The particular religious sexual norms of our species are a puzzle – why are humans so different from other animals in what we [officially] see as acceptable?  

Human sexual behaviour differs from that among other mammals, in the fact that it is narrowly restricted by widespread social and religious norms.  

These norms forbid behaviour that is routine among other mammals.  Perhaps these norms are enforced most strongly by the monotheistic religions (Christianity, Islam, Judaism).

In other mammals, we see that homosexuality, and promiscuous recreational sex, "every which way", are routinely enjoyed.  [Balcombe]


Humans are different from other mammals in that we have social, religious and cultural norms (expected standards of behaviour that are like social legal laws).  

Humans are unique among the great apes in that our breeding system is largely monogamous.  


Eighty-four percent of the world's cultures allow a man to marry multiple wives.  Very few men in these cultures, however, have the resources to support a large family.  In reality, then, most families in the world contain one man and one woman.  [de Waal & Lanting]



Monogamous animals partner up with a single mate, sometimes for the duration of a breeding season and less commonly over multiple seasons and years.  Monogamy has particular advantages, and is often the chosen strategy where young are more vulnerable and require both parents for protection and feeding.  In serial monogamy, having different partners each season helps maintain genetic diversity.  [BBC 01]  



Polygynous sexual behaviour is the system in which a single male mates with multiple females, but each female mates with only one male.  This usually entails fierce competition between the males during the breeding season.  Females invest more heavily in their offspring and all the parental duties fall to the mother.  They become much more choosy about their mate as a result, while the males attempt to have as many mates as possible in order to leave a maximum number of offspring.  However many males fail to win or impress a female and remain unmated their entire lives.  [BBC 02]  



Polygynandrous describes a multi-male, multi-female polygamous mating system, such as that seen in lions and bonobos.  Females are usually more numerous than the males and mating occurs only within the group.  The advantage of this form of polygamy is greater genetic diversity, less need for males to compete with each other and greater protection for the young.  [BBC 03]


Mate guarding  

Mate guarding is the seclusion of females, by males, away from the reproductive clutches of other males.  It has two aspects: 1) monopolising: keeping the females to oneself for the purposes of reproduction; 2) bodyguarding: protecting the females from harm by other males.  



Great ape mating systems  



Evolution of patriarchy

The present hypothesis is that the patriarchy and the religious enforcement of narrow sexual norms are a result of:   

  1. the evolution of generalised sexual monogamy as the human mate-guarding strategy [Chapais],
  2. the consequent “self-domestication” of early humans that made widespread cooperation possible [Tomasello],
  3. as groups grew large (>150 people), the evolution of group-wide social norms [Tomasello],  
  4. the sacralisation (making sacred) and institutionalisation of certain of these norms [Tomasello],
  5. the adoption of cooperative norms by organised religion as part of its cooperative enterprise. [Norenzayan].  

The key implication of this scenario is that the hierarchy based on fighting ability, in great apes, is no longer generally available to human males.  At the same time, males still wish to prove how masculine they are.  The goal of having a good place in the hierarchy, monopolising females, is still available to human males.  This monopolisation is achieved through societal control as well as purely individual control.  Societal control is therefore, partly, a transformation of the great ape masculine hierarchy into a different form.  

This model predicts that, where patriarchy is strongly institutionalised,


The future of patriarchy

1.  bodyguarding

Patriarchy is harmful to females except in its “bodyguarding” aspect.  Females are at a slight physical disadvantage compared with males, and protective "bodyguarding" of females by males is generally a good idea.  

2.  monopolising

At the same time, both genders wish for pair-bonded marital relationships, so it is redundant for males to need to actively monopolise their females, because females want precisely the same thing, and in fact have a lot more invested in the situation than males (it is one of their few chances to reproduce).  




1. The evolution of monogamy – the “stone tools” hypothesis  and evidence for it

Male primates want to monopolise as many females as possible, leading to mate guarding.  The hypothesis is that the introduction of the use of stone tools by pre- and early humans evened out the sexually competitive advantages between males based on size, leading to a situation where one male was only able to monopolise one female.  


... all types of marital unions could be cultural variants ultimately derived from the same ancestral mating pattern.  What, then, was that stem pattern like?  

