Sections

Services

Information

UK United Kingdom

Hunting or climate change? Megafauna extinction debate narrows

What is the oldest debate in Australian science? Probably, the argument over what caused extinction of our Pleistocene megafauna – the diprotodons, giant kangaroos, marsupial tapirs, über-echidnas and…

There’s not much left to show megafauna were hunted, but that doesn’t prove they weren’t. Peter Murray

What is the oldest debate in Australian science? Probably, the argument over what caused extinction of our Pleistocene megafauna – the diprotodons, giant kangaroos, marsupial tapirs, über-echidnas and other big and bizarre creatures that used to live here.

In 1877 the great English anatomist Sir Richard Owen suggested that these big animals had been driven extinct by “the hostile agency of man”. That is, hunting did it, in a process we now call overkill. Other people responded that climate change must have been the cause, and it was on.

A string of recent studies from a wide range of disciplines - geochronology, palaeoecology, palaeontology, and ecological modelling - have supported Owen’s opinion. But the argument continues. Why?

The main reason is that many Australian archaeologists reject overkill. They have looked for direct evidence that people killed megafauna, and they haven’t found it. No great piles of bones around ancient campsites; no diprotodon skeletons with spears stuck in their ribs; no arsenal of specialised weapons for bringing down large prey. Very few archaeological sites even have remains of people and megafauna in close association.

Some archaeologists conclude that megafauna-hunting just did not happen, or if it happened it was rare and insignificant. Often this conclusion is stated with a ringing confidence that dismisses all non-archaeological evidence for overkill.

But they have not asked a crucial question: if people did hunt megafauna to extinction, how much evidence of killing should we now be able to get from archaeological sites? A new paper by archaeologists Todd Surovell and Brigid Grund suggests the answer to that question is “very little or none”.

Surovell and Grund point out, first, that the period when archaeological evidence of killing of megafauna could have been formed is a small fraction of the total archaeological record of Australia. People arrived here between about 50,000 and 40,000 years ago. This is also the interval during which animals like diprotodon disappeared. A comparison of archaeological and fossil dates suggests humans and megafauna overlapped for only about 4,000 years continent-wide, and modelling suggests that if hunting caused extinction it would have been all over in less than 1,000 years in any place.

This means that no more than 8%, perhaps as little as 2%, of the Australian archaeological record covers the period of human-megafauna interaction. The “smoking gun” evidence of overkill should therefore be rare. Surovell and Grund show that the problem of finding such evidence is even worse than that, for two reasons.

First, when people first arrived their populations were necessarily small. Living sites therefore occurred at low density. As population size grew exponentially, site density increased. So, the very earliest sites must be far rarer than later ones.

But if overkill happened, populations of megafauna would have been going down as humans went up: as the density of sites was rising the proportion of them that could have contained evidence of megafauna kills was falling. Thus, sites with potential to preserve that evidence are actually a tiny proportion, perhaps much less than .01%, of the total archaeological record.

Second, material in archaeological sites degrades with time due to breakdown, weathering and scavenging of bone and removal by erosion. Old sites are eventually buried under sediments. The probability of discovering archaeological sites from the earliest occupation of Australia is intrinsically much lower than for later times, and most of the contents of those sites will have disappeared.

In fact, the very oldest archaeological sites in Australia typically contain only a few stone tools. They can tell us very little about interaction of the first Australians with any animals or plants, let alone reveal a picture of megafauna-killing.

Our fundamental task as scientists is to test hypotheses using evidence. To test the overkill hypothesis, we need a kind of evidence that would differ according to whether the hypothesis is true or false. Obviously, if overkill did not happen, evidence of megafauna-killing should be rare in the archaeological record. But, Surovell and Grund’s analysis makes it clear that if overkill happened, we should still expect evidence of killing to be rare. Therefore, failure to find such evidence does not amount to a test of the overkill hypothesis.

This does not mean that archaeological evidence of killing (or absence of such evidence) is useless in testing the overkill hypothesis. Surovell and Grund show it can be useful, by comparing the archaeological records of Australia, North America and New Zealand. All three places lost their megafaunas when people arrived, but this happened a very long time ago in Australia, and very recently (700 years ago) in New Zealand. North America is intermediate, with human arrival and extinction from 14,000 to 13,000 years ago.

