The fate of the woolly mammoth and other megafauna of the last ice age has long been under debate in the scientific community. The megafauna under question, in addition to the woolly mammoth, include the Irish elk and European elephant among others. The two leading hypotheses as to what caused their extinction are the ‘overkill’ hypothesis in which early humans hunted these beasts to extinction and the climate change hypothesis where changes in climate lead to their extinction.
In the past, the overkill hypothesis has been favoured by most scientists but the climate change hypothesis has been gaining traction very fast due to recent studies. One of the most notable of these studies is one conducted by Alan Cooper and colleagues at the University of Adelaide.
The team was able to extract small samples of DNA from fossils of the megafauna and used radiocarbon dating to estimate how old the fossils were. Comparing the DNA of several fossils of the megafauna, they found out that several fossils that were once thought to be of one species are actually of several different but closely related species.
Using radiometric dating they found several small extinction events, which resulted in species turnover. The overkill hypothesis was generally accepted because these mini extinctions hadn’t been previously identified until the use of DNA analysis. But why do these mini extinction events suggest climate was the cause of extinction? The answer lies in climate change itself.
The small extinction events occurred during warming periods rather than cooling periods, which was previously thought. According to climate data, during the end of the last ice age, global temperatures fluctuated a lot. The temperatures would rapidly increase in a few decades time then gradually decrease over the next 1,500 years. The cycle would then repeat. These warming and cooling events are known as Dansgaard-Oescheger events or D-O for short. Apparently there were around 25 of these events at end of the last ice age.
The mini extinction events occurred during the warming period of these D-O cycles. Cooper and his colleagues think a combination of rapid warming and increased human activity (including hunting) caused the extinction of many of the megafauna.
It is a well known fact that larger animals do not fare well in warm weather, especially the woolly mammoth which is adapted for much colder climates. Large animals like the woolly mammoth and Irish elk have very long gestation period and maturity time making it very difficult for them to adapt to changing climates. These large scale climate fluctuations would have been very difficult to deal with. Partner this fact with increasing human populations and it is no surprise many of these large animals went extinct.
This study suggests that climate had a much bigger effect on the extinction of ice age megafauna than previously thought. It doesn’t disprove the overkill hypothesis but suggests humans had a smaller impact than previously though. The study was published in the journal Nature.