'dem bones tell strange tales

By Razib Khan | October 26, 2010 1:16 am

There is a new paper in PNAS on remains from China which re-order and muddle our understanding of the emergence of anatomical and behavioral modernity in Eurasia. Human remains from Zhirendong, South China, and modern human emergence in East Asia:

The 2007 discovery of fragmentary human remains (two molars and an anterior mandible) at Zhirendong (Zhiren Cave) in South China provides insight in the processes involved in the establishment of modern humans in eastern Eurasia. The human remains are securely dated by U-series on overlying flowstones and a rich associated faunal sample to the initial Late Pleistocene, >100 kya. As such, they are the oldest modern human fossils in East Asia and predate by >60,000 y the oldest previously known modern human remains in the region. The Zhiren 3 mandible in particular presents derived modern human anterior symphyseal morphology, with a projecting tuber symphyseos, distinct mental fossae, modest lateral tubercles, and a vertical symphysis; it is separate from any known late archaic human mandible. However, it also exhibits a lingual symphyseal morphology and corpus robustness that place it close to later Pleistocene archaic humans. The age and morphology of the Zhiren Cave human remains support a modern human emergence scenario for East Asia involving dispersal with assimilation or populational continuity with gene flow. It also places the Late Pleistocene Asian emergence of modern humans in a pre-Upper Paleolithic context and raises issues concerning the long-term Late Pleistocene coexistence of late archaic and early modern humans across Eurasia.

I read the paper, and I really didn’t understand anything between the introduction and discussion. Mostly because it was a detailed exploration of anatomical details, and I’ve never taken an anatomy class. I basically rely on people like John Hawks to tell me what’s going on in that domain. He hasn’t blogged the paper (well, as of this writing), but he did give an assessment to National Geographic:

Still, the jaw and three molars were the only human remains retrieved from the Chinese cave, and the jaw is “within the range” of Neanderthal chins as well as those of modern humans, added paleoanthropologist John Hawks of the University of Wisconsin, Madison.

“If this holds up, we have to reevaluate” the human migration time line, he said.

“Basically, I think they’re right, [but] I want to see more evidence,” Hawks added. “I really, really hope that there can be some sort of genetic extraction from this [fossil].”

The issue of why this is relevant is covered well in the early portion of the paper:

…In eastern Eurasia, the dearth of diagnostic and well-dated fossil remains…has inhibited more than general statements for that region. Fully modern human morphology was established close to the Pacific rim by ∼40 kya, as is indicated by the fossils from Niah Cave in Sarawak…and especially Tianyuan Cave in northern China…The actual time of the transition has remained elusive, because the age of the latest known archaic humans in the region is substantially earlier…The eastern Eurasian age of the transition has been generally assumed to approximate that of western Eurasia (∼50–40 kya), although there have been claims supporting earlier dates for modern human presence in East Asia….

This scenario implies a long term (>100,000 y) restriction of early modern humans to portions of Africa with a brief ∼90 kya expansion into extreme southwestern Asia, followed by a relatively rapid expansion throughout Eurasia after ∼50 kya…The scenario also implies some form of adaptive threshold, roughly contemporaneous with the emergence of the Upper Paleolithic (sensu lato), and a marked behavioral difference between those expanding modern human populations and regional populations of late archaic humans (14).

It is in this context that three fragmentary human remains were discovered in 2007 at Zhirendong, South China…Because it is only well-dated diagnostic human remains that can document the timing and nature of human evolution and dispersal patterns (as opposed to archeological proxies for human biology or imprecise inferences from extant genetic diversity), the Zhirendong remains have the potential to shed light on these ongoing paleoanthropological issues.

jawOK, so the stylized orthodox model would be that anatomically modern humans arose in Africa ~200,000 years ago, and expanded out of Africa ~100-50,000 years ago. Full behavioral modernity emerged a bit later. In the broad outlines I think we can still go with this, but we have reached a level of fine-grained understanding of the evolutionary history of the human past that we need to consider adding detail to the margins of the story. The Denisova hominin, and perhaps H. floresiensis, are a good clue that the human family tree really was bushy, and that the past was filled with players unknown to us. The likelihood of Neandertal admixture also suggest that the other branches of the bush can’t be ignored and considered as without consequence for modern humans. There may be traces of other lineages in other human populations as well; there have long been claims based on inferences from some genetic data of modern populations, but the ability to compare to the Neandertal sequence gave those results from last spring particular credibility. But if the Neandertal admixture results become part of the consensus we should recalculate our probabilities of the other inferences.

