World people, nor the only evidence of pre-Clovis hunting. I find it interesting because of the addition of genetics to the mix of evidence. The specimen is verified as a mastodon, and the bone used to kill it was itself made of mastodon bone:

    We also obtained high-resolution tandem mass spectrometry (MS/MS)–based protein sequences from the projectile point and rib, and used another mastodon sample as a second reference (tables S3 to S6). The MS/MS spectra from the bone point matched the reconstructed mastodon collagen sequences, with the highest scores being within a reference set of collagen sequences (table S7 and supporting table of bone point marker peptides). These results and controls show that the point was fashioned from mastodon bone.

    The conclusion of the paper suggests that the evidence of pre-Clovis megafauna hunting argues against a "blitzkrieg" scenario for megafaunal extinctions. Instead, the authors suggest that the extinction was staged over a period of nearly 2000 years. The invention of Clovis points around 13,000 years ago is proposed to be near the end of the process, which may have begun before 14,800 years ago according to a kill site at Hebior, Wisconsin.

    I think this distinction is just semantic. If 2000 years of human predation eliminated mastodons, mammoths, and all the rest of the megafauna, which occupied North America for more than a million years before that, it looks a lot like "blitzkrieg" to me.

    References

    1. Waters MR, Stafford TW, McDonald HG, Gustafson C, Rasmussen M, Cappellini E, Olsen JV, Szklarczyk D, Jensen LJ, Gilbert MTP, et al. Pre-Clovis Mastodon Hunting 13,800 Years Ago at the Manis Site, Washington. Science. 2011;334(6054):351 - 353.
    Tags: 
    Clovis
    America
    North America
    American Indians
    hunting

  • "First Americans" article

    Tue, 2011-10-18 21:29 -- John Hawks

    Scientific American's November issue has a cover story on the peopling of the Americas, by Heather Pringle, and it has gone online for free: (UPDATE 2006-10-23: Well, that's strange. I read it for free at the link, but now it has gone to paywall. Rats.) "The First Americans: Mounting Evidence Prompts Researchers to Reconsider the Peopling of the New World". The article reviews several Clovis and pre-Clovis news stories from last spring, including some that I covered at the time ("Early New World archaeology news").

    Among the stories recounted is an attempt to redate the opening of the "ice-free corridor" between the Cordilleran and Laurentide ice sheets. The closure between these sheets has been argued to block overland migration into North America before Clovis times. Some geologists are now arguing for an earlier date.

    The big question now is whether the entire corridor lay open during this period, particularly the section to the north. Munyikwa thinks it did. His team recently dated sand dunes farther north, along the Alberta-Northwest Territory border, with similar results. These data, Munyikwa says, fit current thinking about the Laurentide ice sheet. The general consensus among geologists, he notes, “is that the ice sheet retreated in a northeasterly direction as a wide front, as opposed to [moving] in discrete lobes. We envisage that the deglaciated land extended to the north.” If so, explorers from Asia could have entered the corridor around 15,000 years ago, nearly 1,000 years after the route to the western coast opened.

    Not much on the genetics in the article, and now I think it will be interesting when ancient genomics reaches the New World.

    Tags: 
    America
    American Indians
    New World
    Clovis

  • Charles Mann interview

    Fri, 2011-09-02 09:53 -- John Hawks

    Razib Khan posts an interview with author Charles C. Mann, whose new book 1493: Uncovering the New World Columbus Created is an account of the social and ecological effects of the Columbian exchange on the peoples of the Americas.

    I knew that Asians had worked under brutal conditions on the railroads. But I had no idea that something like 250,000 Asian slaves had been taken to the Americas in the 19th century. Similarly, I suspect that most Mexicans don’t know that Mexico City had a thriving Chinatown by the early 1600s. And most Peruvians don’t know that Asians were a significant presence in Lima as early as the 1611 census. And so on.

    I liked his earlier book, 1491 a lot, and I'll be reading the new one soon.

    Tags: 
    books
    America
    American Indians
    history

  • "I would run screaming away"

    Thu, 2011-05-26 07:42 -- John Hawks

    This is such an incredible story about the "Clovis comet" hypothesis, I don't know where to start: "Comet Theory Comes Crashing to Earth".

