sciencehabit writes: Hooked penises, long observed on fly genitalia, seem to function like peacock tails, reports ScienceNOW. That is, they help males beat out their rivals for females. How do scientists know this? They zapped fly penises with a laser, and looked at how successful they were mating. "We can cut the tiniest of structures with the highest of precision," says evolutionary ecologist Michal Polak of the University of Cincinnati in Ohio, "all without harming the fly." The researchers placed cut and uncut males in vials alone with a female. Cut males vigorously attempted to mate, but--unlike the uncut males--most slid off the females, unable to copulate. When cut males did manage to hang on long enough, they proved just as fertile as uncut males, showing that spines had little to do with postinsemination sexual selection. Instead, the genital spines give an advantage before insemination by fastening the genitalia together like Velcro fasteners. The study provides some important insight into one of Darwin's oldest ideas--sexual selection--just cross your fingers this technology never makes it past animal testing.