June 30, 2011

Homo erectus soloensis fades into the past...

Every year or so there seems to be a redating of a key fossil in human evolution. It's nice to see scientific self-correction in action, and soon after Neandertals got a little older, casting doubt on their supposedly long co-existence with modern humans, we now have a redating of Homo erectus soloensis from Java to about 150-550 thousand years ago, but certainly long before there were any anatomically modern humans in the area.

PLoS ONE 6(6): e21562. doi:10.1371/journal.pone.0021562

The Age of the 20 Meter Solo River Terrace, Java, Indonesia and the Survival of Homo erectus in Asia

Etty Indriati et al.

Homo erectus was the first human lineage to disperse widely throughout the Old World, the only hominin in Asia through much of the Pleistocene, and was likely ancestral to H. sapiens. The demise of this taxon remains obscure because of uncertainties regarding the geological age of its youngest populations. In 1996, some of us co-published electron spin resonance (ESR) and uranium series (U-series) results indicating an age as young as 35–50 ka for the late H. erectus sites of Ngandong and Sambungmacan and the faunal site of Jigar (Indonesia). If correct, these ages favor an African origin for recent humans who would overlap with H. erectus in time and space. Here, we report 40Ar/39Ar incremental heating analyses and new ESR/U-series age estimates from the “20 m terrace" at Ngandong and Jigar. Both data sets are internally consistent and provide no evidence for reworking, yet they are inconsistent with one another. The 40Ar/39Ar analyses give an average age of 546±12 ka (sd±5 se) for both sites, the first reliable radiometric indications of a middle Pleistocene component for the terrace. Given the technical accuracy and consistency of the analyses, the argon ages represent either the actual age or the maximum age for the terrace and are significantly older than previous estimates. Most of the ESR/U-series results are older as well, but the oldest that meets all modeling criteria is 143 ka+20/−17. Most samples indicated leaching of uranium and likely represent either the actual or the minimum age of the terrace. Given known sources of error, the U-series results could be consistent with a middle Pleistocene age. However, the ESR and 40Ar/39Ar ages preclude one another. Regardless, the age of the sites and hominins is at least bracketed between these estimates and is older than currently accepted.

Link

5 comments:

  1. That makes much more sense.

    I wouldn't be surprised if erectus had been replaced by Heidelbergensis-like populations between 200,000 and 150,000 years ago in most of Asia.

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  2. Hmm hope they plan to date the Lake Mungo erectus too.

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  3. The report leaves more questions than answers.

    The problem is that especially given the patchiness of the homo erectus record in Asia, that absence of evidence isn't necessarily evidence of absence.

    We know, for example, from Denisovian DNA that some hominin was in Asia as of the arrival of the Out of African AMHs in Asia near the jumping off point for Papua New Guinea ca. 45kya, but have very little in the way of fossil record or tool kit artifacts to support that. The period for which we have rich Neanderthal archaeology in Europe and the Near East, we seem to have little of in Asia. Even our dating for megafauna extinctions seems to be comparatively fuzzy for coastal route Asia relative to Europe or the Americas or Australia or Siberia.

    If Homo Erectus was gone, or had greatly reduced numbers by the time that AMHs arrive, the question is what did them in?

    Is an absence of evidence a functioon of insufficient scientific manpower/archaeological effort in the region, poor preservation conditions (much of the area of wet and hot), local hominin's use of organic rather than stone tools (e.g. bamboo), or did local Homo Erectus just create fewer identifiably Homo Erectus artifacts, since even at the best African sites their tools are much harder to distinguish from random rocks and brushfires than MSA Neanderthals or AMH artifacts, which are still harder to distinguish from random background than post-MSA AMH materials.

    Alas, paleoclimate data from ca. 600kya to 20kya doesn't seem to be nearly as detailed in Asia as it is in Europe and North Africa, and the climates systmes are distinct enough there that naiively inferring one from the other probably isn't valid for anything but sea level.

    A related absence of evidence/evidence of absence connundrum is the AMH skeletal record in Asia. We have count on your fingers sites of morphologically distinct AMHs from South Asia to all points east in the time period from ca. 100 kya to 50 kya with little eivdence of megafauna extinction, and with some arguable flow over to a few early (i.e. ca. 14kya to 16kya) Paleo-Amerindian sites, whose distinctiveness is hard to assign to genetics v. environment, and then a regular record of modern human activity. This is not a good fit for the usual model in which modern humans who arrive in virgin territory are fruitful, multiply, establish a permanent presence and have dramatic ecological effects, although it does show some parallels to the Levatine AMH presence from ca. 100 kya to 75 kya. Why did Eurasians seem to stumble for the first 50kya out of Africa and then start thiriving ca. 50kya?

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  4. "This is not a good fit for the usual model in which modern humans who arrive in virgin territory are fruitful, multiply, establish a permanent presence and have dramatic ecological effects"

    Perhaps the region was not exactly prime homo habitat, so no major population expansion. Humans seem much more suited to savanah rather than dense forest.

    "We know, for example, from Denisovian DNA that some hominin was in Asia as of the arrival of the Out of African AMHs in Asia near the jumping off point for Papua New Guinea ca. 45kya"

    We don't actually 'know' that the Denisova DNA was present somewhere 'near the jumping off point for Papua New Guinea' any time long before 45kya. Perhaps the population that reached that 'jumping off point' had carried the DNA all the way from where the Denisova DNA was found, somewhere near the Altai.

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  5. @terryt

    I agree - jungles have been shunned by most human groups and have never resulted in appreciable population densities, and the location and timing of "Denisovan" gene contribution is completely up in the air (somewhere between Africa and Asia, sometime between 200,000 and ~50,000 years ago).

    Also, erectus simply was not a target mating partner, while Heidelbergensis-like was - at least up until about ~50,000 years ago, when it seems a huge number of things changed rapidly in Eurasia.

    Sure, the presence of Neanderthals in Europe and West Asia was a hindrance, and so likely was the presence of Heidelbergensis-like in much of Asia. But something else changed ~50,000 years ago that became a turning point. Before than, AMHs tried for ~100,000 years and could not make a dent in Eurasia. After that, everything seems just too easy.

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