Evolution is still a theory, an interpretation, no body has lived long enough to have observed evolution in action. Tetapi jika semua orang sudah yakin bahwa evolution memang sudah terjadi, maka ini baru menjadi "fact"
----- Original Message ----- From: "Rovicky Dwi Putrohari" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Sunday, July 28, 2002 12:45 PM Subject: [iagi-net-l] How evolution really works, and why it matters more than ever > Apakah evolusi sudah menjadi sebuah kenyataan -'natural fact' ? > Paleontologist menyatakan faunal/fossil succession sebagai 'fact' karena > 'kasat' mata. Nah sekarang evolusi apakah sudah bisa dianggap sebagai fakta > alam ? > > RDP > Dari US News terbaru - Cover Story 7/29/02 > http://www.usnews.com/usnews/issue/020729/misc/29evo.htm > ======================== > A theory evolves > How evolution really works, and why it matters more than ever > By Thomas Hayden > > When scientists introduced the world to humankind's earliest known ancestor > two weeks ago, they showed us more than a mere museum piece. Peering at the > 7 million-year-old skull is almost like seeing a reflection of our earlier > selves. And yet that fossil represents only a recent chapter in a grander > story, beginning with the first single-celled life that arose and began > evolving some 3.8 billion years ago. Now, as the science of evolution moves > beyond guesswork, we are learning something even more remarkable: how that > tale unfolded. > > Scientists are uncovering the step-by-step changes in form and function that > ultimately produced humanity and the diversity of life surrounding us. By > now, scientists say, evolution is no long-er "just a theory." It's an > everyday phenomenon, a fundamental fact of biology as real as hunger and as > unavoidable as death. > Darwin proposed his theory of evolution based on extensive observations and > cast-iron logic. Organisms produce more young than can survive, he noted, > and when random changes create slight differences between offspring, > "natural selection" tends to kill off those that are less well suited to the > environment. But Darwin's evidence was fragmentary, and with the science of > genetics yet to be invented, he was left without an explanation for how life > might actually change. > The "modern synthesis" of genetics and evolutionary theory in the 1940s > began to fill that gap. But until recently, much of evolution still felt to > nonscientists like abstract theory, often presented in ponderous tomes like > paleontologist Stephen Jay Gould's 1,464-page Structure of Evolutionary > Theory, published shortly before his death this spring. As theorists argued > over arcane points and creationists stressed uncertainties to challenge > evolution's very reality, many people were left confused, unsure what to > believe. > Nuts and bolts. But away from heated debates in schools and legislatures, a > new generation of scientists has been systematically probing the fossil > record, deciphering genomes, and scrutinizing the details of plant and > animal development. They are documenting how evolution actually worked, how > it continues to transform our world, and even how we can put it to work to > fight disease and analyze the wealth of data from genome-sequencing > projects. "The big story," says evolutionary biologist E. O. Wilson of > Harvard University, "is not in overarching, top-down theory now, but in the > details of research in the lab and in the field." > Scientists have confirmed virtually all of Darwin's postulates. For example, > Ward Watt of Stanford University has demonstrated natural selection in > action. In a hot environment, he found, butterflies with a heat-stable form > of a metabolic gene outreproduced their cousins with a form that works well > only at lower temperatures. "Darwin was more right than he knew," says Watt. > Darwin also held that new species evolve slowly, the result of countless > small changes over many generations, and he attributed the lack of > transitional forms-missing links-to the spotty nature of the fossil record. > By now many gaps have been filled. Dinosaur researchers can join hands with > bird experts, for example, their once disparate fields linked by a series of > fossils that show dinosaurs evolving feathers and giving rise to modern > birds. And last year, paleontologists announced that they had recovered > fossils from the hills of Pakistan showing, step by step, how hairy, doglike > creatures took to the sea and became the first whales. > But new research also shows that evolution works in ways Darwin did not > imagine. Many creatures still appear quite suddenly in the fossil record, > and the growing suspicion is that evolution sometimes leaps, rather than > crawls. For example, the first complex animals, including