Dark manes make lions king.
Lionesses like their mates butch, dark and hairy. Using life-sized dummies with detachable wigs, researchers in Africa have found that female lions favour mates with a dark head of hair1.
Lions' manes sprout at adolescence, in a surprising range of styles - shoulder-length or cropped, black or fair. "One question that's never been answered is why," says Peyton West of the University of Minnesota in St Paul.
After five years watching lions circle and sniff mannequins in Serengeti National Park in Tanzania, West thinks she has the answer. Females prefer a brunette male to a blonde one, she and colleague Craig Packer have found.
Males with high levels of testosterone grow darker hair. These males may be more aggressive and therefore better at defending mates and cubs. "The real reason lions have manes is to signal their health and parenting ability to other lions," says West.
"It sounds a very plausible theory," says Tim Clutton-Brock, who studies animal evolution at the University of Cambridge, UK. People had assumed that manes evolved to protect the head during fights, he says. Although this may be why they first evolved, other lions' taste in hair may have driven the evolution of length and style.
But like the peacock's tail and other animal adornments that lure the ladies, dark hair comes at a price. Brunette animals, like men in tight trousers, "have hotter balls and less sperm", says West. She filmed lions in the Serengeti and in Kenya's Tsavo National Park, using an infrared camera that measures how much heat radiates from the body.
In fact, lions' hair, like men's, reveals a lot about age, health and hormones. Youths and grandpas tend to have shorter manes, and the starved or injured lose their locks.
Males therefore prefer to threaten males with longer and lighter hair, West has found. "It makes sense to approach the guy who is least likely to pick a fight," she says.
It's hard to get hold of stuffed lions. So a toy factory made West four custom-built lion dummies with clip-on manes - either bouffant or clipped - in shades of dark brown or tawny.
The unwieldy animals "arrived in their own private jet", says West; the team then grappled them into a specially constructed trailer. "It was a nightmare," she says.
They offloaded two dummies downwind of a pride in the park, and dressed them in either long and short, or dark and light manes. Nearby lions, attracted by broadcasted calls of hyenas at a kill, circled and approached to sniff under the dummies' tails.
The team also measured testosterone levels in stored blood levels, and used a 30-year record of lion behaviour to back up their findings. "They're lovely results based on imaginative experiments in the wild," says Clutton-Brock.
West, P.M. & Packer, C. Sexual selection, temperature and the lion's mane. Science 297, 1339 - 1343 (2002).
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Pearson, H. Lionesses prefer brunettes. Nature (2002). https://doi.org/10.1038/news020819-10