Polygyny (/pəˈlɪdʒɪniː/; from Neoclassical Greek πολυγυνία from πολύ- poly- "many", and γυνή gyne "woman" or "wife") is the most common and accepted form of polygamy, entailing the marriage of a man with several women. Most countries that permit polygamy are Muslim-majority countries in which polygyny is the only form permitted. Polyandry is illegal in virtually every state of the world.
In some countries where polygamy is illegal, and sometimes even when legal, at times it is known for men to have one or more mistresses, whom they do not marry. The status of a mistress is not that of a wife, and any children born of such relationships were and some still are considered illegitimate and subject to legal disadvantage.
Throughout the polygyny belt stretching from Senegal in the west to Tanzania in the east, as many as a third to a half of married women are in polygynous unions. Historically, polygyny was partly accepted in ancient Hebrew society, in classical China, and in sporadic traditional Native American, African and Polynesian cultures. In India it was known to have been practiced during ancient times. It was accepted in ancient Greece, until the Roman Empire and the Roman Catholic Church.
Boserup (1970) was the first to propose that the high incidence of polygyny in sub-Saharan Africa is rooted in the sexual division of labor in hoe-farming and the large economic contribution of women.
In the regions of shifting cultivation where polygyny is most frequently recorded, labor is often starkly divided between genders. The task of felling trees in preparation of new plots is usually done by older boys and very young men. Wives, on the other hand, are solely or primarily responsible for giving birth and rearing children; cultivating, processing and providing food for the family; and for performing domestic duties for the husband.
An elderly cultivator, with several wives and likely several young male children, benefits from having a much larger workforce within his household. By the combined efforts of his young sons and young wives, he may gradually expand his cultivation and become more prosperous. A man with a single wife has less help in cultivation and is likely to have little or no help for felling trees. According to Boserup's historical data, women living in such a structure also welcome one or more co-wives to share with them the burden of daily labor. However, the second wife will usually do the most tiresome work, almost as if she were a servant to the first wife, and will be inferior to the first wife in status. A 1930s study of the Mende in the west African state of Sierra Leone concluded that a plurality of wives is an agricultural asset, since a large number of women makes it unnecessary to employ wage laborers. Polygyny is considered an economic advantage in many rural areas. In some cases, the economic role of the additional wife enables the husband to enjoy more leisure.
Anthropologist Jack Goody's comparative study of marriage around the world, using the Ethnographic Atlas, demonstrated a historical correlation between the practice of extensive shifting horticulture and polygyny in the majority of Sub-Saharan African societies. Drawing on the work of Ester Boserup, Goody notes that in some of the sparsely populated regions where shifting cultivation takes place in Africa, much of the work is done by women. This favoured polygamous marriages in which men sought to monopolize the production of women "who are valued both as workers and as child bearers." Goody, however, observes that the correlation is imperfect. He also describes more male dominated though relatively extensive farming systems such as those that exist in much of West Africa, particularly the savannah region, where polygamy is desired more for the production of sons whose labor is valued."
Goody's observation regarding African male farming systems is discussed and supported by anthropologists Douglas R. White and Michael L. Burton in "Causes of Polygyny: Ecology, Economy, Kinship, and Warfare", where the authors note: "Goody (1973) argues against the female contributions hypothesis. He notes Dorjahn's (1959) comparison of East and West Africa, showing higher female agricultural contributions in East Africa and higher polygyny rates in West Africa, especially in the West African savannah, where one finds especially high male agricultural contributions. Goody says, "The reasons behind polygyny are sexual and reproductive rather than economic and productive" (1973:189), arguing that men marry polygynously to maximize their fertility and to obtain large households containing many young dependent males."
Most research into the determinants of polygyny has focused on macro-level factors. Widespread polygyny is linked to the kinship groups that share descent from a common ancestor. Polygyny also served as "a dynamic principle of family survival, growth, security, continuity, and prestige," especially as a socially approved mechanism that increases the number of adult workers immediately and the eventual workforce of resident children.
Scholars have argued that in farming systems where men do most of the agriculture work, a second wife can be an economic burden rather than an asset. In order to feed an additional wife, the husband must either work harder himself or he must hire laborers to do part of the work. In such regions, polygyny is either non-existent or is a luxury which only a small minority of rich farmers can indulge.
A report by the secretariat of the UN Economic Commission for Africa (ECA) quotes: "one of the strongest appeals of polygyny to men in Africa is precisely its economic aspect, for a man with several wives commands more land, can produce more food for his household and can achieve a high status due to the wealth which he can command.". According to Esther Boserup, over much of the continent of Africa, tribal rules of land tenure are still in force. This implies that members of a tribe, which commands a certain territory, have a native right to take land under cultivation for food production and in many cases also for the cultivation of cash crops. Under this tenure system, an additional wife is an economic asset that helps the family to expand its production.