    Oh, well how about we start with the fact that the idea's main exponent is living under an alias:

    Indeed, the team’s established scientists are so wedded to the theory they have opted to ignore the fact their colleague “Allen West” isn’t exactly who he says he is.

    West is Allen Whitt — who, in 2002, was fined by California and convicted for masquerading as a state-licensed geologist when he charged small-town officials fat fees for water studies. After completing probation in 2003 in San Bernardino County, he began work on the comet theory, legally adopting his new name in 2006 as he promoted it in a popular book. Only when questioned by this reporter last year did his co-authors learn his original identity and legal history. Since then, they have not disclosed it to the scientific community.

    Well, the whole thing was thoroughly vetted by the National Academy member who coauthored the paper, right?

    After the theory was first announced in 2007 in Acapulco, Mexico, [Vance] Holliday had attempted to collaborate with [NAS member James] Kennett to test the idea. But Kennett effectively blocked publication of the study last year after the results didn’t support the comet theory.

    Err...well...you certainly can't dispute the physical evidence, right? I mean, what about the high concentration of carbon spherules that were associated with the supposed impact?

    On March 25, Boslough reported that radio-carbon dating of a carbon spherule sample shows it is only about 200 years old — an “irregularity” that indicates is it not from the alleged 12,900-year-old impact time.

    This means that a sample from a layer purporting to show a high concentration of spherules at the inception of the Younger Dryas actually only was about as old as the Declaration of Independence.

    The article discusses whether the carbon spherules may have been deliberately "salted" into the samples by someone, presumably West/Whitt himself. The quote I pulled as the title of my post, "I would run screaming," comes from another geologist asked whether he would work with West on anything.

    This story has really unraveled into a geological version of Piltdown. Like Piltdown, there were many people who were outright skeptics from the start -- because the evidence just didn't make sense. And like Piltdown, there are true believers who will not give up even after the physical evidence is shown to be questionable, possibly doctored.

    Anyway, I've written about this several times:

    "A hard bolide to swallow?"

    "The Younger Dryas impact fizzle?"

    You can tell when I really think an idea is nonsense: all the blog post titles end with a question mark!

    Tags: 
    megafauna
    America
    metascience
    extinction
    American Indians
    Clovis
    impacts
    Synopsis: 
    The Clovis impact hypothesis runs off the rails as the strange background of its main proponent comes to light

  • Early New World archaeology news

    Sun, 2011-03-06 18:31 -- John Hawks

    The initial habitation of the Americas has gotten a lot of press attention in the last couple of weeks.

    National Geographic gave us a report on skeletal remains from an underwater cave in Yucatan, called Hoyo Negro ("Skull in underwater cave may be earliest trace of First Americans"). There's no date yet for the human remains, which are associated with megafauna -- but no reason at all to go with the news story's "15,000-20,000 years ago," that's just sensationalism.

    Last week, Science published a report on a child cremation burial from Alaska dating to 11,500 years ago [1]. In the paper, Ben Potter and colleagues compare the Alaskan site (Upward Sun River Site -- USRS) to a site in the western part of the region that was once Beringia, but now is on the Siberian side of the Bering Strait:

    Only one other ancient burial site is known for Beringia: Ushki Lake 1, in Kamchatka, Russia (34–37) (Fig. 1). Ushki Lake 1, Level 7 (Ushki L7) (~13,000 cal yr B.P.) contained an adult burial associated with bone beads in a rock-lined ochre-filled pit separated from the house structures. Ushki Lake 1, Level 6 (Ushki L6) (~12,000 cal yr B.P.) is roughly contemporaneous with USRS Component 3 and contains two unburned burials of children within two separate houses (35, 36). One child burial contained ochre, a pendant, a mat of lemming incisors, and numerous microblades and wedge-shaped cores (the second burial is undescribed) (35). Thus, the USRS burial context is more like Ushki L6 than L7. This replicates technological linkages between continents: Diuktai Culture of Ushki L6 is comparable with the Denali Complex, which dominates the record from 12,000 to 6000 cal yr B.P. in interior eastern Beringia (24, 38), whereas the Ushki Culture of Ushki L7, associated with stemmed points and lacking microblades, arguably has no direct counterpart in North America [(39), but see (34)].

