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Ice-Age megafauna extinctions linked to humans, not climate

Was it humankind or climate change that caused the extinction of a considerable number of large mammals about the time of the last Ice Age? Researchers at Aarhus University have carried out the first global analysis of the extinction of the large animals, and the conclusion is clear -- humans are to blame. A new study,  published by the Proceedings of the Royal Society B: Biological Sciences, unequivocally points to humans as the cause of the mass extinction of large animals all over the world during the course of the last 100,000 years.

Ice-Age megafauna extinctions linked to humans, not climate
Mammoth Hunt [Credit: skyrimnexus]
"Our results strongly underline the fact that human expansion throughout the world has meant an enormous loss of large animals," says Postdoctoral Fellow Søren Faurby, Aarhus University.

Was it due to climate change?

For almost 50 years, scientists have been discussing what led to the mass extinction of large animals (also known as megafauna) during and immediately after the last Ice Age.

One of two leading theories states that the large animals became extinct as a result of climate change. There were significant climate changes, especially towards the end of the last Ice Age -- just as there had been during previous Ice Ages -- and this meant that many species no longer had the potential to find suitable habitats and they died out as a result. However, because the last Ice Age was just one in a long series of Ice Ages, it is puzzling that a corresponding extinction of large animals did not take place during the earlier ones.

Theory of overkill

The other theory concerning the extinction of the animals is 'overkill'. Modern man spread from Africa to all parts of the world during the course of a little more than the last 100,000 years. In simple terms, the overkill hypothesis states that modern man exterminated many of the large animal species on arrival in the new continents. This was either because their populations could not withstand human hunting, or for indirect reasons such as the loss of their prey, which were also hunted by humans.

Ice-Age megafauna extinctions linked to humans, not climate
The European forest elephant is among the animals that 
are now extinct [Credit:WikiCommons]
First global mapping

In their study, the researchers produced the first global analysis and relatively fine-grained mapping of all the large mammals (with a body weight of at least 10 kg) that existed during the period 132,000-1,000 years ago -- the period during which the extinction in question took place. They were thus able to study the geographical variation in the percentage of large species that became extinct on a much finer scale than previously achieved.

The researchers found that a total of 177 species of large mammals disappeared during this period -- a massive loss. Africa 'only' lost 18 species and Europe 19, while Asia lost 38 species, Australia and the surrounding area 26, North America 43 and South America a total of 62 species of large mammals.

The extinction of the large animals took place in virtually all climate zones and affected cold-adapted species such as woolly mammoths, temperate species such as forest elephants and giant deer, and tropical species such as giant cape buffalo and some giant sloths. It was observed on virtually every continent, although a particularly large number of animals became extinct in North and South America, where species including sabre-toothed cats, mastodons, giant sloths and giant armadillos disappeared, and in Australia, which lost animals such as giant kangaroos, giant wombats and marsupial lions. There were also fairly large losses in Europe and Asia, including a number of elephants, rhinoceroses and giant deer.

Ice-Age megafauna extinctions linked to humans, not climate
The giant sloth succumbed to the advance 
of humans [Credit:WikiCommons]
Weak climate effect

The results show that the correlation between climate change -- i.e. the variation in temperature and precipitation between glacials and interglacials -- and the loss of megafauna is weak, and can only be seen in one sub-region, namely Eurasia (Europe and Asia). "The significant loss of megafauna all over the world can therefore not be explained by climate change, even though it has definitely played a role as a driving force in changing the distribution of some species of animals. Reindeer and polar foxes were found in Central Europe during the Ice Age, for example, but they withdrew northwards as the climate became warmer," says Postdoctoral Fellow Christopher Sandom, Aarhus University.

Extinction linked to humans

On the other hand, the results show a very strong correlation between the extinction and the history of human expansion. "We consistently find very large rates of extinction in areas where there had been no contact between wildlife and primitive human races, and which were suddenly confronted by fully developed modern humans (Homo sapiens). In general, at least 30% of the large species of animals disappeared from all such areas," says Professor Jens-Christian Svenning, Aarhus University.

The researchers' geographical analysis thereby points very strongly at humans as the cause of the loss of most of the large animals.

The results also draw a straight line from the prehistoric extinction of large animals via the historical regional or global extermination due to hunting (American bison, European bison, quagga, Eurasian wild horse or tarpan, and many others) to the current critical situation for a considerable number of large animals as a result of poaching and hunting (e.g. the rhino poaching epidemic).

Source: Aarhus University [May 28, 2014]
TANN

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5 comments :

  1. While I'm glad you credited the image properly, I think it's a little misleading to imply that prehistoric humans hunted mammoths with bows and arrows. While wearing leather armor.

    Or maybe I'm wrong and Skyrim is historically accurate, in which case I would love to see an article about the health benefits of eating cheese made from mammoth milk. I've heard it restores both health and stamina, and can be combined with other ingredients to increase magicka.

    ReplyDelete
    Replies
    1. Skyrim can't be historically accurate, because the earth doesn't even exist in that universe

      Delete
  2. As far as I know Mammoths never had any prey that humans could over-hunt, neither did most of the other megafauna mentioned in this article. Why would a hunter-gatherer society choose to hunt the biggest, most dangerous, prey when there are millions of easier animals to kill? And why is the number of mass extinctions higher in North and South America when those were the places that had the fewest number of humans on earth at the time? What tools and techniques did the humans use to commit this mass extinction, and why does the mass extinction seem to only occur in the megafauna of the time? If humans were such a destructive force back then, why aren't there also mass extinctions of animals that are way easier to kill? What if the climate change was brought on by a natural disaster that occurred in North or South America, a disaster which could have had global consequences such as a comet fragment hitting the planet? Wouldnt a catastrophe like that affect megafauna at a much higher rate than more adaptable species? I wish the article would do a better job of explaining the climate change theory before dismissing it. And I also wish there was more actual data from the study, and not mere editorializing.

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    Replies
    1. Mammoths, like elephants (and many large whales) have reproductive rates that assume little to no predation since their size is a natural deterrent to most carnivores. Any hunting by humans puts them in a slow spiral towards extinction because they can't evolve faster reproductive rates to outpace the loss from predation. Mammoth kill sites have been found throughout northern climes, so clearly it happened. This is true for most of the other megafauna that went extinct, though I'm less of an expert on them.

      The number of mass extinctions in North and South America are higher (although whether it's statistically significantly higher is not stated in this article), but it could simply be due to the fact that the Americas didn't see any hominid species until recently (15,000 BP) while Homo erectus had been present throughout the Old World for over a million years and thus megafauna there were more able to co-evolve. This is especially true for Africa, the ancestral home of our species.

      As for the natural disaster, there has been no (to weak) evidence of them in the time frame of the megafaunal extinctions.

      This is a short article describing further advances on the theory of overkill which came into the scientific forefront in 1973 with Paul Martin. I suggest you read his book "Twilight of the Mammoths" which includes many of the details you're requesting. There's also a number of scientific papers you could consult for these details such as the one this article is announcing, as well as:
      Alroy J. 2001. A multispecies overkill simulation of the End-Pleistocene megafaunal mass extinction. Science. 292:1893–1896.
      Or my own, less prominent, paper: https://www.tandfonline.com/doi/full/10.1080/08912963.2017.1383987

      Delete
  3. An addendum to my last comment. The picture used in this article is from Skyrim, and you'd never want to try to kill a mammoth in that game with a bow and arrow in close quarters like that. Just thought it was worth noting.

    ReplyDelete


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