A groundbreaking study from a Harvard University team suggests that monogamy may be genetically programmed within some mammals.
Evolutionary anthropology has for some time tried to understand what natural relationship pattern humans follow, if there is one. In his book Sex at Dawn psychologist Christopher Ryan posits that our prehistoric ancestors practiced multiple kinds of sexual and romantic relationships.
Monogamy became a social institution and one that made sense. Polygamy was the most common practice in the ancient world, but it made women a commodity. Rich men could keep multiple wives for themselves, whole harems, which caused a lot of strife among others, fighting over those who were left. Monogamy however, eliminated this problem and helped seed societal stability.
Even so, multiple societies around the world still practice different forms of pair bonding other than monogamy. Even the most strident monogamist will admit that marriage can prove difficult. There’s things like the four year slump and the seven year itch. Some evolutionary biologists have explained these as a cessation of the pair bonding process.
When we were hunter-gatherers, we traveled in tight-knit bands. Children were raised not only by their parents but by the whole village itself. When the child was old enough to be a little more independent, the parents were free to go off and explore other relationships.
According to renowned anthropologist and love expert Dr. Helen Fisher, there are actually four different, unique personality types when it comes to human love. Each is driven by a preponderance of a certain neurochemical or hormone in the person’s system. And some are better suited for monogamy than others.
In this case, nature may have made some people naturally polyamorous and others monogamous, to ensure stability for raising children, while at other times, ensuring variety within the gene pool and to that end, aiding our survival.
Is there an evolutionary basis for cheating? Getty Images.
Now, a groundbreaking study published in the journal Nature suggests that monogamy may be genetically programmed within us, or at least in mice, to ensure offspring receive proper care. “Parental care is essential for the survival of mammals, yet the mechanisms underlying its evolution remain largely unknown,” the authors write. Researchers at Harvard University studied two breeds of mice to arrive at this conclusion.
The first was the oldfield mouse (Peromyscus polionotus), one of those rare monogamous animals. Only 5% of mammals practice monogamy. Both sexes of this breed are known to be doting parents. They will, together, build an elaborate nest for their young and lick or clean them.
The second breed was the deer mouse (Peromyscus maniculatus), who are promiscuous by nature, and look upon their oldfield cousins as helicopter parents. In most mammalian relationships, males mate with as many females as possible, but do little to help raise the offspring. What researchers discovered, by looking at these two mouse breeds, was distinct genetic variations, which coincided with each type’s relationship style.
Hopi E. Hoekstra was the senior author of the study. She’s an evolutionary biologist. Though oldfield and deer mice won’t mate in the wild, if a male and female are put into the same tank alone together, they will. The resulting offspring are healthy. It was a variety of such hybrids that led them to understand whether or not parenting and relationship styles are genetically influenced.
Is monogamy in our nature, polyamory, or a combination? Getty Images.
In a previous study, Hoekstra and her team took the pups of each type of mouse and placed them in each other’s nest. Researchers wanted to know if the mice acted this way because they were raised to tend to pups, or if each breed of mouse had an instinctual parenting style. The latter proved true. Once this was found, researchers went about investigating each type’s DNA.
They bred five mice, who created 30 hybrid offspring. These were bred and another 769 hybrid mice were born. Researchers looked at the second and third generations, to see what type of parenting each took up. Some put in minimal effort, others were completely aloof, and others still attentive parents. This wide variety of styles allowed researchers to hone into the mice’s DNA and find the differences. They came upon 12 areas or loci which were associated with parental instincts.
Researchers found that one loci controlled just one behavior, nest building, while others controlled more than one. These loci varied in terms of sex. One loci when activated, seemed to make fathers more attentive, but not mothers. Unfortunately, each loci carries many genes, so it’s hard to hunt down which is responsible for what behavior.
In their most recent study, these Harvard researchers looked at one biochemical in particular, vasopressin. This is a bonding neurotransmitter in many species, including rats and humans. Deer mice contain three times the amounts as oldfield mice, however. To find out what role it played, researchers injected oldfield mice with it. Instead of elaborate nests, they acted more like deer mice, and made simple ones. Yet, in terms of care, they were still doting parents.
