What caused the extinction of so many large animals across the world in the late Quaternary? Many scientists think humans and/or climate change were responsible.
In 2014 researchers Sandom, Faurby, Sandel, and Svenning carried out an analysis of available data on extinct animals and the weather. They concluded that although climate change had an impact in Eurasia, it was not a pervasive cause at global level. They think the widespread extinctions were mostly due to the spread of human species out of Africa.
The researchers looked at data on 177 mammal species weighing 10kg or more and that died out between 132,000 and 1,000 years ago. They examined temperatures, rainfall and the presence of humans in the mammals’ territory. The study coverered 229 countries and excluded islands, glaciated countries and Antarctica.
Earlier humans off the hook?
Our species (homo sapiens) and our relatives the Neanderthals, the Denisovans and Homo Erectus were included in the study. The scientists wanted to know whether extinctions were more severe in areas where homo sapiens were the first humans on the scene. It’s widely thought that as older human species gradually co-evolved alongside megafauna over thousands of years they may have had less of an impact.
After running the data, the scientists concluded that the spread of moderns humans had significant effects on megafauna and that the most severe extinctions were in the homo sapiens-only region. They wrote:
“This analysis illustrates that the late Quaternary megafauna extinctions were strongly linked to hominin palaeobiogeography and only weakly to glacial-interglacial climate change. The relationship between hominin palaeobiogeography and extinction magnitude is striking, with universally low extinctions in sub-Saharan Africa (maximum 13%), where hominins and the megafauna have long coexisted, but widespread exceptionally high extinctions in Australia and the Americas, where modern humans were the first hominin present.”
Carrying out an analysis of data from across the world meant that the scientists could compare extinctions in areas that had similar levels of climate change. South America and sub-Saharan Africa had similar levels of climate change. South America had high extinction rates and in sub-Saharan Africa the losses were “minimal.”
The researchers found severe levels of extinction in regions of North America that were “relatively climatically stable.” They note that despite maintaining its Ice Age chaparral vegetation, familiar food for herbivores of the day, California lost 21 megafauna species.
Overkill alone not to blame?
Many people think that humans couldn’t be responsible for wiping out so much of the world’s megafauna. One reason is that the early proposers of the human theory argued that “overkill,” excessive hunting, caused the megafauna extinctions. Critics say there is not enough archaeological evidence, such as butchered bones, from prehistoric human sites to support this.
Of course, as the article’s authors point out, excessive hunting is not the only way to drive a species to extinction. Scientists now suggest that humans could have killed the megafauna by changing habitats and by starting fires. Compared to the timescale of a human lifetime, the megafauna extinctions happened relatively slowly. Some species took centuries to go extinct. I imagine this may support the idea that they suffered from habitat loss.
The findings were shared in an article “Global late Quaternary megafauna extinctions linked to humans, not climate change.” It’s a fascinating read, so take a look if you can by clicking on the link.