Foes and females both have role. (What's the Mane Point?).

Zoologists since the 1800s have pondered the purpose of the lion's mane, conjecturing that the mop either serves to defend against competitors' claws and teeth or to attract a female. Now the first experimental study to consider the question suggests a manes condition advertises high-quality mates to picky females and wards off male adversaries.

Craig Packer and Peyton M. West of the University of Minnesota at Minneapolis-St. Paul examined photographs of 568 male lions in Tanzania's Serengeti National Park taken since 1964. They assessed the shade and length of manes and compared these qualities with long-term demographic and behavioral records of each lion.

The historical data suggest that males with short, light manes are less healthy and inferior fighters when compared with counterparts with thicker, darker manes. Good nutrition and sufficient testosterone, which regulates hair growth and melanin production, are necessary for a showy mane, says West.

In addition, she and Packer tested how Serengeti lions behaved toward unknown individuals based on their mane condition. The scientists developed life-sized stuffed lions and adorned each with one of four mane types: long and dark, short and dark, long and light, or short and light.

Between 1996 and 2000, the two researchers used the dummies to test the reactions of a community of 300 Serengeti lions. In each experiment, the lion watchers deployed two dummies simultaneously, each sporting a different mane variety, while attracting lions with recordings of scavenging hyenas.

The researchers report in the Aug. 23 Science that males and females responded differently. Females approached the darker-maned dummy in 90 percent of the tests, but mane length didn't matter. In contrast, males always chose first to investigate lighter-maned dummies and were significantly more likely to investigate a short-maned dummy than a long-maned one. The researchers infer that a female's dummy choice is driven by mating concerns, while a male's choice is driven by issues of competition.

However, says West, the benefit of displaying your virtues comes at a cost. West and Packer used infrared cameras to show that lions with larger, darker manes get significantly hotter in the African sun.

"Manes offer social advantages but entail ... costs," agrees Bruce D. Patterson at the Field Museum in Chicago. However, Patterson questions the link between testosterone and showy manes, pointing out that factors such as age could independently drive both testosterone amounts and hair growth.

"Folks have wondered about the functional significance of lion manes ... since Darwin," says Kay E. Holekamp of Michigan State University in East Lansing. "The findings are both significant and interesting, not just because they address a longstanding question in a fascinating organism," but also because they include both costs and benefits of a mane.