The term monogamy (literally “one marriage” or “one union” in Greek) is the practice of marriage or sexual partnering with one spouse (as opposed to polygamy where each person has several partners simultaneously). In human society, polygamy has been condemned or restricted by the majority of the world's religions. Anthropologists have observed that, while many societies have permitted polygamy, the majority of human partnerships are in fact monogamous.
Polygamous or successive monogamous partnerships have proven valuable for many species, and for human beings under certain conditions. However, non-monogamous relationships have many challenges that affect not only those involved in the partnership but also their children. Commitment to a monogamous relationship offers much support in the achievement of happiness and maturity as an individual, establishment of a harmonious family and prosperous lineage, and support for contributing to society as a whole.
Marriage is the institution through which a man and a woman typically expect to share their lives intimately in a monogamous relationship, usually referred to in the vows stated at their wedding ceremony. Raising children in a family, holding property, sexual behavior, relationship to society, inheritance, emotional intimacy, health care, and love are a few examples of the rights and obligations often shared by a married couple. The term monogamy, however, may also be applied to a couple who are not formally married, but maintain an exclusive sexual relationship.
Alternatives to monogamy include sexual abstinence—the choice not to participate in sexual activity—and polyamorous relationships involving multiple sexual partners. Polygamy, polygyny, and polyandry are anthropological terms referring respectively to multiple marriages, marriages of multiple women to one man, and of multiple men to one woman.
Biologists have described three types of monogamy: social monogamy, sexual monogamy, and genetic monogamy. Social monogamy refers to a couple that lives together, has sex with one another, and cooperates in acquiring basic resources such as food and shelter. Sexual monogamy refers to a couple that remains sexually exclusive with one another and neither person has outside sex partners. Genetic monogamy refers to the fact that two partners only have offspring with one another, so that all the offspring raised by the pair are genetically related to each partner. Beyond these distinctions, certain combinations of factors may occur:
Social monogamy refers to a male and female's social living arrangement (e.g., shared use of a territory, behaviour indicative of a social pair, and/or proximity between a male and female) without inferring any sexual interactions or reproductive patterns. In humans, social monogamy equals monogamous marriage. Sexual monogamy is defined as an exclusive sexual relationship between a female and a male based on observations of sexual interactions. Finally, the term genetic monogamy is used when DNA analyses can confirm that a female-male pair reproduce exclusively with each other. A combination of terms indicates examples where levels of relationships coincide, e.g., sociosexual and sociogenetic monogamy describe corresponding social and sexual, and social and genetic monogamous relationships, respectively.
Serial monogamy is a form of monogamy in which participants have only one sexual partner at any one time, but have more than one sexual partner in their lifetime. The term "serial monogamy" is more often more descriptive than prescriptive, in that those involved did not plan to have subsequent relationships while involved in each monogamous partnership.
Monogamy is one of several mating systems observed in animals. The percentage of monogamous species is greater in some taxa than in others. Biologists estimate up to 90 percent of avian species are socially monogamous. In contrast, biologists estimate only 3 percent of mammalian species are socially monogamous, although up to 15 percent of primate species are monogamous.
The United Nations World Fertility Report of 2003 noted that 89 percent of all women and men in the world get married by age forty-nine. Not all marriages are socially monogamous. Anthropological studies have reported that 80-85 percent of societies allow polygamous marriage.  
Yet, most of the men in societies that allow polygamy do not obtain sufficient wealth or status to have multiple wives, so the majority of marriages in these societies involve one husband and one wife. Murdock (1981) estimated that 80 percent of marriages in societies that allow polygamy involve only one husband and one wife, a figure confirmed by White's (1988) analysis of marriages in polygamous societies.
An impartial observer employing the criterion of numerical preponderance, consequently, would be compelled to characterize nearly every known human society as monogamous, despite the preference for and frequency of polygyny in the overwhelming majority.
Since this estimate of 80 percent applies to societies where polygamous marriage is a legal or culturally accepted option, the percent of socially monogamous marriages is significantly higher in the world as a whole when societies that do not permit polygamy are included.
