A bat, flying through the night sky, is thirsty. As it flies, it sends out high-pitched squeaks and listens for the returning echoes. It hears a telltale pattern. It hears no echoes form up ahead and the only ones that reflect back at it are coming from straight below. That only happens when the bat flies over a flat, smooth surface like the top of a lake or pond. The bat dives, opens its mouth to take a sip of refreshing water… and gets a mouthful of metal.
In nature, bodies of water are the only large, smooth surfaces around. Waves of sound that hit the surface of still water would generally bounce away, except for those aimed straight downwards. Stefan Greif and Björn Siemers from the Max Planck Institute for Ornithology have found that bats are instinctively tuned to find water using this unique feature (and yes, the institute does mostly, but not exclusively, bird research).
Millions of years before humans invented sonar, bats and toothed whales had mastered the biological version of the same trick – echolocation. By timing the echoes of their calls, one group effortlessly flies through the darkest of skies and the other swims through the murkiest of waters. It’s amazing enough that two such different groups of mammals should have evolved the same trick but that similarity isn’t just skin deep.
The echolocation abilities of bats and whales, though different in their details, rely on the same changes to the same gene – Prestin. These changes have produced such similar proteins that if you drew a family tree based on their amino acid sequences, bats and toothed whales would end up in the same tight-knit group, to the exclusion of other bats and whales that don’t use sonar.
This is one of the most dramatic examples yet of ‘convergent evolution’, where different groups of living things have independently evolved similar behaviours or body parts in response to similar evolutionary pressures.
It is one of a growing number of studies have shown that convergence on the surface – like having venom, being intelligent or lacking enamel – is borne of deeper genetic resemblance. But this discovery is special in a deliciously ironic way. It was made by two groups of scientists, who independently arrived at the same result. The first authors even have virtually identical names. These are people who take convergence seriously!