Did we do it or was it just a coincidence? That's what two groups of researchers are arguing with regards to the demise of mammoths, sabertooth cats, giant ground sloths, horses and other "megafauna" that roamed the Americas when humans wandered over from Asia.
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A team of Australian scientists led by Chris Johnson of the University of Tasmania is arguing that there are serious flaws in recent work by two Brazilian researchers that exonerates humans. The pair that did that work, Matheus S. Lima-Ribeiro and José Alexandre F. Diniz-Filho of the Universidade Federal de Goiás, have answered that nope, their work isn't perfect, but still gets humans off the hook.
"They find that in many places megafauna were apparently extinct before humans arrived; in many others, megafauna coexisted with humans for thousands of years before going extinct," writes Johnson and company in the Oct. 2 issue of the journal Quaternary International. "They conclude that human impact made at most a minor and geographically restricted contribution to megafaunal extinction."
Johnson argues that the Brazilians' conclusions are off because they messed up the dating of fossils and extinctions. They re-analyzed the same data and reached the opposite conclusion: the demise of the big animals followed the arrival of humans by about one or two thousand years. That figure meshes with what models predict in terms of how long it would have taken humans to kill and consume so many animals.
But the Brazilians aren't budging, much.
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"...We are...aware that our approach is not necessarily the best, final way, either to deal with such uncertainties or to solve the puzzle of" the megafuana extinctions, the Brazilians responded, in the same issue of the journal. They go on to defend their conclusions and produce yet another analysis of the data that supports their original conclusion: that the timing is wrong for humans to have wiped out all those beasts.
Who is right? Heck knows. It's a bit of a ping-pong game for those of us watching from the sidelines. But it's just one of those examples of how science works and is played out in the pages of journals. Someday we might have more clarity on it, but for now, we just have to enjoy the game.
Image: Dire wolves battle a saber tooth cat over a carcass in ice age California. (Robert Bruce Horsfall (1913), Wikimedia Commons)