Within every muscle of every living species with a backbone, a protein called myosin tugs on a partner protein to generate a muscle contraction. This function, discovered in mammals a century ago, has been presumed by scientists to be operating in the same way among birds, reptiles, amphibians and fish.

A new study tells a different story. These two proteins, myosin and actin, always work together to activate a muscle, but tiny variations in how they interact change the speed, frequency and energy consumption associated with myosin’s movement – and, as a result, define the nature of a given animal’s related muscle function. An analysis of historic genomic data across species revealed about 50 previously unidentified gene subfamilies that drive those subtle but meaningful differences.