Bats are an extraordinary evolutionary success, the only mammals to conquer the air. Their flying ability has long attracted the attention of engineers and biologists, and it comes through soft, flexible wings unlike those of birds or insects.

Their wings have long muscles embedded in the skin, running front to back, and not attached to any bones. Scientists had suspected that these muscles probably helped shape the wings in flight, but evidence was lacking.

Now, in experiments at Brown University with Jamaican fruit bats, Jorn Cheney, a graduate student in ecology and evolutionary biology, and others, including Kenny Breuer and Sharon Swartz, have found signs that the muscles do indeed contract on the downstroke when bats are flying.