SAVING TINKERBELL :

A theory evolves : How evolution really works, and why it matters more than ever (Thomas Hayden, 7/29/02, US News)

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. [...]

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." [...]

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.)

This hilarious essay reads almost like a parody of Darwinism as filtered through the objections of skeptics. Mr. Hayden cites mostly carefully controlled interventions by humans as evidence than evolution must occur randomly in Nature. From the first example with butterflies, which suggests nothing about speciation; to the circular logic of the absence of fossils being just as conclusive evidence as their presence would be; to a demonstration that intelligent beings can force mutation fairly easily but which fails to explain why we don't see such mutations occur frequently in the absence of human intervention; it's almost as if he were trying to prove his opponents' case. Posted by Orrin Judd at July 22, 2002 7:19 PM