Studies have found that approximately 85-90 percent of married women and around 75-80 percent of married men in the United States are sexually monogamous throughout their marriages. Results from a variety of other countries have also shown that the majority of married people are sexually monogamous during their marriages. The incidence of sexual monogamy varies across cultures, and women appear to be more sexually monogamous than men. Based on the data, it can be concluded that a large majority of people enter socially monogamous relationships at some point in their lives.
Socially monogamous species are scattered throughout the animal kingdom. A few insects are socially monogamous; a few fish are socially monogamous; many birds are socially monogamous; and a few mammals are socially monogamous. These species did not inherit social monogamy from a common ancestor. Instead, social monogamy has evolved independently in different species.
Some factors that have been suggested as contributing to the evolution of social monogamy include:
Other factors may also contribute to the evolution of social monogamy. Moreover, different sets of factors may explain the evolution of social monogamy in different species. There appears to be no "one-size-fits-all" explanation of why different species evolved monogamous mating systems.
Even in the realm of animals, where instinct and genetics dominate sexual behavior, science cannot predict whether or not a species will be monogamous. How much more complex is the issue in human beings, where the mind is able to choose beyond the tendencies and instincts of the physical body, and where the purpose of life is complex and multi-dimensional. Barash and Lipton (2001) have eloquently summarized the complexity of human monogamy:
Monogamy among animals is a matter of biology. So is monogamy among human beings. But in the human case, monogamy is more. It is also a matter of psychology, sociology, anthropology, economics, law, ethics, theology, literature, history, philosophy, and most of the remaining humanities and social sciences as well.
Additionally, since human beings spend a lifetime rearing their children, the nature of the parental bond impacts the next generation to a greater extent than it does in the majority of animal species. The monogamous bond of husband and wife provides a unique relationship that supports the resulting family. Two parents united in the common goal of parenting their children can ensure that their lineage is secure, healthy, and prosperous. When parents are not monogamous, the family structure is less clear, and the children experience a variety of adults with varying degrees of commitment to their future. Consequently, children raised by non-monogamous adults do not fare as well as those raised by monogamous parents.
Culture influences the incidence of social monogamy in human beings. Many cultures have passed laws making social monogamy the only legal form of marriage. The passage of such laws in many cases reflects religious beliefs. In the late twentieth century, international organizations such as the United Nations and the African Union started to promote social monogamy as a way to give women and men equal rights in marriage.
However, it is clear that when the monogamous path is not chosen, consequences occur on all levels, and are enduring:
That sick, used feeling of having given a precious part of myself ... to so many and for nothing, still aches. I never imagined I'd pay so dearly and for so long.
Such an experience is all too common, and all too pervasive. When human beings choose to practice non-monogamous sexual relationships, health issues affect the physical body, psychological issues affect our individual state of mind, and social issues affect our relationships with others, and spiritual issues affect our eternal soul and our relationship with God.
Sexually transmitted diseases (STDs) are both a medical and a social problem. Since the chances of contracting a sexually transmitted disease increase with the number of partners one has, monogamy is a safer option. STDs can affect more than one generation, since many diseases can be transferred at birth. In other cases, the debilitating, even terminal, effects of certain STDs make good parenting difficult if not impossible.
Beyond the transmission of disease, a potential (often intended) consequence of sexual activity is pregnancy. Even when birth control is used, this is a common outcome. The months of pregnancy, birth, and rearing of a child for a woman not involved in a committed monogamous relationship is challenging to say the least. Thus, abortion is a common choice. Even when legally permitted, there are health risks involved in abortion, and beyond the physical consequences are psychological and social scars.
