Beauty really is in the eye of the beholder. Rather than always chasing the best-looking members of the opposite sex, some animals prefer mates that the majority find decidedly unattractive.
鈥淯gly individuals can sometimes do better than good-looking ones,鈥� says evolutionary biologist Rob Brooks of the University of New South Wales in Sydney. If the same holds true for people, then it may be time to stop worrying about how closely you adhere to the Hollywood ideal of attractiveness.
Studies of how birds, fish and people choose mates have found that members of the same species tend to find the same things attractive. For instance, peahens prefer to mate with brightly coloured, long-tailed peacocks, while women prefer tall men. Those attractive traits are supposed to signal beneficial characteristics such as an increased chance that any offspring will survive.
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But there are problems with the idea that all animals prefer the same features. For a start, you would expect birds and fish of the same species 鈥� and perhaps people too 鈥� to look far more similar than they do, because evolutionary forces would have moulded them into a super-attractive archetype.
What鈥檚 more, most of us know from experience that one person鈥檚 dog is another person鈥檚 sex god 鈥� and that makes some evolutionary biologists cautious about assuming that animals have only one ideal of attractiveness. 鈥淧eople say 鈥業 don鈥檛 like what my mate down the pub likes鈥�. How do you reconcile that with a universal Hollywood idea of attractiveness?鈥� says Brooks.
Spots and tails
To find out, he joined forces with John Endler, an ecological geneticist at James Cook University in Townsville, to observe how individual female guppies choose between different males. They found that although all the females liked males with bright orange spots and large tails, a minority of females also liked males with black markings.
鈥淚t鈥檚 a nice result,鈥� says Raoul Mulder, an evolutionary ecologist at the University of Melbourne. 鈥淚t explains why certain very rare colour patterns continue to persist in guppy populations.鈥�
Brooks says that previous studies failed to detect idiosyncratic mate choice because they looked at what whole populations found attractive on average. 鈥淏ut you don鈥檛 mate with an average, you mate with an individual,鈥� he says. There may be a good reason that attractiveness is idiosyncratic, Brooks says. What benefits one individual might not necessarily benefit another.
For example, says Brooks, this may be what happens with immune system proteins called MHC molecules. The more diverse a selection you inherit from your parents, the better equipped you are to fight off disease. Men with different MHCs smell differently, and not only can women detect that difference, but they also tend to prefer the smell of men whose MHCs complement their own. This makes sense because any children resulting from such a pairing would have more diverse MHCs (New 杏吧原创, 10 February, p 36).
鈥淢HC is a great example of a real genetic benefit to mate choice that isn鈥檛 uniform,鈥� says Brooks.
More at: Evolution (vol 55, p 1644)