Studies show that some may be better suited for monogamy than others. Getty Images.
According to their genetic research, the vasopressin gene only accounts for 6.7% of nest building instincts in male oldfield mice, and 2.9% in females. This opens the door to whether or not human pair bonding and parenting could be influenced by an instinct imprinted on our DNA. Though we’re a far cry from mice, we share many of the same neurotransmitters and hormones, along with other mammals.
Differences in biochemical makeup or neurotransmitters may signal how a species cares for its young, and whether it’s monogamous, promiscuous, or a mixture of the two. In exploring other species and working our way up, we may find out more about ourselves, even what relationship pattern or parenting style works best. Perhaps, we’ll find the genetic underpinnings of Dr. Fisher’s theory.
To learn what similar genetic underpinnings have so far been identified in our species, click here:
Which came first, monogamy or the social contract? Evolutionary psychologists and biologists think the latter.
As Big Think has discussed before, our prehistoric ancestors got busy a little differently than we tend to. According to Christopher Ryan, our ancestors were promiscuous, hypersexual, and shameless about it. In his book Sex at Dawn, Ryan goes on to mention that our evolution has given us features which reflect this, such as our reproductive systems, which have little in common with those of other monogamous animals.
But this raises the question: why are the overwhelming number of cultures across the planet today celebrating monogamy? Has there been some kind of major psychological evolution across our species? Or are we just fooling ourselves? Perhaps the idea that monogamy is our natural state is a “noble lie” designed to help us?
In his work The Naked Ape, Desmond Morris offers us an answer. He supports the standard model of long-term partnerships for homo sapiens, but makes note of our peculiar, hypersexual, biology. He goes on to suggest the shift to monogamy was done socially, not biologically or psychologically, as our ancestors evolved into hunters to secure the cooperation of all males in the group with the assurance of reproductive rights.
As he puts it: “If weaker males were going to be expected to co-operate on the hunt, they had to be given more reproductive rights. The females would have to be more shared out, the sexual organization more democratic, less tyrannical. Each male, too, would need a strong pairing tendency. Furthermore, the males were now armed with deadly weapons and sexual rivalries would be much more dangerous: again, a good reason for each male being satisfied with one female.”
The first article of the social contract is monogamy. If Morris is correct.
Ryan suggests the opposite, that property and civilisation drove the need for monogamy. In Sex at Dawn, he describes the effect of agriculture on our sexual nature: “Land could now be possessed, owned, and passed down the generations. Food that had been hunted and gathered now had to be sowed, tended, harvested, stored, defended, bought, and sold. Fences, walls, and irrigation systems had to be built and reinforced; armies to defend it all had to be raised, fed, and controlled. Because of private property, for the first time in the history of our species, paternity became a crucial concern."
In either case, it seems that humans are not biologically or psychologically disposed to mate for life. It appears that we have psychological tendencies to promiscuity and a biology to match. Perhaps this is why so much time and money is spent every year in marriage counseling to save the monogamous ideal, on relationship books, on pornography, and on viagra. Of course, that would also explain the popularity of dating apps such as Tinder. Tinder is worth more than a billion dollars, sees ten million daily users, and nearly a third of all those users are also married. A fifth of its users report using the app for hookups.
Fear not for the future though, Millennials are having less sex than their parents did. And those statistics for Tinder use must mention that the majority of users are college aged. The state of social monogamy is safe for now. We may not be built for monogamy, but our societies are. Is Tinder going to be the end of the social contract? Probably not, but it will remind us of exactly what monogamy is – a social structure that we often seek escape from.
Morris, Desmond. The Naked Ape; a Zoologist's Study of the Human Animal. London: Cape, 1967. Print.
Ryan, Christopher, and Cacilda Jethá. Sex at Dawn: The Prehistoric Origins of Modern Sexuality. New York: Harper, 2010. Print.