When population geneticist Lisa Meffert began growing houseflies in her lab at the University of Houston back in 1982, she probably never expected that her experiments with the fast-breeding arthropods would throw into question some of the basic axioms of conservation biology. But her findings have done just that, and in the process have created a great deal of consternation among conservation biologists who adhere to traditional breeding techniques, particularly those trying to replenish dangerously low populations of endangered species.

Essentially, biologists have two options for bringing animals back from the brink of extinction. They can aim for the maximum number of offspring, or try to maximize genetic diversity: call it quantity versus quality. Usually biologists prefer quality, breeding the surviving adults as equally as possible, thus limiting the mating of prolific breeders-and thereby detrimental inbreeding-while allowing slow breeders to catch up and gain better representation among the progeny.