Thursday, 3 January 2013

Unravelling the Mystery Behind the Extinction of the Woolly Mammoth

In past blogs we have looked at the various different factors that could have potentially caused the extinction of megafauna during the Late Quaternary. We have also looked at some examples of megafauna that became extinct, as well as looking at reasons behind extinction patterns in the continents of Africa and Australia. We are sadly almost coming to an end of ‘The Might of Megafauna Reasons for Mass Extinction’, however in this blog I will like to explore the mystery behind the extinction of one of the most renown megafauna; the woolly mammoth.

Mammoths are common mammals
 in popular film. Examples include;
Manny in Ice Age
If you ask anyone to name a species of extinct megafauna they generally say ‘the woolly mammoth’.  In fact, the mammoth is frequently shown on popular films such as Ice Age or 10,000 BC, which both show the various natural and anthropogenic forcing factors that could have driven its extinction. The woolly mammoth (Mammuthus primigenius) was a herbivorous mammal that inhabited  the open steppe-tundra’s of Eurasia and North America from late Middle Pleistocene 300 ky BP. The species survived through different climatic cycles until they vanished during the Holocene around3.6 kr BP (Nogues-Bravo et al 2008). If you look at my previous blog; 'Some examples of extinct megafauna in relation to climate and human impacts', it is apparent that the causes of extinction for the woolly mammoth are unclear. The last area in which they inhabited was Wrangel Island in Arctic Siberia, and the most likely explanation for their disappearance has mostly focused on climatic and anthropogenic forcing mechanisms. Both these mechanisms alone are credible causes of extinction (as we have seen in past blogs), but a combination of climatic changes and increased human pressures might provide a better explanation of the extinction of this species.

Could a combination of Climate and Man be responsible
for the extinction of the mammoth?
The proposal that climate was responsible for the extinction of the woolly mammoth is reinforced by Nogues-Bravo et al (2008) who found that suitable climate conditions for the mammoth reduced drastically between the Late Pleistocene and the Holocene resulting in 90% of it is geographical range disappearing between 42 ky BP and 6 ky BP. Such climatic extremes would have caused a significant decrease in the mammoth’s population size, and consequently would have made them more vulnerable to extinction when hunting occurred. There is also a correlation between the reduction of climatically suitable areas, an increase in anthropogenic activities (probably driven by increased population densities) and the gradual disappearance of the woolly mammoth. Many people believe that the warming of the climate during the Holocene was responsible for the demise of these great beasts, for example Ugan & Byers (2007) completely disregard the overkill hypothesis, believing that large climatic shifts would have caused the mammoth to die out. However, evidence shows that mammoths had previously survived period of warming, which suggests that a combination of climate and anthropogenic impacts might be more plausible mechanisms of extinction. Climatic warming resulted in mammoths moving to less hostile areas such as Arctic Siberia (where the latest recordings of mammoths have been found), which suggests that other factors must have contributed to the complete extinction of this species. Climatic oscillations are highly important to this debate as they would have modified the landscape and reduced the geographic range in which mammoths could survive.

I found this useful map in Nogues-Bravo et al 2008 showing the projected climatic suitability for the woolly mammoths Pleistocene and Holocene. The red areas indicate the climatic areas of suitability for mammoths. Black dots are records of mammoth presence. Black lines represent the northern limit of modern humans. 
The proposal that man played a significant part in the extinction of the mammoth are shown where human populations started dispersing across northern Eurasia around 40 ky BP (Nogues-Bravo et al 2008). Research carried out by Nogues-Bravo et al (2008) led to the creation of a model which combined changing climatic conditions and the intensification of human hunting using fossil records and climate simulations. Results from this investigation show that altering climate conditions was responsible for; reducing the distributional range of the mammoth, a decrease in the species population size, and ultimately an increase in the risk of extinction. When climate is combined with the intensification of hunting, the extinction of the woolly mammoth was inevitable. Nogues-Bravo et al also reveals that one woolly mammoth killed every three years by each human being in-habiting its distribution range would be sufficient to lead the species to extinction (2008). Similarly Haynes (2003) states that even low levels of hunting could eradicate a whole mammoth population. Therefore, human hunting alone had the potential to be solely possible for the extinction of the species; however there is lack of evidence (in the form of kill sites) which supports this belief.  Conversely, in the absence of human hunting, mammoths might have been able to survive in refuge spots (small climatically suitable areas) thus environmental change alone appears insufficient to account for such extinction patterns (Stuart 2005). Consequently the most widely held belief is that the synergy between the collapse of suitable climatic conditions combined with the northward increase in human population densities set the place and time of the mammoths extinction (Nogues-Bravo 2008). The likelihood of humans causing extinction of mammoths  through introducing new pathogens (hyper disease theory )is highlighted by Rothschild & Laub in 2006 (see hyper disease blog) . In this investigation, it was shown that the extinction of a particular type of mammoth was caused by human carried tuberculosis and found in 52% of the 118 skeletons surveyed. However, this theory lacks much needed evidence to support it, including proof of a disease that has the capabilities to wipe out an entire species.