Applying the same logic to all three cases, we predict that if overkill caused megafaunal extinction in each place the archaeological evidence of killing should be abundant in New Zealand, rare in North America, and vanishingly rare in Australia. That is exactly what we find.

There is so much evidence showing New Zealand’s moa were heavily hunted that nobody doubts overkill was the main cause of their extinction. In North America, there are undoubted kill sites for mammoths, mastodons and a few other species, but this evidence is far thinner than in New Zealand. Australian archaeology is yet to reveal any convincing evidence for megafauna-killing.

So, far from disproving overkill, the archaeological evidence from Australia is actually consistent with the overkill hypothesis.

Join the conversation

61 Comments sorted by

  1. Andrew Glikson

    Earth and paleo-climate scientist

    Invoking changes in climate toward the end of the last glacial termination (~14 000 - 10 000 years-ago) as the factor for disappearance of megafauna needs to explain why extinction has not happened during previous glacial terminations (124 000, 240 000, 320 000, 420 000 years-ago), when climate changes were as abrupt as in the last termination.

    report
    1. Mike Archer AM

      Professor, Evolution of Earth & Life Systems Research Group at UNSW Australia

      In reply to Andrew Glikson

      Andrew, see my comment above--megafaunal species WERE going extinct at many points during the Pleistocene, long before humans arrived. You're buying into the spin here; the actual record of extinctions does not support the view that humans had anything to do with these losses, but it is increasingly clear that bouts of climate change DO correlate with bouts of megafaunal extinction. The take home message for Tim Beshara, since he asked, is that we DO need to worry about the impacts of future climate…

      Read more
    2. Christopher Johnson

      Professor of Wildlife Conservation and ARC Australian Professorial Fellow at University of Tasmania

      In reply to Andrew Glikson

      Andrew

      The point about previous glacial cycles is a good one. Climate changes during the last glacial cycle were similar to previous ones (see Masson-Delomotte et al 2010: http://www.sciencedirect.com/science/article/pii/S0277379109003369).

      The article cited by Mike Archer (Cohen et al) in another comment does not show unprecedented climate conditions associated with megafaunal extinction. It does make it clear water levels in Lakes Eyre and Frome fell at various times during the last glacial…

      Read more
    3. Guy Cox

      logged in via email @guycox.com

      In reply to Andrew Glikson

      Well, if you are going to claim human influence how do you explain that humans and megafauna co-existed for around 10,000 years? See http://www.abc.net.au/catalyst/stories/2904980.htm

      Humans exterminated the moa in a tiny fraction of that timespan,

      Remember that in Europe it was climate change, not humans, that made mammoths and cave bears (Ursus speleaus) extinct even though we have perfectly clear evidence that both species were hunted. Here in Australia we have no evidence of hunting of megafauna and abundant evidence that they co-existed with humans. And we know that the megafuanal extinction coincided with a period of drought.

      Why are we still flogging this dead horse?

      Guy Cox

      report
    4. David Dent

      Artist

      In reply to Andrew Glikson

      There were extinctions during previous climate change events. What is significant about this one is the high number of extinct species (arguably including Clovis people) at the period roughly coinciding with the Younger Dryas. The climate change then may be a little misleading if anything. It may not even have been brought on by an impact event as the dates seem a little out. But what is appearing clearer now is that there was an impact event at c 12 900 bp consistent with multiple impacts across…

      Read more
  2. Sean Lamb

    Science Denier

    Megafauna disappeared in New Zealand in the absence of settlement.
    After 1200 Maori probably hunted the moa probably to the brink of extinction, but this was a moa no larger than an emu. The really big species of moa had gone long before.

    report
    1. Christopher Johnson

      Professor of Wildlife Conservation and ARC Australian Professorial Fellow at University of Tasmania

      In reply to Sean Lamb

      "Megafauna disappeared in New Zealand in the absence of settlement...."

      We have excellent data both on extinction of moa and colonization of NZ, showing that there was no decline of moa (or other megafauna) before human arrival, but a very rapid crash to extinction of all of them within a short time after human arrival, mostly in just a few decades. The literature on this is huge and unequivocal.

      report
    2. Sean Lamb

      Science Denier

      In reply to Sean Lamb

      Ahh well, maybe I am wrong. But I was always taught that larger species of moa had already gone. I believe there were a number of species..