linearSo how does it change things? One of the authors of the PNAS paper, Erik Trinkaus, has long made claims of hybridization from the fossil record, and this work falls in line with that tradition. The key here is the fossils seem to exhibit derived features, not ancestral ones. Derived features imply common ancestry of the populations which share the derived traits. If so, Trinkaus and company seem to be pointing to Alan Templeton’s “Out of Africa again and again.” On the other hand, I can’t but help think of Luke Jostins‘ plot of hominin cranial capacities as a function of time: separate lineages all seemed to be going on the same general path in terms of direction. I don’t make the claim here that H. sapiens sapiens was inevitable, but perhaps a common suite of traits which we associate with advanced hominin lineages, in particular the branch of which we are the terminus, were being selected for across the whole clade. In other words, perhaps anatomical modernity exhibits some element of convergent evolution, while behavioral modernity is the true hallmark of H. sapiens sapiens. It sounds crazy, and I don’t really believe it necessarily, but we live in crazy times. We had a neat and tidy story for 20 years between 1985 and 2005, but all good things have to end.

CATEGORIZED UNDER: Evolution, Human Evolution
  • onur

    perhaps anatomical modernity exhibits some element of convergent evolution, while behavioral modernity is the true hallmark of H. sapiens sapiens

    Normally the opposite is expected to be true: that behavioral modernity was inevitable while anatomical modernity (except cognitive anatomical traits like brain size and brain organization) wasn’t.

  • http://www.kinshipstudies.org German Dziebel

    “In other words, perhaps anatomical modernity exhibits some element of convergent evolution, while behavioral modernity is the true hallmark of H. sapiens sapiens.”

    This is exactly the conclusion I reached in The Genius of Kinship. Levels of extant linguistic, kinship and cultural variation (for which archaeological signatures will always be weak) and evolutionary sequences derived from them may help generate robust working hypotheses for the dispersals of the human species. These hypotheses can then be mapped onto genetic and archaeological data for optimization. As the Zhirendong jaw seems to suggest, behaviorally modern humans could evolve their core biological features in the “East” (Asia) just as likely as in the “West” (Africa). But it’s precisely in America, parts of Asia and the Sahul (i.e. in the “East”) that we encounter high levels of linguistic diversity as measured in terms of isolates, small-range, mid-range and large-scale families as well high degrees of typological conservatism and archaism. Africa and Europe are linguistically very homogeneous and typologically derived, which makes them unlikely geographic sources for behaviorally modern humans.

    “Because it is only well-dated diagnostic human remains that can document the timing and nature of human evolution and dispersal patterns (as opposed to archeological proxies for human biology or imprecise inferences from extant genetic diversity)…”

    I think well-dated diagnostic human remains can successfully debunk ideas ostensibly based on earlier well-dated diagnostic human remains. As far as the ability of fossils to provide positive answers to the questions of origin and dispersals of living taxa, I’m very skeptical. Ancient human remains shouldn’t be treated as a “record” for humanity but rather as “paper” onto which diachronic patterns derived from modern human populations are inscribed.

  • gcochran

    Dziebel is of course insane, but he stands out because he’s insane in a non-standard way: he’s his own nut. Sometimes that can be refreshing. One gets tired of the conventional nonsense.

  • Tomek R.

    German Dziebel Says:
    “But it’s precisely in America, parts of Asia and the Sahul (i.e. in the “East”) that we encounter high levels of linguistic diversity”

    The regions you mention didn’t have countries and government standarizing languages.

  • http://www.kinshipstudies.org German Dziebel

    “One gets tired of the conventional nonsense.”

    Just like I got tired of Multiregional and out-of-Africa. But I’m still entertained by Gcochran’s tweets.

    “The regions you mention didn’t have countries and government standarizing languages.”

