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much faster than neutral ones. Exactly which mutations natural selection will favor, how- On the Origin of ever, depends on the environment in which we live. And over the past 10,000 years, we humans have dramatically changed that envi- Tomorrow ronment. We have fostered new diseases to which humans have adapted, for example. But in other cases, civilization has shielded us could bring about this change consciously, from the environment, weakening the power through cultural . of natural selection. As the world celebrates the 150th anniver- One of the best known examples of sary of the publication of On the Origin of human-driven evolution is malaria. Early Species this year, scientists continue to think farmers cleared forests and created fields deeply about what comes next. But the com- where malaria-carrying mosquitoes could lay plexity of evolution still makes forecasting eggs in pools of water. As malaria spread, nat- hard. “As Yogi Berra once said, ‘Prediction is ural selection favored those humans with very difficult. Especially about the future,’ ” defenses against the disease. One such says Stephen Stearns, an evolutionary biolo- defense comes from a variant of a hemoglobin gist at . gene that makes it hard for parasites to repro- Yet evolutionary biologists also feel a new duce in blood cells. One copy of the gene sense of urgency about understanding what reduces your chance of contracting malaria. lies ahead. Since Darwin’s day, humans have Two copies cause sickle cell anemia. gained an unprecedented influence over our On the other hand, civilization has also own evolution. At the same time, our actions, blunted some of natural selection’s power over be it causing climate change, modifying the humans, particularly in the 150 years since genomes of other organisms, or introducing Darwin published On the Origin of Species. on December 18, 2009 invasive species, are creating new sources of Back then, for example, some children had the natural selection on the flora and fauna around misfortune to be born with defective copies of IN THE FINAL WORDS OF THE FINAL us. “The decisions we and our children make a gene for an enzyme that breaks down amino sentence of On the Origin of Species, Charles are going to have much more influence over acids in the food they ate. This disorder, known Darwin gave a nod to the future. “There is the shape of evolution in the foreseeable as phenylketonuria, generally led to severe grandeur in this view of life, with its several future than physical events,” says Andrew brain damage. Few people with severe powers, having been originally breathed into a Knoll, a paleontologist at Harvard University. phenylketonuria were able to pass on their

few forms or into one; and that, whilst this genes. But today, now that scientists know www.sciencemag.org planet has gone cycling on according to the Shaping our genome what causes the disease, people with phenylke- fixed law of gravity, from so simple a begin- If there’s one thing that’s certain, it’s that tonuria can enjoy fairly normal lives simply by ning endless forms most beautiful and most humans, like other living things, will continue being careful about the foods that they eat, and wonderful have been, and are being, evolved.” to evolve. “Evolution is unstoppable,” says they pass their genes on to their children. Other Darwin recognized that as long as the Lawrence Moran of the University of Toronto medical advances, from eyeglasses to antibi- ingredients for the evolutionary process still in Canada. But that doesn’t mean that humans otics, may also allow some potentially detri- exist, life has the potential to change. He didn’t are marching on a path toward mental genes to become more believe it was possible to forecast evolution’s becoming giant-brained, tele- THE YEAR OF common than in the past. Downloaded from course, but he did expect humans would have pathic creatures out of Star Trek. Yet medical advances and other a big effect. In his day, they had already All it means is that the human DARWIN changes to human life have not demonstrated their power with the triumphs of genome will continue to change stopped natural selection, nor will domestication, such as breeding dogs from from generation to generation. they in the future. HIV, for exam- wolves. Darwin recognized that we humans A background mutation rate ple, first evolved into a human can also wipe out entire species. He knew the guarantees this process. Each pathogen in the early 1900s and dodo’s fate, and in 1874 he signed a petition to baby’s DNA carries about 130 today takes a devastating toll in save the last surviving Aldabra giant tortoises new mutations. Most of them many parts of the world. Genes (JUPITERIMAGES.COM); WIKIPEDIA/GEORGE RICHMOND, FROM ORIGINS, RICHARD LEAKEY AND ROBERT LEWIN (JUPITERIMAGES.COM); WIKIPEDIA/GEORGE RICHMOND, FROM ORIGINS, RICHARD LEAKEY AND ROBERT on the Seychelles Islands in the Indian Ocean. have no effect on our well-being. that provide some resistance to the Darwin also expected that our own species People can pass these neutral virus may be favored by natural SCIENCE would change. As Western powers colonized mutations down to their offspring This essay is the last selection in places where HIV is other parts of the world, he predicted that without harm, and over time, a in a monthly series. For particularly common. more on evolutionary some populations would become extinct. But small fraction of them will end up origins online, see the Even in affluent parts of the Darwin also felt a cautious optimism. “Look- spreading across entire popula- Origins at . world like the United States, nat- ing to future generations,” he wrote in The tions, or even the entire species, sciencemag.org/origins. ural selection has not stopped. For more on the Descent of Man, “there is no cause to fear that thanks to random luck. Origin of Tomorrow, Subtle differences in people’s the social instincts will grow weaker, and we Natural selection can cause listen to a by health influence how many chil- author Carl Zimmer at may expect that virtuous habits will grow mutations that help individuals www.sciencemag.org/ dren they have and thus can grad-

stronger.” And unlike other species, humans survive and reproduce to spread multimedia/podcast. ually change entire populations. CREDITS (TOP TO BOTTOM): K. SUTLIFF/

