Monogamy

Monogamy is a form of marriage in which an individual has only one spouse during their lifetime or at any one time (serial monogamy), as compared to polygamy or polyamory. In current usage, monogamy often refers to having one sexual partner irrespective of marriage or reproduction. The term is also applied to the social behavior of some animals, referring to the state of having only one mate at any one time.

Etymology
The word monogamy comes from the Greek words "μονός", monos which means one or alone, and "γάμος", gamos which means marriage.

Notion and aspects of monogamy
Traditionally there are two meanings of monogamy: one is applied to marriage of human beings, described specifically by Aristotelianism and Thomism as rational animals (in Latin: animal rationale). The other also encompasses relationships between non-human animals.

Among human beings monogamy has two aspects:


 * 1) principle of marrying only once in a lifetime, opposed to digamy
 * 2) marriage with only one person at a time, opposed to bigamy or polygamy

Monogamy, as applied to human marriage, is explored by human sciences or humanities which assume as a principle that capacities or attributes associated with personhood substantially distinguish human beings from the rest of the animal world. Karol Wojtyła in his book Love and Responsibility postulated that monogamy, as an institutional union of two people being in love with one another, was an embodiment of an ethical personalistic norm, and thus the only means of making true human love possible.

Human monogamy's legal aspects are taught at faculties of law. There are also philosophical aspects, the field of interest of e.g. philosophical anthropology and philosophy of religion, as well as theological ones.

The second meaning of monogamy, relating to non-rational animals as well as humans is a major field of interest in biology and other related disciplines.

Modern researchers, along the lines of the theory of evolution, approach human monogamy as not intrinsically different from any other metazoan monogamy. They postulate the following four aspects of monogamy:
 * Social monogamy refers to two partners living together, having sex with each other, and cooperating in acquiring basic resources such as shelter, food, and money.
 * Sexual monogamy refers to two partners remaining sexually exclusive with each other and having no outside sex partners.
 * Genetic monogamy refers to two partners only having offspring with each other.
 * Marital monogamy refers to marriages of only two people.

Varieties of monogamy in biology
Recent discoveries have led biologists to talk about the three varieties of monogamy: social monogamy, sexual monogamy, and genetic monogamy. The distinction between these three are important to the modern understanding of monogamy.

Monogamous pairs of animals are not always sexually exclusive. Many animals that form pairs to mate and raise offspring regularly engage in sexual activities with partners other than their primary mate. This is called extra-pair copulation. Sometimes these extra-pair sexual activities lead to offspring. Genetic tests frequently show that some of the offspring raised by a monogamous pair come from the female mating with an extra-pair male partner. These discoveries have led biologists to adopt new ways of talking about monogamy: "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." (Reichard, 2003, page 4) Whatever makes a pair of animals socially monogamous does not necessarily make them sexually or genetically monogamous. Social monogamy, sexual monogamy, and genetic monogamy can occur in different combinations.

When applying these terms to people, it's important to remember that social monogamy does not always involve marriage. A married couple is almost always a socially monogamous couple. But couples who choose to cohabit without getting married can also be socially monogamous. The popular science author Matt Ridley in his book The Red Queen: Sex and the Eveolution of Human Nature, described the human mating system as "monogamy plagued by adultery".

Serial monogamy
Serial monogamy is a mating practice in which individuals may engage in sequential monogamous pairings, or in terms of humans, when men or women can marry another partner but only after ceasing to be married to the previous partner.

One theory is that this pattern pacifies the elite men and equalizes reproductive success. This is called the Male Compromise Theory. Such serial monogamy may effectively resemble polygyny in its reproductive consequences because some men are able to utilize more than one woman’s reproductive lifespan through repeated marriages.

Reproductive success
Evolutionary theory predicts that males would be apt to seek more mating partners than females because they obtain higher reproductive benefits from such a strategy. Accordingly, males developed many behavior strategies that allow them to acquire more reproductively capable sexual partners. Therefore, in order to monopolize periods of more than one female’s reproductive life span without being considered polygamous and thus breaking social norms of a monogamous society, males try to remarry women younger than themselves. A study done in 1994 found a significant difference between ages of remarried men and women because the men have a longer reproductive window.

