One night last winter, over drinks in downtown Los Angeles, the biologist David Gruber told me that human beings might someday talk to sperm whales. In 2020, Gruber founded Project CETI with some of the world’s leading artificial-intelligence researchers, and they have so far raised $33 million for a high-tech effort to learn the whales’ language. Gruber said that they hope to record billions of the animals’ clicking sounds with floating hydrophones, and then to decipher the sounds’ meaning using neural networks. I was immediately intrigued. For years, I had been toiling away on a book about the search for cosmic civilizations with whom we might communicate. This one was right here on Earth.

Sperm whales are the planet’s largest-brained animals, and their nested social structures are immense. About 10 whales swim together full-time as a unit. They will sometimes meet up with others in groups of hundreds. All of the whales in these larger groups belong to clans that can contain as many as 10,000 animals, or perhaps more. (The upper limit is uncertain, because industrial whaling reduced the animals’ numbers.) Sperm whales meet just a fraction of their fellow clan members during their lifetime, but with those they do meet, they use a clan-specific dialect of click sequences called codas.

I recently visited the paleontologist Nick Pyenson in his office at the end of a long corridor of fossils at the Smithsonian Museum of Natural History. As we hefted a sperm whale’s skull out of a fiberglass crate, he told me that the clans likely date back to the Ice Age and that a few could be hundreds of thousands of years old. Their codas could be orders of magnitude more ancient than Sanskrit. We don’t know how much meaning they convey, but we do know that they’ll be very