George is a typical Midwestern American male in the prime of his life, with an attractive spouse named Martha. George is a devoted husband, Martha an attentive wife. The couple has four young children, a typical home in a lovely valley full of corn and bean fields, and their future looks bright. But George is occasionally unfaithful. So, occasionally, is Martha. No big deal: That's just the way life is in this part of America.
This is a true story, though the names have been changed, and so, for that matter, has the species. George and Martha are prairie voles. They don't marry, of course, or think about being faithful. And a bright future for a vole is typically no more than 60 days of mating and pup-rearing that ends in a fatal encounter with a snake or some other prairie predator.
But if you want to understand more about the conflict in human relationships between faithfulness and philandering, have a peek inside the brain of this wee rodent. Researchers have been studying voles for more than 25 years, and they've learned that the mating behavior of these gregarious creatures uncannily resembles our own-including a familiar pattern of monogamous attachment: Male and female share a home and child care, the occasional dalliance notwithstanding. More important, researchers have discovered what drives the animals' monogamy: brain chemistry. And when it comes to the chemical soup that governs behavior associated with what we call love, prairie vole brains are a lot like ours.
Scientists are careful to refer to what voles engage in as "social monogamy," meaning that although voles prefer to nest and mate with a particular partner, when another vole comes courting, some will stray. And as many as 50 percent of male voles never find a permanent partner. Of course, there is no moral or religious significance to the vole's behavior-monogamous or not. Voles will be voles, because that's their nature.
Still, the parallels to humans are intriguing. "We're not an animal that finds it in our best interest to screw around," says Pepper Schwartz, a sociologist at the University of Washington, yet studies have shown that at least one-third of married people cheat. In many cases, married couples struggle with the simple fact that love and lust aren't always in sync, often tearing us in opposite directions. Vole physiology and behavior reinforce the idea that love and lust are biochemically separate systems, and that the emotional tug of war many of us feel between the two emotions is perfectly natural-a two-headed biological drive that's been hardwired into our brains through millions of years of evolution.