Monogamy (/məˈnɒɡəmi/ mə-NOG-ə-mee) is a form of dyadic relationship in which an individual has only one partner during their lifetime—alternately, only one partner at any one time (serial monogamy)—as compared to non-monogamy (e.g., polygamy or polyamory). 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.
Terminology
The word monogamy derives from the Greek μονός, monos ("alone"), and γάμος, gamos ("marriage").
The term "monogamy" may be referring to one of various relational
types, depending upon context. Generally, there are four overlapping
definitions.
- marital monogamy refers to marriages of only two people.
- 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 sexually monogamous relationships with genetic evidence of paternity.
For instance, biologists, biological anthropologists, and behavioral ecologists often use monogamy in the sense of sexual, if not genetic (reproductive), exclusivity. When cultural or social anthropologists and other social scientists use the term monogamy, the meaning is social or marital monogamy.
Marital monogamy may be further distinguished between:
- classical monogamy, "a single relationship between people who marry as virgins, remain sexually exclusive their entire lives, and become celibate upon the death of the partner"
- serial monogamy, marriage with only one other person at a time, in contrast to bigamy or polygamy.
Frequency in humans
Bronze sculpture of an elderly Kashubian married couple located in Kaszubski square, Gdynia,
Poland, which commemorates their monogamous fidelity, through the time
of their separation, while he temporarily worked in the United States.
Distribution of social monogamy
According to the Ethnographic Atlas
by George P. Murdock, of 1,231 societies from around the world noted,
186 were monogamous; 453 had occasional polygyny; 588 had more frequent
polygyny; and 4 had polyandry.
However, this does not take into account the relative population of
each of the societies studied, and the actual practice of polygamy in a
tolerant society may actually be low, with the majority of aspirant
polygamists practicing monogamous marriage.
Divorce and remarriage can thus result in "serial monogamy", i.e.
multiple marriages but only one legal spouse at a time. This can be
interpreted as a form of plural mating, as are those societies dominated
by female-headed families in the Caribbean, Mauritius and Brazil where there is frequent rotation of unmarried partners. In all, these account for 16 to 24% of the "monogamous" category.
Prevalence of sexual monogamy
The
prevalence of sexual monogamy can be roughly estimated as the
percentage of married people who do not engage in extramarital sex. 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.
Surveys conducted in non-Western nations (2001) 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.
Many surveys asking about extramarital sex in the United States
have relied on convenience samples: surveys 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 (1974, 1983, 1993) reported that 12–26% of married women and 15–43% of married men engaged 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 (1994, 1997) found that about 10–15% of women and 20–25% of men
engage in extramarital sex.
Research by Colleen Hoffon of 566 homosexual male couples from the San Francisco Bay Area (2010) found that 45% had monogamous relationships. 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
homosexuals surveyed expected to be in a monogamous relationship after
age 30.
Prevalence 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. 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 native Yanomami Indians of Amazon forest in 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, reported rates of extrapair paternity, in different
societies, ranging from 0.4% to over 50%.
Covert illegitimacy is a situation which arises when someone who
is presumed to be a child's father (or mother) is in fact not the
biological father (or mother). Frequencies as high as 30% are sometimes
assumed in the media, but research by sociologist Michael Gilding traced these overestimates back to an informal remark at a 1972 conference.
The detection of unsuspected illegitimacy can occur in the context of medical genetic screening, in genetic family name research, and in immigration testing.
Such studies show that covert illegitimacy is in fact less than 10%
among the sampled African populations, less than 5% among the sampled
Native American and Polynesian populations, less than 2% of the sampled
Middle Eastern population, and generally 1%-2% among European samples.
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.
Evolutionary and historical development in humans
A pair of New Zealand kaka parrots at Auckland Zoo
Biological arguments
Monogamy exists 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.
However, some scientists argue that monogamy evolved by reducing
within-group conflict, thus giving certain groups a competitive
advantage against less monogamous groups.
Paleoanthropology and genetic studies offer two perspectives on
when monogamy evolved in the human species: paleoanthropologists offer
tentative evidence that monogamy may have evolved very early in human
history whereas genetic studies show that monogamy evolved much more recently, less than 10,000 to 20,000 years ago.
Orangutan males are not monogamous and compete for access to females.
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.
Cultural arguments
Plough agriculture. The castle in the background is Lusignan. Detail from the calendar Les très riches heures from the 15th century. This is a detail from the painting for March.
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. These cultural processes may have nothing to do with relative reproductive success. For example, anthropologist Jack Goody's comparative study utilizing the Ethnographic Atlas
demonstrated that monogamy is part of a cultural complex found in the
broad swath of Eurasian societies from Japan to Ireland that practice
social monogamy, sexual monogamy and dowry (i.e. "diverging devolution",
that allow property to be inherited by children of both sexes).
Goody demonstrates a statistical correlation between this cultural
complex and the development of intensive plough agriculture in those
areas. Drawing on the work of Ester Boserup,
Goody notes that the sexual division of labour varies in intensive
plough agriculture and extensive shifting horticulture. In plough
agriculture farming is largely men's work and is associated with private
property; marriage tends to be monogamous to keep the property within
the nuclear family. Close family (endogamy) are the preferred marriage partners to keep property within the group.
