One has no legs and swims in the ocean, and the other has four legs and lives in rivers, but a genetic study shows that the whale and the hippo are close relatives in evolutionary history.

The study, by researchers at the Tokyo Institute of Technology in Japan and Pennsylvania State University at University Park, Pa., compared gene sequences from the minke whale, the sperm whale and the hippopotamus. It found the diverse animals share a sequence of genes inherited from an ancient common ancestor.

Until 1985, it was generally thought that pigs were more closely related to whales. Other genetic studies since have suggested the whale-hippo link. The new study, researchers say, confirms that the hippo is the closest living relative to the whale.

The genetic analysis was conducted by Masato Nikaido and Norihiro Okada of the Tokyo Institute and by Alejandro Rooney of Penn State.

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