In all likelihood its essence lay in the single major feature that transcends all types of marital arrangements: their selective and relatively stable character.  Regardless of the exact nature of marital unions, men and women form enduring pair-bonds, a term that encompasses more than strictly dyadic, monogamous unions.  In polygynous unions two or more women are paired with a single man, who is in fact maintaining two or more distinct pair-bonds simultaneously.  The same applies to polyandrous unions, with a woman maintaining several pair-bonds concurrently.  This is precisely why the expression “pair-bonding” is commonly used to characterize the human mating system even though a large number of marital unions are not limited to a single dyad.  Pair-bonding is, essentially and simply, the opposite of sexual promiscuity – short-term mating relations with several partners.  It includes all types of enduring reproductive relations between particular males and females.  Pair-bonding thus refers to a specific property of mating arrangements: their duration.  

... much of the sexual promiscuity in humans takes place premaritally, and the permissive character of premarital sex only serves to emphasize the social importance of marital unions.  Moreover, sexual promiscuity by married individuals is universally disapproved of.  Thus not only are stable breeding bonds consistently present across human societies, but they prevail over promiscuity.  For that matter, procreation in humans is expected to take place in the context of marital bonds.  All human societies differentiate between legitimate and illegitimate children, a distinction that further illustrates the centrality of pair-bonding in the human mating system.  Logically, therefore, the stem ancestral pattern out of which emerged all known human mating arrangements, whether polygynous, polyandrous, or even homosexual, is the enduring breeding association itself. [Chapais]


1.1  main factors leading to particular mating systems


As mating systems evolve as a result of the outcome of competition between individuals to maximize their reproductive success, they are inevitably linked to individual reproductive strategies shaped by sexual selection.  ...

Differences in mating systems are created by variation in the potential of males to monopolize access to females, and can be understood by considering the vast differences in reproductive potential between male and female mammals. ... predation risk and food availability influence female distributions, with male distributions then following suit according to males’ best strategies for maximizing reproductive success.  This is based on Bateman’s principle that female reproduction is limited by access to the physical resources they need to reproduce (i.e., food), while male reproductive success is limited by access to fertile females.  The operational sex ratio (the ratio of fertile females to sexually active males) that emerges is a measure of the degree to which males can monopolize reproduction with females.  The degree to which any one male can successfully defend exclusive mating access with females results in variation in the intensity of sexual selection mechanisms (intrasexual competition, mate choice, sexual conflict), which ultimately explains the variation we see among and within different mating systems.  [Petersdorf]  


Therefore, density of distribution of females is proportional to density of food distribution.  If we assume that the area of territory that a male can defend is fixed, then we know that this area can support more or less females depending on the density of food that it can support.  

Individual males will attempt to monopolise as many females as they can, as a fundamental part of their strategy to reproduce as much as possible.  The mating frequency of a male depends largely on his place in the dominance hierarchy of his group.  


The biological explanation for sexual rivalry between males is as follows.  A female can only be fertilized by one male.  By keeping other males away from her a male increases the certainty that he will be the father of her child.  ...

Whereas the males fight for the right to fertilize as many females as possible, the situation for the female is completely different.  Whether she copulates with one or one hundred males, it will not alter the number of children she will give birth to.  [de Waal]  

Dense distribution of food and females

leads to polygynandry (multi-male multi-female mating), because the territory contains too many females for a single male to monopolise.  [Chapais]

Sparse distribution of food and females

leads to polygyny (single-male multi-female harems), because a single male is able to monopolise all females in the unit territory.  [Chapais]  

This hypothesis finds support in the observation that savanna baboons, which typically form large multimale multifemale groups, may sometimes subdivide into polygynous units in harsher ecological conditions.  [Chapais]


1.2  environments of pre- and early humans


Palaeoanthropologists are trying to unravel the role of climate change in human evolution.  In sub-Saharan Africa, geological evidence from the last 10 million years suggests a trend towards cooling temperatures, while the uplift of the East African Rift System led to increased dryness.  These factors probably caused a shift from woodland to grassland.  Superimposed on such long-term trends was extreme climate variability, with East African lakes fluctuating between high and low water levels. ...