Breakup
Serial monogamy has always been closely linked to divorce practices. Whenever procedures for obtaining divorce have been simple and easy, serial monogamy has been found. As divorce has continued to become more accessible, more individuals have availed themselves of it, and many go on to remarry. Barry Schwartz, author of The Paradox of Choice: Why less is more, further suggests that Western culture's inundation of choice has devalued relationships based on lifetime commitments and singularity of choice. It has been suggested, however, that high mortality rates in centuries past accomplished much the same result as divorce, enabling remarriage (of one spouse) and thus serial monogamy.

Mating system
Monogamy is one of several mating systems observed in animals. However, a pair of animals may be socially monogamous but that does not necessarily make them sexually or genetically monogamous. Social monogamy, sexual monogamy, and genetic monogamy can occur in different combinations.

Social monogamy refers to the overtly observed living arrangement whereby a male and female share territory and engage in behaviour indicative of a social pair, but does not imply any particular sexual fidelity or reproductive pattern. The extent to which social monogamy is observed in animals varies across taxa, with over 90 percent of avian species being socially monogamous, compared to only 3 percent of mammalian species and up to 15 percent of primate species. Social monogamy has also been observed in reptiles, fish, and insects.

Sexual monogamy is defined as an exclusive sexual relationship between a female and a male based on observations of sexual interactions. However, scientific analyses can test for paternity, for example by DNA paternity testing or by fluorescent pigment powder tracing of females to track physical contact. This type of analysis can uncover reproductively successful sexual pairings or physical contact. Genetic monogamy refers to DNA analyses confirming that a female-male pair reproduce exclusively with each other.

The incidence of sexual monogamy appears quite rare in other parts of the animal kingdom. It is becoming clear that even animals that are overtly socially monogamous engage in extra-pair copulations. For example, while over 90% of birds are socially monogamous, "on average, 30 percent or more of the baby birds in any nest [are] sired by someone other than the resident male." Patricia Adair Gowaty has estimated that, out of 180 different species of socially monogamous songbirds, only 10% are sexually monogamous. Offspring are far more successful when both the male and the female members of the social pair contribute food resources.

An example of this was seen when scientists studied red winged blackbirds. These birds are known for remaining in monogamous relationships during the course of mating season. During the course of the study, the researchers gave a few select males vasectomies just before mating season. The male birds behaved like they do every season, establishing territory, finding a mate, and attempting to make baby birds. Despite apparent social monogamy, the female birds whose partners were surgically altered still became pregnant, indicating that overt social monogamy did not predict for sexual fidelity. These babies were cared for by their sterile adoptive fathers.

The highest known frequency of reproductively successful extra-pair copulations are found among fairywrens Malurus splendens and Malurus cyaneus where more than 65 percent of chicks are fathered by males outside the supposed breeding pair. This discordantly low level of genetic monogamy has been a surprise to biologists and zoologists, as social monogamy can no longer be assumed to determine how genes are distributed in a species.

Evolution in animals
Socially monogamous species are scattered throughout the animal kingdom: A few insects, a few fish, about nine-tenths of birds, and a few mammals are socially monogamous. There is even a parasitic worm, Schistosoma mansoni, that in its female-male pairings in the human body is monogamous. The diversity of species with social monogamy suggests that it is not inherited from a common ancestor but instead evolved independently in many different species.

The occurrence of social monogamy in vertebrates is directly related to the presence or absence of estrus (oestrus); the trait in which the female is sexually excited during ovulation. Estrus is a trait confined to placental mammals. This explains why social monogamy is so rare in these mammals since the estrus female will, generally, mate with any proximate male. Birds, which are notable for a high incidence of social monogamy, do not have the trait of estrus.

Researchers have observed a mixed mating system of monogamy and polygyny in the European pied flycatcher.

Evolution of monogamy in humans
It is important to have a clear understanding of the nomenclature of monogamy because scientists use the term monogamy for different male-female relationships. Biologists, biological anthropologists, and behavioral ecologists often use the term monogamy in the sense of sexual, if not genetic, monogamy as defined above in The notion and aspects of monogamy. To clarify the difference, sexual monogamy simply means an individual has only one mating partner throughout their lifetime while genetic monogamy is only used to describe sexually monogamous relationships with genetic evidence of paternity. Since maternity is always certain, genetic evidence is unnecessary. When cultural or social anthropologists and other social scientists use the term monogamy, the meaning is social monogamy, as defined above. In human societies, social monogamy is often defined as monogamous marriage.

