Climate change knocked mammoths down, humans finished them off

Blogging on Peer-Reviewed ResearchDid our ancestors exterminate the woolly mammoth? Well, sort of. According to a new study, humans only delivered a killing blow to a species that had already been driven to the brink of extinction by changing climates. Corralled into a tiny range by habitat loss, the diminished mammoth population became particularly vulnerable to the spears of hunters. We just kicked them while they were down.

i-10551e8b7936704d4ad487138ad9cb04-Mammoth.jpgThe woolly mammoth first walked the earth about 300,000 years ago during the Pleistocene period. They were well adapted to survive in the dry and cold habitat known as the 'steppe-tundra'. Despite the sparse plant life there, the woolly mammoths were very successful, spreading out in a belt across the Northern hemisphere.

Their fortunes began to change as the Pleistocene gave way to the Holocene. The climate around them started to become warmer and wetter and the shrinking steppe-tundras greatly reduced the mammoth's habitats. The species made its last stand on the small Wrangel Island in Siberia before finally succumbing to extinction.

But climate change isn't the whole story. About 40,000 years ago, those relentless predators - human beings - started encroaching into the woolly mammoth's range in northern Eurasia. Which of these two threats, climate change or human hunters, sealed the mammoth's fate?

Climate change has been blamed in the past, but some scientists have noted that the species had survived through other warm spells, including a period about 126,000 years ago that shrunk its habitat to a larger extent than the Holocene warming. The arrival of humans also fits the general timing, but some sources claim that there is little direct evidence of our ancestors actually hunting mammoths.

Two-hit combo

i-6229b66a66efb07fc1d111f8b0df7d0b-Mammoth_skeleton.jpgDavid Nogues-Bravo from the National Museum of Natural Sciences in Madrid thinks that the two factors worked together, with climate changes weakening the population and humans finishing it off. Taking factors like temperature and rainfall into account, he ran simulations of the mammoth's prehistoric climate at five time points over a span of 120,000 years. These models were bolstered by data from the carbon-dated fossil remains of woolly mammoths that lived throughout Eurasia during this time period.

The simulations showed that the area of land containing suitable habitats for the mammoths was incredibly sparse about 126,000 years ago. Then, the giants were most likely confined to the very north of Eurasia but as the climate cooled, their geographical range increased by 26 times to encompass much of the northern continent.

The turning point happened about 42,000 years ago when their habitat started to shrink catastrophically over the course of 36,000 years, relegating the species to an area just 11% of its former size. Even so, their range was still larger than it was at the previous low.

Kill Mammoth

Nogues-Bravo then modelled how the mammoths that were still around 6,000 years ago would have reacted to being hunted by humans where their ranges overlapped. He found that even with an optimistic estimate of the population's size and strength, each human would have had to kill just one mammoth every three years to drive the species to extinction. With a pessimistic appraisal of mammoth numbers, the death of just one mammoth every 200 years at the hands of each human would have been enough to seal their fate.

The diagram below shows the beast's plight over time. The red areas represent suitable habitat, and the green areas less so. The black line shows the frontline of the human invasion.


If humans had never arrived in northern Eurasia, the mammoths might still have made it. Nogues-Bravo suggests that they would probably have survived in small pockets of suitable habitat and made use of fringing and less welcoming areas, as they probably did during the warm spell 126,000 years ago. But they never got the chance. Our ancestors delivered the coup de grâce to a failing population that was too small to withstand the hunting pressures they were subjected to.

Image from PLoS; painting by Mauricio Anton; photo by Rama

Reference: Nogués-Bravo, D., RodrÃÂguez, J., Hortal, J., Batra, P., Araújo, M.B. (2008). Climate Change, Humans, and the Extinction of the Woolly Mammoth. PLoS Biology, 6(4), e79. DOI: 10.1371/journal.pbio.0060079

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I think it was in Guns, Germs and Steel that Jared Diamond pointed out that a good way of dating when humans first entered a new territory is to check and see when the mass extinctions happened. That's been the case for just about every continent or island inhabited by humans.

Popular depictions of mammoth kills, With paleohunters chucking and even thrusting spears into a wildly thrashing beast not withstanding, Mammoths might have been easy.Pigmys hunt African elephants by planting a cluster of spears in front of a sleeping elephant and then kicking them in the trunk to cause them to charge and impale themselves. Even so,a small band of hunter-gatherers can't afford to take many chances in the process of acquiring lunch. Judging by the bones, much of the time they stuck to eating turtles.

By BlindSquirrel (not verified) on 02 Apr 2008 #permalink

So they did die out from exhaustion building all those huge the pyramids (as depicted in 10,000BC)?!!

a sleeping elephant

Forest elephants are rather solitary, aren't they? Mammoths seem to have lived in herds... Also, don't pygmies use poisoned spears? I don't think there are any poisonous plants in a mammoth steppe.

By David Marjanović (not verified) on 04 Apr 2008 #permalink

You know, every time I read about the demise of the mammoths and the other Pleistocene megafauna, I am struck by the almost desperate efforts made by paleontologists and archeologists to come up with some sort of alternative reason for their extinction, other than the MOST obvious, and that is they were quite simply killed and eaten. I have heard and read all the arguments, all the discussions, but yet, at the end of the day, every single alternative theory is proven demonstrably false. Every one, and every time!

