Megafauna extinction: Man or climate?

Next up in the fight between Man and Earth: overhunting and climate change battle it out to see who was responsible for the extinction of Pleistocene Megafauna.

Size comparison of mega fauna

Megafauna are giant animals, typically weighing more than 44kg, that were successful across Eurasia, America and Australia during the Pleistocene (which lasted from 2.6 - 0.1 million years ago). The Quaternary extinction event saw the loss of many of these large beasts, at the same time as the last ice age. The extinctions of animals such as giant kangeroos, woolly mammoths, bear sized wombats and huge armadillos spanned from 40,000 years ago to as recently as 10,000 years ago. 

Woolly Mammoth

The last American glacial maximums were between 30,000 - 14,000 years ago in North America and 12,500 - 11,800 years ago in South America, as discussed in 'American megafaunal extinctions'. The latest ice age in Australia reached a maximum around 21,000 years ago. Climate is therefore a strong contender for the changing conditions and subsequent loss of life during the Megafauna extinction event. 

It is however no coincidence that humans were radiating out of Africa at this time, from around 70,000 years ago, spreading through Asia, Australia and finally America where tribes set up in megafauna territories. Africa has retained many species of megafauna, unlike in other continents, which could be because the species here had longer to learn and adapt to homo sapiens, whereas other encounters between man and megafauna across the globe happened more rapidly, giving species less time to adapt. The human hunting of these large targets is a likely cause of their extinction.

Migration pattern of homo sapiens out of Africa

Humans are thought to have contributed to extinctions due to factors other than hunting; human lit fires, which in Australia are believed to have been used to clear pathways through the bush, are another way humans could have impacted the climate and habitat of the areas they first colonised. This was discussed by Cheryl Jones in 'Early humans wiped out Australia's giants', 2010.

Controversially, Research led by the University of New South Wales last year suggests that megafauna extinctions in Australia were caused by climate change alone, rather than human influences. They state there is a lack of evidence of that humans hunted megafauna, and that by the time Aboriginal tribes arrived in Australia there were less than 20 megafauna species left. 

This is where the timing of extinctions and arrival of homosapiens becomes important; if the majority of megafaunal extinctions happened before humans emerged from Africa then climate change must have been the cause of extinction. Although if the emergence of homo sapiens matches the time these giant species went extinct then humans could be responsible. 

It may be that the onset of a colder climate had already altered vegetation and reduced the number of viable habitats, threatening larger species, but hunting by humans was the final blow. The two factors go hand in hand as climate change may have been the driving force of human migrations out of Africa.

The global scientific gathering met earlier this year to discuss this topic at the Oxford megafauna conference. They concluded that hunting by humans was a 'decisive factor' in the megafauna extinctions.

Want to see what some of these giant beasts would have looked like? Check out the megafauna video.