Evolutionary history of human monogamy
The date when monogamy evolved in the human lineage is heatedly debated with differing views from within the field of paleoanthropology and from genetic studies. Ultimately, there are two prevailing views on the evolutionary history of monogamy in humans: monogamy evolved very early in human lineage and monogamy evolved much more recently, less than 20,000 years ago.

Paleoanthropological estimates of the time frame for the evolution of monogamy are primarily based on the level of sexual dimorphism seen in the fossil record because, in general, the reduced male-male competition seen in monogamous mating results in reduced sexual dimorphism. According to Reno et al., the sexual dimorphism of Australopithecus afarensis, a human ancestor from approximately 3.9–3.0 million years ago, was within the modern human range, based on dental and postcranial morphology. Although careful not to say that this indicates monogamous mating in early hominids, the authors do say that reduced levels of sexual dimorphism in A. afarensis “do not imply that monogamy is any less probable than polygyny”. However, Gordon, Green and Richmond claim that in examining postcranial remains, A. afarensis is more sexually dimorphic than modern humans and chimps with levels closer to those of orangutans and gorillas. Furthermore, Homo habilis, living approximately 2.3 mya, is the most sexually dimorphic early hominid. Plavcan and van Schaik conclude their examination of this controversy by stating that, overall, sexual dimorphism in australopithecines is not indicative of any behavioral implications or mating systems.

The genetic evidence for the evolution of monogamy in humans is more complex but much more straightforward. While female effective population size (the number of individuals successfully producing offspring thus contributing to the gene pool), as indicated by mitochondrial-DNA evidence, increased around the time of human (not hominid) expansion out of Africa about 80,000–100,000 years ago, male effective population size, as indicated by Y-chromosome evidence, did not increase until the advent of agriculture 18,000 years ago. This means that before 18 000 years ago, many females would be reproducing with the same few males.

Scientists discuss the evolution of monogamy in humans as if it is the prevailing mating strategy among Homo sapiens, although only approximately 17.8% (100) of 563 societies sampled in Murdock’s Atlas of World Cultures has any form of monogamy. These societies with monogamy account for much larger than 17.8% of the World population. Therefore, “genetic monogamy appears to be extremely rare in humans,” and “social monogamy is not common, ... often reduc[ing] to serial polygyny in a biological sense”. This means that monogamy is not the predominant mating system among the hominid lineage and probably never was.

In Herodotus's Histories, which contains some of the earliest anthropological writings, Herodotus writes about a few societies and tribes that did not opt for social monogamy at the time (circa 500 BC). One tribe he mentions had open relationships in the villages and after puberty the boys were assigned their 'fathers' according to whom they most resembled. He mentions other socially open tribes where mating openly outside in the daylight was observed. It is postulated that the reason he notes these tribes is because they were not the norm in Ancient Greece, where monogamy prevailed at that time.

Biological
Monogamy, or at least social monogamy, does exist in many societies around the world, and it is important to understand how these marriage systems might have evolved. In any species, there are three main aspects that combine to promote a monogamous mating system: paternal care, resource access, and mate-choice; however, in humans, the main theoretical sources of monogamy are paternal care and extreme ecological stresses. Paternal care should be particularly important in humans due to the extra nutritional requirement of having larger brains and the lengthier developmental period. Therefore, the evolution of monogamy could be a reflection of this increased need for bi-parental care. Similarly, monogamy should evolve in areas of ecological stress because male reproductive success should be higher if their resources are focused on ensuring offspring survival rather than searching for other mates. However, the evidence does not support these claims. Due to the extreme sociality and increased intelligence of humans, H. sapiens have solved many problems that generally lead to monogamy, such as those mentioned above. For example, monogamy is certainly correlated with paternal care, as shown by Marlowe, but not caused by it because humans diminish the need for bi-parental care through the aid of siblings and other family members in rearing the offspring. Furthermore, human intelligence and material culture allows for better adaptation to different and rougher ecological areas, thus reducing the causation and even correlation of monogamous marriage and extreme climates.

