Quaternary extinction event: climate change or humans?

      During the Late Quaternary period (last 50,000 years) mass megafauna extinctions occurred throughout Eurasia, Australia, and the Americas.  These extinctions coincide with the ending of the last ice age and the global expansion of modern humans (Homo sapiens sapiens). 

     As a result there has been consistent debate over whether climate change or human hunting and disease transmission caused what is known as the Quaternary extinction event.

     Research by Lorenzen et al. recently published in Nature analyzed ancient DNA, species distribution models and the human fossil record to understand how climate change and human expansion impacted the demographic history of species that suffered extinctions during the Quaternary and species that had their ranges significantly reduced.  The researchers focused on four different time periods in between 42,000 and 6,000 years ago. 

    The results suggest that the Quaternary extinction event must be understood on a species-specific basis.

Wooly rhinoceros (Coelodonta antiquitatis)

     For example, the woolly rhinoceros (Coelodonta antiquitatis) seemed to have suffered extinction solely as a result of climate change, however ground sloths (Megatherium) and giant armadillos (Glyptodon) suffered extinction as a result of human encroachment.  Musk oxen (Ovibos moschatus) suffered range reduction as a result of climate change, however range reduction for the wild horse (Equus ferus) seems to have been strongly influenced by humans. 

     There was no specific genetic makeup, taxa, range type or continental location that could be specifically correlated with climate change or anthropogenic effects.  However all fauna obviously had large size in common.      

    The team concluded that these results indicate that different species respond in vastly different ways to climate change, habitat redistribution and human encroachment.  In short, one variable, whether it is climate change or human encroachment, will never be able to explain an entire extinction event, which effected thousands of different species on several continents.

     However, this study also confirms that anthropogenic effects are not only changing global ecosystems in the present day, but have also played an important role in shaping global ecosystems of the past.

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Lorenzen et al.  2011.  Species-specific responses of Late Quaternary megafauna to climate and humans.  Nature 479: 359-364