Are Humans a Monogamous Species?

Are We a Monogamous Species: Of Course Not! 


Are we a monogamous species? Of course not. Whoever thought that one up was being normative – making up rules for others to obey, telling us how to behave – rather than being observative – seeing what we really do.

The narrative arc of a pair bond1 is well told in a cartoon. A young man is kneeling before his beloved, presenting her with a diamond ring in its box, raised up to her eye level. He asks, “Will you make me the one who one day rues the day I met you?” With their hands conjoined, right to left, her left hand raised to accept the gift, her eyes and mouth open in astonishment, she delightedly says “Ohhh, yes!” How soon, how soon, before the day that they rue their meeting?

A paralegal told me that during the virus lockdown, in one week their office had twelve new divorce cases, many of them with the request “get us out of this as soon as possible!”

Why does what began in certitude, this mate, end in certitude, not this mate!? What goes wrong?

Maybe nothing has gone wrong, instead something has gone right. What if the question “what goes wrong” is itself entirely wrong? What if divorce, the end of the pair bond, is as natural as its beginning? What if the duration of pair bonds is naturally distributed on a curve with some ending almost immediately and others lasting a lifetime? What if the mean duration is 4 to 7 years?

The lifespan of a pair bond is widely known and expressed in the phrase “the seven-year itch.”2 It is also expressed in “The middle years are the hardest. When we are young, we want each other. When we are old, we need each other.” That expresses the life span of a conventional pair bond: the early need and excitement, the forced continuation of it during the middle years, and a different bond as we age. There are a variety of reasons for establishing and maintaining a pair bond: sex and reproduction in youth, and assistance and companionship in old age. Our needs change as we age. We change as we age. The same mate may not fill all the needed roles.3

The average length of a pair bond is shorter than the female reproductive span implying that a female may, and should, have several pair bonds during her reproductive years. That is our evolutionary morality. What we would do naturally. Our natural mating system is ‘serial monogamous pair bonds with occasional extra-pair copulations.’4

The pair bond is, by all animal, by all mammalian, by all primate, by all hominin, standards a very unusual mating and reproductive system. How did we get here from there? We are not ‘there’ any more, we are somewhere else, here, in a synthetic authoritarian imposed ‘moral’ system that has attempted to bind us into a self- and culturally-imposed pair bond jail, a cage. A cage match ensues and we rue the day we met. “Any mate but this one!” Well maybe not just any mate will do.

Is the real puzzle then why we stay rather than why we stray?

How then did our cultural -morality come to be dominated almost exclusively by the ideal of monogamous true love forever preached to us by a wide variety of self-appointed authorities and upheld by state legal sanctions? That question is of ‘here and now.’ To understand here and now, I begin with ‘there and then,’ with a putative construction of our evolutionary morality:

From Puberty to the Pair Bond

Two different herds of wild horses are grazing near each other. A filly, a post-puberty female, notices the dominant male in the other herd. He’s a hunk! She has never seen anything so attractive before. She turns to face him and takes a few hesitant steps, then turns back to the comfort of her herd. She is about to perform something difficult and dangerous, yet enticing and delightful. She is going to transfer from her natal herd to her new home in the nearby herd.

After a few moments of gathering up her courage, she takes a few more steps, then retreats again. Her heart must be beating wildly as her hormones surge for the first time in a wild dance of desire and fear. She is going to lose all her friends, her mom, the comfort of the herd she has known since infancy. All because that big guy over there looks so good. The dominant stallion of the other herd has noticed this dance of desire, “she’s cute!” When she has reached the half-way point, he detaches from his herd, trots to her, and escorts her home.5

She has transferred or emigrated, bringing a new gene set into her new herd, a necessary function for small-scale groups that will become inbred unless new genes are imported. The needs of the other group for her genes have become a necessity, a sexual desire and compulsion, placed upon her. She is a tool for their survival at the same time as she is seeking novel genes from them. She needs their genes as much as they need hers. Her male offspring will remain with this new herd, and her female offspring will also transfer to another herd or back to her natal herd carrying some of her mom’s genes with her.   Female horses are the carriers of genes between various herds.

This is transfer, emigration, instinctive out-breeding, or exogamy6 It is chemo-morality, instinctive sexual morality generated and governed by hormones stimulated by visual and/or pheromonal signals. It is entirely possible that the neighboring herd smells so good. There is no element of a well-thought our decision and no cost-benefit ratio. It is impulsive and compulsive.

The story does not end here. There is more for our transferee has to become a part of her new herd. Sex will be an essential part of this process because it is the way that her genes transfer into the herd.

Let’s leave our filly in the southwestern United States and return to Neryl Joyce in Baghdad, Iraq.7 She had separated from her service in the Australian army to become a mercenary soldier in Iraq. She signed a contract with a security service seeking an increased income, a bit of novelty and excitement. She got more than she bargained for.

