Sunday, September 26, 2010

Volcanoes Responsible for Neandertal Extinction?

National Geographic has picked up a story in which it is argued that the European populations of Neandertals became extinct because of the environmental degradation caused by a number of large volcanoes that erupted over a very short period of time around the Würm interglacial. The author, Ker Tan writes:
The researchers examined sediments layer from around 40,000 years ago in Russia's Mezmaiskaya Cave and found that the more volcanic ash a layer had, the less plant pollen it contained.

"We tested all the layers for this volcanic ash signature. The most volcanic-ash-rich layer"—likely corresponding to the so-called Campanian Ignimbrite eruption, which occurred near Naples (map)—"had no [tree] pollen and very little pollen from other types of plants," said study team member Naomi Cleghorn. "It's just a sterile layer."

The loss of plants would have led to a decline in plant-eating mammals, which in turn would have affected the Neanderthals, who hunted large mammals for food.
The authors argue that the only reason modern humans did not become extinct is that they had "fallback" populations in Africa and Asia.

Some problems:
  • The most recent Neandertal remains at Zafarraya Cave are dated to around 26 ky BP, which means that Neandertals managed to hang around for between 15 and 20 thousand years after these eruptions. This does not argue for an extinction event of any kind, unless the Neandertal populations just dwindled away.
  • There are Neandertal and modern human remains pretty continuously throughout the tale end of the Early Würm glaciation and the Late Würm glaciation (the Würm interglacial was between 34 and 37 ky BP), suggesting that, while the volcanoes may have erupted around this time, their impact may have been limited.
I will be curious to read the Current Anthropology article when it comes out in October. CA is one of the rare journals that not only publishes articles, it also publishes commentary on those articles.

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