March 28, 2005
OUT, OUT DAMN SPOTS:
Dances with fruit flies (Thomas Hayden, 3/28/05, US News)
The fly, at first, looks like nothing so much as a tiny matador. Now standing still, now feinting left or darting right, he circles the petri dish arena, waving a black-tipped wing at his quarry like a red cape. But he's a lover, not a fighter, and his dance is intended to induce the fruit fly equivalent of a swoon. Scientists can no more explain why female Drosophila biarmipes flies go gaga for manly markings than they can determine what it is that attracts teenage girls to Ashton Kutcher. But the spots--unheard of in biarmipes' s cousin, the widely studied lab fly D. melanogaster --are helping to shed light on even more vexing questions of animal evolution. Among them: How can species with nearly identical DNA turn out as different as biarmipes is from melanogaster, or as humans are from chimpanzees?
We're living at a strange moment in America. Once again, evolution is becoming a controversial topic. But while school boards are revisiting the 19th-century debate over whether evolution even happens, 21st-century scientists are beginning to show exactly how the natural phenomenon works. Using the powerful tools of molecular biology and comparative genomics, they're finding specific changes in the DNA that can account for 17,000 species of butterfly or why insects have only six legs instead of a dozen. And while some 55 percent of Americans balk at the idea that humans evolved at all, analysis of the genes that build our bodies shows our clear kinship not just to the apes but all the way back to bugs, worms, and beyond. Along the way, scientists are starting to find concrete explanations for everything from our large brains to just exactly how the fruit fly--or the leopard, for that matter--got its spots.
Sean Carroll, in whose University of Wisconsin-Madison laboratory the biarmipes flies danced, has been at the head of the new wave of evolutionary studies for two decades. An investigator with the Howard Hughes Medical Institute, Carroll sets out in his engaging new book, Endless Forms Most Beautiful (W. W. Norton), to introduce us to the field he helped found: evolutionary developmental biology, or "evo devo." [...]
All fruit flies have the genes needed to make wing spots, including a gene for black pigment called, confusingly enough, Yellow. That gene is turned on at low levels throughout all fruit fly wings, but only male biarmipes flies have the characteristic spot. Writing recently in Nature, Carroll's research team reported finding mutations in a genetic switch for Yellow in biarmipes flies that allow a finer level of control; one part of the switch keeps gene expression low throughout the wing, while another cranks up expression at the tips, creating the characteristic spot.
It's just one small step in the twisting path of evolution, of course. But it's not hard to see how many such changes in gene switches--accompanied by even small survival advantages such as females who prefer spotted mates--could lead over time to a new species, with little change in the genes themselves. It's a principle that is found again and again throughout the animal kingdom, Carroll says, and one that should help solve one of the greatest biological mysteries of recent years. [...]
Speaking recently in his office--a space so comfortably cluttered it almost resembles a nest--sporting shaggy hair and dressed in jeans and sneakers, Carroll seems about as content as a man can be. But the critics of evolution--he calls them deniers--are really starting to get under his skin.
No wonder Mr. Carroll is upset; he's begged all the important questions and accidentally added weight to the arguments of his opponents, yet still folks don't agree with him. At the end of the day he and his cronies have used intelligent design to demonstrate that drosphila don't speciate no matter how much you isolate them. Posted by Orrin Judd at March 28, 2005 7:59 PM