      The New Zealand Giant Penguin certainly fell off the twig without the assistance of culinary exploitation.

      report
    3. Sean Lamb

      Science Denier

      In reply to Sean Lamb

      Incidentally, there is a tradition that was told to me by an Otago University ecological history academic, that oral tradition among Ngai Tahu attribute the extinction of the moa to large fires caused by a meteor strike in the South Island.
      Personally I always thought this was simply a defensive attempt at deflection (not really necessary when you compare the record of the Pakeha in terms of extinction) and seemed improbable and unnecessary explanation. The academic didnt endorse this tradition, she didn't dismiss it either.

      Interestingly this meteor crater was discovered perhaps after when I spoke with her
      http://en.wikipedia.org/wiki/Mahuika_crater
      But whether this would have sparked fires or if it was the incident Maori tradition refers to, I can't say

      report
  3. David Paxton

    Veterinarian

    Thanks for the conversation/. Your comments are valid regarding the narrow archeological window we look through. There is also the matter of competition for food 60,000+ years ago by an entirely new predator (Homo sapiens) (and, I argue, dogs and cats in association) in a more or less untouched marsupial world. This would especially be the case if land management by fire (see Bill Gamage) was already being practised by the new arrivals to terra incognita. The mega fauna would not have had much chance, especially if they were in evolutionary cul de sacs.

    report
    1. Murray Webster

      Forestry-Ecology Consultant/Contractor

      In reply to David Paxton

      When do dogs and cats appear in the archealogical record? I have read that dogs are within the last 7 000 years and cats the last 300. That would rule them out of any association with megafauna extinction

      report
  4. Murray Webster

    Forestry-Ecology Consultant/Contractor

    This debate appears to have become political to some extent. It is a major factor in the evolution of Australian ecology. But this presents a problem for people who believe that nature should be left to itself and we should not interfere. Discounting arguments that the first peoples in Australia did cause the mega fauna extinction, supports the idea of wilderness areas and passive management in national parks, which appeals to a significant proportion of the voting public.

    report
    1. Peter Yard

      Software Developer / Technnical Writer

      In reply to Murray Webster

      I suspect some of the support for the Climate Change argument may be due to respect for the practices of current Aboriginal peoples. But of course they are not the same people who first arrived here. Culture and cultural adaptation would have changed dramatically over 50,000 years. It has always seemed to me that the first influx of homo sapiens was the cause of the extinctions simply because the megafauna had survived so many previous interglacials. Add to that the fact that extinctions seem to follow humans about wherever they go then, well, it doesn't paint a cheery picture of us.

      report
    2. Murray Webster

      Forestry-Ecology Consultant/Contractor

      In reply to Murray Webster

      Peter, That is my summation as well.... That's nature and evolution isn't it, a competition between species? Any other species would do the same to replicate?

      Ironically we would have to socially evolve beyond our prime replication directive (i.e 'un-natural') to contain the damage we are causing to the biosphere.

      report
    3. Peter Yard

      Software Developer / Technnical Writer

      In reply to Murray Webster

      The Hunting or Climate Change views are still hypotheses. There's no clear data I have seen yet for either. In light of that I am wary about getting too partisan, and also I don't want to go into a Dunning Kruger mode of thought. But one thing worries me. Mike Archer mentions the intensity of the last Glacial Maximum may have been worse than in previous glacial periods, but the extinctions of megafauna in other places occurs at different times, they can't all be due to the same climate cause so either Australia is a special case or it may be a human caused event (allowing for the vagaries of the fossil record). I look forward to some hard data, either way, on this.

      report
    4. David Simpson

      Writer

      In reply to Murray Webster

      Hi Peter
      You wrote:
      "Add to that the fact that extinctions seem to follow humans about wherever they go then, well, it doesn't paint a cheery picture of us."