    That reference to the stemmed points becomes important in the next paper, published in Science this week by Erlandson and colleagues [2]. The report is a description of a mixed archaeological assemblage from the Channel Islands of California, with a few artifacts from a shell midden dating to 12,200 BP [2]. The date is not all that early, not earlier than Clovis. It's interesting because it seems to further the evidence for a distinct archaeological tradition in the West, with inland occurrence and possible connections to South America.

    If Arlington Springs [skeletal remains dating to 13,000 BP] is included, the earliest Paleocoastal Channel Island sites are contemporary with Clovis and Folsom sites of the continental interior (6, 8, 20). The island sites provide evidence for Terminal Pleistocene seafaring, island colonization, and a diversified maritime economy, adding to the variability of Paleoindian adaptations in the Americas. The stemmed points and crescents dated as early as 12,200 cal BP link these early island assemblages to those found in interior Western Pluvial Lakes Tradition (WPLT) sites found around many lakes and marshes in North America’s Far West (15). Stemmed point fragments have also been recovered in the basal levels of Paisley Caves, dated to ~14,300 cal BP (21), and the Paleocoastal stemmed points and crescents from the Channel Islands seem unlikely to be descended from Clovis. Such WPLT assemblages may provide a logical technological link among Terminal Pleistocene stemmed point traditions of Northeast Asia (22), the Pacific Northwest, and possibly early stemmed point traditions widely distributed in South America (23).

    The Clovis industry was a very short-term phenomenon, and spread across an area of North America that makes an unlikely link to the rest of the Americas. Seems more like a cul-de-sac in some sense. Movement down the western coast makes more sense, but the cultural traces of early Paleoindians have been scarce. But these seem to be adding up to something -- the stemmed point in Paisley, now the earliest site with biological evidence of humans in the Americas, is interesting in this regard. It's not a radical revision of the timeline; this is all about a relatively short period of pre-Clovis occupation, maybe 2000 years as we understand it now. The research is beginning to make more connections among early occurrences, making them seem more like a system than like outliers.

    UPDATE (2011-03-07): A reader (who should know) chides me for describing Clovis as a "cul-de-sac" industry, noting the distribution of fluted points is much more widespread. Another reader expresses some interest in the ecological setting of these stemmed points across the broader West. I will return to the issue soon, which deserves a fuller review than this.

    References

    1. Potter BA, Irish JD, Reuther JD, Gelvin-Reymiller C, Holliday VT. A Terminal Pleistocene Child Cremation and Residential Structure from Eastern Beringia. Science [Internet]. 2011;331:1058–1062. Available from: http://dx.doi.org/10.1126/science.1201581
    2. Erlandson JM, Rick TC, Braje TJ, Casperson M, Culleton B, Fulfrost B, Garcia T, Guthrie DA, Jew N, Kennett DJ, et al. Paleoindian Seafaring, Maritime Technologies, and Coastal Foraging on California's Channel Islands. Science [Internet]. 2011;331:1181–1185. Available from: http://dx.doi.org/10.1126/science.1201477
    Tags: 
    archaeology
    North America
    America
    Beringia

  • Quote: Boyd on New World pigmentation clines

    Tue, 2010-09-28 16:44 -- John Hawks

    I'm using some statistics out of William Boyd's 1956 printing of Genetics and the Races of Man[1]. It gives a good accounting of blood group data known more than fifty years ago, which I'm using to illustrate my intro lectures. Meanwhile, there are some interesting passages, from the standpoint of today's knowledge of the human genome and its variation.

