A Theory Evolves
How evolution really works, and why it matters more than ever
Arms race. For microbiologist Richard Lenski, evolution is an obvious reality. Since 1988, the Michigan State University professor has been following 12 populations of the bacterium E. coli. With a new generation every 3.5 hours or so, this is evolution on fast-forward. The populations were once genetically identical, but each has adapted in its own way to the conditions in its test-tube home. The same speedy adaptation, unfortunately, can be readily seen in hospitals, where powerful antibiotics provide a major selective advantage for bacteria that evolve resistance. As bacterial evolution outwits one antibiotic after another, notes Harvard evolutionary biologist Stephen Palumbi, treating infections has become an evolutionary arms race. "It's a cycle of escalation, and the entity that can make the last turn of the cycle wins," says Palumbi. "So far, there's no indication that it's going to be us." The answer, he says, is not just new antibiotics but new strategies based on evolution.
"The key is to tip the balance of selection in favor of mild organisms," says evolutionary biologist Paul Ewald of Amherst College. That can mean measures as simple as having doctors scrub their hands to prevent the spread of the dangerous, antibiotic-resistant strains from their sickest patients. Making life difficult for virulent microbes can actually guide the species' evolution, weeding out the most harmful variants. In the case of malaria, the trick is keeping mosquitoes away from people bedridden with virulent strains. "If you mosquito-proof the houses," says Ewald, "then only people walking around outside can spread the disease, and that will be a mild form."
Evolutionary theorists may be able to guess how specific microbes will evolve, but not the fate of the whole panoply of life. "You can't predict what organisms will look like millions of years from now," says Knoll. Chance events, small and large, make all the difference, as mutations arise at random and unpredictable mass extinctions set life on a new course.
One mass extinction is easy to foresee: the one already underway because of our logging and paving and polluting. Things don't look good for most large mammals--they can't compete with us for space and resources. The outlook is brighter for species that depend on humans, like farm animals and crop plants, as well as rats and cockroaches. But this mass extinction is different from the last, 65 million years ago. "The day after the meteorite hit," says Knoll, "the planet started to heal. The problem now doesn't go away. It gets bad and it stays bad as long as our evolutionary history continues."
God and man. Which brings us to one final result of evolution, the odd, upright, and curiously self-obsessed ape in the mirror. We've turned the tables on evolution, curing diseases and changing our environment to suit us, rather than the other way around. But don't think that frees us from further evolutionary changes. Incurable epidemics that strike the young are still a powerful selective force. A mutation that boosted resistance to HIV, for example, could spread quickly by allowing those who have it to survive and have children. "We continue to accumulate mutations," says Sarah Tishkoff, a geneticist at the University of Maryland. "But we're altering evolution." Assisted reproduction allows some people to beat natural selection, she notes, while birth control gives an evolutionary leg up to those who don't use it.
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