For longer life, give her a choice.

Give female fruit flies their pick of mates generation after generation, and their descendants will start living longer.

That finding supports the good-genes theory, which predicts that ladies somehow choose the gentlemen with the better heredity, says Daniel E.L. Promislow of the University of Georgia in Athens. It also shows that sexual selection can benefit animals instead of just fostering extravagant courtship.

Eighteen years ago, Linda Partridge of University College London developed this approach and reported that fruit fly larvae have a competitive edge when their mothers choose among males. Promislow expanded and fine-tuned the test. He found that after some 10 generations, mortality rates were 10 percent lower in mate-choosing lineages compared with lineages whose females were stuck in vials with only one possible mate. Promislow's results appear in the Sept. 1 Proceedings of the National Academy of Sciences.