Dolphins may not be the second smartest species on earth—next to mice—as The Hitchhiker's Guide to the Galaxy contends, but they do appear to have culture. Marine biologists have noticed that some wild dolphins in Australia's Shark Bay, most of them females, keep marine sponges on their snouts for protection as they root around the seafloor for food. Researchers suspected it was learned tool use, but they couldn't discount a direct genetic cause for the behavior. Now, based on DNA samples from 13 “spongers” and 172 nonspongers, biologists from the University of New South Wales in Sydney have found that all the spongers are related to one another and probably share a recent ancestor, but they don't fit a pattern in which a gene could be causing the tool use. Hence, they conclude in the June 21 Proceedings of the National Academy of Sciences USA that daughters are most likely learning the behavior from their mothers.