Thursday, September 21, 2006

Science and Attraction

A recent article in The Scientist discusses what makes us attractive. Based on the principles of sexual selection (a principle tightly bound to evolution), both females and males search for the best mate based on cues that imply physical and genetic fitness (good genes). For instance, many male birds are very colorful (think peacock), indicating that they are healthy enough to spend vast amounts of energy on looking good. Here are some human features that may indicate physical and genetic fitness:

1. Waist-to-hip ratio. People actually study this. Men are more attracted to women with a smaller waist to hip ratio (smaller waist, larger hips). Logically, this indicates a woman’s ease of childbirth. But apparently it is also related to “age, pregnancy, and several nasty diseases." Interestingly, “Men of the Hadza hunter-gatherer tribe prefer women with a waist-to-hip ratio of 0.78, close to the actual ratios of 17-24 year-old Hadza women. American men prefer curvier women, with an average ratio of 0.68, as precisely modeled by Playboy centerfolds.”

2. MHC complex compatibility. Genetically encoded, our MHC complexes contain the potential sequences for antibodies that protect us from huge numbers of pathogens via the immune system. Since we have two sets of the MHC complexes (one from Mom, the other from Dad), we’d double our immunity by getting parents with two different sets of MHC complexes. Somehow, our MHC complexes are reflected in body odor, and women prefer the body odor of men with different MHC complexes than our own. Another interesting point: “There is evidence that this preference is reversed in women taking oral contraceptives.”

3. Left-right symmetry. I learned back in my ‘Deis Faces class that more symmetry is considered more beautiful. Consider Harry Connick, Jr.: incredibly lopsided, incredibly ugly. Then there’s Liz Taylor: quite symmetric, quite beautiful. (I also learned that averageness is also beautiful. One study took photographs of many people and combined them to make an “average” person, who was more attractive than each of the real people.)

4. Dance ability. Here’s what got me, and keep in mind that like any measure of attractiveness, it doesn’t apply to everybody, and in practice, many other things come into play. This study(1) found that dancing ability can be a measure of body symmetry, which may or may not be related to genetic fitness. This paper is interesting, and short, worth the read. They took Jamaican kids, evaluated their body symmetry, and video taped them dancing (individually). Then they used some movie magic to subtract their body features, leaving only their dance moves, then had other Jamaicans evaluate their dancing ability. The higher-rated dancers turned out to be more symmetric people. The question now is whether body symmetry is actually an indicator of genetic fitness.

1. W. M. Brown et al., "Dance reveals symmetry especially in young men," Nature, 438:1148-50, 2005.

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