Economic Michèle Tertilt concludes that countries that practice polygyny are less economically stable than those that practice monogamy. Polygynous countries usually have a higher fertility rate, fewer savings reserves, and a lower GDP. Fertility would decrease by 40%, savings would increase by 70%, and GDP would increase by 170% if polygyny was banned. Monogamous societies present a surge in economic productivity because monogamous men are able to save and invest their resources due to having fewer children. Polygynous societies have a higher concentration of men investing into methods of mating with women, whereas monogamous men invest more into their families and other related institutions.
Despite the expenses of polygynous marriages, men benefit from marrying multiple wives through the economic and social insurance that kinship ties produce. With a large network of in-laws, these men have the ties they need to compensate for other economic shortages.
Some analysts have posited that a high libido may be a factor in polygyny, although others have downplayed its significance. The sex drive as a factor in some Asian cultures was sometimes associated with wealthy men and those that were adjunct to an aristocracy, although such libidinal perceptions were at times discarded in favor of seeing polygyny as a factor of traditional life. Other explanations postulate that polygyny is a tool used to ward off inclinations towards infidelity.
Some research that show that males living in polygynous marriages may live 12 percent longer. Polygyny may be practiced where there is a lower male:female ratio; this may result from male infants having increased mortality from infectious diseases.
Polygynous marriages play a huge role in maintaining the hold of gender roles across the continent of Africa. Even though African women make up more than half of the continent's population, women hold subordinate positions in comparison to African men. Polygyny helps uphold inequality between the two genders by creating a legal bond through marriage that binds women into a subordinate role. Women across the continent are responsible for a large portion of the production of farming (sustainable and cash crops) yet, men married to these women reap the benefits and are allowed to redistribute their gains throughout the family as they would like. Inequality between husbands and wives are common in countries where polygyny is more frequently practiced because of limited education. Polygyny continues to enforce the male domination that has been seen in societies all over with the belief that women are inferior to men with the exclusion of few matriarchal societies. In Africa polygyny was believed to be part of the way to build an empire. It was not until the post colonialism era in Africa that polygyny began to be viewed as unjust or taboo. According to Natali Exposito, "in a study of the Ngwa Igbo Clan in Nigeria identified five principal reasons for men to maintain more than one wife: because having more than one wife allows the Ngwa husband to (1) have the many children that he desires; (2) heighten his prestige and boost his ego among his peers; (3) enhance his status within the community; (4) ensure a sufficient availability of labor to perform the necessary farm work and the processing of commercial oil-palm produce; and (5) satisfy his sexual urges.” Out of all of the reasons stated none are beneficial to the wives, but instead only beneficial to the husbands. In Egypt, feminist have fought for polygamy to be abolished, but it is viewed as a basic human right so the fight has been unsuccessful. In countries where polygyny is practiced less frequently, women have more equality in the marriage and are better able to communicate their opinions about family planning.
Women participating in polygynous marriages share common martial problems with women in a monogamous marriage; however, there are issues uniquely related to polygyny which affects their overall life satisfaction and have severe implications for women's health.Women practicing polygyny are susceptible to sexually transmitted diseases, infertility, and mental health complications.Among the Logoli of Kenya, the fear of AIDS or becoming infected with the HIV virus has informed women's decisions about entering polygynous marriages. Some view polygyny as a means to prevent men from taking random sexual partners and potentially introducing STDs into relationships. Interviews conducted with some of the Logoli tribe in Kenya suggested they feared polygynous marriages because of what they have witnessed in the lives of other women who are currently in such relationships. The observed experiences of some of the women in polygynous unions tend to be characterized by frequent jealousy, conflicts, competition, tensions, and psychological stresses. Some of the husbands fail to share love and other resources equally; and envy and hatred, and sometimes violent physical confrontations become the order of the day among co-wives and their children. This discourages women from entering a polygynous marriage.Research shows that competition and conflict can intensify to unbearable level for co- wives causing women to commit suicide due to psychological distress. Findings show that the wife order can affect life satisfaction. According to Bove and Valeggia, women who are senior wives often misuse their position to obtain healthcare benefits in countries one wife can become a recipient. The conflict between co-wives can attribute to the higher rates of mental health disorders such as anxiety, depression, and paranoia 
Various methods have been used to reduce the amount of jealousy and conflict among wives. These include sororal polygyny, in which the co-wives are sisters; and hut polygyny, in which each wife has her own residence and the husband visits them in rotation. A clear status hierarchy among wives is also sometimes used to avoid fighting by establishing unequivocally each wife's rights and obligations. Although there are several harmful aspects of this practice related to women, there are some reported personal and economic advantages for women such as sharing household and childrearing responsibilities. Also, wives share companionship and support with co-wives.