    On skin pigmentation -- this is the earliest statement I've run across of the argument that the New World pigmentation cline is shallower than the Old World cline because of the relative recency of occupation (pp. 178-180):

    The aborigines of the New World, though not by any means identical, agree in having on the whole considerable skin pigmentation. If pigmentation is adaptive, and conforms to climate, why are not the Eskimo and the inhabitants of Tierra del Fuego as light as Europeans? This looks like a considerable difficulty, but the solution is probably comparatively simple. The aborigines of the New World have not been here for more than about 25,000 years, or about 1000 generations. They are by origin Asiatic, and in Asia skin pigmentation is fairly heavy. Unless the selection of light skin as opposed to dark were fairly intense, the time elapsed has simply not been enough to allow for much adaptation to occur (12). As a matter of fact, the populations which might have been expected to become lighter, namely the Fuegans and the Eskimo, have probably had a shorter time in which to achieve this end than other American aborigines, for it is reasonable to suppose that the Fuegians did not reach their present home until long after their northern neighbors were well installed. And all students of the Eskimo agree in recognizing them as probably the most recent (aside of course from the whites) arrivals in America. It could well be that there has just not been enough time for selection to bleach the skins of the American aborigines.

    Reference 12 is Haddon's Races of Man, which I have requested from the library.

    I'm following up, because skin pigmentation is one of the traits most clearly subject to recent rapid selection. The new mutations that lighten skin tone in Europe and Asia are only partially shared between those populations. Many alleles are very common in one population, but nearly absent in the other. So far, the estimates of dates for these new variants are all within the last 20,000 years, but many remain undated. So we can't specify the level of pigmentation of people 15,000-20,000 years ago, yet, but it would have been substantially darker than those populations today.

    Which leaves us with the same question, but from the opposite perspective. We now know that pigmentation evolved rapidly in Eurasia, the strong gradient of pigmentation having increased greatly within the last 20,000 years. We also know that the occupation of temperate South America began quite early, with people having been there longer than 10,000 years. So why did the New World end up with a more gradual cline -- darker pigmentation in the temperate and Arctic regions, lighter in the tropics than in the Old World? Was selection less intense? Can we attribute the difference to demography? Or chance?

    Boyd next alluded to a demographic explanation -- low population density:

    In any case, the pre-Columbian population was so sparse compared with that of Asia and India that on a statistical basis alone we should be justified in asserting that skin pigmentation conforms to climate.

    Them's some tricky statistics.

    We would of course today recognize that the sheer number of people is not especially relevant; much more powerful is the independent occurrence of a similar response in two long-separated populations. But Boyd was concerned with a different issue: Some had been claiming pigmentation as a neutral trait, making it more useful as a race marker:

    This has been denied chiefly by those who were concerned to prove skin color a non-adaptive character, so that it might safely be used in the classification of races (12). Since the more up-to-date students of anthropology have given up the idea of relying on non-adaptive characters, or even believing that any such exist (13), there is no longer much dispute about the probable adaptive value of skin color (emphasis added).

    Well, makes me glad to be an "up-to-date" student! There in fact has been an ongoing debate about "non-adaptive characters" as concerns the relationship of Pleistocene people. Many geneticists were surprised to discover the persistence of Neandertal genes, but in fact the skeletons of Upper Paleolithic Europeans clearly bear Neandertal traits. The debate for the last 30 years hasn't been chiefly about the presence of these traits, but instead about whether they were adaptive. Some argued that adaptive traits were not suitable evidence for a relationship, because they could emerge by parallelism in distinct populations.

    Others observed that adaptive traits were more likely to be shared among populations linked by gene flow.

    Now, of course, we have remaining unanswered questions about these shared traits. The shared traits are clearest between Upper Paleolithic Europeans and European Neandertals. We don't have genetic information yet telling us about the extent of Neandertal gene sharing with these early Europeans. Was it more than elsewhere? The traits would argue for it.

    What about the Neandertal genes in populations far from Europe? One might expect Neandertal-like morphology to show up at some low level. Of course morphological features are polygenic, so that phenotypic resemblance falls much faster than genic identity. And Holocene populations have continued to evolve. Maybe early Asian skeletal remains like the Upper Cave skulls (ca. 11,000-20,000 years old) actually reflect that Neandertal heritage to a greater extent than recent samples.

    Then there is the likelihood of other contributions, more local ones, to later populations.

    Returning to the topic of pigmentation, many of us used to assume that the light skin of Europeans in part reflects Neandertal ancestry. That is, just as Boyd suggested, it would have taken a lot longer than 25,000 years to get the current strong cline of skin pigmentation in the Old World. If you could have longer, getting lighter pigmentation from earlier inhabitants of Europe, for example, you could explain a stronger cline with the same strength of selection.

