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Apparently, even pre-industrial humans were environmental villains. A new study blames our ancestors for starting global warming by wiping out the mammoths. From the story:

Mammoths used to roam modern-day Russia and North America, but are now extinct—and there’s evidence that around 15,000 years ago, early hunters had a hand in wiping them out. A new study, accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union (AGU), argues that this die-off had the side effect of heating up the planet. “A lot of people still think that people are unable to affect the climate even now, even when there are more than 6 billion people,” says the lead author of the study, Chris Doughty of the Carnegie Institution for Science in Stanford, California. The new results, however, “show that even when we had populations orders of magnitude smaller than we do now, we still had a big impact.”

How did we do that?  By killing the mammoths, we let birch trees take over grasslands, because the mammoths weren’t there anymore to kill the saplings.  (What about the rights of the trees against the pachyderms?  Doesn’t anybody care about that?)
The trees would change the color of the landscape, making it much darker so it would absorb more of the Sun’s heat, in turn heating up the air. This process would have added to natural climate change, making it harder for mammoths to cope, and helping the birch spread further.

And that means we have impacted the planet much earlier than thought:
Earlier research indicated that prehistoric farmers changed the climate by slashing and burning forests starting about 8,000 years ago, and when they introduced rice paddy farming about 5,000 years ago. This would suggest that the start of the so-called “Anthropocene”—a term used by some scientists to refer to the geological age when mankind began shaping the entire planet—should be dated to several thousand years ago. However, Field and colleagues argue, the evidence of an even earlier man-made global climate impact suggests the Anthropocene could have started much earlier. Their results, they write, “suggest the human influence on climate began even earlier than previously believed, and that the onset of the Anthropocene should be extended back many thousands of years.”

If so, good for us.  The warming temperatures made it so we could grow more food, populate greater portions of the earth, and eventually thrive to the point that we could step beyond naked evolution and exert some control over our environment.

But we aren’t exceptional.  No, not us.  Still, we have been causing the earth to warm for thousands of years, and that would seem to mean we changed the course of evolution itself.  That’s pretty remarkable for  just another animal in the forest.

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