It's not easy being beautiful, especially when you're a male lion. New research suggests that what lady lions love most and what other males fear most is a leo with a long, dark mane--which is precisely the worst sort of 'do to have in Africa's often sweltering environs.

Biologists have long pondered the purpose of the lion's hot, conspicuous mane, which seems at first glance like more trouble than it's worth. Evolutionary theory holds that there should be some benefit gained from it, but what might that be? Two hypotheses have been put forth. The first holds that the extra fur protects the lion from injuries to the neck and shoulders. The second posits that the mane makes the lion more attractive to lionesses and more intimidating to other males.

In the new work, Peyton M. West and Craig Packer of the University of Minnesota studied the reactions of male and female lions to various types of manes, using dummy lions to model the various coifs. They found that whereas females fell for dummy males with dark manes (as opposed to blondes), males avoided the brunettes. Males also avoided dummies sporting long manes.

As it turns out, mane color and length may be pretty good indicators of a lions health and fitness. "Dark color tends to be found in high-testosterone males," West observes. "Therefore, it isnt surprising that females would prefer darker manes and males would be intimidated. But there is no correlation between testosterone and mane length." Males pay more attention to mane length because recently injured lions have shorter manes, she explains.

The males dark allure comes at a significant cost. "A male with a dark mane may have to work harder to stay cool, behaviorally or physiologically, and is advertising that toughness, along with his toughness in battle," West remarks. (Longer manes, on the other hand, do not appear to retain additional heat.) In some especially hot regions, however, all that fur costs too much, and the males go maneless.

"As climate changes, things like lion manes, the brightness of bird plumage and the size of deer antlers may be sensitive bioindicators, Packer muses. "They can tell you how well an animal is doing in the environment." The team's findings were published today in the journal Science.