Monogamy isn't unique to humans; the prairie vole keeps only one mate. Unlike many rodents, when a young prairie vole meets a stranger, the two don't attack each other.
Instead, if they are both sexually available, their instinct tells them their chance to find a mate may be now or never because the receptors in these voles' brains give the voles a intoxicating and permanent sense of pleasure from monogamy.
When two, unrelated sexually available voles meet, their brain chemistry instantly begins to alter causing a variety of complex chemical interactions.
At first, the chemicals cause a heightened level of attraction and passion and afterward a lower stress and eventually a feeling of safety and security. Simply put, the presence of two unmatched voles in the same place is so powerful they begin to regulate each others brain chemistry, altering it permanently.
Forty-eight hours after their first meeting, the two voles hit their peak and they mate. For 24 hours. Straight. After the mating, the voles are described to be "addicted to one another as junkies to smack," according to Hungarian researchers Sources: Smithsonian National Zoo, The Nature Conservancy