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Lost species. Darwin worried that that eventually scientists will be able to alter the Aldabra giant tortoise (left) the genes of future generations. would become extinct like the But even if a child was born with engi- dodo (below). neered genes in our lifetime, that milestone wouldn’t mean much for the evolution of our Framingham, but they have yet species. Those engineered genes would be to determine exactly what swamped by the billions of mutations that advantage each trait confers— emerge naturally in the babies born every year. a situation that evolutionary Yet although engineered genes aren’t likely to biologists often face when doc- provide enough reproductive advantage to umenting natural selec- spread on their own, they may still become tion. Nevertheless, based common. John Hawks, an anthropologist at the on the strength of the nat- University of Wisconsin, Madison, speculates ural selection they have that if genetic engineering becomes cheap measured, the scientists enough and provides an attractive trait—such predict that after 10 gener- as staying thin—economics could spread a In a report published online 26 October in ations, the women of gene even if natural selection can’t. “I think the Proceedings of the National Academy of Framingham will give people would buy it,” says Hawks. Sciences, Stearns and his colleagues docu- birth, on average, a few mented natural selection in 2238 U.S. women. months younger than today, have 3.6% lower Human-powered evolution The women were subjects in the Framingham cholesterol, and will be 1.3% shorter. Genetically engineered humans may still be Heart Study, which has tracked the health of Of course, even this prediction is subject to science fiction, but genetically engineered thousands of people in Framingham, Massa- change. Women with higher cholesterol may animals, plants, and microbes are all here chusetts, since 1948. The scientists searched eventually be able to enjoy higher fertility rates already. In 2008, farmers planted 125 million for traits that were correlated with having a thanks to cholesterol-lowering drugs, says hectares of genetically modified crops. Many higher number of children. Then they checked Stearns, wiping out the differences in repro- of these crops carry genes from other species. on December 18, 2009 to see whether those traits tended to be passed ductive rates. “Selection is always operating,” Corn, cotton, and other plants have been engi- down from mother to child—in other words, says Stearns, “but the traits on which it oper- neered to carry a gene produced by bacteria, whether they were genetically based. ates shift with ecology and culture.” for example, so that they can make an enzyme

(26 AUGUST 2009), BY PERMISSION FROM MACMILLAN PUBLISHERS LTD. “The decisions we and our children make are going to have much more influence 461 over the shape of evolution in the foreseeable future than physical events.” NATURE , www.sciencemag.org

ET AL. —Andrew Knoll, Harvard University

The scientists discovered that a handful of Along with natural selection, it’s also con- that can kill insects. With big countries such as traits are indeed being favored by natural ceivable that one day genetic engineering will China and India dramatically ramping up their selection. Women with a genetic tendency for change human DNA directly. In September, use of genetically modified crops, this evolu- low cholesterol, for example, had more chil- scientists at the Oregon National Primate tionary trend will likely continue. dren on average than women with high cho- Research Center reported that they could In the near future, scientists may start to lesterol. A greater body weight was also replace the DNA in the mitochondria of a engineer life in a more profound way, man- Downloaded from linked with greater reproductive success, as monkey embryo with mitochondrial DNA ufacturing new species from scratch. The was shorter height, lower blood pressure, an from another monkey. In July, scientists at the idea would be to design a microbe on a com- older age at menopause, and having one’s first Center for Regenerative Medicine in puter, combining genes with different func- child at an earlier age. Barcelona, Spain, reported that they had tions into genetic networks. Scientists could Stearns and his colleagues now know repaired human stem cells carrying genes for then synthesize the new genome from raw which traits are selected in the women of an inherited blood disorder. Both studies hint DNA and insert it into an empty microbial

Engineering genomes. Humans are finding many ways to radically manipulate DNA, from genetically modified cotton (left) to bacteria with “transplanted” genomes

CREDITS: (TOP) MAIK DOBIEY; (INSET) WIKIPEDIA; (BOTTOM) ISSOUF SANOGO/AFP/GETTY IMAGES; JCVI; M. TACHIBANA (INSET) WIKIPEDIA; (BOTTOM) ISSOUF SANOGO/AFP/GETTY IMAGES; JCVI; M. TACHIBANA CREDITS: (TOP) MAIK DOBIEY; (center) to monkeys born from DNA transferred to empty eggs.