A 2012 study found that oxytocin effects social distance between adult males and females, and may be responsible at least in part for romantic attraction and subsequent monogamous pair bonding. An oxytocin nasal spray caused men in a monogamous relationship, but not single men, to increase the distance between themselves and an attractive woman during a first encounter by 10 to 15 centimeters. The researchers suggested that oxytocin may help promote fidelity within monogamous relationships.

Cultural
Despite the human ability to avoid sexual and genetic monogamy, social monogamy still forms under many different conditions, but most of those conditions are consequences of cultural processes. For example, during times of major economic / demographic transitions, investing more in a fewer offspring (social monogamy not polygyny) increases reproductive success by ensuring the offspring themselves have enough initial wealth to be successful. This is seen in both England and Sweden during the industrial revolution and is currently being seen in the modernization of rural Ethiopia. Similarly, in modern industrialized societies, fewer yet better-invested offspring, i.e. social monogamy, can provide a reproductive advantage over social polygyny, but this still allows for serial monogamy and extra-pair copulations.

Betzig postulated that culture/society can also be a source of social monogamy by enforcing it through rules and laws set by third-party actors, usually in order to protect the wealth or power of the elite. For example, Augustus Caesar encouraged marriage and reproduction to force the aristocracy to divide their wealth and power among multiple heirs, but the aristocrats kept their socially monogamous, legitimate children to a minimum to ensure their legacy while having many extra-pair copulations. Similarly—according to Betzig—the Christian Church enforced monogamy because wealth passed to the closest living, legitimate male relative, often resulting in the wealthy oldest brother being without a male heir. Thus, the wealth and power of the family would pass to the “celibate” younger brother of the church. In both of these instances, the rule-making elite used cultural processes to ensure greater reproductive fitness for themselves and their offspring, leading to a larger genetic influence in future generations. Furthermore, the laws of the Christian Church, in particular, were important in the evolution of social monogamy in humans. They allowed, even encouraged, poor men to marry and produce offspring which reduced the gap in reproductive success between the rich and poor, thus resulting in the quick spread of monogamous marriage systems in the western world. According to B. S. Low, culture would appear to have a much larger impact on monogamy in humans than the biological forces that are important for non-human animals.

Religious and anthropological sources
Betzig's contention that monogamy evolved as a result of Christian socio-economic influence in the West is weakened by monogamy being widespread idea in the ancient Middle East much earlier. In Israel's pre-Christian era, an essentially monogamous ethos underlay the Jewish creation story (Gn 2) and the last chapter of Proverbs. During the Second Temple period, apart from economic situation which supported monogamy even more than in earlier period, the concept of mutual fidelity between husband and wife was a quite common reason for strictly monogamous marriages. The will that the marriage remains monogamous was explicitly expressed in some marriage documents. Examples of these documents were found in Elephantine. They were similar to those found in neighbouring Assyria and Babylonia. Study shows that ancient Middle East societies, though not strictly, were practically at least on commoners level monogamous. Halakha of the Dead Sea Sect saw prohibition of polygamy as coming from the Pentateuch (Damascus Document 4:20–5:5, one of the Dead Sea Scrolls). Christianity adopted a similar attitude (cf. 1 Tm 3:2,12; Tt 1:6), which was in conformity with Jesus' approach.

But a monogamist viewpoint within Judaism was clearly reflected also in the Mishnah and the baraitot (Yevamot 2:10 etc.). Some sages condemned marriage to two wives even for the purpose of procreation (Ketubot 62b). R. Ammi, a Palestinian amora states:

Such attitude possibly was enhanced by Roman customs, which prohibited polygamy, especially after 212 AD, when all the Jews became Roman citizens. Jesus of Nazareth contended that core problem was faithfulness to the Torah. According to him, monogamy was a primordial will of the Creator described in Genesis, darkened by the hardness of hearts of the Israelites. As John Paul II interpreted the dialogue between Jesus and the Pharisees (Gospel of Matthew 19:3–8), Christ emphasized the primordial beauty of monogamic spousal love described in the Book of Genesis 1:26–31, 2:4–25, whereby a man and woman by their nature are each ready to be a beautifying, total and personal gift to one another:

From this viewpoint, monogamy rests upon a long history of evolution of human culture directly determined by the nature of human person and inspired by the light of the divine revelation received in a religious experience. It is a question of philosophical anthropology, philosophy of religion, as much as of theology.