Like the filly, Neryl has to become a valued member of her platoon. Her life may depend upon their willingness to value and protect her at the possible cost of their life. She assumes that by displaying military bearing and competence she can become a valued and significant member of that small-scale social group, the platoon, thereby gaining care and protection:

“Anyhow, I knew firsthand what is was like to be underestimated. As a woman in this industry, I would have to fight hard to be taken seriously. I was now in a man’s world, and that meant proving I was as capable as, if not better than, my male teammates. I was no longer an officer in the army. There were no more planning war games, delivering orders, or leading my soldiers. I was just a security contractor, paid to follow orders and do my job. And that was what I was going to do. ….In the army, a good leader … would bind all the members together into a formidable team.”

She desired to be a formidable member of a formidable team.

In the previous essay on sexual behavior, I looked at this behavior in terms of signaling: To some males she would be radiating sexual desirability rather than or in addition to military competence. To other males she would have been an irritating pushy broad telling them how to do their job.8

There may be another signal: Neryl transferred into the platoon. In evolutionary terms that appears to be a sexual transfer. How did the filly gain membership in the new herd? By being sexually available. Female chimpanzees transfer.9 How does a female chimpanzee become a member of her new troop? By soliciting sex from males in the group.10

Neryl wanted to be an interchangeable element in an otherwise all male platoon. She assumed that friendliness and competence would grant her this. It did for some of the guys. But can it be that she also inadvertently signaled that as a transferee she should be sexually available, that she activated an ancient evolutionary male knowledge of how to incorporate a new female into the group? Is it an accident that introduction of a new female increases the testosterone level of the males in a group?

Neryl was a transferee into a hyper-masculine, hyper-testosteronized, group. She intended to gain admission into the platoon, a small-scale hyper-care society, to gain their care and protection based upon her significance to her fellow members garnered by competence and friendliness. She did not wish to gain admission by sexual availability although that is a major route for transferring females.

After leaving employment in the security company, she later remarried. And that brings us to the Pair Bond.11

Evolution of the Human Pair Bond12

It is all the fault of our large brains, large heads, upright posture and bipedalism. The encephalization quotient (a rough measure for the ratio of brain size to body size and an indicator for the consequent head size and intelligence) for chimpanzees and bonobos is 2.2 – 2.5. The quotient for humans is 7.4 – 7.8 – approximately 3 times larger. The second problem is that our upright posture and bipedalism has required extensive changes in the geometry of the pelvis. The consequences of these changes and increased head size are profound. Human childbirth is much more difficult than for chimpanzees and bonobos, and the death rate for both human mother and child are higher. To reduce this, we have evolved pre-mature birth of highly altricial infants – smaller heads and bodies yield lower birth mortality, but require extensive care for much longer. Our larger brain requires more time to mature and thus our age of self-sufficiency is higher.

Human brains are energy hogs, generally requiring about 20% of our daily caloric input. Assuming a 150-pound human and subtracting a skeletal weight of 15% because bones do not consume a lot of calories, leaves approximately 125 pounds of flesh. Assuming a daily input of 2000 calories, the brain consumes 400 calories or about 130 calories per pound. The remaining flesh consumes 1600 calories or about 13 calories per pound – one tenth the rate of energy consumption of the brain. These are approximations, back-of-the-envelope figures, useful primarily for understanding the evolution of the pair bond. Our energy needs and long development time makes long term parental care necessary. This cannot be supplied solely by a foraging/gathering female who may be further burdened by a staircase of older children. Assuming a birth spacing of 4 to 6 years and an age of self-sufficiency of around 15 years: a human female could have 2 or 3 dependent children at a time. Human females need help.

Fortunately, help was nearby, the father:

Family Man

Other females in the social group are close as are older siblings. But because hominid and presumably human females transfer (emigrate) from their natal group late in adolescence, females in the group are not closely related. Evolution has supplied them with strong maternal instincts and this is sufficient for them to alloparent, but evolution has favored entraining the male as they are the primary provider of those wunnerful energy sources meat, fat and marrow.

I have now arrived at The Family Man, devoted to and protective of his mate and offspring. Just as I used Da Vinci’s drawing of the Vitruvian Man as an avatar of Morphological Man and extended it to Physiological Man with blue balls, I offer here as an avatar of Family Man, the stick figures seen in the rear windows of automobiles13 that depict mom and pop and each of the children of that family. Heartwarming bragging indeed, and unusual primate behavior: the pair bond and the domestication of the male to the needs of the female and their offspring.

The other day, I walked through the local park. One of the first things I saw was a father playing catch with his 5-year-old daughter. She was pretty good at both catching and throwing so they had clearly played together many times before. He was laughing, encouraging her and both were having fun. Around the corner and I saw another father lying on the ground, surrounded by his wife, three kids, and 5 bicycles. He was singing to his family audience.

