Sometimes opposing adages fight to a draw: “Better safe than sorry” versus “Nothing ventured, nothing gained.” But when it comes to “Opposites attract” versus “Birds of a feather flock together,” the data are in: we end up with partners like ourselves. A study of 291 newlywed couples found spouses to be closer in values, religiosity, and political attitudes than would be predicted by chance . Scientists have a term for this: positive assortative mating. (It’s negative assortative mating when opposites attract.)
The human species isn’t the only one that flocks together. A meta-analysis of assortative mating in animals based on traits such as size and color found that nearly all the assortment was positive . Not that sorting by size and color is limited to animals: humans tend to marry people with a similar level of body fat , and online daters stick to their own race .People also gravitate toward mates whose faces look like theirs. In one study, subjects who were presented with a series of photos were able to pair a woman’s image with that of her partner, based on facial similarities—even when only isolated features (noses, mouths, eyes) were displayed .
Friendly people apparently seek same: a field experiment in rural Senegal found spouses to have corresponding levels of generosity . People with less desirable qualities also attract one another. Having bipolar disorder or major depression makes you more likely to marry someone else with an affective disorder . Alcoholics, too, tend to pair up, with potentially disastrous results for their future offspring .