Beyond the physical dangers of uncommitted, multiple sexual relationships are the effects on one's psychological health. These effects include:
These consequences can be more profound and long-lasting than the physical consequences. For those who do not recognize the commitment necessary in entering into a sexual relationship, particularly adolescents, friendships can be ruined by the introduction of sexual activity in the relationship. From a caring, mutually beneficial relationship involving communication and activities shared in a larger social group, the sexually active couple becomes self-centered and possessive, quickly becoming suspicious and jealous of any attention their partner pays to another. When one individual is not committed to a monogamous relationship, the expectation of commitment from the partner is also lowered.
The desire for romantic love is natural and healthy in adolescents, and part of normal psychological development. However, the inclusion of sexual activity prematurely has been noted to greatly reduce the creativity and emotional excitement of young people, leaving them "flat-souled" and impoverished in ideals, hopes and imagination.
Psychological studies of monogamous relationships have revealed three significant issues: First, satisfaction is often raised to initial high levels, but equally often declines during the first years of marriage. Second, attachment, the need for physical and emotional closeness, plays an important role in many aspects of monogamous relationships. Finally, although some people question the duration of marriage as a worthwhile goal, most people expect their marriages to last a long time. If it fails, the psychological consequences of ending a sexual relationship have been found to be emotionally traumatic.
The events of falling in love and getting married raise people's feelings of happiness and satisfaction to unusually high levels. It is natural for these feelings of happiness and satisfaction to return to more normal levels over time.
When two people fall in love and develop an intimate relationship, they begin to include their partners in their concepts of themselves. People feel like they acquire new capabilities because they have the support of close partners. "I might not be able to handle parenthood by myself, but with the help of my partner's good parenting skills, I'll be a good parent." This overlap of the concepts of self and partner has been called "self-expansion."
People generally experience a high level of self-expansion at the beginning of relationships when they constantly learn new things about themselves and their partners. Rapid self-expansion pushes satisfaction to very high levels. However, as the relationship matures, the rate of self-expansion slows, and people experience a relative decline in satisfaction.
Once couples are married, they have to deal with the inevitability of arguments and conflict. Couples who deal poorly with arguments and conflict build up a history of negative emotional interactions that erodes marital satisfaction.
How well couples handle conflict and stress depends on their vulnerabilities, the kinds of stresses they face, and their processes of adaptation. Couples who handle conflict and stress poorly become less and less satisfied with their relationships over time. Those who succeed in dealing with conflict, through mutual support and good communication, on the other hand, develop deep trust and closeness in their relationship. Such relationships result in greater satisfaction and long-lasting happiness that is qualitatively different from the excitement of the early stages of a relationship.
Attachment is the tendency to seek closeness to another person, to feel secure when that person is present, and to feel anxious when that person is absent.
Attachment theory was originally developed by John Bowlby and Mary Ainsworth to describe children's desires for closeness with their parents. Hazen and Shaver noticed that interactions between adult romantic partners shared similarities to interactions between children and caregivers. Romantic partners desire to be close to one another. They feel comforted when their partners are present and anxious or lonely when their partners are absent. Romantic relationships serve as secure bases that help partners face the surprises, opportunities, and challenges life presents. People who have secure attachment styles have been found to express greater satisfaction with their relationships than people who have other attachment styles.  Secure attachment styles may lead to more constructive communication and more intimate self-disclosures, which in turn increase relationship satisfaction.
Studies of couples in laboratories and studies of people in long-lasting marriages have identified several factors that contribute to the duration of monogamous relationships.
One pattern that predicts relationship duration is the balance of positive and negative interactions. Positive interactions can repair damage done by negative interactions. Stable and happy couples consistently engage in at least five positive interactions for every one negative interaction. People who use humor and gentleness to soothe the feelings of their partners, and who respond calmly to the negative emotional expressions of their partners, are less likely to break up with their partners.
Not everyone agrees the duration of a relationship indicates the success of a relationship. Some people reject the idea of "till death do us part" in favor of "as long as love shall last." Constantine and Constantine have clearly summarized this perspective:
For our part, to stay together for the longest possible time is a poor goal for marriage. Other ends—growth, fulfillment, happiness, among others—are more important and may demand shorter relationships if they are given priority. People change and the marriage that was valid at one time may lose its validity.