A molecular genetic study of global human genetic diversity argued that
sexual polygyny was typical of human reproductive patterns until the
shift to sedentary farming communities approximately 10,000 to 5,000
years ago in Europe and Asia, and more recently in Africa and the
Americas.
A further study drawing on the Ethnographic Atlas showed a statistical
correlation between increasing size of the society, the belief in "high
gods" to support human morality, and monogamy.
A survey of other cross-cultural samples has confirmed that the absence
of the plough was the only predictor of polygamy, although other
factors such as high male mortality in warfare (in non-state societies)
and pathogen stress (in state societies) had some impact.
Woman farming, using a digging stick in the Nuba Mountains, South Sudan.
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.
Other theorists use cultural factors influencing reproductive
success to explain monogamy. 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.
Arguments from outside the scientific community
Karol Wojtyła (later, Pope John Paul II) 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. Some writers have suggested that monogamy may solve the problems they view as associated with non-monogamy and hypergamy such as inceldom.
Alexandra Kollontai in Make Way for the Winged Eros
argues that monogamy is an artifact of capitalist concepts of property
and inheritance and wrote, "The social aims of the working class are not
affected one bit by whether love takes the form of a long and official
union or is expressed in a temporary relationship. The ideology of the
working class does not place any formal limits on love." Later, "Modern
love always sins, because it absorbs the thoughts and feelings of
'loving hearts' and isolates the loving pair from the collective. In the
future society, such a separation will not only become superfluous but
also psychologically inconceivable." One of the tenets of the new
proletarian morality is "mutual recognition of the rights of the other,
of the fact that one does not own the heart and soul of the other (the
sense of property, encouraged by bourgeois culture)."
Ancient societies
The
historical record offers contradictory evidence on the development and
extent of monogamy as a social practice. Laura Betzig argues that in the
six large, highly stratified early states, commoners were generally
monogamous but that elites practiced de facto polygyny. Those states
included Mesopotamia, Egypt, Aztec Mexico, Inca Peru, India and China.
Tribal societies
Monogamy has appeared in some traditional tribal societies such as the Andamanese, Karen in Burma, Sami and Ket in northern Eurasia, and the Pueblo Indians of the United States, apparently unrelated to the development of the Judeo-Christian monogamous paradigm.
Ancient Mesopotamia and Assyria
Both
the Babylonian and Assyrian families were monogamous in principle but
not entirely so in practice since polygyny was frequently practiced by
the rulers.
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. The 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
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 although even then they lived with only
one wife. Egyptian women had right to ask for a divorce if her husband
took a second wife. 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 the wife a Lady of the house. The Instruction of Ankhsheshonq suggests that it is wrong to abandon a wife because of her barrenness.
Ancient Israel
As
against Betzig's contention that monogamy evolved as a result of
Christian socio-economic influence in the West, monogamy appeared
widespread 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
(530 BCE to 70 CE), apart from an 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.[citation needed]
Some marriage documents explicitly expressed a desire for the marriage
to remain monogamous. Examples of these documents were found in Elephantine. They resemble those found in neighbouring Assyria and Babylonia.
Study shows that ancient Middle East societies, though not strictly
monogamous, were practically (at least on commoners' level) monogamous.[65][66] 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 conformed with Jesus' approach. Michael Coogan,
in contrast, states that "Polygyny continued to be practised well into
the biblical period, and it is attested among Jews as late as the second
century CE."
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 for 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). Roland de Vaux states that "it is clear that the most common form of marriage in Israel was monogamy".
The Mishnah and the baraitot clearly reflect a monogamist viewpoint within Judaism (Yevamot 2:10 etc.). Some sages condemned marriage to two wives even for the purpose of procreation (Ketubot 62b). R. Ammi, an amora states:
Whoever takes a second wife in addition to his first one shall divorce the first and pay her kettubah (Yevamot 65a)
Roman customs, which prohibited polygamy, may have enhanced such an attitude - especially after 212 AD, when all the Jews became Roman citizens. However, some Jews continued to practice bigamy (e.g. up to medieval times in Egypt and Europe). Fourth-century Roman law forbade Jews to contract plural marriages.
A synod convened by Gershom ben Judah around 1000 CE banned polygamy among Ashkenazi and Sephardic Jews.
Ancient Greece and ancient Rome
The
ancient Greeks and Romans were monogamous in the sense that men were
not allowed to have more than one wife or to cohabit with concubines
during marriage.
Early Christianity
According to Jesus Christ 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:
Jesus avoids entangling himself in juridical or casuistic controversies; instead, he appeals twice to the "beginning". By doing so, he clearly refers to the relevant words of Genesis, which his interlocutors also know by heart. (...) it clearly leads the interlocutors to reflect about the way in which, in the mystery of creation, man was formed precisely as "male and female," in order to understand correctly the normative meaning of the words of Genesis.
Contemporary societies
International
Western European societies established monogamy as their marital norm. Monogamous marriage is normative and is legally enforced in most developed countries. Laws prohibiting polygyny were adopted in Japan (1880), China (1953), India (1955) and Nepal (1963). Polyandry is illegal in most countries.