African apes still live in forest and woodland habitats, suggesting that they were important in early hominin evolution.  Bipedal, ground-living primates like the early hominins probably lived in open, seasonal woodlands rather than in dense tropical forests.  Here food resources are less predictable, and exploiting them successfully requires flexibility in diet and in foraging behaviour.  [Roberts]


1.3  “two-step hypothesis” for evolution of monogamy:  

  1. polygynandry (like chimpanzees and bonobos) =>
  2. polygyny (like gorillas) => monogamy (maximally constrained polygyny)


The fossil record indicates that early hominids (australopithecines) were anatomically more similar to chimpanzees and bonobos than to gorillas in terms of absolute body size and relative brain size.  The fact that early hominids had a chimpanzee-like body mass suggests that their diet had more in common with the chimpanzee diet than with the low-quality diet of gorillas.  This in turn suggests that the behavioral ecology of early hominids, in terms of group size, group composition, ranging pattern, and so forth, more closely resembled that of chimpanzees.  [Chapais]


Therefore we suggest that the earliest human/pre-human mating system was multi-male multi-female like our closest relatives, the chimpanzees and bonobos.  

If the ecological conditions of pre-humans became more harsh and difficult over time, this suggests a move from polygynandry to polygyny, as a territory could support fewer females, and these could have been monopolised by a single male.  


A phenomenon whose evolution was progressive, irregular, and largely cultural did equalize the competitive abilities of hominid males, namely, the rise of technology.  Any tool, whether it was made of wood, bone, or stone, and whatever its initial function, from digging up roots to killing animals, could be used as a weapon in the context of intraspecific [within species] conflicts, provided it could inflict injuries.  Armed with a deadly weapon, especially one that could be thrown some distance, any individual, even a physically weaker one, was in a position to seriously hurt stronger individuals.  In such a context it should have become extremely costly for a male to monopolize several females.  Only males able to monopolize stone tools or males forming coalitions could do so.  But because all males can make tools and form coalitions, generalized polygyny was bound to give way eventually to generalized monogamy.  [Chapais]


The first indirect evidence for stone tool use in pre-humans comes from 3.39 million years ago, with fossils of Australopithecus afarensis in Ethiopia.  The first direct evidence appears in East Africa around 2.5 million years ago.  The first Homo species arose around this time.  [Roberts]  


First, polygyny is much more common than monogamy in primates and mammals in general, attesting to the intensity of sexual competition among males and the recurrent capacity of males to monopolize more than one female.  Second, some primate species exhibit the multiharem structure, but none display the multimonogamous family structure, an observation that further illustrates the importance of male sexual competition.  Third, the fact that a majority of human societies are polygynous strongly suggests that the ancestral hominid pattern was generalized polygyny, not generalized monogamy, and that in the course of human evolution some factors operated as strong constraints on the feasibility of polygynous unions ...

If monogamy did not evolve as a result of specific selective pressures, the drive for polygyny was merely checked, not eliminated.  Polygyny could reemerge whenever some males secured more competitive power or were able to attract several females based on attributes other than physical prowess.  Human societies amply testify to this reemergence.  [Chapais]


1.4  the “parental collaboration hypothesis” suggests that pair-bonding serves an adaptive function for humans, i.e., that enduring parental pair-bonding is especially useful or necessary for human thriving, and/or surviving, and/or reproducing.  

There is good evidence that this hypothesis is true: that in humans, having two parents is beneficial for reproductive success.  

In the other great ape species, the fathers do not take care of the infants.  All caring is done by the mothers.  

In humans, the infants are provisioned (fed) for much longer – until around the age of 16-17 – than in other great apes; and human mothers have more than one infant at a time, whereas mothers of other great ape species only have one infant at a time.  Human infants are therefore much more costly in terms of resources to look after than other great ape infants.  Moreover, in hunter-gatherer societies, the big game hunted by fathers provides much more nutritional value per unit of work than plant foods.  

Not only are human infants more costly to look after than other great ape infants, but in hunter-gatherer societies, the fathers help to meet this cost by hunting.  [Chapais]  


Human families as we know them are variants of the same model, the latest in a series of models that thrived in the hominid evolutionary tree.  One may envision polygynous or monogamous families that were essentially mating units in which the father’s contribution was basically procreative, others in which family members enjoyed some level of mutual tolerance around food gathered on a sporadic or regular basis, and still others in which mutual coprovisioning was characterized by various degrees of sexual specialization.  But however different, all versions of the hominid family shared the same fundamental feature: the enduring breeding bond.  All had in common the father’s presence and recognition.  [Chapais]


[back to contents]


2.  The self-domestication of early humans


We begin with the origins of early humans’ more expansive (compared with other great apes’) helping and sense of sympathetic [empathic] concern for others.  That is to say, we are concerned ... with how great apes’ prosociality towards kin and friends became early humans’ morality of sympathy [general empathic concern].  It arose, we will argue, in the context of a general “taming” of the species and a newly collaborative way of obtaining basic resources.  ...

