Some seals can mimic human speech, keep a musical beat, and sing eerie songs that sound straight out of a science fiction film. But for decades, scientists couldn't explain how these animals hear so well in both air and water — something no other mammal can do.
Now, researchers at London's Natural History Museum have cracked the case. By scanning more than 200 living and fossil seal specimens using a powerful imaging technique called micro-CT scanning, they discovered the answer lives in a surprising place: a spongy tissue inside seal ears that fills with blood.
This cavernous tissue serves a dual purpose. When seals dive deep underwater, the tissue swells to protect their ears from crushing pressure changes. But here's the clever part — because blood has almost the same density as seawater, sound waves pass right through instead of bouncing off like they do in human ears. This lets seals hear clearly whether they're hauled out on rocky shores or swimming in the ocean depths.
"We now know that the cavernous tissue in their ears holds the answer," said Dr. James Rule, the study's lead author and a Scientific Associate at the Natural History Museum. "Fossils of seals and their relatives suggest that this extraordinary mechanism evolved more than 26.7 million years ago, with all modern seals inheriting their amphibious hearing from this one event."
The team found that ancient seal relatives like Potamotherium and Puijila — animals that lived on land — only heard well in air. But Enaliarctos, one of the earliest marine seals from roughly 23 million years ago, would have been among the first to develop the ability to hear underwater. This shift likely gave these ancient seals a major survival advantage as they ventured into the sea.
The research, published in the journal Proceedings of the Royal Society B, drew on specimens the Natural History Museum has collected from around the world over hundreds of years. Dr. Natalie Cooper, a Merit Researcher at the museum, said the collections were essential. "This research simply wouldn't have been possible without these specimens."
The findings aren't just scientifically fascinating — they could help protect seals in a noisy world. Ocean noise from ships, oil drilling, and construction makes it harder for seals to find mates and communicate with each other. "By understanding how these animals hear, we can start to put solutions in place," Dr. Cooper said. In other words, knowing the secret behind seals' remarkable ears might be the first step toward keeping them safe.