    I no longer think this is necessary. It's still possible that we got some pigmentation variants from Neandertals, but we haven't found any yet. And we've been looking. It does seem that Neandertals had some of their own pigmentation variants. Maybe we'll find many more of those, maybe not.

    References

    1. Boyd WC. Genetics and the Races of Man. Boston: Little, Brown and Company; 1956.
    Tags: 
    quotes
    introgression
    Zhoukoudian
    America
    pigmentation
    recent selection
    Neandertal DNA
    China
    American Indians

  • Amazon structures

    Wed, 2010-01-06 17:30 -- John Hawks

    More evidence of dense Precolumbian habitation of the Amazon basin:

    Hundreds of circles, squares, and other geometric shapes once hidden by forest hint at a previously unknown ancient society that flourished in the Amazon, a new study says.

    Satellite images of the upper Amazon Basin taken since 1999 have revealed more than 200 geometric earthworks spanning a distance greater than 155 miles (250 kilometers).

    On the one hand it's cool that they are able to find these with satellite imagery. On the other hand, it's sad that in the Amazon they can find these with techniques that were developed to find sites in deserts.

    Tags: 
    South America
    America

  • The Younger Dryas impact fizzle?

    Tue, 2009-10-13 00:40 -- John Hawks

    In 2007, R. B. Firestone and colleagues published evidence of an extraterrestrial impact, roughly coincident with the onset of the cold climate event known as the Younger Dryas. This event, around 12,900 years ago, is around about the time of some (but not all) megafaunal extinctions in North America, it is also around the time (but not precisely) of the Clovis culture. The paper argued that the impact event may have "contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America".

    Last year, I reported on widespread dissatisfaction with this impact hypothesis. Some critics didn't think that there was any evidence of megafaunal trauma from the impact, some didn't think that the dates matched any "adaptive shifts", and in particular the end of the Clovis culture.

    And then others didn't think that there had been an impact at all. These were in some ways the most worrisome, because they directly questioned the supposed evidence in support of an extraterrestrial event -- "microspherules" of magnetic material, clustered in sedimentary contexts at precisely 12,900 years ago in sites across much of North America.

    Now, in the Proceedings of the National Academy of Sciences (where Firestone and colleagues originally published their observations), Todd Surovell and colleagues have published a remarkable paper that tests the Firestone impact hypothesis: "An independent evaluation of the Younger Dryas extraterrestrial impact hypothesis." Most critiques attempt to find an alternative explanation for a set of original observations. In this paper, Surovell and colleagues merely attempt to replicate the original observations at multiple sites, and fail -- as their abstract tersely states,

    We were unable to reproduce any results of the Firestone et al. study and find no support for Younger Dryas extraterrestrial impact.

    Just like that -- it's about as hard-hitting as you're going to see in a scientific research paper.

    Of course, this paper only examined one out of a number of observations that Firestone and colleagues had adduced in support of the impact hypothesis. But in the introduction to their paper, Surovell and colleagues reference several other recent studies that re-examined other aspects of the evidence:

    A series of critiques of the original Firestone et al. article (1) have been published recently (8-10). Pinter and Ishman (8) argue that the suite of markers used to indicate impact are inconsistent with "any single impactor or any known event." Furthermore, they provide alternative explanations for many of the observed marker peaks. For example, glassy and metallic microspherules are known components of atmospheric dust derived from the constant influx of micrometeorites. An independent evaluation of the charcoal evidence was recently published by Marlon et al. (9). Examining concentrations of charcoal from 35 pollen cores across North America, they found no evidence for large-scale, continent-wide wildfires specifically associated with the onset of the [Younger Dryas].

    In the current case, the results are very simple: they went looking for a spike in the number of impact-generated particles coincident with the Younger Dryas. They looked at seven sites with long and continuous records of sedimentation across that interval. They found the supposed impact-generated particles, but not patterned with any kind of spike.