Incidence of social monogamy
The United Nations World Fertility Report of 2003 reports that 89% of all people get married before age forty-nine. The percent of women and men who marry before age forty-nine drops to nearly 50% in some nations and reaches 100% in other nations.

Incidence of sexual monogamy
The incidence of sexual monogamy can be roughly estimated as the percentage of married people who do not engage in extramarital sex. Several studies have looked at the percentage of people who engage in extramarital sex. These studies have shown that extramarital sex varies across cultures and across genders.

The Standard Cross-Cultural Sample describes the amount of extramarital sex by men and women in over 50 pre-industrial cultures. The amount of extramarital sex by men is described as "universal" in 6 cultures, "moderate" in 29 cultures, "occasional" in 6 cultures, and "uncommon" in 10 cultures. The amount of extramarital sex by women is described as "universal" in 6 cultures, "moderate" in 23 cultures, "occasional" in 9 cultures, and "uncommon" in 15 cultures. These findings support the claim that the amount of extramarital sex differs across cultures and across genders.

Recent surveys conducted in non-Western nations have also found cultural and gender differences in extramarital sex. A study of sexual behavior in Thailand, Tanzania and Côte d'Ivoire suggests about 16–34% of men engage in extramarital sex while a much smaller (unreported) percentage of women engage in extramarital sex. Studies in Nigeria have found around 47–53% of men and to 18–36% of women engage in extramarital sex. A 1999 survey of married and cohabiting couples in Zimbabwe reports that 38% of men and 13% of women engaged in extra-couple sexual relationships within the last 12 months.

The issue of extramarital sex has been examined frequently in the United States. Many surveys asking about extramarital sex in the United States have relied on convenience samples. A convenience sample means surveys are given to whoever happens to be easily available (e.g., volunteer college students or volunteer magazine readers). Convenience samples do not accurately reflect the population of the United States as a whole, which can cause serious biases in survey results. It should not be surprising, therefore, that surveys of extramarital sex in the United States have produced widely differing results. These studies report that about 12–26% of married women and 15–43% of married men engage in extramarital sex. The only way to get scientifically reliable estimates of extramarital sex is to use nationally representative samples. Three studies have used nationally representative samples. These studies have found that about 10–15% of women and 20–25% of men engage in extramarital sex.

A majority of married people remain sexually monogamous during their marriages. The number of married partners who engage in extramarital sex never exceeds 50% in studies using large or nationally representative samples. Yet, the incidence of sexual monogamy varies across cultures. People in some cultures are more sexually monogamous than people in other cultures. Women also appear to be more sexually monogamous than men.

In the U.S., some studies have found that the majority of gay male couples are not monogamous. Research by Colleen Hoffon of 566 gay male couples from the San Francisco Bay Area found that only 45% had monogamous relationships. That study was funded by the National Institute of Mental Health. However, the Human Rights Campaign has stated, based on a Rockway Institute report, that "GLBT young people... want to spend their adult life in a long-term relationship raising children." Specifically, over 80% of the lesbians and homosexuals surveyed expected to be in a monogamous relationship after age 30.

Incidence of genetic monogamy
The incidence of genetic monogamy may be estimated from rates of extrapair paternity. Extrapair paternity is when offspring raised by a monogamous pair come from the female mating with another male. Unfortunately, rates of extrapair paternity have not been extensively studied in people. Many reports of extrapair paternity are little more than quotes based on hearsay, anecdotes, and unpublished findings. Simmons, Firman, Rhodes, and Peters reviewed 11 published studies of extra-pair paternity from various locations in the United States, France, Switzerland, the United Kingdom, Mexico, and among the Yanomamo Indians of South America. The rates of extrapair paternity ranged from 0.03% to 11.8% although most of the locations had low percentages of extrapair paternity. The median rate of extrapair paternity was 1.8%. A separate review of 17 studies by Bellis, Hughes, Hughes, and Ashton found slightly higher rates of extrapair paternity. The rates varied from 0.8% to 30% in these studies, with a median rate of 3.7% extrapair paternity. A range of 1.8% to 3.7% extrapair paternity implies a range of 96% to 98% genetic monogamy. Although the incidence of genetic monogamy may vary from 70% to 99% in different cultures or social environments, a large percentage of couples remain genetically monogamous during their relationships. A review paper surveying 67 other studies of nonpaternity reporting rates of nonpaternity in different societies ranging from 0.4% to over 50% was recently published by Kermyt G. Anderson.

