When we attempt a long-term relationship, we are fighting against our genetic programming. Our genes urge us to have sex and make babies. Unfortunately for the companionship, fidelity, and love in our relationships, they also urge us to move on to other partners, or be unfaithful to our spouse.
This viewpoint is sometimes called the 'selfish gene' approach to understanding animal behavior. The basic premise is that our bodies and brains are merely transient machines geared to the preservation and proliferation of our genes.
Selfish genes are also subtle genes. Genes don't talk, but they motivate behavior by creating feelings, emotions, desires, and thoughts. Genes do this by building and maintaining our brains, and by altering the neurochemicals with which our brains function. Whenever scientists talk about some evolved behavior or characteristic, such as a monogamous inclination, a dad protecting his offspring, or a wife taking lovers, they are talking about a function of the brain that has evolved over time because it led to more offspring (who then had similar inclinations).
The premise is really very simple. The human mind - like any other organ - was designed for the purpose of transmitting genes to the next generation, and the feelings and thoughts it creates are best understood in these terms. Sexual desires, falling madly in love, wanting children, and mothering instincts, are all genetically-programmed brain functions. These are the more obvious examples of your genes' strategy. Other, less obvious, examples of your genes' wiles are your everyday shifting moods and attitudes toward a mate, such as, trust, suspicion, jealousy, revulsion, warmth, boredom, and so on. These emotions are the handiwork of evolution, and they remain with us today because in the past they led to behaviors that helped propagate genes.
The basic premise is that your selfish genes manipulate your brain chemistry to accomplish their goals. The two most selfish goals are motivating you to:
- engage in fertilization behavior to make more babies, and
- move on to new partners to create greater variety in the species.
These two goals are accomplished by turning on the reward circuit (an area the size of a pea, deep within a primitive part of the brain) by means of a blast of the neurochemical dopamine. Dopamine is released whenever we eat or engage in sex, both of which are important for the survival of our genes. Not surprisingly, we are programmed to crave dopamine. The lure we get from eating is a little squirt of dopamine. With each climax we get a huge blast of dopamine. All addictive substances increase dopamine. That is why they are addictive.
In short, your brain is wired to experience dopamine as pleasure (although it is more accurately "craving"). Dopamine is why you crave sex. Your genes take this clever trick a step further. Here's a genetically-programmed behavior that uses dopamine and the reward circuit to encourage you to change partners. It is found in nearly all animals, so perhaps you will recognize it.
Males of most species have a definite urge to seek variety in their sexual partners. This is called the 'Coolidge Effect'. So, for example, if a male rat is introduced to a female rat in a cage, there will be an initial frenzy of copulation. Then, progressively, the male will tire and, even though there is no apparent change in her receptivity, he eventually reaches a point where he has little apparent libido and simply ignores her.
However, if the original female is removed and a fresh one introduced, the male is immediately restored to vigor and enthusiasm and starts copulating. This process can be repeated with fresh females until the male rat nearly dies of exhaustion. It bears pointing out that the rat's renewed vigor is not improved health but rather repeated surges of dopamine. It floods the pleasure/reward circuit of his brain and urges him on - an event very similar to snorting cocaine.
From the point of view of the rats' genes, and ours, fertilization opportunities with a new set of genes are more important than the health, happiness, or harmony of the gene machines themselves (us).
The same effect is seen even more strikingly in farm animals. Rams and bulls are unmistakably resistant to repeating sex with the same female. Thus, for breeding purposes, it is unnecessary for a farmer to have more than one male to service all his sheep and cows. A single determined, but worn-out, bull can be relied upon to do the rounds of all available cows, and a single ram will eventually service all the sheep in his domain.
Wonder how rams and bulls identify and reject those that they have already serviced? Experimental attempts to disguise a past ewe or cow by covering her face and body, or masking her odors fail. That's because her pheromones identify her as 'already serviced,' causing the male move on to less-familiar females.
What are pheromones? Pheromones are odorless chemicals emitted from sweat glands, which we use to communicate with one another. (The purpose of bodily hair, specifically the pubic hair of both males and females, is to collect and disperse these pheromones.) Pheromones travel significant distances. When detected by a special organ in the nose of the opposite sex, they act like a switch to turn on behaviors and alter the hormonal system of the receiver. This is how animals can sniff another of their species and know what they ate last, how dominant they are, how healthy they are, and whether they're in heat.
What about humans? The Coolidge Effect is alive and well and may, in part, utilize the same mechanism to urge a husband to cheat on his wife as it does the bull to parcel out his semen. As with bulls, pheromones play a big part in human choice of whom to pursue.
For example, a husband goes to an office party with lots of women, but spies his future mistress across the way, and is instantly infatuated. Before he even sees her face, her pheromones have already drifted across the room affecting his body chemistry, pumping up his dopamine levels, and leading to a craving to cheat - with her specifically. Her pheromones signal him, "Dude, she's got the biggest blast of dopamine you are ever going to get!" (whether that's true or not).
Why her? It's not her breasts or long legs. In fact she may not be especially attractive to others. No, it's her immune system he desires. Honest. Pheromones attract sexual partners based on how dissimilar their immune systems are. That's because our genes want us to make babies with someone who has an immune system as different from ours as genetically possible. Why? The offspring of such a union will have a much stronger immune system than if the parents had genetically-similar immune systems. The babies will be equipped to defend against a larger variety of germs and have a better chance of survival.
The more different our immune systems are, the bigger the buzz of dopamine we get from each other's pheromones. And the more likely we are to do something foolish. This pheromone signaling appears to be a mechanism for love at first sight.
Pheromones may also push humans apart. A Canadian newspaper not long ago reported that the post-coital prolactin rise is linked with the growth of new brain cells. However, these new cells all migrate straight to the part of the brain that governs smell, where they modify the olfactory bulb. These changes play a role in mothers' recognition of offspring...and, perhaps, an (as yet) unknown role in male/female mating (or post-sex repulsion?).
Although it is well known that men experience the Coolidge Effect, you might be surprised to learn that recent studies suggest that the phenomenon is also alive and well in women. Anthropologists agree that the women of hunter-gatherer societies had as many, or more, sexual partners than did the men. Social, legal, and religious pressure has suppressed this tendency in more modern times - until very recently. But with the loosening of social and religious mores, biology's agenda is becoming increasingly obvious.
If we want to counter the unconscious manipulations of our selfish genes, we need to take conscious steps to increase the quantity of bonding neurochemicals we produce.