The initial move in the direction of human morality was addition by subtraction.  Specifically, what had to be subtracted was great apes’ almost total reliance on dominance – either by individuals or by coalitions – to settle any and all disputes.  Individuals had to become less aggressive and less bullying if they were going to forage together collaboratively and share the spoils peaceably at the end.  The proposal is that this began happening soon after the emergence of the genus Homo some 2 million years ago in a transformation that may be thought of as a kind of self-domestication.  [Tomasello]  


This self-domestication was very likely the product of three intertwined processes:  

  1. the evolution of pair-bonding, both polygynous and monogamous,  
  2. the necessity for early humans to be able to scavenge peacefully together on the same carcass, and  
  3. cooperative breeding.  [Tomasello]

We can see that 1) relates to sex, 2) to food, and 3) to childcare: perhaps the three most basic necessities for thriving, surviving and reproducing.  


2.1  consequences of pair-bonding for peaceful cooperation.  

Family bonds would have been strengthened, because:  

  1. fathers knew who their offspring were, because the pair-bond meant that only he could have mated with their mother;  
  2. offspring knew who their fathers were, as the adult male who provisioned, mated with, and spent a lot of time with their mother;  
  3. offspring knew who their brothers and sisters were, as the other infants who were looked after by their mother and father; and
  4. all family members could identify each other as such, through their mother, father, and siblings.  [Chapais]  

Infants know who their mother is through the mother-infant bond.  

Generalised monogamy would likely have been accompanied by a general reduction in male-to-male aggression.  Intermarrying between families in different groups would have strengthened the bonds between groups.  [Chapais]    


2.2  tolerance around, and sharing of, scavenged big game.  

Chimpanzees do not share their food, except very unwillingly, and bonobos also do not share as a rule, although they are more likely to do so.  Humans will share their best consumables with complete strangers and hospitality is seen as a virtue.  

It is likely that before humans began hunting, there was an intermediate stage of scavenging game, including large carcasses that other creatures also wanted to feed on.  


Individuals would have been forced to work together in a coalition [a cooperative unit] to chase away the lions or hyenas feasting on a carcass before they themselves could scavenge.  Any individual who then hogged all the meat would have been the target of another coalition aimed at stopping him.  ... in general, almost all contemporary hunter-gatherer groups are highly egalitarian, and overly dominant individuals are quickly brought down to size by coalitions of others.  Evolutionarily this would have meant that there was social selection against bullies, food hogs, and other dominants, and thus social selection for individuals who had a greater tolerance for others in cofeeding situations.  Indeed, in modern-day chimpanzees, collaboration in an experimentally created foraging task goes best when the pair is made up of individuals who are tolerant of one another around food.  [Tomasello]


This meant that early humans were forced to share their food with anyone who could help them to keep the other creatures away from carcasses.  This was a major innovation in general prosociality.  


2.3  the pacifying effect of cooperative breeding.  

We do not know how cooperative breeding evolved, but it may partly have been a result of generalised food-sharing in the context of cooperative coalitions of early humans being forced to share in large scavenged carcasses.  It must have also been the result of other factors coming together, as everything has multiple causes.  If most or all members of a small group were taking part in child care, this must naturally have had a pacifying effect on the whole group.  We must remember that fathers were now provisioning their own children, something that other great ape fathers do not do.  


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3.  The evolution of social norms

Outline of argument (see below for explanation):  [Tomasello]  


small groups:


large groups:


Scaling up of cooperation within groups, from personal small groups to impersonal large groups: leads to:


Coordination and partner control problems solved by:  


See also:  reputation, forgiveness, partner control


3.1  small groups

When early humans first started learning to cooperate, it would most likely have been in temporary pairs or small teams who came together for a particular task.  Important features of this situation are the joint goal, mental role-reversal, and agent-independence: each individual sees the goals and intentions of all the others, as part of their understanding of the cooperative venture; and each role may in principle be filled by any other person with the right skills.  Therefore, people and roles were seen as interchangeable; and here we see an early form of objectivity: the view from many places.