The women's rights movements seek to make monogamy the only legal form of marriage. The United Nations General Assembly in 1979 adopted the Convention on the Elimination of All Forms of Discrimination Against Women,
Article 16 of which requires nations to give women and men equal rights
in marriage. Polygamy is viewed as inconsistent with the Article as it
gives men the right of multiple wives, but not to women. The United
Nations has established the Committee on the Elimination of Discrimination against Women (CEDAW) to monitor the progress of nations implementing the Convention.
People's Republic of China
The founders of Communism determined that monogamous marriage inherently oppressed women and therefore had no place in communist society. Friedrich Engels
stated that compulsory monogamy could only lead to increased
prostitution and general immorality, with the benefits of restricting
capital and solidifying the class structure. As he spelled out in The Origin of the Family, Private Property and the State (1884),
The first class antagonism which appears in history coincides with the development of the antagonism between man and woman in monogamian marriage, and the first class oppression with that of the female sex by the male. …[T]he wellbeing and development of the one group are attained by the misery and repression of the other.
The monogamous family is distinguished from the pairing family by the far greater durability of wedlock, which can no longer be dissolved at the pleasure of either party. As a rule, it is only the man who can still dissolve it and cast off his wife.
However, the communist revolutionaries in China chose to take the
Western viewpoint of monogamy as giving women and men equal rights in
marriage. The newly formed Communist government established monogamy as
the only legal form of marriage.
"The 1950 Marriage Law called for sweeping changes in many areas of family life. It forbade any 'arbitrary and compulsory' form of marriage that would be based on the superiority of men and would ignore women’s interests. The new democratic marriage system was based on the free choice of couples, monogamy, equal rights for both sexes, and the protection of the lawful interests of women. It abolished the begetting of male offspring as the principal purpose of marriage and weakened kinship ties which reduced the pressure on women to bear many children, especially sons. With arranged marriages prohibited, young women could choose their own marriage partners, share the financial cost of setting up a new household, and have equal status in household and family decision-making. The Government then initiated an extensive campaign of marriage-law education, working jointly with the Communist Party, women’s federations, trade unions, the armed forces, schools and other organizations."
Africa
The African Union has adopted the Protocol on the Rights of Women in Africa (the Maputo Protocol).
While the protocol does not suggest making polygamous marriage illegal,
Article 6 does state that "monogamy is encouraged as the preferred form
of marriage and that the rights of women in marriage and family,
including in polygamous marital relationships are promoted and
protected." The protocol entered into force on 25 November 2005.
Varieties 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
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.
Social monogamy does not always involve marriage in humans. 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 Evolution 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.
Serial monogamy may also refer to sequential sexual
relationships, irrespective of marital status. A pair of humans may
remain sexually exclusive, or monogamous, until the relationship has
ended and then each may go on to form a new exclusive pairing with a
different partner. This pattern of serial monogamy is common among
people in Western cultures.
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.
Men with more serial marriages are likely to have more children than
men with only one spouse, where the same is not true of women with
consecutive spouses.
A study done in 1994 found that remarried men often had a larger age
difference from their spouses than men who were married for the first
time, suggesting that serial monogamy helps some men extract a longer
reproductive window from their spouses.
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.
Elacatinus,
also widely known as neon gobies, also exhibit social monogamy.
Hetereosexual pairs of fish belonging to the genus Elacatinus remain
closely associated during both reproductive and non-reproductive
periods, and often reside in same cleaning station to serve client fish. Fish of this genus frequently mate with a new partner after they are widowed.
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 low occurrence of social monogamy in placental mammals
has been claimed to be related to the presence or absence of estrus—or
oestrus—the duration of sexual receptivity of a female. This, however,
doesn't explain why estrus females generally mate with any
proximate male nor any correlation between sexual and social monogamy.
Birds, which are notable for a high incidence of social monogamy, do not
have estrus.
Researchers have observed a mixed mating system of monogamy and polygyny in the European pied flycatcher.
Psychology
Psychological studies of social monogamy have relied heavily on
observations of married couples. These studies focus on relationship
satisfaction, duration and attachment.
Neuroendocrine bases
The North American microtine rodent's (vole) complex social structure
and social behavior has provided unique opportunities to study the
underlying neural bases for monogamy and social attachment. Data from
studies using the Microtis ochrogaster or prairie vole indicate
that the neuroendocrine hormones, oxytocin (in female prairie voles) and
vasopressin (in male prairie voles) play a central role in the
development of affiliative connections during mating. The effects of
intracerebroventricular administration of oxytocin and vasopressin have
been shown to promote affiliative behavior in the prairie vole but not
in similar, but non-monogamous montane voles. This difference in
neuropeptide effect is attributed to the location, density, and
distribution of OT and AVP receptors. Only in the prairie voles are OT
and AVP receptors located along the mesolimbic dopamine reward pathway,
presumably conditioning the voles to their mates odor while
consolidating the social memory of the mating episode. This finding
highlights the role of genetic evolution in altering the neuroanatomical
distribution of receptors, resulting in certain neural circuits
becoming sensitive to changes in neuropeptides.