These were Family Men, exemplars of one of the high goods in our moral universe. Accustomed to these behaviors and finding them to be normal, we miss the exceptional, the unusual, of them. Chimpanzee and bonobo males do not provide any infant care. How did we get from that basic hominid model to contemporary human behavior? By first placing the human male within an overall social matrix with extensive bonds to the other members of that social group. Social bonding is mediated by the hormone oxytocin.14 These social group bonds are intensified with a sexual mate to form the pair bond which extends to consequent offspring. Not all human males care for their offspring. One possible source of indifference might be an unequal distribution of caring behavior in the male, as if we are not fully adapted to the evolution of the pair bond, just sufficiently.

We do not need to explain why we stray, for sexual mate variety is moral behavior in the hominids and virtually all of the primates. What needs to be explained is why we stay – why we bond. I found a sufficient explanation in the evolution of our unusually large brains with high energy consumption, then the evolution of premature birth of highly altricial infants, and the consequent need for higher quality food and increased male provisioning of his offspring. These needs were met by the evolution of the pair bond and the domestication of the human male, both of which have difficult consequences, and these new attributes have evolved or been modified in the deep time since their inception.

The End of the Pair Bond

The pair bond violates the basic hominid model of sexual behavior, both in the early and modern (civilizational) human behavioral model by bonding the male to the female for a period of time and excluding variety. It is a common truism that all good things come to an end, and the pair is no exception. That is an exaggeration, for it is also known that some pair bonds last a lifetime and some pair bonds were never a good thing. An astute observer of human mating told me that the woman will generally determine the end of the pair. This is consistent with the female initiating the pair bond: she signals ‘come hither’ and then ‘go thither.’15

In an economically unconstrained pair bond such as exhibited in foraging hunter gatherer societies, the partners would simply drift away if they had discovered that their temperaments were not or were no longer compatible. If they no longer like each other, why remain. If the mother and her children could now forage for themselves, and they had the support of the social group, there was no longer a reason to maintain that particular pair bond. This is the evolutionary logic behind the four to seven-year itch.

A major source for the end of the pair bond is falling in love with another partner and the intense desire to possess the source of this intense emotion. A granddaughter married in a civil procedure and her husband wanted a large church wedding the next year for the benefit of his family. On Wednesday before the ceremony he told her that the marriage was over and the church wedding was cancelled. He had fallen in love again with his high school girl friend and she was pregnant. Was he morally deficient or was he exhibiting an ancient human evolutionary morality?

Was she also exhibiting an evolutionary morality? I asked her about their marriage. She said that when they were good, they were good; but when they were bad, they were very bad. Clearly her ex had decided that there was a better life somewhere else. But could my granddaughter have contributed to this decision or even have made the decision, somehow unknown to her, a decision never reported to her conscious mind.16

Here is a possible story, a Scientific Wild Ass Guess: let’s take as given that in the early evolution of the pair bond, the female initiates and terminates most bonds for her own reasons. She needs to entrain the male in her decisions and has evolved signaling systems that make the male think them to be his own good ideas. Let’s look at a common truism in this light: during the pair bond and in the communication between the two ‘he feels invaded and she feels evaded.’ She is signaling a decision and consequent behavior to the male who had not yet made the same decision. She is pushing him away.

Could this granddaughter have made the decision to end the marriage and signaled it to her husband entirely without her conscious knowledge? And that he read her correctly? This is a difficult suggestion, for she was utterly devastated. But once again, this story is in the context of civilization which has highly modified our moral behaviors. Like the beginning, the end has been modified in civilization with difficult consequences. Our decisions are heavily influenced by economics rather than by evolutionary morality and are thus more difficult to parse.

We are obviously unable to adequately evaluate the attributes, personality or quality of a prospective mate. We are compelled to reproduce, and reproduction does not and cannot be even slightly concerned about our happiness. The second jaw of the vise is our cultural and legal insistence on monogamy, true love forever, and the maintenance of a pair bond. Same pair bonds become a cage match, a fight to the end. Is it any wonder that we write to advice columnists and cry on TV shows?


Are we a monogamous species?  There is no evidence that we ever were or ever will be a life-long monogamous species.  Yet many of us live monogamous lives in a morality dominated by normative, not evolutionary, monogamy – artificially forced monogamy.  Why?


There is one more attribute that males evolved: the mighty hunter to provide higher quality food. This was undoubtedly mediated by testosterone and we now may see the male with elevated levels of two competing hormones: testosterone and oxytocin, elevated masculinity and elevated femininity, in the same hormonal system. An odd couple indeed! The signal system that releases either hormone must be quite complex, and careful to get it right.