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Alien invaders. Human- introduced species such to build skeletons and shells from calcium car- as kudzu and cane toads bonate. Organisms will need to adapt to sur- (inset) can drive evolu- vive in these new conditions. tion in new directions. “We know that things can evolve quickly, but can they evolve fast enough?” asks their predators. Scien- Palumbi. He and many other scientists sus- tists have discovered pect that for many species the answer is no. that the toads are Unless we can ease up on the biosphere, they evolving in their new warn that the biggest feature of evolution in home: Toads at the the near future will be extinctions. leading edge of the Knoll points out some disturbing parallels invasion are growing between today’s crisis and a pulse of mass longer legs and mov- extinctions that occurred 252 million years ing faster than their ago, wiping out an estimated 96% of species in ancestors, speeding the oceans and 70% of species on land. A rapid cell that would up the invasion. The native species are increase in carbon dioxide in the atmosphere come to life. J. responding as well. Australian snakes are led, among other things, to ocean acidifica- and his colleagues at the evolving resistance to the cane toad poison. tion. For animals that depended on calcium J. Craig Venter Institute Stephen Palumbi, a biologist at Stanford carbonate, “you had about a 90% chance of in Rockville, Maryland, University in Palo Alto, California, expects going extinct,” says Knoll. “Corals, sponges, have taken a series of key steps toward that that human-induced natural selection will brachiopods, they all kicked the can.” goal, such as performing a “genome trans- become much stronger in the future. “In the Knoll doesn’t expect human-driven mass plant” on a microbe. last century, we were having a big impact, but extinctions to be as bad as that ancient one. But If Venter succeeds, his artificial life would it wasn’t everywhere,” says Palumbi. “But they could still be unimaginably huge. “If we be a triumph of human ingenuity, but it would global climate change is an ‘everywhere’ lose half the species on the planet, our grand- probably be a minor blip on the biosphere’s impact, and that’s different.” children are not going to see them restored,” on December 18, 2009 radar. Synthetic biologists want to make Plants and animals are already responding says Knoll. “It will take millions of years.” microbes to serve our own ends, such as mak- to the warming climate by shifting their A drop in biodiversity may bring with it a ing fuel and medicines. Burdened with genes ranges to find the most comfortable tempera- collapse of many ecosystems. Coupled with for these functions, the microbes will likely be tures. But moving won’t be a solution for a rapid increase in global temperatures, ill equipped to compete in the wild against many species, which will face barriers such as ocean acidification, and other changes, we species that have adapted for millions of years. deserts or cities. They will have to adapt to may be pushing the environment into a state For the foreseeable future, synthetic microbes survive—a process scientists have already we’ve never experienced as a civilization.

will probably survive only in the refuge of a detected in some species, such as red squirrels Such a stress could put our species under www.sciencemag.org laboratory or a fermentation tank. “I will ven- in Canada, which have evolved to breed ear- intense natural selection as well. ture a prediction,” says Adam Wilkins, a biol- lier in the spring. ogist at the University of Cambridge in the Extra carbon dioxide is creating a second Taking the long view United Kingdom. “This kind of biotech engi- worldwide evolutionary pressure as it dis- One way or another, life will survive this cur- neering might succeed in creating some rather solves into the ocean. There it is turning into rent crisis. But where is life headed in the very weird and wonderful organisms. But the net carbonic acid and lowering the pH. Continued distant future? To find out, planetary scientist effect on evolution will be nil—that is, outside acidification will make it King-Fai Li of the California Institute of the laboratory.” more difficult for corals Technology in Pasadena and his col- Downloaded from But humans, Wilkins is quick to point out, and other marine animals leagues built a model of and the sun don’t need synthetic to have a big and watched it evolve for billions of years. effect on the evolution of life. Chainsaws, In their simulation, the sun gets brighter, fishing lines, and smokestacks do just fine. as it has since it first formed. The extra Many fisheries, for example, have established energy speeds up the rate at which carbon rules for keeping fish only above a certain dioxide is drawn out of Earth’s atmosphere, size. As a result, natural selection has favored cooling it off. But after about 2 billion fish that become sexually mature at smaller years, this cooling mechanism breaks sizes. On land, hunters have had a similar down, and Earth heats up, ending up like its effect by going after big game. Bighorn sheep, lifeless neighbor, Venus. for example, now grow horns 25% smaller But Li’s model does not include a clever than they did 30 years ago. species like our own, which can use its brain to Humans have also triggered bursts of evo- influence the planet. Would it be possible to lutionary change by introducing species to extend the life span of Earth’s biosphere? “I new habitats. In Australia, for example, cane am not going to rule out any talented civiliza- toads brought in from South America in 1935 tions that will be able to do that,” says Li. have became a continent-wide pest. They’re Taking a toll. Increased carbon dioxide from burn- –CARL ZIMMER devouring some small native species, and ing fossil fuels is lowering the pH of the oceans, Carl Zimmer is the author of The Tangled Bank: An Intro-

their poisonous skin is killing off some of destroying corals. duction to Evolution (Roberts and Co., 2009). LEE PHOTOGRAPHY/CORBIS QLD AUSTRALIA/WIKIPEDIA; (BOTTOM) BRUNO DE GIUSTI/WIKIPEDIA; (INSET) LARRY PARK, CREDITS: (TOP) SCOTT EHARDT/WIKIPEDIA; (INSET) SPRINGBROOK NATIONAL

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