Let's look at each in turn that I am aware of.... First, the collapse of the 'mammoth steppe' environment theory. the 'mammoth steppe' is an environment that was CREATED by mammoths, and depended upon mammoths to survive (much like the African savannah today). All the studies showing the progressive loss of the 'mammoth steppe' as being a cause for the extinction of the mammoth, should simply turn this scenario on its head, as being indicative of the loss of mammoths to maintain the environment, not the other way around. And of course, with the loss of this environment and the mammoths that created it, comes the loss of all the other species as well (and the same thing can happen in Africa with the loss of elephants). There is not one plant species described for the 'mammoth steppe' that is not still extant, and mostly in the same places they have always been; it is simply a matter of not having the environment altered periodically by herds of mammoths trundling through that prevents them from establishing themselves as densely as during the Pleistocene.
A corollary of this argument regards the specialization of the mammoths themselves, and that they somehow were restricted to the 'mammoth steppe' because of their dietary requirements. In fact, mammoths in North America were found from Alaska, all the way down to Florida, Mexico and Central America, which covers a HUGE range of biotic ecologies, vegetation types, relative rainfall, etc, etc. In other owrds, mammoths were not particularly exclusive to ANY particular environment, but could live almost anywhere there was some sort of vegetation. What IS true is they were not fond of dense coniferous forests or jungles, but surprise, surprise, there was ANOTHER proboscidean that DID, and that is the American Mastodon, and its bizarre relatives, the Gomphotheres. In other words, if the environment gets increasingly bad for mammoths for some reason, it gets BETTER for mastodons, which means that the spread of the boreal forest after the last glaciation SHOULD have been bonanza time for mastodons, but of course, THEY went extinct at the same time too. Finally, given the amazing ability of mammoths and other large herbivores to travel large distances in search of food, there seems to be no reason in the face of changing environmental conditions for them to not simply GO SOMEWHERE ELSE (which is what elephants do). For some reason, paleontologist seem to 'skip over' this bit when examining the changing ecology of their favored digging sites, as if the ability to travel hundreds, or even thousands of miles is somehow negligible (and you can still see the migrations of the herds happening today in Africa, and among the caribou, and the bison too!)!

The next argument for extinction involves extinction caused by the spread of diseases caused by animals migrating from Asia to North America and South America and vice versa..... First off, these kinds on interchanges and migrations had been taking place for MILLIONS of years prior to the end of the Pleistocene, and while certainly some animals came into competition for which they were not suited and became extinct, MOST did quite well in their new environments and continued to spread. Yes, there is always a possibility that a 'new' disease could be introduced, and probably did on occasion. However, all historical evidence shows that in such cases, there will be a quick die-off, but then there are always SOME animals that are resistant to those diseases, and will very quickly reproduce to 'fill in' the population gap in just a few generations. Paleontologically and geologically speaking, such a 'blip' is almost unnoticeable in the fossil record, which is why there is no fossil evidence for it EVER happening! Even in historical times, such terrifically fatal things as small pox, measles, etc introduced to North America did not 'wipe out' the native Americans, and they bounced back quite quickly within just a few generations. Once again, this a 'theory' with no legs!

The third (and most recent) theory for the megafauna extinctions can perhaps best be described as 'astronomical interventions' by comets, asteroids and the like. While there is some evidence for a possible meteor strike in Canada around that time, it was certainly not on the scale of the asteroid that finished the dinosaurs at the end of the Mesozoic, and had almost no impact at all on the many other species that are still extant (and from the fossil record, it appears it had little impact on the mammoths either). This particularly to be in evidence when looking at both mastodons living in South America, as well as mammoths (and mastodons) living in Asia, where there is virtually NO evidence for such an astronomic catastrophe (as against the end of the Mesozoic, where the 'KT Boundary is evident world-wide).

So there you have it, there is NO ecological or environmental reason why mammoths and the rest of the Pleistocene megafauna should not be alive and well, but for ONE difference, and that difference is MAN and his technology.

Which leads me into another point, this time giving a slap to the Archeologists..... For some reason, Archeologists have always equated a bit of technology with culture, as if someone with a can opener in China is somehow in the same culture as an Englishman with the same sort of can opener. Nothing could be further from the truth!!!! Technology exists almost in exclusion to culture, and technology spreads like wildfire, across cultures, terrain, religion, you name it. THERE IS NO CORRELATION BETWEEN CULTURE AND TECHNOLOGY!!! So when you read learned articles about 'Clovis people lived here, and spread there,' or anything along those lines, that is absolute RUBBISH!!! Tool technology transfers very quickly, and a very successful tool type will fly across the world in no time, and even in ancient times. further, such tools and technology are ALWAYS subject to local interpretation for local purposes. In other words, just because some Europeans invented a really good point for hunting large animals (Solutrean), does NOT mean those people had to make the journey all the way across the Atlantic ocean for a similar large point to appear in North America. Instead, one of TWO thigs can happen, either A, the tool design travels from band to band who find it useful, all across the 'mammoth steppe,' or B, there are intelligent people here who come to the same conclusion about what is needed to bring down a mammoth (Clovis). There is NO reason for physical travel of any particular people, as long as trading and other social relationships continue to exist.

So what is the point of all this? i think the main point is that there is FAR more to be learned by examining the current batch of scientists, their motives, agendas and biases, than there is to be learned by examining extinct animals!!

By Eric Husher (not verified) on 11 Jan 2009 #permalink

If a small hunting band wanted an abundant supply of fresh tender meat with a relatively small risk, they may realize that the above conditions could be met by following a pregnant mammoth until at the time of birth. Then to quickly dispatch the youngster and run off to a safe place until the parent realized her young was dead and left the scene. Then the hunters could return to butcher the "veal" like animal and consume it before the meat spoiled.
Under this scenerio, a small population of hunters with low technology could cause mammoths would die out in a local are in one generation.

By Jerry Meyer (not verified) on 25 Nov 2009 #permalink