"Similarity, of course, is only one of many criteria people use in choosing social partners," the researchers conclude. "Physical appearance, status, control of resources, reciprocity, location and family situation all provide constraints and exert influence as well."
But that old claim that opposites attract still persists, despite decades of research showing that "it just ain't so," Rushton says.
"Research has been clear, over and over again, that you can be opposite on one or two dimensions, but overall it's similarity that rules," he says.
The husband may love steak, and the wife may hate it. But too much of that can kill a relationship.
"Just think if you were married to somebody and you had the exact opposite political attitude," he says. "You wouldn't be able to greet each other over the breakfast table. It would just be awful."
Lee Dye's column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.