The New York Times Book Review
, May 27, 2001 Link
A review of The Evolution Explosion: How Humans Cause Rapid Evolutionary Change
, by Stephen Palumbi (Norton, 2001)
No one set out to create dogs. When Paleolithic hunters tossed scraps of meat to some curious wolves, they didn't have a Doberman or a shar-pei in mind. And yet, by creating the conditions that favored doglike traits, our ancestors unconsciously steered their evolution. Since those early days of genetic engineering, we've become more aware of our evolutionary powers. Starting around 10,000 years ago, people began breeding and hybridizing plants and animals, selecting the traits they wanted in their cows and corn, their pigs and potatoes.
Today scientists can graft genes from flounders into strawberries. But despite our accelerating cleverness, much of the evolution we cause is still unplanned. Sometimes it's even disastrous. No one set out to breed strains of tuberculosis-causing bacteria resistant to antibiotics, but we have done just that. According to Stephen R. Palumbi, the author of ''The Evolution Explosion,'' it is time we started taking responsibility for our evolutionary actions. We will pay for the consequences if we don't.
As Palumbi explains, scientists now recognize that evolution is not some primordial force that disappeared with the dinosaurs. They can watch it transform animals and plants over the course of years, not eons. On the Galápagos Islands, the beaks of finches expand and shrink as droughts and rains change the supply of seeds the birds eat. When guppies in Trinidad find themselves in ponds full of predators, evolution dulls the flashy red spots that males use to attract females, leaving them with a drab, inconspicuous body. Take away the predators, and gradually the sexy colors re-evolve. We humans create rapid bursts of evolutionary change as well. For decades, fishermen in the Pacific Northwest have caught pink salmon returning to the rivers of their birth to mate. By killing big fish rather than small ones, the fishermen encouraged the evolution of slow growth. Pink salmon have evolved to be two-thirds the size of their ancestors that lived only 50 years ago.
Palumbi, a biologist at Harvard, does an excellent job of showing how man-made evolution is not only real but relevant. A person infected with H.I.V. becomes a Darwinian test chamber, in which viruses continually adapt to their host's immune system and the drugs used against them. The success of the newest anti-AIDS regimens lies in their ability to stop H.I.V. from evolving, at least for the time being. ''We must learn how to control evolution in order to survive the evolutionary skills of H.I.V.,'' Palumbi writes.
The same can be said for the insects that gorge themselves on our crops. They have evolved resistance to just about every pesticide used against them over the past century. Now scientists are offering farmers a new weapon: they have inserted a bacterial gene into plants that produces an insect poison. These plants can grow their own pesticide. This technology may sound like a magic bullet, but Palumbi predicts that it will fail if farmers ignore the reality of evolution. Under a constant, intense pressure to evolve resistance, mutant insects will emerge that can't be stopped by the poison. In order to put off this evolutionary defeat, farmers will have to set aside parts of their fields for ordinary plants. These refuges will shelter insects that do not carry resistance genes, offering them crops they can eat without being poisoned. They will mate with bugs from other parts of the field and stop the resistance genes from becoming too widespread.
Farmers, in other words, will have to sacrifice some of their crops if they don't want resistant insects. Unless they have a firm grip on the facts of evolution, they may be sorely tempted to skip the refuges. If they do, they'll create a race of mutant pests that will ruin everyone's crops.
For the most part, Palumbi has chosen his evolutionary examples well. Even our own biochemistry, he points out, has evolved over the past few thousand years. Cattle-herding peoples who are different in many respects have evolved the same ability to digest milk as adults; genetic disorders like cystic fibrosis may be byproducts of adaptations that protect against cholera and other diseases. And diseases like AIDS and malaria are continuing to shape the human genome.
But when Palumbi turns to the way culture evolves, his book bogs down. In 1976, Richard Dawkins of Oxford University proposed that elements of culture spread and evolve like genes. These ''memes,'' as he called them, could be nothing more than jokes or jingles, or they could be entire technologies or religions. ''Memetics'' -- the study of memes -- is trendy these days, but Palumbi correctly points out that in many ways ideas do not evolve like DNA. Yet his arguments are ultimately unsatisfying, not because they are weak but because memetics is less a science than a grab bag of analogies and untestable thought experiments. Palumbi ends up boxing with a cloud.
He might have made better use of those pages by giving his readers a clearer sense of the ways scientists link the small-scale changes he describes so well to evolution on its grandest scales. The shifting fates of genes from one generation to the next are not what make evolution so astonishing, or so difficult for some people to accept. The bone that really sticks in their craw is evolution's ability to build complex organs and bodies without relying on a blueprint. Life has been evolving for four billion years, and the processes that Palumbi describes have been acting on it since the beginning. By comparing the genes and fossils on different branches of the tree of life, scientists can reconstruct the history that produced the animals, plants and microbes that are still evolving today. ''The Evolution Explosion'' is a good introduction to the Darwinian change that is taking place all around us, but it's far from the whole story.
Copyright 2001 The New York Times Company. Reprinted with permission.