In one type of fruit fly, Drosophilia melanogaster, but not in others, researchers found a gene that carries instructions for making a motor that gives this species’ sperm extra horsepower. The researchers were not looking specifically for such a gene but came across it serendipitously during a general investigation of motor proteins. Various creatures boast these proteins, which make it possible for them to get around in salt water or fresh water, or in a reproductive canal, by lashing or spinning threadlike tails. “The tail of D. melanogaster‘s sperm is twice as long as the fly itself,” researcher Daniel Hartl points out. “Other fruit flies may have tails as long as 20 times their body length, intricately coiled inside their sex organs until ready for use. We have no idea why they grow so long.” Finding a gene with instructions for making such a protein promised the possibility of a view into a corner of evolution that no one had seen before.