For each task, there would have been better or worse, successful or less successful ways of fulfilling the roles, and the successful ways would have become to be recognised as ideal ways, the right ways – ‘role ideals’.  

3.1.1  partner control in small groups

If a pair or small number of people is cooperating to obtain food, then all individuals need to be good cooperators: to pull their weight, help where necessary, see the project through to completion, share the rewards fairly, etc., otherwise the success of the venture could be negatively affected, or it could even fail.  

The moral aspects of this are important: individuals would expect a cooperative partner to help them in response to need, and to treat them with respect.  

To this end, since people are at least partly selfish, there need to be mechanisms for promoting or ensuring good cooperative behaviour and discouraging or preventing cheating or free-riding.  These policing mechanisms are collectively called ‘partner control’.  They would include protesting against unfair treatment, or the threat of punishment, or of rejection and finding a new partner.  

At this time, perhaps 2 million years ago, moral norms were not in place in society, and the cognitive skills of cooperation were still evolving. If someone is offended against, he can make a ‘respectful protest’ towards the offender, making his resentment known and appealing to the offender’s ‘cooperative identity’.  


Second-personal protest ... treats the offender respectfully as a competent cooperative partner, and if she lives up to that by respecting the claim, then she keeps this identity; if not, then she is at risk of losing her cooperative identity.  The attempt at partner control represented by second-personal protest is thus implicitly backed up – in the event that the offender compounds the disrespect by disregarding the protest – by the threat of exclusion via partner choice: if you do not shape up, I will ship out.  [Tomasello]  


3.1.2  cooperative identity  

A cooperative identity is how one is seen by oneself, and others, as a good cooperator.  It is a source of our worth in the eyes of ourselves and others.  We are always being monitored by others, and in turn, each of us is always monitoring others in general.  


3.2  large groups

Small groups became very successful over time and expanded, becoming, we believe, large tribes made up of smaller bands.  In the archaeological record, by around 150,000 years ago, we see cultural differences marked out between large groups.  There were two problems associated with this expansion in size:

1) how to coordinate people on a large scale, with interpersonal negotiations difficult or impossible between large numbers of people who did not know each other;

2) partner control: how to prevent cheating or free-riding and to promote good behaviour, since interpersonal protest between large numbers of people who did not know each other is difficult or impossible; and we may not know someone’s reputation enough to judge whether they are a good cooperator before joining forces with them.  

The first was solved by similarity, culture, conventions, and group loyalty; the second by the (linked) introduction of social norms, enforcing an objective standard of right and wrong, and good and bad, by everyone on everyone equally, through a variety of authority mechanisms.  

3.2.1  solving the coordination problem through loyalty and similarity

As groups grew larger, division of labour would have increased, which in turn increased the interdependence of everyone in the group, as each person was even more dependent on others in the group to supply necessaries of life.  This would have led to increased loyalty to the group.  

At the same time, it would have been necessary that everyone in the group did things in the same way, so that people who had never met could work together easily.  This similarity of behaviour would have strengthened feelings of group membership and identity.


3.3  partner control in large groups

3.3.1  conventional cultural practices, agent-independence and objectivity

Over time, together with mechanisms of cultural transmission (teaching, showing, communicating by word of mouth)  there would have built up a body of common knowledge of the better or worse ways to do things, and in fact, the ‘way we do things’ ultimately leading these conventional cultural practices to be considered the right and wrong ways to do things.  

At the same time, individuals would have been aware that the collective intention of the group provided the standard for what were the right and wrong ways, and that individuals were interchangeable within this system, leading to an ‘objective’ (i.e. rational, group-wide) way of looking at things.  

3.3.2  social norms

These objectively right ways to do things became conventional norms, and the morally right ways to treat others became moral norms: together called social norms: the taken-for-granted shared expectation that in ‘these’ circumstances, ‘we’ behave ‘this’ way.  