      When you consider the probability that 99.9% of all the species that have ever existed are extinct, it's pretty harsh to pin that charge on homo sapiens.
      Extinction seems to be the natural way of things - and necessarily overall, neither good nor bad, just different.

      report
    5. Peter Yard

      Software Developer / Technnical Writer

      In reply to Murray Webster

      @David Simpson: Since multicellular life is over 500 million years old then yes a lot of organisms have gone extinct. However, they usually last quite some time. I find it extremely curious that all these populations of megafauna just happen to go extinct around the time that humans are introduced into the mix.

      Now consider this scenario. The continent is going through some bad times and now a new top level predator arrives on the scene. Why now? Because the sea level is lower because the dry…

      Read more
    6. Glenn Tamblyn

      Mechanical Engineer, Director

      In reply to Murray Webster

      This debate reflects something you see in many fields of science - competing theories that are discussed in a rather black&white, either/or manner. When in reality the actual situation is far more likely to be a compounded mix of both.

      I find it inconceivable that our arrival didn't have some sort of impact but working out what and thus assigning a proportion of the extinctions to human activity is much harder.

      Did we actively predate smaller animals, thus reducing predation against birds and…

      Read more
  5. Tim Beshara

    Executive Officer

    So Chris, what does the megafauna extictions mean for our current ecological management? Are our ecosytems hollow shells of what they once were? Does the loss of functions once provided by megafauna mean that our ecosystems are changing or in decline?

    report
    1. Tom Keen

      PhD Candidate; Ecology & Evolutionary Biology.

      In reply to Tim Beshara

      The loss of large apex predators has certainly had (and continues to have) large effects on Australian ecosystems, particularly since the arrival of invasive mesopredators (medium sized predators, e.g. foxes and cats) which have helped to decimate many of Australia's native mammal and bird populations. This article is relevant to your questions: https://theconversation.edu.au/can-australia-afford-the-dingo-fence-7101

      This doesn't necessarily mean our current ecosystems (or what is left of them) are "hollow shells" of what they once were - but they are under enormous pressure from anthropogenic activities.

      report
    2. Christopher Johnson

      Professor of Wildlife Conservation and ARC Australian Professorial Fellow at University of Tasmania

      In reply to Tim Beshara

      Tim

      All good questions. My strong feeling, supported by a bit of evidence, is that the loss of mega-herbivores had big effects on the structure and composition of vegetation. In some respects, the flora is still reacting to the shock of megafaunal extinction.

      report
  6. Tom Keen

    PhD Candidate; Ecology & Evolutionary Biology.

    Thanks for a great article.

    I have been passively following this debate for a while now, and I can't help but question whether there are actually that many researchers out there still strongly pushing the climate argument. Most proponents of the overkill hypothesis tend to acknowledge that climate shifts probably played some synergistic role, but I haven't read anything in a long time that attempts to refute the overkill hypothesis. Is the debate still active?

    report
    1. Mike Archer AM

      Professor, Evolution of Earth & Life Systems Research Group at UNSW Australia

      In reply to Tom Keen

      I'm sorry to take issue here but Chris's article and the deduction about the principle cause of the extinction of Australia's megafauna are fraught with errors. There should be a paper coming out shortly in an international journal that will explain why. When hard evidence rather than circumstantial inference and apriori presumptions are put on the table, climate change unquestionably stands up as the most plausible explanation for these extinctions. The same is increasingly clear with respect to…

      Read more
    2. Murray Webster

      Forestry-Ecology Consultant/Contractor

      In reply to Tom Keen

      Pleased to read your input Mike, perhaps we will actually have some informed Conversation.

      One query, Is there any "hard evidence for humans killing" any animals from the archaeological record, say prior to 20 000 yrs ago?

      I infer that by "hard evidence" you mean:

      "great piles of bones around ancient campsites; no diprotodon skeletons with spears stuck in their ribs; no arsenal of specialised weapons for bringing down large prey"

      Does any hard archaeological evidence exist for any hunting by Aborigines prior to the last glacial maxima?

      regards
      Murray

      report
    3. Tom Keen

      PhD Candidate; Ecology & Evolutionary Biology.