    You are using a very primitive argument to shoot down a systematic pattern.

  • Glenn Allen Nolen

    gcochran publishing without even doing a Google search on Primary Torsion Dystonia (PTD) is a definition of insanity in my book.

  • gcochran

    I did, of course – then went back and read the primary literature on DYT1 torsion dystonia, the kind found in Ashkenazi Jews – even looked up and talked to a retired key researcher: but what was I supposed to have found? Other than what I did find?

  • Glenn Allen Nolen

    And you’re the so-called expert. That’s hilarious.

  • http://www.kinshipstudies.org German Dziebel

    “And you’re the so-called expert. That’s hilarious.”

    Good example and good critique. In the recent decades, thanks to technological developments, political shifts, etc., we’ve seen a tremendous surge in information and its desiloization (in and outside of humans origins research). The walls have simply come down. It’s time to piece it all together, and it’s really hard, or impossible to be an expert. We can only be students. The importance of the Zhirendong find is that it demonstrates that the out of Africa theory was crafted with an old expert approach to knowledge production. If I’m a university professor specializing in paleobiology, archaeology or genetics, it means by the year 2000 I’ve had access to ALL relevant finds, theories and approaches to formulate the final theory of human origins and then to slap on a label and broadcast it in the media, thus relieving future generations of experts of the need to prove it. But now it’s clear that “experts” just fool themselves and confuse others.

  • gcochran

    Example of what? Nolen says that I didn’t do Google searches on dystonia, but of course I did. I then ended up reading case reports, neurological studies, reports on the genetic epidemiology, on the molecular basis of the disease (low-penetrance dominant), etc, etc.

    And Dziebel says that this a good example – uh, I don’t get it? I strongly suspect that there’s nothing to get.

  • Glenn Allen Nolen

    German Dziebel says:

    “The walls have simply come down.”

    You’re right about that.

    gcochran says:

    “uh, I don’t get it?”

    And you probably never will.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    glenn, do you mind actually saying something instead of casting aspersions?

  • Glenn Allen Nolen

    Sorry Razib, I have issues with his research. I will not post again.

  • http://www.kinshipstudies.org German Dziebel

    “glenn, do you mind actually saying something instead of casting aspersions?”

    In defense of Glenn, Gcochran initiated the aspersions.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    yes, but not at him. i would be curious about glenn’s opinions on dystonia.

    but fair enough. let’s call a truce and move on.

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  • dave chamberlin

    Hoping I don’t conjure up more who is more insane type comments I would simply like to know how controversial or scientifically confirmed the correlations between higher intellegence and Primary Tortion Dystonia really are.

  • gcochran

    Edward Flatau first diagnosed this disease in 1911. He described the mental status of this first patient:

    ” Although he could no longer study because of his illness, he now showed an intellectual development far exceeding his age, excellent capacity for interpretation, good memory, and an amiable, cheerful and patient character as well as a critical judgment as regarding his illness: he merely would like to be healthy in order to be able to learn more. ”

    Second patient: ” completely normal mentally. He shows extraordinary mental development for his age, learns very well and dominates his associates with his knowledge. ”

    At least nine subsequent reports ( before 1970) have commented on the unusual intelligence of patients with dystonia. Those reports typically described patients as “intelligent” , “bright and intelligent with considerable fortitude”, or “brightest” in the family. Following two decades of clinical experience with the disorder, Irving S. Cooper
    observed that the children were above average in intelligence and unusual in their maturity and insight concerning their condition and abilities.
    Roswell Eldridge did a small study about 1970, which found an IQ elevation of about 10 points (over a ethnically & age-matched control group).

    I don’t consider this evidence overwhelmingly strong: but it certainly is suggestive. There are recent cases along the same lines: see http://www.austinmama.com/onbeingnormal.htm. You’d think that this would have been worth investigating – a mutation that noticeably boosted IQ would be interesting, yes? And Eldridge worked in neurogenetics at NIH, so he was hardly a voice crying in the wilderness. Yet when he proposed a study, the silence was deafening.

    Note this is DYT1 dystonia. There are other genetic dystonias, but to my knowledge no one has noticed a similar IQ boost in any of them.

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  • James

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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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