Human evolution at the crossroads

Survivalistians: Coping with doomsday

Survivalistian: Protective brow and skin layer contribute to "radiation hardening."

Surviving doomsday is a story as old as Noah’s Ark, and as new as the post-bioapocalypse movie “28 Days Later.”

Catastrophes ranging from super-floods to plagues to nuclear war to asteroid strikes erase civilization as we know it, leaving remnants of humanity who go their own evolutionary ways.

The classic Darwinian version of the story may well be H.G. Wells’ “The Time Machine,” in which humanity splits off into two species: the ruthless, underground Morlock and the effete, surface-dwelling Eloi.

At least for modern-day humans, the forces that lead to species spin-offs have been largely held in abeyance: Populations are increasingly in contact with each other, leading to greater gene-mixing. Humans are no longer threatened by predators their own size, and medicine cancels out inherited infirmities ranging from hemophilia to nearsightedness.

“We are helping genes that would have dropped out of the gene pool,” paleontologist Peter Ward observed.

But in Wells’ tale and other science-fiction stories, a civilization-shattering catastrophe serves to divide humanity into separate populations, vulnerable once again to selection pressures. For example, people who had more genetic resistance to viral disease would be more likely to pass on that advantage to their descendants.

If different populations develop in isolation over many thousands of generations, it’s conceivable that separate species would emerge. For example, that virus-resistant strain of post-humans might eventually thrive in the wake of a global bioterror crisis, while less hardy humans would find themselves quarantined in the world’s safe havens.

Patterns in the spread of the virus that causes AIDS may hint at earlier, less catastrophic episodes of natural selection, said Stuart Pimm, a conservation biologist at Duke University: “There are pockets of people who don’t seem to become HIV-positive, even though they have a lot of exposure to the virus — and that may be because their ancestors survived the plague 500 years ago.”

Evolution, or devolution?
If the catastrophe ever came, could humanity recover? In science fiction, that’s an intriguingly open question. For example, Stephen Baxter’s novel “Evolution” foresees an environmental-military meltdown so severe that, over the course of 30 million years, humans devolve into separate species of eyeless mole-men, neo-apes and elephant-people herded by their super-rodent masters.

Even Ward gives himself a little speculative leeway in his book “Future Evolution,” where a time-traveling human meets his doom 10 million years from now at the hands — or in this case, the talons — of a flock of intelligent killer crows. But Ward finds it hard to believe that even a global catastrophe would keep human populations isolated long enough for our species to split apart.

“Unless we totally forget how to build a boat, we can quickly come back,” Ward said.

Even in the event of a post-human split-off, evolutionary theory dictates that one species would eventually subjugate, assimilate or eliminate their competitors for the top job in the global ecosystem. Just ask the Neanderthals.

“If you have two species competing over the same ecological niche, it ends badly for one of them, historically,” said Joel Garreau, the author of the forthcoming book “Radical Evolution.”

The only reason chimpanzees still exist today is that they “had the brains to stay up in the trees and not come down into the open grasslands,” he noted.

“You have this optimistic view that you’re not going to see speciation (among humans), and I desperately hope that’s right,” Garreau said. “But that’s not the only scenario.”

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