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The Biological Basis of Monogamy

Over the ages, mating and bonding have seemed as something that occurred through emotional rather than intellectual reasoning. How and why people love each other has been as elusive as our understanding of love itself.

Bonding Begins With Our Furry Friends

Oddly enough, our understanding of the bonding of mates begins with the prairie voles, because these furry little creatures have taught us the critical biochemicals needed for creating and maintaining successful social relationships. These guys represent the 3% of mammals that form monogamous pairs that bond for life. They huddle and groom each other, hang around the nest, and generally exhibit human-like social behavior (high levels of compatible behavior). When their offspring are born, they are attentive, good parents who share nesting and pup-raising responsibilities.

By studying their genes and biochemistry, we have been able to glimpse into our human neurochemistry that enables us to form and maintain social relationships. And how do we know this? We know this not only by detecting these hormones in successful relationships, but also by seeing that these essentials are lacking in those poor souls who can not form meaningful emotional bonds with others – like autistics.

The Rogue Vole

And to prove this point, the prairie voles have a close cousin, called the montane vole, who is just their opposite. The montane vole is a “wham-bam thank you ma’am” promiscuous sex roamer who, (although they are almost identical to the prairie vole), lack the key genes that enable their counterparts to be parents of year on the Midwest prairie.

And it is significant to point out here that meaningful relationships do not pertain only to romantic partners, but to all partners – parents and children, co-workers and business partners, and down the line.

So back to our loving prairie voles, who are now mating and producing the two key hormones necessary for bonding -- oxytocin and vasopressin. This is a natural process. Over time, researchers have discovered that when they administer an injection of these two chemicals into the voles -- without their actual mating -- they still form a bond to each other. That’s how powerful the influence of these bonding chemicals really are.

Humans Are Similar

These two biochemicals are also present in humans, and are also wired to form a powerful reception with the neural circuits in our brain that relate to reward and reinforcement. For example, in the brain of a female prairie vole mating, scientists have measured -- in the reward center of her brain -- a 50% increase in dopamine! That’s some jolt of pleasure one doesn’t forget.

Now prairie voles are members of the rodent family, though far removed cousins. When rats were studied, we learned that they never associate sex with a particular female, which is why they are not monogamous. Yet they do have a similar ability to identify other rats by their smell. And if scientists disable this genetic ability (by eliminating the key gene) they lose this identifying ability. The voles and rats possess what is called the Vomero-Nasal Organ, which is sensitized to subtle differences in aromas. So why do the voles have a more profound sensory memory that allows them to identify their mates so accurately?

The Key Brain Area

When researchers studied the prairie voles, they found that these creatures have a unique area in their brain that, upon mating with another, encodes the memory by generating new brain cells in this special area. And it is this ability, which is enabled by the hormones vasopressin and oxytocin. Meaning the vole’s olfactory memory (memory through smell) is linked to the pleasure-reward areas of their brains. And as sex activates the release of vasopressin and oxytocin in people as well, the researchers involved further hypothesize that this linking of identity with pleasure-reward imprinting is the active factor why human behavior and that of other mammals have become monogamous.

So don’t let this information cloud over your appreciation of your partner’s loyalty. Just see this physiological-psychological behavior as Nature’s way of establishing favorable social bonding through a biological instinctive mechanism.

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Sources: Neuroendocrine Bases of Monogamy Trends Neuroscience 1998 Feb;21(2):71-5 Mammalian Species No.355, pp. 1-9 Microtus ochrogaster American Society of Mammalogists April 26, 1990 Pdf i0076-3519-355-01-0001 (www.science.smith.edu) Aspects of Reproduction and Development in the Prairie Vole Museum of Natural History, University of Kansas 10:129-161 Removal of the Vomero-Nasal Organ Disrupts the Activation of Reproduction in Female Voles Physiology and Behavior 40:349-355

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