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Sunday, Dec. 13, 2009

NATURAL SELECTIONS

How to survive a 'fearful age'?

If the habitat for humans goes seriously south, so too may our species


The other day I attended a preview screening of "The Road," the new film of Cormac McCarthy's post-apocalyptic 2006 novel of the same name.

It made for harrowing viewing, imagining a wasteland Earth from which, following an unspecified cataclysm, almost all life had disappeared. In that devastated environment, humans faced a terrible choice: Starve, or eat each other. It was a fun evening out.

There is clearly a morbid public appetite for destruction on the silver screen at the moment.

"The Road" has none of the computer-graphic, end-of-the-world porn of movies such as "2012" or "The Day After Tomorrow" — but it is far more affecting. The director, John Hillcoat, is on record saying that the themes in "The Road" resonate deeply in this "fearful age." He was referring, of course, not only to fears of global terrorism, but of climate change and mass extinction.

Whether we fear global warming enough to change our ways, however, is another matter — just as it is whether or not the current crop of disaster movies will have an effect on our behavior.

But "The Road" set me thinking about how humans might evolve in a climate-changed future. And a clue can be found from an ecological disaster in the distant past.

Whether we change our ways or not, most scientists agree that we're living in what has been called the "anthropocene" — an era of Earth's history in which humans are having a massive impact on the environment and ecosystems. It is also a time of sweeping extinctions.

We've had five mass extinctions since life on Earth began more than 4 billion years ago. The last one, called the Cretaceous-Tertiary extinction event, followed a meteor strike 65 million years ago that famously is blamed for wiping out the dinosaurs. The sixth one — the one happening now — is less obviously dramatic, but could be just as devastating. And, put simply, its cause is habitat destruction as a result of human activity.

Let's take the pessimistic view and assume that we don't change our energy-use habits quickly enough, and don't manage to find a way of getting carbon dioxide out of the atmosphere to prevent catastrophic global warming. How would we survive?

Billions wouldn't.

As to the rest, if you look at the biggest mass extinction in Earth's history, the Permian-Triassic extinction event 252 million years ago, you may get a good idea of where we might find sanctuary: Antarctica.

But that mass extinction event has been a bit of a puzzle. Unlike other mass wipeouts, it wasn't caused by a meteor impact. Many scientists now believe it was caused by global warming.

Humans weren't to blame back then — we hadn't evolved at that time. Instead, it's thought that a massive release of methane from the seabed, and volcanic activity in what is now Siberia, could have triggered global warming that rapidly heated the planet. Antarctica might have provided a haven of relatively cool land where mammals waited out the greenhouse effect.

The idea gains support from the discovery there of fossils of a new species of mammal suggesting that some land animals may have survived the Permian- Triassic extinction by living in cooler climates in Antarctica.

Jorg Frobisch of the Field Museum in Chicago, and colleagues, have named the new species Kombuisia antarctica. It belongs to a larger group of extinct mammal relatives, called anomodonts, that were widespread and were the dominant plant-eaters of their time.

"Members of the group burrowed in the ground, walked the surface and lived in trees," said Frobisch. It was considerably different from today's mammals. Turtle-beaked and the size of a domestic cat, it probably laid eggs like spiny anteaters and platypus do today.

"It's likely that it didn't nurse its young and didn't have fur, and it is uncertain whether it was warm blooded," said Frobisch's colleague, Kenneth Angielczyk.

Kombuisia antarctica was not a direct ancestor of living mammals, but it was among the few lineages of animals to survive that Permian-Triassic extinction event in which the fossil record shows millions of species — a massive 70 percent of terrestrial vertebrates and up to 96 percent of all marine species — went extinct.

Antarctica was in a different place 250 million years ago. Then a part of a supercontinent called Pangea that comprised all the land masses, it was located further north, was warmer and wasn't covered with permanent glaciers. But the refuge of Kombuisia antarctica in that region probably wasn't the result of a seasonal migration but rather a longer-term southerly shift of its habitat.

Fossil evidence suggests that small and medium-size animals were more successful at surviving the mass extinction than larger ones. This could be due to them having engaged in "sleep-or-hide" behaviors such as hibernation, torpor and burrowing in order to survive in a difficult environment.

It's interesting to speculate that this is the way the human species may evolve in the distant future. Bears hibernate; perhaps a future version of humans will evolve the same trick.

"The new discovery fills a gap in the fossil record and contributes to a better understanding of vertebrate survival during the end-Permian mass extinction from a geographic as well as an ecological point of view," Frobisch said.

In case you're wondering, you can't buy land on Antarctica. The Antarctic Treaty of 1959 currently protects the continent from military activities and development that would damage its ecology. But for how much longer, I wonder?

The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is "Hito wa Ima mo Shinka Shiteru (The Evolving Human: How New Biology Explains your Journey through Life)."


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