      In reply to Tom Keen

      Thanks for the comment Professor Archer - you certainly answered my question! I look forward to reading your upcoming paper.

      report
  7. Glenn Tamblyn

    Mechanical Engineer, Director

    There is perhaps a more nuanced approach to this question. What impact did all the consequences of man's arrival in Australia have on the survival of the Mega Fauna. It may not have, almost certainly wasn'tjust direct predation on the megafauna that killed them. When did humansd first start fire-stick farming. What effect might predation on smaller species have had on the entire food chain etc.

    report
    1. Murray Webster

      Forestry-Ecology Consultant/Contractor

      In reply to Glenn Tamblyn

      Seen this paper?

      Rule S., et al. 2102 The Aftermath of Megafaunal Extinction: Ecosystem Transformation in Pleistocene Australia. Science 335, . pp 1483-1486

      It would take some dramatic new discoveries to usurp the "humans did it" theory.

      report
  8. David Paxton

    Veterinarian

    Professor Johnson has wriitten an interesting conversation. With the gift of hindsight it is easy to see that the arrival of Homo sapiens would have great impact (sooner or later). And thank you, Murray Webster, for additional comment. I think that the orthodox view that the dog and cat arrived quite recently is unimaginative to the point of incuriosity. Archaeological evidence (bones) is likely to be lacking in this instance because of the behaviour of dogs and cats, and there are other forms of information: cave painting, DNA, hypothesese on natural selection, and simple logic, for example: apply these and the gate posts move apart. People came here, probably on bamboo rafts, tens of thousand of years ago. The animal they were most likely to bring (for food and security) would be the dog. Please visit www.compositeconversationalist.com . Best wishes.

    report
    1. Murray Webster

      Forestry-Ecology Consultant/Contractor

      In reply to David Paxton

      David:

      There is no record ever of dogs/dingos in Tasmania prior to European settlement, and coincidentally, is the only place that Thylacine survived into the 20th Century.

      Seems like there is still a lot of debate about when the dingo arrived. These authors suggest 4600 - 18300 yrs BP. That's a huge range, but still would have them arriving long after mega-fauna extinction.

      http://www.australiangeographic.com.au/journal/the-dingo-came-to-australia-from-southern-china.htm

      re your link: I do talk to my dogs on a daily basis...Can you reference any scientific papers?

      report
    2. Christopher Johnson

      Professor of Wildlife Conservation and ARC Australian Professorial Fellow at University of Tasmania

      In reply to David Paxton

      David

      The evidence that dingoes came in about 4,000 years ago, from SE Asia, is pretty overwhelming. The time of arrival is confirmed by cave paintings (dingoes appear only in relatively recent art styles), DNA, and the fossil record; there is also the fact that dingoes turn up at about the same time in Australia and New Guinea (where they are known as NG singing dogs). Their place of origin is confirmed by the fact that Australian dingoes are very closely related and morphologically similar to living dingoes in SE Asia, which in turn are descended from Asian wolves.

      As for cats, they arrived later, almost certainly with the British. An old idea of a pre-British introduction from Dutch or Portuguese ships landing on the west coast has been comprehensively refuted by Ian Abbot, see:
      http://www.publish.csiro.au/paper/WR01011.htm

      report
  9. David Paxton

    Veterinarian

    Thank you for the replies, Murray and Christopher, and thanks for the references. I think there is a jury on this case, and I think the jury is still out. I am not sure which branch of science you regard as the senior judge, but the science of human orgins and of extended phenotypes/mutualistic symbionts begs to ask the question: why do we try to draw the line under the dog/cat when we have so much further to go in this debate? Murray, please may I refer you to my book (see www.compositeconversationalist.com) and also to references on dog in French caves, dog skulls Belgium and Siberia about 30,000+ years old, Tasmanian Aborigines stealing colonials' dogs. Even if "science" refers only to what smells of formaldehyde or needs to be plugged in to a power outlet, then I can see how the dog and cat could be overlooked for more exotic subjects. Sorry, in a hurry.

    report
  10. Mark King

    Senior Lecturer, Psychology and Counselling and Researcher, CARRSQ at Queensland University of Technology

    What I like about this approach is the application of a logic that recognises the context of archaeological sites in terms of timescale and demographics. I wonder if there are further adjustments that can be made, e.g. the likelihood that bones would actually remain clustered at kill/cook sites (scavengers, flash floods, etc). As a separate point, I think that the terminology used in this area often conveys a false impression, as if the killing of the megafauna took place in the same way as the…

