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DNA Suggests Cultural Traits Affect Whale Evolution

In some species of whales, behaviors learned within families may be altering the course of genetic evolution. In the current Science, Hal Whitehead of Dalhousie University in Halifax, Nova Scotia, claims that an unusual pattern of genetic markers in sperm whales, pilot whales, and killer whales implies that matriarchs of those species teach their offspring as-yet-unidentified behaviors that give them a substantial survival advantage, a situation thus far documented only in humans.

To study the effects of intense hunting of sperm whales in the Pacific Ocean, Whitehead and his wife, marine biologist Linda Weilgart, collected data on the whales' vocalizations and tail scars, which may indicate how well an animal fends off predators. They also gathered sloughed-off skin samples for genetic testing. While the researchers found no clear geographical pattern to the whales' markings and vocalizations, they did find a genetic pattern: The whales' mitochondrial DNA (mtDNA), which is inherited only from the mother, indicated that groups with similar calls and markings were related.

Whitehead concludes that the whales are passing on their calls, and presumably other behaviors, within family groups. When he studied published genetic analyses of other whales, Whitehead found that sperm, pilot, and killer whales--species in which offspring spend their lives with their mothers and maternal relatives--have very low mtDNA diversity, less than one-fifth that of other whales. He proposes that the diversity must have narrowed in the course of whale evolution as mtDNA "hitchhiked" on the success of behaviors passed from older females to calves, such as feeding techniques, methods for fending off predators, and baby-sitting. In a computer model, Whitehead found that a theoretical cultural behavior that gives a 10% reproductive advantage and is passed to 95% of daughters will reduce mtDNA diversity to almost zero in 300 generations.

"It's a provocative idea, a really neat idea," says marine biologist Bernd Wursig of Texas A&M University, Galveston. But it's hard to make a strong case for such a radical notion because so little is known about whale behavior and genetics, he and other whale experts say. Whitehead admits that the theory "is far from proven," but it "fits the data better than any other explanation."