Distinct digits may have evolved by using DNA that makes the cloaca

Evolution has adapted the digits of mammals for an enormous range of uses, from our opposable thumbs to the spindly digits that support bat wings to the robust bones that support the hoofs of horses. But how we got digits in the first place hasn't been entirely clear. The fish that limbed vertebrates evolved from don't have obvious digit equivalents, and the most common types of fish just have a large collection of rays supporting their fins.

Despite this uncertainty, we have identified some genes that seem to be essential for both digit formation and the development of rays in the fins of fish, suggesting that there are parallels between the two. But a new study suggests that these parallels are a bit of an accident, and digits come by re-deploying a genetic network that controls a compl