Prairie voles are often regarded as the animal kingdom's mascots of monogamy. As the only mammalian species genetically inclined toward pairing up 'til death do they part, the rodents have been studied extensively to find out what keeps them together in the wild. Along with improved chances for survival, the bonding oxytocin and vasopressin are the key neurological ingredients to the voles' faithfulness. Pair bond-promoting vasopressin in particular, which saturates the nucleus accumbens, a brain structure pivotal in sensing satisfaction, drives vole pairs to lifelong coupling. In one experiment at Emory University, scientists blocked vasopressin receptors in prairie vole brains, resulting in an outbreak of adultery [source: Yong]. Conversely, cranking up the levels of vasopressin in brains of meadow voles -- the prairie voles' promiscuous cousins -- sparked a monogamy movement.