Sunday, August 14, 2016

yes George, your species IS a planet-scraping biological weapon, period.


Guardian |  A few months ago, a well-publicised paper claimed that the great beasts of the Americas – mammoths and mastodons, giant ground sloths, lions and sabretooths, eight-foot beavers, a bird with a 26-foot wingspan – could not have been exterminated by humans, because the fossil evidence for their extinction marginally pre-dates the evidence for human arrival.

I have never seen a paper demolished as elegantly and decisively as this was at last week's conference. The archaeologist Todd Surovell demonstrated that the mismatch is just what you would expect if humans were responsible. Mass destruction is easy to detect in the fossil record: in one layer bones are everywhere, in the next they are nowhere. But people living at low densities with basic technologies leave almost no traces. With the human growth rates and kill rates you'd expect in the first pulse of settlement (about 14,000 years ago), the great beasts would have lasted only 1,000 years. His work suggests that the most reliable indicator of human arrival in the fossil record is a wave of large mammal extinctions.

These species were not just ornaments of the natural world. The new work presented at the conference suggests that they shaped the rest of the ecosystem. In Britain during the last interglacial period, elephants, rhinos and other great beasts maintained a mosaic of habitats: a mixture of closed canopy forest, open forest, glade and sward. In Australia, the sudden flush of vegetation that followed the loss of large herbivores caused stacks of leaf litter to build up, which became the rainforests' pyre: fires (natural or manmade) soon transformed these lush places into dry forest and scrub.

In the Amazon and other regions, large herbivores moved nutrients from rich soils to poor ones, radically altering plant growth. One controversial paper suggests that the eradication of the monsters of the Americas caused such a sharp loss of atmospheric methane (generated in their guts) that it could have triggered the short ice age which began about 12,800 years ago, called the Younger Dryas.

And still we have not stopped. Poaching has reduced the population of African forest elephants by 60% since 2000. The range of the Asian elephant – which once lived from Turkey to the coast of China – has contracted by 97%; the ranges of the Asian rhinos by over 99%. Elephants distribute the seeds of hundreds of rainforest tree species; without them these trees are functionally extinct.
Is this all we are? A diminutive monster that can leave no door closed, no hiding place intact, that is now doing to the great beasts of the sea what we did so long ago to the great beasts of the land? Or can we stop? Can we use our ingenuity, which for two million years has turned so inventively to destruction, to defy our evolutionary history?