Evolution will occur wherever organisms display variation, differences in fitness, and the capacity for inheritance. Humans have always sped up the process: consider purebred dogs, cats, and horses. "The difference is one of scale," says professor of biology Stephen R. Palumbi. "Our ecological footprint has increased enormously in the last 10,000 years. The species that have learned to live with us--and on us--have learned to rapidly adapt to the conditions we humans have created."
Scores of fascinating examples show up in Palumbi's new book, The Evolution Explosion: How Humans Cause Rapid Evolutionary Change (W.W. Norton). "There are a huge number of compelling ways in which evolution impacts everyday life," he reports. Yet while teaching Science B-55, "Evolutionary Biology," Palumbi could find no single source that consolidated such information, and therefore wrote a book of his own.
The second chapter, "Right Before Your Eyes," makes the case that evolution "can be really quick. You can see it happening right now," he says. "The ecological settings that promote evolution include insect pests, weeds, control of diseases, and changes in ocean life as a result of our over-harvesting certain species of fish." (Palumbi, a marine biologist, wrote "Empty Nets," March-April, page 48.) Evolution can move with special velocity in organisms that generate rapidly. Consider its speed in humans infected with HIV, a virus that has evolved greatly since its discovery two decades ago. "Every person harboring HIV is an evolutionary dynamo," Palumbi says. "In one year, HIV can evolve differences as large as those between humans and chimpanzees."
"A lot of the selective pressures we exert are accidental," Palumbi continues. For example, in preparing operating rooms for surgery, standard procedure used to include spraying all surfaces with antibiotics. This effectively selected for a line of bacteria resistant to those antibiotics (all others would die) and produced virulent bacterial strains that can cause fatal infections in surgical patients.
"We used DDT all over the world to eradicate malaria, and consequently caused evolution of DDT-resistant mosquitoes," Palumbi continues. Noting that up to 25 percent of antibiotic use in the United States is for livestock, he argues that, evolutionarily speaking, cattle growers use these antibiotics "in exactly the wrong way--the same antibiotic every year, in low doses, mixed with the feed daily." Similar behavior by poultry farmers has produced new strains of salmonella that are resistant to tetracycline and erythromycin. Furthermore, when people either accidentally or purposely bring plants or animals into new environments, they can create invasive species. "When we move an insect to a new area, it may learn to eat totally different plants than it did before--plants like our soybeans," says Palumbi. "Sometimes they're 'ready'--maybe an insect is already eating grain, but has to adapt to living in a silo."
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| Common reed (Phragmites australis) grows in an English marsh, right. Human disturbances like sewage runoff help the spread of this invasive plant that colonizes polluted wetland edges, then crowds out native marsh grass, growing to 10 feet or more and blocking vistas. |
| © Papilo/Corbis |
Technology, of course, vastly enlarges the human ecological footprint. "Having industrialized the production of antibiotics and pesticides, we now produce massive amounts," Palumbi observes. "Last year, there were 500 million pounds of pesticides used in the United States--two pounds for each person." Furthermore, with biotechnology we are now producing genetic variants never seen before on this planet. "We can take a gene from a bacterium and slip it into an insect," Palumbi says. "Or put a gene from one plant into another plant. We then introduce these things into the world, where they will evolve."
To appreciate the unruliness of the problem, Palumbi suggests that we imagine the first computer virus able to evolve. Such a digital pestilence would be an elusive target, changing in response to efforts by computer security professionals to track it down and disable it. In fact, the renegade code would have certain characteristics of living organisms. Depending on the virus's programming--its genetics, if you will--it might even evolve so rapidly as to become nearly impossible to eradicate or block. It would, in other words, resemble many biological organisms whose evolution has been shaped or created by human activity.
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| A biologist in New York stands amid 1,500 acres of purple loosestrife, another invasive plant. |
| Associated Press/Michael Okoniewski |
The Evolutionary Explosion is not overly prescriptive. But its examples are so provocative that they inevitably raise questions of choice, ethics, and human destiny. "There are consequences to the way we live our lives on the planet, and turning our backs on those consequences is foolish," Palumbi says. "We are inevitably causing evolutionary changes, and they're going to be around forever."
~Craig Lambert
Stephen Palumbi e-mail address:
spalumbi@oeb.harvard.edu