As mentioned above, the youngest remains of woolly mammoths are found on Wrangel Island (7,000-4,000 yr BP). This example shows how mammoths managed to survive climatic changes largely due to the separation of the island around 12,000 BP which consequently altered local topography and climatic features, which permitted relictual preservation of communities of steppe plants (Vartanyan et al 1993). With this example, it is interesting to note that skeletal remains on the island were of dwarf mammoths probably because of the insularity effect, combined with a response to the general trend toward unfavourable environment during the Holocene (Vartanyan et al 1993). Research has shown that other areas e.g. Mongolia, might have been of suitable climatic conditions for mammoths to survive. No records of mammoth remains have been found in these regions, suggesting that mammoths remained in High Arctic Siberia (small geographic distribution), which would have challenged the survival of the species when faced with human hunting pressures.  It is also possible that climate might exacerbate human impacts (Wroe et al 2006), resulting in increased levels of hunting for survival.

Skeletal remains of a dwarf Mammoth found on Wrangel
In conclusion, a definite cause of extinction of the woolly mammoth has yet to be determined and will continue to be subject of debate for a very long time. Many believe the influence of climate was responsible for extinction, causing colder winters, warmer summers and drier conditions (Oard 2000), however the survival of mammoths into the Holocene as well as the adaptability (dwarfing) shown on Wrangle Island shows that this extinction process is complex. Glen MacDonald of the University of California (Nature Communications) stated that ‘findings dispel the idea of any one factor, any one event, as dooming the mammoths’. This reinforces evidence to suggest a multitude of factors can be linked to the demise of the mammoths. Overall, I strongly believe that habitat change (caused by shifting climate) would have decreased the population of the species and would have driven mammoths to areas such as Arctic Siberia. This, combined with human pressures (hunting practices) provides a strong explanation for the extinction of the woolly mammoth.

The link below gives a great overview of the mammoth mystery:

Remains of a mummified baby woolly mammoth named Lubya


  1. Hi Josh
    Interesting post - as you say the Woolly Mammoth is possibly the most widely known example of megafaunal extinction.

    Do you personally believe this was due to a combination of anthropogenic and climatic effects? Or do you think the evidence behind one is more heavily weighted? For example that anthropogenic effects were greater, as increases in human populations lead to more hunting but also more manipulation of their environment and resulting changes to the climate.
    I also thought that both of these may be responsible for population decline; but the resulting low genetic diversity could have been a large factor in their dying out at this stage.


  2. Hi Harriet,

    Haha yeah, everybody loves the mammoth!
    Personally I believe that the extinction of the woolly mammoth was caused by a combination of factors. I believe both Climate and anthropocentric effects are interlinked, and therefore it is hard to say that one has more weight then the other. As mentioned in the blog, Homo Sapiens had the ability to easily wipe out the mammoth, however the lack of evidence (in the form of kill sites) supporting this belief makes me believe that climate was (in part) responsible. Yes, you are completely right, having a low genetic diversity may account for the extinction of mammoth. However it would take a forcing factor (such as the climate system or human overkill) to really push the species into extinction. Therefore, climatic instability, human overkill and having a low genetic diversity would have made the extinction of the mammoth almost inevitable.

    Hope this helps