In effect, such social norms conventionalized and collectivized the process of evaluating and protesting against noncooperators and thus scaled up second-personal [me and you] partner control into group-level social control, with the aim of ensuring the smooth functioning of social interactions within the group.  [Tomasello]


3.3.3  generalised enforcement and reputation

By this time, around 150,000 years ago, we believe that language had been invented, and so a person’s public cooperative identity could become widely known among the group, which obviously would help to keep them in line.  An individual could be punished directly or through their reputation for violating social norms. The ultimate threat would have been expulsion from the group, which would make the survival of an individual much more difficult.  


... in addition to following social norms, modern humans will also enforce social norms on one another, including from a third-party position as an unaffected observer.  [Tomasello]

[in young children] ... the norm enforcer is acting not just as an individual expressing a personal opinion but, rather, as a kind of representative of the cultural group.  The fact that particular social norms were created by the group is prima facie evidence for the individual that they are good for the group and its functioning, and this makes it a good thing, a legitimate group-minded thing, for the individual to enforce them on everyone.  [Tomasello] ...

Social norms are thus presented to individuals as impartial and objective.  In principle, any member of the culture may be their voice, as representative of the culture and its values.  In principle, any member of the culture may be their target, since they apply in an agent-independent manner to everyone alike (perhaps within some demographic or contextual specifications).  And, in principle, the standards themselves are “objective” in that they are not how the enforcer or other group members want things to be but, rather, the morally right and wrong ways for things to be.  This three-way generality – agent, target, and standards – explains why the voice of norm enforcement, like that of teaching, is generic: “It is wrong to do that.”  The norm enforcer refers the violator to an objective world of values that he himself may consult directly and impartially to see that his behavior is morally wrong.  ... the objectification of moral judgments in this way is crucial to the perceived legitimacy of the process because it provides a common metric by which one may judge one’s own and another’s moral values, “bonding individuals together in a shared justificatory structure.”  Thus, social norms ... come to have an independent and objective reality for individuals such that moral violations become less about injuring the particular person and more about rupturing the moral order.  [Tomasello]  


3.4  “our group is right and everyone else is wrong”  

An implication of having objectively right group-wide social norms is that those in other groups are seen as objectively wrong if they differ from “ours”.  




4.  The sacralisation and institutionalisation of sexual norms  





Nashville Statement (articles 1-4 of 14)

A Christian Evangelical manifesto




WE AFFIRM that God has designed marriage to be a covenantal, sexual, procreative, lifelong union of one man and one woman, as husband and wife, and is meant to signify the covenant love between Christ and his bride the church.  

WE DENY that God has designed marriage to be a homosexual, polygamous, or polyamorous relationship.  We also deny that marriage is a mere human contract rather than a covenant made before God.  



WE AFFIRM that God’s revealed will for all people is chastity outside of marriage and fidelity within marriage.

WE DENY that any affections, desires, or commitments ever justify sexual intercourse before or outside marriage; nor do they justify any form of sexual immorality.



WE AFFIRM that God created Adam and Eve, the first human beings, in his own image, equal before God as persons, and distinct as male and female.

WE DENY that the divinely ordained differences between male and female render them unequal in dignity or worth.



WE AFFIRM that divinely ordained differences between male and female reflect God’s original creation design and are meant for human good and human flourishing.

WE DENY that such differences are a result of the Fall or are a tragedy to be overcome.






BBC 01 –

BBC 02 –  

BBC 03 –  

Balcombe, Jonathan – “Pleasurable Kingdom – animals and the nature of feeling good”

Chapais, Bernard – “Primeval Kinship – how pair-bonding gave birth to human society”

Norenzayan, Ara – “Big Gods – how religion transformed cooperation and conflict”

Petersdorf, Megan and James P Higham – “Mating Systems”: New York University: in “The International Encyclopedia of Primatology”, ed. Agustin Fuentes  

Plavcan, J. Michael – “Body Size, Size Variation, and Sexual Size Dimorphism in Early Homo,” Current Anthropology 53, no. S6 (December 2012): S409-S423   

Roberts, Dr Alice – “Evolution – the human story”

Tomasello, Michael – “A Natural History of Human Morality”  

de Waal, Frans – “Chimpanzee Politics – power and sex among apes”

de Waal, Frans and Frans Lanting – “Bonobo – the forgotten ape”





No-one ever says thank you.  

Nicole Bennett Fite