worms, mollusks, > and shrimplike arthropods, show up some 545 million years ago; > paleontologists have searched far and wide for fossil evidence of gradual > progress toward these advanced creatures but have come up empty. > "Paleontologists have the best eyes in the world," says Whitey Hagadorn of > Amherst College, who has scoured the rocks of the Southwest and California > for signs of the earliest animal life. "If we can't find the fossils, > sometimes you have to think that they just weren't there." > A new understanding of Earth's history helps explain why. Scientists have > learned that our planet has been rocked periodically by catastrophes: > enormous volcanic eruptions that belched carbon dioxide, creating a super > greenhouse effect; severe cold spells that left much of the planet enveloped > in ice; collisions with asteroids. These convulsions killed off much of > life's diversity. Once conditions improved, says Harvard paleontologist Andy > Knoll, the survivors found a world of new opportunities. They were freed to > fill new roles, "experimenting" with new body plans and evolving too rapidly > to leave a record in the fossils. > We may owe our own dominance to the asteroid impact that killed the > dinosaurs 65 million years ago. As mammals, we like to think that we're > pretty darned superior. The sad truth: "Mammals coexisted with dinosaurs for > 150 million years but were never able to get beyond little ratlike things," > says Knoll. "It was only when the dinosaurs were removed that mammals had > the ecological freedom to evolve new features." > Whether evolution worked fast or slow, theorists labored to explain how it > could produce dramatic changes in body structure through incremental steps. > Half an eye would be worse than none at all, creationists were fond of > arguing. But "partial" eyes turn out to be common in nature, and biologists > can trace eye evolution from the lensless flatworm eyespot to the complex > geometry of vertebrate eyes. Now "evo-devo" biologists, who study how > fertilized egg cells develop into adults, are discovering powerful new ways > evolution can transform organisms. They are finding that changes in a > handful of key genes that control development can be enough to drastically > reshape an animal. > Master switches. The central discovery of evo-devo is that the development > and ultimate shape of animal bodies are orchestrated by a small set of genes > called homeotic genes. These regulatory genes make proteins that act as > master switches. By binding to DNA, they turn on or shut down other genes > that actually make tissues. All but the simplest animals are built in > segments (most obvious in creatures like centipedes, but also apparent in > human vertebrae), and the Hox family of homeotic genes interacts to > determine what each segment will look like. By simple genetic tinkering, > evo-devo biologists can tweak the controls, making flies with legs where > their antennae should be, or eyeballs on their knees. > This might seem like little more than a cruel parlor trick, and the > resulting monstrosities would never survive in nature. But small changes in > these master-switch genes may help explain some major changes in > evolutionary history. This past winter, evo-devo biologists showed that an > important animal transition 400 million years ago, when many-legged > arthropods (think lobsters) gave rise to six-legged insects, was due to just > a few mutations in a Hox gene. In the past few months, researchers have > found that a change in the regulation of a growth- factor gene could have > resulted in the first vertebrate jaw. And, incredibly, researchers reported > in the journal Science last week that a single mutation in a regulatory gene > was enough to produce mice with brains that had an unusually large, wrinkled > cerebral cortex resembling our own. (No word, though, on whether the mutant > mice gained smarts.) > Some critics of evolution argue that animals are so complex and their parts > so interconnected that any change big enough to produce a new species would > cause fatal failures. Call it the Microsoft conundrum. But just as Judge > Thomas Penfield Jackson managed to delete that company's Web browser on his > own computer without crashing the operating system, evo-devo biologists are > learning how evolution can tweak one part of an animal while leaving > everything else alone. The key to modifying the machine of life while it's > running, says biologist Sean Carroll of the University of Wisconsin- > Madison, is mutations in the stretches of DNA that homeotic proteins bind > to. > "If you change a Hox protein, you might mess up the whole body," says > Carroll. "But if you change a control element, you can change a part as > small as a bristle or a fingernail." He