Did sexist white males cause the extinction of the woolly mammoth, or was it climate change?

Ever since 3,599 years ago humans have been asking the question "Why did our furry elephant go extinct?"

What caused the woolly mammoth's (not to be confused with the also-woolly mastodon) extinction? Climate warming in the Holocene might have driven the extinction of this cold-adapted species, yet the species had survived previous warming periods, suggesting that the more-plausible cause was human expansion.
The woolly mammoth went extinct less than four thousand years ago. The bones of miniaturized woolly mammoths have been found in Siberia dating to about 3,600 years ago. Indeed, woolly mammoths, the furry elephant of the north, was around recently enough that it overlaps with the invention of writing by humans, and is depicted in a drawing on the wall of at least one example of a dynastic Egyptian building, along with a number of other unusual (for Egypt) but perfectly real animals.

There are all kinds of reasons why an animal may go extinct, but the case of the woolly mammoth may be linked to a broader phenomenon ... a mass extinction event that happened during the latter part of the Pleistocene. The woolly mammoth is one of several members of the exclusive megafauna set of mammals (and some non-mammals) that seem to have gone extinct over the last few thousand years, across the globe. The giant ground sloth, various giant armadillo like creatures, the mastodon (like the mammoth, an elephant), a giant bear, camels, horses, a giant buffalo ... in Australia, various giant wombats and kangaroos, and at least one giant lizard and one giant snake ... have all gone extinct over the last few hundred thousand years or so, with what seems to be a distinct concentration in the last few tens of thousands of years.

It is the case that humans seem to have appeared on the scene just about the same time as this or that extinction, and this has led many to to say "J'accuse, Homo sapiens ... It is YOU who have made these animals become EXTINCT!" in a thick French accent.

However, this may be a case of improper species profiling. Now, don't get me wrong. I'm not totally against species profiling when National Security is at stake. We don't really know that the Medfly will destroy all the crops in California if it is let to reproduce wantonly in the Sunshine State, but other, very similar fruit flies have proved a bane for our fruit and thus we are justified in a certain degree of prejudice. Also, it has become fashionable, and probably for good reason, to link humans with arbitrary bad things. Indeed, the extinction of our furry former friends the Woolly Mammoth would have been caused by sexist white males. So, an accusation like this may be likely to go unquestioned.

So, humans have often been on the scene of extinctions, sometimes even with a sort of smoking gun .... whereby by the last few known examples of a particular species are found in food middens or to have the marks of human butchery tools on them ... but in other cases, there is not a clear link between the humans and the extincting species. In some cases, there has been what looks like a reasonable circumstantial case, where humans are "known" to have arrived on a certain continent, say North America or Australia, at a certain "time" and just about that "time" some "species" just "happens" to go "extinct." Get the picture? But any time any such argument was made prior to recent years, subsequent research has demonstrated that the "time" of either human arrival or the disappearance of the presumed victim is not what was previously estimated, and what looked like a good correlation between human shenanigans and species disappearance de-correlated and the story fell apart under intense questioning.

What has happened recently, of course, is that we have given up on thinking we know when humans entered the New World or Australia. (If you think I'm wrong about that, let me know, we'll talk...)

In working out the possible involvement of humans ... white males or otherwise ... one must give fair consideration to the alternatives. One step in the right direction might be to reconstruct the history of suitable habitats for the species in question, and to examine the pattern of habitat availability over time. If the species in question happens to go extinct because its habitat vanished, this may be quite visible in the ancient record, and we might be able to exonerate humans.

Ah, but things are never so simple. If humans are known to be hunters of a certain species, then we would expect that habitat reduction would simply increase the likelihood that humans were directly involved, because humans would be less likely to wipe out a widespread species than a rare species confined to certain limited habitats. (On the other hand, if the much ensmallened habitat of a nearly vanished species happens to be in a place where there are very few humans, this may provide the humans with a sort of alibi.)

A paper just out in PLoS examines this question. There is good news and bad news about this paper. The good news is that it is well done and definitively answers the question: What was happening with woolly mammoth habitats at the time of their extinction? The bad news is that this paper only looks at the last major cycle of habitat loss due to "natural" climate change, and does not look at earlier cycles which could not have involved humans. Also, this exact sort of analysis needs to be done with many other habitat/species sets. In this way, having models for several habitat species sets over several Pleistocene cycles, we can seek patterns, and we can begin to compare what happens with humans vs. without humans in the picture

From the paper:

...In this study, we combined paleo-climate simulations, climate envelope models (which describe the climate associated with the known distribution of a species--its envelope--and estimate that envelope's position under different climate change scenarios), and a population model that includes an explicit treatment of woolly mammoth-human interactions to measure the extent to which climate changes, increased human pressures, or a combination of both factors might have been responsible. Results show a dramatic decline in suitable climate conditions for the mammoth between the Late Pleistocene and the Holocene, with hospitable areas in the mid-Holocene being restricted mainly to Arctic Siberia, where the latest records of woolly mammoths in continental Asia have been found. The population model results also support the view that the collapse of the climatically suitable area caused a significant drop in mammoth population size, making the animals more vulnerable to increasing hunting pressure from expanding human populations. The coincidence of the collapse of climatically suitable areas and the increase in anthropogenic impacts in the Holocene are most likely to have been the coup de grace, which set the place and time for the extinction of the woolly mammoth.

The map of diminishing envelope looks like this:

View larger image

We are left still not knowing what happened to the Woolly Mammoth. It is tempting to assume that once their range was restricted, humans would have easily finished them off, but the area to which their range was restricted probably never had that many humans living in it. Simple range restriction followed by any one of a number of bits of bad luck would have done it.

The technology to bring the Woolly Mammoth back is almost within reach. We should start thinking about that as an option. Just for fun.

Related posts from other blogs:

Not Exactly Rocket Science: Climate change knocked mammoths down, humans finished them off
A Blog Around the Clock: So, why did the mammoths REALLY go extinct?

Source:

(Sorry for the odd formatting ... this is an automatically generated reference that allows important inter-tube magic to happen so I don't want to mess with it...)
Nogués-Bravo, D., RodrÃÂguez, J., Hortal, J., Batra, P., Araújo, M.B., Barnosky, A. (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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