Husbands and wives in long-lasting marriages have been found to agree on the following as the top seven reasons for their success:
These reasons indicate that marriage is most likely to be successful when both partners are committed to a monogamous relationship.
Virginity has generally been held sacred within a society. The custom of the virgin bride stemmed from patriarchal ideas of ownership and entitlement, even though it was also the only form of birth control. Virginity has been recognized as a precious gift, to be shared with a special person, and not wasted on a casual fling.
When society regards monogamy as the norm, the family unit is stable, sexual activity is maintained exclusively between the monogamous partners, and various social norms regarding sexual behavior are kept. When a society does not give high regard to monogamy, various social consequences ensue which impact families, communities, and the nation as a whole.
A culture that does not support monogamous, committed marriages for life does not provide the environment that is needed to allow a husband and wife to sustain a marriage in difficult times. When husband and wife do not seriously commit to practice fidelity to each other until death, many difficulties become insurmountable and divorce becomes the common, and accepted, result.
Extramarital affairs strike at the very heart of the family—the marriage vow. Infidelity destroys the trust and bonds of love; all involved are deeply affected. A marriage may survive infidelity, but only with serious commitment and effort on the part of all involved. In a society that does not value monogamy, such commitment and effort are often lacking and divorce becomes the likely outcome.
The results of divorce affect not only the partners, but also the children, leading to a new generation of adults for whom enduring, monogamous relationships are viewed as unattainable. Children of divorce have been found to suffer long-term consequences, including serious problems of personal identity, alcoholism and drug abuse, higher than average rates of suicide, and fears of abandonment, mistrust in relationships, and an unwillingness to have children of their own.
The business of prostitution and the practice of sex outside of marriage feed upon each other. Prostitutes are victims of the system that reduces them to sexual objects, many of whom become trapped in the sex slave trade. Prostitution has been responsible for the enslavement of large numbers of young girls, condemning them to a short life of violence, shame, and disease.
Although people regard pornography as a harmless outlet for sexual energy, it has been linked to crimes of rape and sexual abuse. Long-term exposure to pornography has also been shown to create emotional withdrawal, greater acceptance of violence toward women, less sympathy toward victims of rape, and a general desensitization to violence.
Single parents, especially those who are still very young, face unprecedented challenges in rearing their children. A married couple, committed to each other and to their family, encounter stress and difficulties in learning how to adjust to the needs of their growing children. A single person, dealing with the emotional, financial, and other practical aspects of raising a child, is in great danger of failure. Unmarried teenagers who become pregnant face almost insurmountable challenges to complete sufficient education to ensure a career that can support their children. Poverty is a common outcome, defrayed only by government welfare programs.
The world's religions have generally regarded the bond of marriage between a man and a woman as "divinely ordained," and adultery as the worst sin: "No other sin has such a baneful effect on the spiritual life."
In Judaism and Christianity, it is written that "a man leaves his father and his mother and cleaves to his wife, and they become one flesh" (Genesis 2:24), emphasizing the depth of the connection between husband and wife. The immutability of this relationship is further emphasized in Christianity by Jesus' commentary on that verse: "So they are no longer two but one flesh. What therefore God has joined together, let not man put asunder" (Mark 10:8-9).
Religions also teach that a man should have only one wife, and a woman one husband:
The uniqueness of the relationship between husband and wife is noted in the Judeo-Christian commandments: "You shall not commit adultery" and "You shall not covet your neighbor's wife" (Exodus 20: 14-17). Adultery is regarded as a major sin throughout religious teachings, with serious consequences:
This concern of religious teachings to warn people not to commit adultery but to practice fidelity to their spouse reflects the belief common to all faiths that the consequences of sexual activity that breaks the monogamous marital bond are extremely serious.
