The researchers measured genetic similarity by comparing 1.7 million individual DNA building blocks, known as single nucleotide polymorphisms, in the study participants. They compared the genetic makeup of the married couples to other randomly chosen people of the opposite sex in the same pool of study participants.

Domingue says the actual mechanism for a person being drawn to another person's genetic similarities is probably complicated and multifaceted-"just a whole host of things".

The researchers note that people usually pick spouses with similar backgrounds and characteristics in addition to education, including race, religion, age, income and body type. Genetic similarity can be added to the list, they say.

"For example, people clearly care about height in picking partners. To the extent that tall people marry other tall people, that is going to result in genetic similarity among spouses. But it is difficult to know whether height or genes is driving this decision," Domingue says.