Give a mouse embryo a stretch of bat DNA, and its limbs grow a little longer, a new genetic study shows. The change, though small, may illustrate one evolutionary step on the path to wings.
Charles Darwin suggested that a series of such minor changes would be key to building new body features, like wings, from old ones. "If you have lots of these changes over time—and with natural selection—ultimately you'll end up with some structure like a bat wing," says study leader Richard Behringer, a developmental biologist at the University of Texas M.D. Anderson Cancer Center in Houston.
To support this idea, Behringer's team examined a gene called Prx1 that controls bone growth by turning on other genes. Lab mouse embryos missing the gene grow puny limbs and misshapen heads, and pups die at birth. A short stretch of DNA near, but not part of, Prx1 enhances its activation, helping a cell control how much of the gene's protein gets made.