People disagree strongly about the value of monogamy. For example, some people believe monogamous marriage oppresses women and burdens people with unrealistic expectations of lifelong sexual monogamy. Monogamy from this perspective promotes sexism and leads to needless suffering. Other people believe monogamy promotes women's equality and provides a context to deepen trust and intimacy. Monogamy from this perspective provides a foundation for social progress and offers people more secure relationships.
Criticisms of monogamy vary in scope. Some criticisms reject all types of monogamy as inherently negative. Other criticisms accept social monogamy as a positive form of relationship, but reject sexual monogamy as an unnatural constraint on sexual behavior. Still other criticisms accept all types of monogamy as positive forms of relationship, but reject that idea that monogamy should be imposed on all people as the only legal option.
Friedrich Engels, a colleague of Karl Marx and pioneer in communist philosophy, wrote about monogamous marriage in his book, The Origin of the Family, Private Property, and the State. Engels described monogamous marriage as a social institution designed for two main functions. First, monogamous marriage ensured wealth was passed down to biologically related offspring. Second, monogamous marriage trapped women in a life of unpaid domestic and childrearing labor. Engels believed the communist revolution would undermine both of these functions. A communist society would no longer allow wealth to be passed down to biological offspring, and a communist society would socialize the work of raising children. Monogamous marriage would then no longer serve any purpose and eventually would fade away.
According to Engels, the rise of monogamous marriage coincided with oppression of women by men:
Thus when monogamous marriage first makes its appearance in history, it is not as the reconciliation of man and woman, still less as the highest form of such a reconciliation. Quite the contrary. Monogamous marriage comes on the scene as the subjugation of the one sex by the other; it announces a struggle between the sexes unknown throughout the whole previous prehistoric period. In an old unpublished manuscript, written by Marx and myself in 1846, I find the words: 'The first division of labor is that between man and woman for the propagation of children.' And today I can add: The first class opposition that appears in history coincides with the development of the antagonism between man and woman in monogamous marriage, and the first class oppression coincides with that of the female sex by the male.
The way to undo this oppression, according to Engels, was to grant women and men equal rights in marriage and to socialize the care of children so women could work and earn their own livings. These changes would free women from financial dependency on men, and allow women to dissolve marriages with tyrannical husbands. Monogamous marriage would become an agreement people entered purely for love and desire. Later generations, growing up without the oppressive history of monogamous marriage, might find alternative ways of arranging their private relationships.
Some feminists have criticized monogamous marriage for many of the same reasons as Engels. For example, Julia Penelope has claimed "Both monogamy and non-monogamy name heteropatriarchal institutions within which the only important information is: how many women can a man legitimately own?" However, feminism encompasses a broad range of writers and ideas with a diverse range of views on marriage, and it would be unfair to characterize all feminists as opposed to monogamous marriage.
Many authors have criticized lifelong sexual monogamy as unnatural and unrealistic. They contend that humans have never been a sexually monogamous species, and that cultural expectations of sexual monogamy place enormous burdens on individuals to fulfill all the sexual needs of their partners. These expectations are quite unrealistic given how much variety exists in people's sexual desires and sex drives. In addition, sexual desires and sex drives can change over time due to circumstances (such as periods of high stress or poor health) and due to normal aging (such as changes in hormonal levels). Loving partners can find themselves mismatched in terms of their current sexual desires or sex drives. Thus, it has been argued that the failure to live up to unrealistic expectations of lifelong sexual monogamy causes people needless suffering.
The defense of monogamy is as varied and rich as its criticism. Generally, the viewpoint in defense of monogamy contends that monogamy actually promotes the equality of woman and secure relationships.
Despite Engels' argument that monogamous marriage oppressed women, the communist revolutionaries in China viewed monogamy as a means of giving women and men equal rights in marriage. This view has since been echoed by women's rights movements in nations that allow polygamy. In nations that do allow polygamy, especially where it takes the form of polygyny (men taking several wives), women often feel the practice of polygamy makes them second-class citizens and lowers their quality of life. The women's rights movements in these nations want to make monogamy the only legal form of marriage.
