Human love lives are complex. One of the underlying reasons may be that we have two conflicting genetic programs at work in our limbic system, both of which have subtle, but powerful influences on our intimate relationships.
I will discuss those programs, and the tension between them, at length in other posts, but here let me clarify what I mean by some terms I will be using. I'll update this post as needed.
The limbic system, pictured above, is a very old part of the brain, which is surprisingly similar in all mammals. This explains why experiments on rats can help scientists understand how human brains function. As my husband observed, "Scientists aren't doing experiments on rats to learn how to help rats with their erections and addictions."
So why should lovers care about their brain's limbic system? Because it is the part of the brain from which our emotions and drives arise. It's where we experience the thrills of sexual arousal and orgasm (and their aftermath). The limbic system is also where we fall in (and out) of love. It operates subconsciously, recording our likes and dislikes, coloring our impressions, and judging every experience and person constantly...and instantly.
Our rational brain (cerebral cortex) can temper the non-stop input from the limbic system, but the limbic brain trumps the rational brain with discouraging frequency. Worse yet, it has its own agenda, set by evolution, which often conflicts with our conscious wishes.
When I refer to genetic "programs," I am referring to predictable inclinations produced by very small, extraordinarily powerful structures, systems or wiring in the limbic system. For example, one tiny structure within the limbic system is the hypothalamus. Although it comprises less than one percent of the brain's weight, it is the central player that integrates our nervous system with our endocrine system, determining which hormones are released. Some of the tiny structures within the hypothalamus are pictured here.
Other brain mechanisms wouldn't look like structures to most of us. Some consist of nothing more than tiny nerve cell receptors for particular neurochemicals. These can determine a species' behavior simply by making it more sensitive to certain stimuli. Voles (mouse-like rodents) that pair bond, appear to do so as a result of such increased sensitivity (due to specific nerve cell receptors for key neurochemicals).
This is a good place to explain what these programs are not. They are not "hardwiring." Yet they can bleep very persuasive signals. The urge to drink when thirsty is a program, critical to our survival as a species. We may override it for a time, but we can't just turn it off by force of will because it is a motivational system built into our limbic system.
We also have a program that urges us to pair bond--as well as one that urges us to stray. Yet our programming alone can't force us to do either, as many monks and nuns would attest. Interestingly, romantic love (pair bonding) can sometimes be a stronger program than the drive to have sex. As anthropologist Helen Fisher has observed, people don't kill themselves when their sexual overtures are rejected, but abandoned lovers have been known to stalk and kill ex-sweethearts or themselves. Pair-bonding mammals, too, show measurable stress when they lose a mate. (Prairie voles confirm guys have feelings too)
At the same time, the urge to have sex with novel mates (Coolidge Effect) often erodes our pair bonds. The tension between these programs obviously shows up in different cultures in different ways. On average, it may push us toward serial monogamy...with some fooling around on the side. All things being equal, we bond long enough to fall in love with our children, who benefit from having two caregivers. Yet we also tend to increase the genetic variety of our offspring by changing mates.
Programs do not guarantee that a mammal will behave in a certain way, or even that every individual within a species will experience the same inclinations. (There are always outliers, that is, exceptions, who vary from the norm.) Nevertheless, programs can produce very powerful, predictable urges and inner conflicts in most of us. They can drive our behavior without our conscious awareness and cause us to rationalize actions we know we will later regret.
Evolution molds these subconscious programs based on natural selection. For example, we're wired to gorge on high calorie food because our ancestors didn't have refrigerators and had to store extra calories as fat to increase their chances of survival (and procreation). These days it takes a lot of willpower to stick to a healthy diet thanks to that underlying program. (Read Mean Genes by Burnham and Phelan for a brilliant, entertaining discussion of our genes' hidden agendas.) The point is that "just doing what comes naturally" can carry us where we do not want to go.
This genetic-success aspect of our programming is especially critical for lovers to understand. The genetic programs in our love lives are not there to help us "live happily ever after." They are there to motivate us to produce offspring who will carry our genes into the future. They're why orgasm feels good and the grass might appear greener with a new sexual partner.
At the same time, one of the most important determinants of individual human happiness and well-being appears to be a harmonious relationship, or pair bond. Fortunately for lovers who wish to strengthen their pair bonds, there are time-honored methods of steering our genetic programs in the direction of closer emotional bonds.
And for science buffs: Growing evidence of a lingering post-orgasm cycle (links to studies)