    Read more
  11. Mike Archer AM

    Professor, Evolution of Earth & Life Systems Research Group at UNSW Australia

    Chris, until our paper comes out, we'll have to agree to disagree. Suffice it to say that when you do put hard data on the table, you'd have to be very determined NOT to see that the majority of megafaunal species were gone long before humans reached Australia. We've also detailed more about the significant differences between the glacial maxima. The facts are that the glacial maxima were not equally stressful and the last one was more severe than previous episodes, whether you want to believe Cohen…

    Read more
  12. Mike Archer AM

    Professor, Evolution of Earth & Life Systems Research Group at UNSW Australia

    Peter (Yard)--clear thinking there. The interval in Australia that was characterised by particularly challenging climates for our biota was the late Pleistocene one that started about 40-45 thousand years ago. Yes, this would have been a globally challenging period and it's likely that species on other continents were challenged by the same climatic event. But, as you say, the continents are not all the same and the impact of climate change was not necessarily equivalent on all continents at the…

    Read more
  13. Guy Cox

    logged in via email @guycox.com

    So the hypothesis for which there is no evidence - hunting - has to be right. Yet the fact of climate change is indisputable. To put it mildly, the climate over the past 100,1000 years has been studied in minute detail. We know what climate changes were occurring. Further, there exist known sites where massive numbers of megafauna died in mud unable to reach the water they needed to survive as the lakes they depended on dried up. We cannot do a controlled experiment here, but we certainly can look at the balance of the evidence.

    report
  14. James McCartney

    student

    I'm having trouble following the logic in this article. It's stated that "the archaeological evidence from Australia is actually consistent with the overkill hypothesis"- there is no evidence that humans ever interacted with (e.g., hunted) megafauna, and as Prof. Johnson argues, you'd expect that evidence to be rare/absent anyway due to the antiquity of the deposits. Right... BUT, if humans actually had nothing to do with megafaunal extinctions - that is, they didn't over-hunt them to extinction…

    Read more
    1. Tom Keen

      PhD Candidate; Ecology & Evolutionary Biology.

      In reply to James McCartney

      "This sounds like a massively illogical flaw in how the existing archaeological record can be used to test the overkill hypothesis."

      Actually, the article clearly states that "failure to find such [archaeological] evidence does not amount to a test of the overkill hypothesis". I.e., it is not evidence for *or* against the overkill hypothesis. However, the existing evidence for kill sites (or lack thereof) is at least consistent with the overkill model, based on what you would expect to find probabilistically…

      Read more
  15. Mike Archer AM

    Professor, Evolution of Earth & Life Systems Research Group at UNSW Australia

    James, you've hit the name on the head--citing the lack of evidence for overkill as evidence for overkill is over kill of the scientific method. But if you put this strange argument aside and ask what are the facts rather than the apriori assumptions about overkill, you come up with a very different overview. The facts are that there is no credible hard evidence to demonstrate that humans did any overkilling in Australia or North America. But there is credible evidence that the megafauna on both continents was in decline long before humans arrived in either place--which means something other than humans is responsible. That 'something' is climate change. I find it hard to understand why this better-supported interpretation is so hard for some to accept, particularly given ubiquitous acceptance that climate change currently underway will inevitably cause a whole new avalanche of extinctions.

    report
    1. Tom Keen

      PhD Candidate; Ecology & Evolutionary Biology.

      In reply to Mike Archer AM

      Doesn't the near-universal acceptance that current climate change could cause a wave of extinctions stem from the near-unprecedented rapidity of current climate change, and the synergistic effects between climate change and other anthropogenic factors causing biodiversity loss (habitat loss, fragmentation, invasive species, overexploitation, etc.)?

      report
    2. James McCartney

      student

      In reply to Mike Archer AM

      Tom- with due respect, this IS hypothesis testing. Yes, Prof. Johnson explicitly stated that the lack of evidence is NOT a test of the extinction hypothesis, but then in his final sentence of the article he uses the archaeological record (or lack of) as a TEST of the overkill hypothesis ("the archaeological evidence from Australia is actually consistent with the overkill hypothesis"). Likewise, your statement that "the existing evidence for kill sites...is at least consistent with the overkill model…

      Read more
    3. Tom Keen

      PhD Candidate; Ecology & Evolutionary Biology.