The United Nations began to promote social monogamy as the preferred form of marriage in 1979, when the General Assembly adopted the Convention on the Elimination of All Forms of Discrimination Against Women, an international bill of rights for women that over 180 nations have agreed to implement. Article 16 of the Convention requires nations to give women and men equal rights in marriage. Polygamy is interpreted as inconsistent with Article 16, because it extends the right of multiple spouses to men but not to women.
Many authors claim sexual monogamy promotes security, intimacy, and stability in relationships. Their claim stems from observations of couples exploring "open marriage" where partners agree that each is free to engage in extramarital sexual relationships. Although some people have happy and stable open marriages, sexual non-monogamy proves too difficult for most couples to manage and their relationships suffer as a consequence:
Any number of sexual innovators, over the past 60 or 70 years, have argued for a third alternative—a combination of permanence with permissiveness: that is, permanent adherence to the marriage, for the sake of child-rearing and social stability, combined with freedom for each partner to have additional emotional and physical relationships outside the marriage, But thus far, all variations upon this theme have proven disruptive to the marriages of most of those who have practiced them, and too threatening to the majority of those who have not to be seriously tried out. Relatively few people, even today, manage to make permissive marriage work at all, let alone work better than exclusive marriage. For although marriage no longer has the structural support of religion, community, law, or practical necessity, today there is something else that makes exclusivity, or the appearance of it, immensely important—namely, the loneliness and disconnectedness of modern life, which creates a deep need in modern man and woman to belong, and to have a binding emotional connection to someone else. And since for most people sex is so closely bound up with deep emotions, extramarital sexual acts are severely threatening to the emotional identity and security that marriage seems to offer.
Thus, many have concluded that the harmony of the conjugal relationship is best served by sexual exclusivity:
It is not that I feel any deep-rooted moral objection to a lack of sexual exclusiveness in long-term relationships. It is rather that I am increasingly aware of the difficulties that the vast majority of humans have in coping with it. The ideal of the open marriage seems to me to be a fine one. In addition to the central primary relationship, it recognizes other less permanent, sexual or non-sexual relationships, which may in themselves be mutually rewarding and self-fulfilling. But few primary relationships can survive such apparent if unintended challenges. The essential security of the dyad is weakened, and further undermined by the ravages of jealousy.
Human beings have free will, and thus have a choice whether to commit to a monogamous relationship or to choose another path. One alternative choice is sexual abstinence. This can be for religious, moral, or other reasons. While this choice can be the best for some, or for all during a limited time period (such as in adolescence and preparation for marriage), clearly abstinence cannot be the choice of all for all time or the human species would not continue.
"Polyamory" is another alternative, which involves multiple loving relationships. As noted above, such relationships have proven difficult to maintain successfully. Communities which have tried group marriage have encountered serious difficulties, leading to the breakdown of the group. Issues of jealousy and feelings of inadequacy when faced with one's partner's continual intimate relationships with others surfaced despite members' best efforts to avoid them. Production of children led not to happy families with multiple parents, but the decision that group members should not procreate.
Since the "Sexual Revolution" a common alternative to monogamy has become promiscuity— the practice of making relatively casual and indiscriminate choices. Applied to sexual behavior, it refers to sexual intercourse that is not in the framework of a long term monogamous sexual relationship. The impact of widespread promiscuity on society has been immense.
A perspective that is refreshingly clear, moving from the confusion of the twentieth century, comes from Crittenden:
What we rarely hear is how liberating marriage can actually be. The negative, that we are no longer able to live entirely for ourselves, is also the positive: We no longer have to live entirely for ourselves.
Monogamy is the opportunity to grow beyond the borders of the self and live for the sake of someone else. Through the willingness to live in an exclusive special relationship, for the sake of that other, it may be that one's own dreams and desires are finally fulfilled. Certainly, when those dreams include the experience of long-lasting and deep love, the creation of new life in the form of children, and the extension of one's lineage into future generations, a committed monogamous relationship offers much to be recommended over the alternatives.
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