A brand new study published in June supports my longheld conviction that humans are the primary cause of late Pleistocene megafauna extinctions. This paper, co-authored by Chris Sandom and others, is the first of its kind. Other studies of late Pleistocene megafauna extinctions examined data on a regional scale but Sandom’s study reviewed global data. They looked for correlations between extinctions and both climate change and human expansion. Extinctions were closely correlated with human colonization but little correlation was found between extinctions and climate change, although there was a weak correlation between climate change and extinctions in Eurasia. The authors of this study identified 177 species of mammals, weighing over 20 pounds, that had become extinct between 132,000 BP-1000 BP. They disregarded data more recent than 1000 BP because extinctions caused by humans during this time period are an historical fact. The climate data included rates of change in average annual temperatures and precipitation and temperature and precipitation anomalies between 20,000 BP-the present day. Data from between 132,000 BP-20,000 BP lend even less support for a correlation between climate change and extinctions.
The researchers found the introduction of humans into new regions was always associated with high rates of extinctions. In regions such as Africa, Europe, and southern Asia; where humans or archaic humans have long been present, extinctions were lower. Africa suffered just 18 late Pleistocene extinctions, Europe had 19, and Asia had 38. However, in regions where mammals evolved without the presence of hominids, extinction rates were high upon the entrance of man. South America had 62 late Pleistocene megafauna extinctions, North America had 48, and Australia had 26. Southeastern North America was a hotspot of anthropogenic-caused extinctions and so were southern South America, southern Australia, and western Europe. Texas had 1 of the highest number of extinct species with 33, while Uruguay suffered the highest rate of extinctions at 78%. Climate has changed little over the past 20,000 years in southern South America, yet this region suffered the highest rates of extinction of any.
Map showing correlations between human expansion, climate change, and extinctions. In this study megafauna extinctions were correlated with human expansion rather than climate change, and southeastern North America was a hotspot of anthropogenic-caused extinctions.
Some scientists hypothesize that animals living in regions devoid of humans are naive to the threat posed by human hunters. This supposedly explains why Africa and southern Asia had lower rates of extinctions than other regions. Animals living there knew to avoid man and to take aggressive action or flee when confronted by people. Other scientists suggest tropical diseases kept human populations lower in Africa and southern Asia, thus explaining the higher survival rates of large mammals in these regions. Probably, both explanations are valid, but I think the second is the greater factor. Animals are smart enough to quickly learn the danger of man. I’m certain American megafauna didn’t stay naive for more than 1 generation. Vast areas of Africa and Asia remained uninhabitable for millennia, thanks to such tropical diseases as malaria, and I think this is the better explanation for the greater survival rates of megafauna there. The abundance of wildlife in the Chernobyl Exclusion Zone (See: https://markgelbart.wordpress.com/2011/10/28/the-chernobyl-exclusion-zone/) shows just how detrimental the presence of humans is for large wild animals–it’s worse than radiation poisoning.
Southeastern North America had a pleasant temperate climate during the late Pleistocene, and it was blessed with plenty of natural resources. It’s likely human populations increased more rapidly here than in any other region of the continent. As the human population increased, large mammal populations decreased here. I really wish I could have seen Georgia’s natural environment before people ruined it.
Sandom, Chris; et. al.
“Global Late Quaternary Megafauna Extinctions Linked to Humans, not Climate Change”
Proceedings of the Royal Society of Biological Sciences June 2014