    They suggest a different model for the presence and accumulation of the magnetic particles:

    Alternatively, it may be that the presence, absence, and relative abundance of magnetic materials, especially the spherules, is due to characteristics of the parent material and depositional environment instead of some sort of continent-wide extraterrestrial process. The characteristics of the local depositional setting before, during, and after 12.9 ka have not been addressed by the proponents of the impact hypothesis. The zones producing the YDB ‘‘impact markers’’ are typically associated with soils (stable surfaces) or shifts in the depositional environment (e.g., alluvial to lacustrine conditions at Blackwater Draw, Lubbock Lake, Murray Springs, and Lake Hind; buried soils in the Carolina Bays and at Lommel, Belgium).

    One might imagine atmospheric particles accumulating on stable paleosols over long stretches of time, generating a local spike in the number of such particles in the stratigraphic column. In any event, the data presented here don't bear out the hypothesis of any unusually large impact event.

    I'm not a geologist, and I have no special insight into the analyses here, beyond reading the charts. But remember that the impact hypothesis made a tremendous media splash. Maybe more damaging to the scientific side of things, the hypothesis that the Younger Dryas cold period came from an extraterrestrial force, made it seem for a moment less necessary to investigate terrestrial sources of cooling at the terminal Pleistocene. The science will correct itself, but the public perception of the climate changes at the end of the Ice Ages will need quite a bit more nursing to get a more realistic perspective on the story.

    References:

    Firestone RB and lots of others. 2007. Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling. Proc Nat Acad Sci USA, 104:16016-16021. doi:10.1073/pnas.0706977104

    Kerr RA. 2008. Experts find no evidence for a mammoth-killer impact. Science 319:1331-1332. doi:10.1126/science.319.5868.1331

    Surovell TA, Holliday VT, Gingerich JAM, Ketron C, Haynes CV, Jr, Hilman I, Wagner DP, Johnson E, Claeys P. 2009. An independent evaluation of the Younger Dryas extraterrestrial impact hypothesis. Proc Nat Acad Sci USA (early) doi:10.1073/pnas.0907857106

    Tags: 
    disasters
    paleoclimate
    Clovis
    impacts
    climate
    North America
    Pleistocene
    America

  • Double the migrations, double the fun

    Mon, 2009-01-12 00:25 -- John Hawks

    Several news stories have reported on an article by Ugo Perego and colleagues, titled "Distinctive Paleo-Indian Migration Routes from Beringia Marked by Two Rare mtDNA Haplogroups." The Discover blog, 80beats, has a good two-paragraph summary of the results:

    In the study, published in Current Biology [subscription required], a team led by geneticist Antonio Torroni analyzed entire genomic sequences of mitochondrial DNA, the genetic material in cells’ energy-generating units that gets passed from mothers to children…. The researchers focused on the disparate geographic distributions of two rare mitochondrial DNA haplogroups — which are characterized by a distinctive DNA sequence derived from a common maternal ancestor — that still appear in Native Americans [Science News]. Both haplogroups appear to have arisen about 16,000 years ago.

    The researchers found that all the people with the D4h3 haplogroup presently live in South America, while those with the X2a haplogroup live in Canada and the United States, which suggests that the two genetically distinct bands of early humans struck off in different directions around 16,000 years ago.

    I don't have a lot to say about this. Tracking the frequencies and geographic distribution of rare haplotypes poses different issues than doing so for common alleles. Two closely related populations might nevertheless differ in the presence or absence of rare alleles.

    I really just wanted to post with reference to a broader point. If the data don't distinguish between a single migration at one time and multiple migrations at different times, then it's pretty much certain that they won't distinguish between a single migration and multiple migrations at one time.

    The two-simultaneous-migrations model might solve problems so far unaddressed by other models. But it's not obvious that it solves any -- there's no test here, just a discussion of the plausibility of the scenario. Each of these scenarios for New World habitation involves the dispersal of many populations across thousands of years. That means lots of free parameters, even in the simplest of the models. Given that necessary complexity, it seems pretty likely that there's a way for the simplest model to account for the frequencies of two rare alleles. It will take a whole lot more genetic comparisons to really test hypotheses about the founding population.

    References:

    Perego UA and 15 others. Distinctive Paleo-Indian Migration Routes from Beringia Marked by Two Rare mtDNA Haplogroups. Curr Biol 19:1-8. doi:10.1016/j.cub.2008.11.058

    Tags: 
    mtDNA
    Beringia
    migrations
    America

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