      In reply to Mike Archer AM

      James - from my reading, the paper's hypothesis is that the further back in time the megafauna-human overlaps occurred, the less archaeological evidence there should currently be for kill sites. That is a testable hypothesis, and one that Surovell and Grund found evidence for. And again, I do not think this argument is being presented as evidence for the overkill hypothesis - it is simply a demonstration that the lack of kill sites found in Australia is *consistent* with (i.e. not contradictory to) the overkill hypothesis. In other words, according to this model, the lack of kill sites in Australia does not constitute evidence against the overkill hypothesis.

      I'm not trying to take sides in this debate either, but I think we should at least try to fairly understand the point (or points) being made by the author.

      report
  16. David Dent

    Artist

    Interesting conversation on a subject I discuss regularly with my partner who is an ice core researcher and though her work is not directly related to the topic it is in the area of helping improve chronology which may help in future. I am an artist and history graduate not a scientist so the points I am about to make are questions to consider rather than being able to offer any evidence as such.
    But they are important questions I hink when discussing this.

    The first I would like to raise is…

    Read more
    1. Mike Archer AM

      Professor, Evolution of Earth & Life Systems Research Group at UNSW Australia

      In reply to David Dent

      Spot-on David. There is an issue about the hypothetical late Pleistocene meteorite, however. There's no credible hard evidence for it and in any case, with most of the megafauna disappearing from NA long before the end of the Pleistocene, a meteorite couldn't be responsible for all of the extinctions of North America's megafauna. But your comments about the well-understood usage strategies of hunter/gatherer communities world-wide are correct--and a powerful argument against the idea that early Australians over-killed Australia's megafauna as soon as they arrived. That makes no sense and is not supported by hard evidence of any kind--just apriori assumptions and strangely contorted arguments.

      report
  17. David Dent

    Artist

    Yes Mike re the hunter gatherer cultures. But of course that doesn't mean that a culture didn't emerge that may have completely changed from this model. Various cultures can change dramatically from traditional hunting to new basis. This can happen through new resource exploitation or even through paranoia that result in massive dramatic changes to the environment . The problem is it is unlikely to be through traditional hunting so even if the extinctions were human caused they are looking for the…

    Read more
    1. Mike Archer AM

      Professor, Evolution of Earth & Life Systems Research Group at UNSW Australia

      In reply to David Dent

      David, you raise many very interesting points, most of which I agree with--the main point being that 'overkill' by indigenous hunter/gatherer peoples would have been an enormously improbable cause of extinction. There is another recent paper in PNAS (Brace et al., 'Serial population extinctions in a small mammal indicate late Pleistocene ecosystem instability) with the following abstract indicating that changes in key small mammal prey species caused by climate change can significantly destabilise…

      Read more
  18. David Dent

    Artist

    Latest research this summer:

    Bunch TE, Hermes RE, Moore AM, et al. (June 2012). "Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago". Proc Natl Acad Sci U S A 109 (28): E1903–12. doi:10.1073/pnas.1204453109. PMID 22711809. (http://www.pnas.org/content/early/2012/06/14/1204453109.full.pdf)

    Abstract: It has been proposed that fragments of an asteroid or comet impacted Earth, deposited silica-and iron-rich microspherules and other proxies across…

    Read more
    1. Mike Archer AM

      Professor, Evolution of Earth & Life Systems Research Group at UNSW Australia

      In reply to David Dent

      Wow, David, I've missed that paper--very exciting stuff! My last awareness was from those who had failed to find the trace indicators and were questioning whether any meteor impact event had occurred at all. This, however, is strong evidence that it did and that it could well have been a significant factor in precipitating ecosystem instability with associated extinctions.

      report
  19. Tom Jackson

    Pastoralist

    Whatever the cause of Megafauna extinction, the interesting part of this debate is what it means for our present situation. Did fire-stick farming replace the role of large herbivores in recycling nutrients in our largely arid rangelands and in keeping the country open and grassy for the remaining smaller herbivores and for their hunting?
    When this practice was severely disrupted following European settlement, how quickly did the environment change?
    Can we replace both megafauna and fire nutrient recycling with PROPERLY MANAGED livestock grazing?
    I would suggest that attempts to return country to some mythical pristine state by simply locking it up as is being attempted by the Department of Environment and Conservation in WA rangelands will result either in the stalling of nutrient recycling or in an increase in devastating wildfires. Both will accelerate further extinctions.

