A Theory Evolves
How evolution really works, and why it matters more than ever
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 longer "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.
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