explains that genetic accidents can > set the stage by duplicating segments, creating spares that are free to > evolve while the other segments carry on with their original function. > Biologists now believe that appendages like insect wings and the proboscis a > mosquito jabs you with evolved from spare leg segments. > Making do. This process may be rapid, but it's not elegant. Instead of > inventing new features from scratch, evolution works with what it has, > modifying existing structures by trial and error. The result is a messy > legacy of complicated biochemical pathways and body parts that are more > serviceable than sleekly designed. Although proponents of intelligent design > hold that organisms are too "perfect" to have arisen by chance, science > shows that organisms don't work perfectly at all; they just work. > While many scientists busy themselves figuring out the history and mechanics > of evolution, others are already putting it to use. Jonathan Eisen of the > Institute for Genomic Research in Rockville, Md., deciphers the information > stored in organisms' genomes for clues to their ancestry and how they > function. For him, evolution is as critical a tool as DNA-sequencing > machines and supercomputers. "If I didn't approach everything with an > evolutionary perspective," says Eisen, "I'd miss out on most of the > information." > That's because genomes are the handiwork of evolution, and their origin can > be key to making sense of them. Researchers analyzing the human genome, for > example, reported finding a series of human genes that were also common in > bacteria but absent from invertebrates like fruit flies. They concluded that > bacterial genes had infiltrated vertebrate animals, helping to shape our > genetic identity. But the explanation turned out to be more mundane. Knowing > how evolution often prunes away unneeded genes, Eisen and several others > showed most of the suspect genes had simply been dropped during the > evolutionary history of flies. The moral of the story: "I'm begging people > to treat evolution as a science and not just tack it on as an explanation > afterwards," says Eisen. > 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. > A quick survey of the human condition reveals any number of desirable > improvements-surely evolution could take care of hernias and osteoporosis > and the appendix, which serves no greater purpose than to become inflamed? > But those annoyances usually don't keep the annoyed from passing on their > genes. And with precious little geographic isolation-one of the main drivers > of speciation-left in our global village, we'll probably have to wait until > a space colony gets cut off for several thousand generations before a new > human species evolves. > Of course, it's the idea that human beings themselves are products of > evolution that provokes most of the attacks on evolution. Such rejections > leave most scientists mystified."The scientific narrative of the history of > life is as exciting and imbued with mystery as any other telling of that > story," says Knoll. The evidence against evolution amounts to little more > than "I can't imagine it," Ewald adds. "That's not evidence. That's just > giving up." > Many researchers simply ignore the debates and press on with their work. But > as evolution becomes an applied science, others say it's more urgent than > ever to defend its place in the schools. "HIV is one of the world's most > aggressively evolving organisms," says Palumbi. If it weren't for the > virus's adaptability, which helps it foil the body's defenses and many > drugs, "we would have kicked HIV in the teeth 15 years ago." But doctors > don't learn about evolution in medical school, he says, leaving them about > as well prepared to combat HIV as a flat-Earth astronomer would be to plan a > moon shot. > "Somewhere in high school in this country is a student who's going to cure > AIDS," Palumbi says. "That student is going to have to understand > evolution." > With Jessica Ruvinsky, Dan Gilgoff, and Rachel K. Sobel > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > Visit IAGI Website: http://iagi.or.id > IAGI-net Archive: http://www.mail-archive.com/iagi-net%40iagi.or.id/ > ===================================================================== > Indonesian Association of Geologists [IAGI] - 31st Annual Convention > September 30 - October2, 2002 - Shangri La Hotel, SURABAYA > --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] Visit IAGI Website: http://iagi.or.id IAGI-net Archive: http://www.mail-archive.com/iagi-net%40iagi.or.id/ ===================================================================== Indonesian Association of Geologists [IAGI] - 31st Annual Convention September 30 - October2, 2002 - Shangri La Hotel, SURABAYA