    report
  20. David Dent

    Artist

    Just came across this paper Grayson et al 2002 which appears to be discussing very much the same as the author here and actually answering many of the points raised by Mr Johnson.
    http://faculty.washington.edu/grayson/jwp02.pdf

    While there will be significant updates on this, I rather like the way Grayson puts it here:

    "Indeed, it is significant that for 33 extinct genera, and for 26 of the 28
    extinct herbivores, there is no archaeological evidence at all for hunting,
    and only a limited…

    Read more
    1. Christopher Johnson

      Professor of Wildlife Conservation and ARC Australian Professorial Fellow at University of Tasmania

      In reply to David Dent

      David

      The Grayson paper is actually a good example of the view that if we don't have archaeological evidence of hunting of megafauna in North America (or Australia), that means it didn't happen. My article (and the paper by Surovell on which it is based) is a response to that simplistic idea. It uses a different set of arguments to those developed earlier by Martin. So, in attacking Martin (in what I consider to be an overly personal way, not worthy of a scientific publication), Grayson is certainly not trumping the later arguments summarized in my article.

      report
    1. Mike Archer AM

      Professor, Evolution of Earth & Life Systems Research Group at UNSW Australia

      In reply to David Dent

      It is an interesting and increasingly important area for research--changes in the small mammals over the same mid to late Pleistocene interval of time when the large mammals were declining. In Australia this is beginning to reveal important insights. In the Rockhampton area, e.g., it's now clear that about 50% of the small mammals went extinct at least regionally between the mid to late Pleistocene. Finding it difficult to envisage minimammal overkills by early humans (who hadn't yet arrived in Australia…

      Read more
    2. Christopher Johnson

      Professor of Wildlife Conservation and ARC Australian Professorial Fellow at University of Tasmania

      In reply to David Dent

      David

      That paper is interesting and contains good data. But, those data definitely do not constitute evidence against the idea that human hunting caused megafaunal extinction; nor do they provide anything more then weak evidence that climate change might have contributed.

      Brace et al show that climate change during the last glacial cycle had significant effects on the collared lemming. I expect that climate change during the last glacial cycle had significant effects on practically every species…

      Read more
  21. David Dent

    Artist

    Hi Christopher. I think the suggestion is the lemming population has decreased at certain other times of climate change too during glacial periods. I also think it isn't a wild stretch to suggest that small animals can repopulate areas and it is easier to survive harsh climate change as small pockets can survive. It can with megafauna too as the Wrangel island mammoths, certain sloths, and animals that are large and survive even today like bison and polar bear. But small animals need less food so…

    Read more
  22. Cathy Holland

    Retired

    The megafauna extinction was caused by a galactic superwave that hit our planet and overwhelmed our atmospheric and magnetic protection. Ice core studies verify this.

    report
    1. Cathy Holland

      Retired

      In reply to Cathy Holland

      Ice core studies show that this has happened every 13,000 and 26,000 yrs., causing major climate changes, as well as major extinctions. The bad news, we are overdue for another one.

      report
    2. Cathy Holland

      Retired

      In reply to Cathy Holland

      Galactic superwaves originate from the center of the galaxy and are caused by the collision of suns drawn together via the black hole. Although this may seem chaotic, the ice core evidence shows that it occurs rather regularly and the force fields sent out from these collisions seem to have hit our planet on a rather regular schedule.

      report
    3. Stephen Wroe

      Associate Professor at University of New England

      In reply to Cathy Holland

      Sorry to clog things - previous claims that there was nothing unusual about the last few glacial cycles really needs to be addressed because it is fundamental to the argument for human causation - and it is incorrect. Evidence for trending, albeit stepwise, deterioration over multiple cycles has been around for decades - and it is mounting - with further and very recent evidence from ice core data indicating that things began to change as far back as 700-800kya - and not only in Australia - with…

      Read more