The evolution of the male hunter is of great interest, for we possess none of the usual weapons of a predatory species. There are two major human attributes that contribute to hunting success. First, our loss of hair which allows for faster rejection of metabolic heat and thus we can pursue a prey into heat exhaustion. We are cursorial or persistence hunters. Second, our intelligence allows us to develop a wide range of hunting technologies.

We are ensconced in two competing food morality systems, predator and prey. We are animals and are obligate eaters of other biologic materials. No wonder we are confused about the morality of food.

An interesting detail is buried in the two transfer stories: these were relatively rapid decisions. No time information was included with either story, but it seems likely that the dance of desire consumed maybe 15 – 20 minutes. Human pair bonding is replete with “I fell in love at first sight,” a nearly instantaneous decision. Falling out of love may be quite as rapid.

I did not find any psychological studies comparing the durability of pair bonds based upon falling in love at first sight vs a long courtship. A long courtship could consume a significant portion of the 4-7 year lifespan of a pair bond. A short courtship would not allow for learning much about the prospective mate. A common expression for this is “sin in haste, repent at leisure.” Our reproductive compulsion may activate a fast decision over a slow “getting to know you,” a triumph of wild desire, hope, and sex over a slow carefully thought out cost benefit analysis.

Do I expect the normative elites, TV show hosts, advice columnists, etc. to ever consider our evolutionary morality? Nope! They promote a lifelong monogamous pair bond in the face of the known violations of it. Why?

It seems that the general public is adopting a more relaxed mating and sexual behavior, particularly in the acceptance of the end of the pair bond and its formal end – divorce. Extra-pair copulations remain a problem for many, for it violates the monogamous core of the bond. But it happens. Despite millennia of social, cultural, and legal prohibitions, the compulsion remains. That alone should be a pointer to the complexity of our evolutionary morality.

It is interesting to note that many normative elites also promote an after-life where all family is gathered about an eternal hearth in everlasting harmony that was lacking in real life. This is an imaginary projection of the intense early phase of the pair bond, falling in love, this mate forever, none other, and the issue of this mating, my children and the memory of my parents, in love forever. None of the agonies of our real lives. In this unearthly and utopian vision there is no room for extra-pair copulations, for multiple sequential pair bonds and step-families. There is no room for the basic hominid model of sexual variety modified but not entirely replaced by the pair bond.

It is also interesting to note the parallels between the promotion of the pair bond and the adoption of private property as organizing principles of civilization. As we own property, we own mates and children. As we must own property over time, so must we own mates and children over time also. Is this a function of our evolutionary morality or of our economic necessity?

The primary force for the endurance of the middle years of an ill-suited pair bond: is economic. Within civilization, women generally have fewer economic resources for themselves and for their children. As the children usually remain with their mother, she has fewer and more constrained choices. While she may desire the end of the bond, she may elect to remain in it for her children’s sake.

I read Robert Ardry many years ago and have carried in my mind a putative construction of human male transfer based upon my observation of several pair bonds in which the male transferred into the female’s social group and religion. In one case, the son of a friend fell in love with a girl whose fundamental Christian morality required him to sever all ties with his non-religious parents. They were enormously hurt by this. Another case: the son of a Protestant minister fell in love with an Irish Catholic girl, and in the words of one of his daughters, he became more Catholic than the bishop.

Clearly both contemporary human sexes may transfer. There appears to be sufficient evidence that in foraging hunter-gatherer human societies, the female sexually transfers. There is evidence that male transfer also occurs, but that is usually due to losing a dominance contest or being driven out for inability to get along.

  1. I introduced the pair bond in  


  3. This essay focuses on the reproductive pair bonds – the early phase. It is probable that in the the third phase, old age, the pair bond may be more durable as it serves different needs. I also ignore our middle years of forced bonding for now. 


  5. I wish I had the source for this story. I read it somewhere sometime and was delighted by its vivid description of the process. Robert Ardry wrote a similar story about a female primate crossing an African river under the same compulsion. 

  6. Exogamy is usually defined as culturally enforced, sanctioned and controlled transfer. 


  8. Her statement, “…if not better…,” suggests she tried too hard and was not accorded significance, care and protection of the platoon, which admittedly had serious leadership problems. 

  9. In some primate species, males transfer. 

  10. This is a short version of a more detailed process. For more information see: She will also gain significance to the females in her new troop by alloparenting their infants.((  

  11. I will return to Neryl Joyce and her rape in a future essay. 



  14. For more information scroll down in this article to the section titled Bonding 

  15. The National Center for Health Statistics reports that from 1975 to 1988 in the US, in families with children present, wives file for divorce in approximately two-thirds of cases. In 1975, 71.4% of the cases were filed by women, and in 1988, 65% were filed by women.  

  16. I wrote about sub-conscious decisions that are made entirely without the participation of the conscious mind in