Pedigree errors are a well-known source of error in medical studies. When attempts are made to try to study medical afflictions and their genetic components, it becomes very important to understand nonpaternity rates and pedigree errors. There are numerous software packages and procedures that exist for correcting research data for pedigree errors.

Monogamy in ancient societies
Monogamy, as the studies of private life in ancient Egypt, Mesopotamia, Assyria and Israel give evidence, was a basic family model in the civilizations of the ancient Middle East.

Ancient Mesopotamia and Assyria
Both the Babylonian and Assyrian families were monogamous in principle. In the patriarchal society of Mesopotamia the nuclear family was called a "house". In order "to build a house" a man was supposed to marry one woman and if she did not provide him with offspring, he could take a second wife. Code of Hammurabi states that he loses his right to do so, if the wife herself gives him a slave as concubine. According to Old Assyrian texts, he could be obliged to wait for two or three years before he was allowed to take another wife. The position of the second wife was that of a "slave girl" in respect to the first wife, as many marriage contracts explicitly state.

Ancient Egypt
Monogamy is believed to be basic family model also in ancient Egypt. Although an Egyptian man was free to marry several women at a time, and some wealthy men from Old and Middle Kingdoms did have more than one wife, monogamy was the norm. There may have been some exceptions e.g. a Nineteenth Dynasty official stated as proof of his love to his deceased wife that he had stayed married to her since their youth, even after he had become very successful (P. Leiden I 371). This may suggest that some men abandoned first wives of a low social status and married women of higher status in order to further their careers. But even then they lived with only one wife. Egyptian women were allowed by law not to tolerate her husband taking a second wife, as they had right to ask for a divorce. Many tomb reliefs testify to monogamous character of Egyptian marriages, ''officials are usually accompanied by a supportive wife. "His wife X, his beloved"' is the standard phrase identifying wives in tomb inscriptions''. The instruction texts belonging to wisdom literature, e.g. Instruction of Ptahhotep or Instruction of Any, support fidelity to monogamous marriage life, calling wife a Lady of the house. Instruction of Ankhsheshonq suggests that it is wrong to abandon a wife because of her barrenness.

Ancient Israel
Traditional Jewish biblical story of the origins of man presents the first human beings in a monogamous marriage (Gn 2:21-24). The patriarchs of Seth's line followed the same pattern (e.g. Noah in Gn 7:7). Monogamy was abandoned for the first time in the reprobate line of Cain, when Lamech took two wives (Gn 4:19).

The patriarchs followed the customs of the time, cf. e.g. the Code of Hammurabi (ca 1700 B.C.). Abraham took a concubine because of Sarah's barrenness. Monogamy among patriarchs can be described as relative — there was never more than one lawful, wedded wife. The restrictions were not always observed as in the case of Jacob and Esau.

Under Judges and the monarchy, old restrictions went into disuse, especially among royalty, though the Books of Samuel and Kings, which cover entire period of monarchy, do not record a single case of bigamy among commoners — except Samuel's father. The wisdom books e.g. Book of Wisdom, which provides a picture of the society, Sirach, Proverbs, Qohelet portray a woman in a strictly monogamous family (cf. Pr 5:15-19; Qo 9:9; Si 26:1-4 and eulogy of perfect wife, Proverbs 31:10-31). The Book of Tobias speaks solely of monogamous marriages. Also prophets have in front of their eyes monogamous marriage as an image of the relationship of God and Israel. (Cf. Ho 2:4f; Jer 2:2; Is 50:1; 54:6-7; 62:4-5; Ez 16). As a conclusion Roland de Vaux states, that it is clear that the most common form of marriage in Israel was monogamy.