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sabato 15 agosto 2015

Humans caused giant ancient mammal extinction

(Image credit: Thinkstock)
The largest mammals ever to roam the earth, a group of gigantic ancient mammals known as megafauna, were wiped out by human activity and not as the result of a changing climate, new research from experts at a quartet of prominent UK universities has revealed.



Lead investigator Lewis Bartlett from the University of Exeter, along with colleagues from the universities of Cambridge, Reading, and Bristol, state that their findings conclusively prove that mankind was the dominant force that wiped out the massive creatures over the last 80,000 years, although they also noted that climate change may have also played a minor role.
Bartlett’s team used advanced statistical analysis, running thousands of scenarios mapping the different ranges of times during which each species is known to have become extinct, as well as when humans were known to have arrived in different parts of the world. The authors then took that data and compared it to climate reconstructions from the past 90,000 years.
The results of their analysis show beyond a reasonable doubt that man was the main reason these creatures were wiped out, as the correlation between the spread of humans and the extinction of different species show that the former was the main cause of the latter.
How and why humans caused megafauna demise remains unknown
In a statement, the researchers explained that humanity was “the main agency causing the demise [of megafauna], with climate change exacerbating the number of extinctions.” In Asia and other parts of the world, however, they found patterns of species loss that couldn't be accounted for through either of these two catalysts and require additional analysis.
“As far as we are concerned, this research is the nail in the coffin of this 50-year debate,” Bartlett said. “Humans were the dominant cause of the extinction of megafauna. What we don’t know is what it was about these early settlers that caused this demise. Were they killing them for food, was it early use of fire or were they driven out of their habitats? Our analysis doesn’t differentiate, but we can say that it was caused by human activity more than by climate change. It debunks the myth of early humans living in harmony with nature.”
“Whilst our models explain very well the timing and extent of extinctions for most of the world, mainland Asia remains a mystery,” added Dr. Andrea Manica. the lead supervisor on the paper. "According to the fossil record, that region suffered very low rates of extinctions. Understanding why megafauna in mainland Asia is so resilient is the next big question.”
The findings have been published in the journal Ecography.




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