Symmetry Is Sexy: The Science of Sex

I’ve al­ways been fas­ci­nat­ed by sym­me­try in na­ture. From the ra­dial sym­me­try of a snowflake or a star­fish, to the bi­lat­er­al sym­me­try of a crab shell or a hu­man body, na­ture’s abil­i­ty for com­ple­men­ta­tion is as­tound­ing. But the fact that sym­me­try is so wide­spread is no co­in­ci­dence. Whether it’s a bird or a hu­man, sym­me­try means good genes, and that means at­trac­tion.

Hu­mans, like most an­i­mals, ex­hib­it mir­ror sym­me­try, mean­ing we are rough­ly the same on both sides. This is some­thing we sub­con­s­cious­ly find ap­peal­ing in our mates. For in­s­tance, men are more at­tract­ed to wo­m­en with sym­met­ri­cal fea­tures. In a study at the Uni­ver­si­ty of New Mex­i­co in Al­bu­querque, fe­males with sym­met­ri­cal faces were not on­ly more at­trac­tive to their male peers than fe­males with asym­met­ri­cal faces, they al­so had a high­er num­ber of pre­vi­ous sex­u­al part­n­ers and tend­ed to lose their vir­gini­ty at an ear­li­er age.

The si­t­u­a­tion is true for a man’s at­trac­tive­ness to a wo­m­an as well. Though wo­m­en are more apt to look for things like sta­tus and dom­i­nance, which may be stronger in­di­ca­tors of fit­ness than sym­me­try, we still val­ue match­ing com­po­nents. Studies have found that wo­m­en achieve greater sex­u­al sat­is­fac­tion with part­n­ers who are sym­met­ri­cal, and find sym­met­ri­cal dancers more at­trac­tive than asym­met­ri­cal ones. This in­di­cates body, not just fa­cial sym­me­try, is an im­por­tant com­po­nent of at­trac­tion.

Sym­me­try’s role in mate se­lec­tion is based on the hy­poth­e­sis that it can give clues to un­der­ly­ing ge­net­ic fit­ness. Asym­me­try can show flaws in the ge­net­ic code or a pre­dis­po­si­tion to dis­ease—some­one you don’t want your genes com­min­gling with. Be­cause of the abil­i­ty of sym­me­try to ad­ver­tise some­one’s health, it is an out­ward clue to help us se­lect a good mate.

Yet it stands to ques­tion whether we find sym­met­ri­cal faces and bodies more at­trac­tive be­cause they’re healthi­er, or be­cause that’s what we’re used to. Look at the cov­er of any fashion mag­azine and it’s easy to con­clude that most mod­el­s’ faces are al­most mir­ror im­ages of each other, with very lit­tle skew­ing. Does our idea of at­trac­tive­ness have more to do with na­ture, or the norm?

Evi­dence shows that sym­me­try is an at­trac­tive trait within and across cul­tures, in­di­cat­ing it’s im­por­tant re­gard­less of cul­tu­r­al norms. A study com­par­ing the pref­er­ences of peo­ple in the Unit­ed King­dom with the Hadza, a hun­ter-gather­er so­ci­e­ty of Tan­za­nia, found that sym­me­try was more at­trac­tive than asym­me­try across both cul­tures. In fact, sym­me­try was an even big­ger cue of at­trac­tive­ness in the Hadza than in the Brits, suggest­ing that eco­log­i­cal pres­sures may be a se­lec­tive pres­sure for this so­ci­e­ty, forc­ing it to find out­ward signs of ge­net­ic qual­i­ty. Sym­me­try is one of th­ese signs. Fur­ther­more, men with high­er stand­ing (the good hun­ters) placed greater val­ue on sym­me­try in the fe­male face than men of low­er stand­ing; that is, men of high qual­i­ty were more dis­crim­i­nat­ing, and one way in which they dis­crim­i­nat­ed was by fa­cial sym­me­try.

Sym­me­try may be at­trac­tive from an evo­lu­tio­nary per­spec­tive, but does it re­al­ly mean healthy? Look no fur­ther than Hol­ly­wood to see that the peo­ple we think of as the “most” at­trac­tive, while sym­met­ri­cal, aren’t ne­ces­sar­i­ly the ones you’d want bear­ing, rais­ing, or touch­ing your kids (Brit­ney Spears, for ex­am­ple). Does our face give clues to over­all health?

Re­search in­di­cates that in an­i­mals and hu­mans, sym­me­try can be a good in­di­ca­tor of health. Those with out­ward signs of sym­met­ri­cal de­vel­op­ment do tend to be healthy. On­ly a few studies have looked at the corol­lary of this; that is, does asym­me­try in­di­cate bad health? A study done in 1997 found that peo­ple with fa­cial asym­me­try are more like­ly to have psy­cho­log­i­cal, emo­tio­n­al, and phy­si­o­log­i­cal dis­tress than those with sym­met­ri­cal faces. How­ev­er, it’s tough to parse out whether they have th­ese problems be­cause they’ve been per­ceived to be unat­trac­tive through­out their lives, or whether their psy­cho­log­i­cal dis­tress­es are due to ge­net­ic caus­es (most like­ly a com­bi­na­tion of both). Per­haps sym­me­try tells us some­thing about phys­i­cal fit­ness, but gives us few­er cues about a per­son­’s psy­cho­log­i­cal at­tributes.

Even if sym­me­try does equal at­trac­tion in our minds, it’s one of mul­ti­ple fa­cial cues we use to judge who’s hot and who’s not. One of things we find most at­trac­tive is when some­one looks just like us; re­search­ers be­lieve this is be­cause we’ve looked at our par­ents faces since we were young, and want some­one who looks like them. Just as peo­ple of­ten look like their dogs, cou­ples al­so tend to look like each other. (A ques­tion I’d like to see an­sw­ered: do adop­tees or peo­ple not raised by their bi­o­log­i­cal par­ents still pre­fer to date peo­ple that look like them?)

And then there are phy­si­o­log­ic cues be­yond sym­me­try. One of the best known is a wo­m­an’s waist to hip ra­tio. Nu­mer­ous studies have found that wo­m­en with a waist-to-hip ra­tio of around 0.7 are the most at­trac­tive to men. (This ra­tio means your waist is small­er than your hips.) This so-called “hour-glass fig­ure” may in­di­cate that a wo­m­an has de­posit­ed fat around her hips and is ready to bear chil­dren. Most en­cour­ag­ing­ly, this ra­tio holds true for a wide range of weights.

Whether we want their kids or mere­ly want to make out, those peo­ple whose bodies look healthy, ge­net­i­cal­ly fit, and able to re­pro­duce are most at­trac­tive to us. This means sym­me­try, hips, and a fa­miliar face can go a long way to land­ing a lover.

Up­dat­ed Novem­ber 23, 2008
First pub­lished Fe­bruary 2008