Human evolution at the crossroads

Unihumans: Will we all be assimilated?

Unihuman: Skin tones blend. Larger eyes are associated with greater "domestication."

Biologists say that different populations of a species have to be isolated from each other in order for those populations to diverge into separate species. That's the process that gave rise to 13 different species of "Darwin's Finches" in the Galapagos Islands. But what if the human species is so widespread there's no longer any opening for divergence?

Evolution is still at work. But instead of diverging, our gene pool has been converging for tens of thousands of years — and Stuart Pimm, an expert on biodiversity at Duke University, says that trend may well be accelerating.

"The big thing that people overlook when speculating about human evolution is that the raw matter for evolution is variation," he said. "We are going to lose that variability very quickly, and the reason is not quite a genetic argument, but it's close. At the moment we humans speak something on the order of 6,500 languages. If we look at the number of languages we will likely pass on to our children, that number is 600."

Cultural diversity, as measured by linguistic diversity, is fading as human society becomes more interconnected globally, Pimm argued. "I do think that we are going to become much more homogeneous," he said.

Ken Miller, an evolutionary biologist at Brown University, agreed: "We have become a kind of animal monoculture."

Is that such a bad thing? A global culture of Unihumans could seem heavenly if we figure out how to achieve long-term political and economic stability and curb population growth. That may require the development of a more "domesticated" society — one in which our rough genetic edges are smoothed out.

But like other monocultures, our species could be more susceptible to quick-spreading diseases, as last year's bird flu epidemic illustrated.

"The genetic variability that we have protects us against suffering from massive harm when some bug comes along," Pimm said. "This idea of breeding the super-race, like breeding the super-race of corn or rice or whatever — the long-term consequences of that could be quite scary."

Environmental pressures wouldn't stop
Even a Unihuman culture would have to cope with evolutionary pressures from the environment, the University of Washington's Peter Ward said.

Some environmentalists say toxins that work like estrogens are already having an effect: Such agents, found in pesticides and industrial PCBs, have been linked to earlier puberty for women, increased incidence of breast cancer and lower sperm counts for men.

"One of the great frontiers is going to be trying to keep humans alive in a much more toxic world," he observed from his Seattle office. "The whales of Puget Sound are the most toxic whales on Earth. Puget Sound is just a huge cesspool. Well, imagine if that goes global."

Global epidemics or dramatic environmental changes represent just two of the scenarios that could cause a Unihuman society to crack, putting natural selection — or perhaps not-so-natural selection — back into the evolutionary game. Then what?

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