In evolutionary biology, there is a deeply rooted supposition that you can’t go home again: Once an organism has evolved specialized traits, it can’t return to the lifestyle of its ancestors.There’s even a name for this pervasive idea. Dollo’s law states that evolution is unidirectional and irreversible. But this “law” is not universally accepted and is the topic of heated debate among biologists.

A scanning electron microscope image of an American house dust mite. (Credit: G. Bauchan and R. Ochoa)
Now a research team led by