Today polygyny is more widespread in Africa than in any other continent. Some scholars see the slave trade's impact on the male-to-female sex ratio as a key factor in the emergence and fortification of polygynous practices in regions of Africa. Generally in rural areas with growing populations, the higher the incidence of polygyny, the greater the delay of first marriage for young men. The higher the average polygyny rate, the greater the element of gerontocracy. Quite apart from the rate of polygyny, the distribution of wives may be uneven.
Polygynous marriage was preferred among the Logoli and other Abalulya sub ethnic groups. Taking additional wives was regarded as one of the fundamental indicators of a successfully established man. Large families enhanced the prestige of Logoli men. Logoli men with large families were also capable of obtaining justice, as they would be feared by people, who would not dare to use force to take their livestock or other goods from them. Interviews with some of the contemporary Logoli men and women who recently made polygynous marriages yielded data which suggest that marrying another wife is usually approached with considerable thought and deliberation by the man. It may or may not involve or require the consent of the other wives and prospective wife's parents. A type of "surrogate pregnancy" arrangement was reported to have been observed, in which some wives who are unable to bear children, find fulfillment in the children and family provided by a husband taking additional wives. Some of the men indicated that they were pressured by their parents to marry another wife, who could contribute additional income to the family. Some of the young polygynous men indicated that they were trapped in polygyny because of the large number of single women who needed and were willing to take them as husbands although they were already married. Most of those second and third wives were older women who had not yet married.
Customary law, one of the three legal systems in operation in Nigeria (The other two being Nigerian common law and Sharia law) allows for the legal marriage of more than one woman by a single man.
Unlike those marriages recognised by Sharia, there is no limit to the number of legal wives allowed under customary law. Currently polygyny is most common within royal and noble families within the country, and is largely practiced by the tribes native to its north and west. Although far less popular there, it is none the less also legal in Nigeria's east and south.
Many majority-Muslim countries retain the traditional sharia, which interprets teachings of the Quran to permit polygamy with up to four wives. Exceptions to this include Albania, Tunisia, Turkey, and former USSR republics. Though about 70% of the population of Albania is historically Muslim, the majority is non-practicing. Turkey and Tunisia are countries with overwhelmingly Muslim populations that enforce secularist practices by law. In the former USSR republics, a prohibition against polygamy has been inherited from Soviet Law. In the 21st century, a revival of the practice of polygamy in the Muslim World has contributed to efforts to re-establish its legality and legitimacy in some countries and communities where it is illegal.
The original wife (or legal wife) was referred to as the 正室 zhèngshì /정실 (main room) both in China, Japan and Korea. 大婆 dàpó ("big woman/big wife") is the slang term. Both terms indicate the orthodox nature and hierarchy. The official wife was called "big mother" (大媽 dàmā), mother or aunt. The child of the concubine addressed the big mother as "aunt".
The written word for the second woman was 側室 cèshì /측실 and literally means "she who occupied the side room". This word was also used in both Korea and Japan. They were also called 妾 qiè/첩 in China and Korea. The common terms referring to the second woman, and the act of having the second woman respectively, are 二奶 (èrnǎi), literally "the second wife".
In mainland China, polygamy is illegal under Marriage Law passed in 1980. This replaced a similar 1950 prohibition. It is tolerated in Tibet.
Polygyny where wives are of equal status had always been illegal in China, and had been considered a crime in some dynasties. In family laws from Tang to Qing Dynasties, the status of a wife, concubines and maid-mistresses couldn't be altered. However, concubinage was supported by law until the end of the Qing/Ching dynasty of the imperial China (1911). In the past, Emperors could and often did have hundreds to thousands of concubines. Rich officials and merchants of the elite also took concubines in addition to legal wives. The first wife was the head or mother wife; other wives were under her headship if the husband was away. Concubines had a lower status than full wives, generally not being seen in public with their husband and not having rights to decisions in the house. Children from concubines were considered inferior to those of the wife and did not receive equal wealth/legacy from their father. However they were considered legitimate, therefore had many more rights to inheritance of status and wealth than illegitimate children conceived outside a marriage.
Polygamy was de facto widely practiced in the Republic of China from 1911 to 1949, before Kuomintang was defeated in the Civil War and forced to retreat to Taiwan. Zhang Zongchang, a well-known warlord, notably declared he had three 'unknowns' - unknown number of rifles, unknown amount of money, and unknown number of concubines. 不知道自己有多少枪，不知道自己有多少钱，不知道自己有多少姨太太 After the People's Republic of China was founded in 1949, polygamy was strictly prohibited.
Chinese men in Hong Kong could practice concubinage by virtue of the Qing Code. This ended with the passing of the Marriage Act of 1971. Kevin Murphy of the International Herald Tribune reported on the cross-border polygamy phenomenon in Hong Kong in 1995. In a research paper of Humboldt University of Berlin on sexology, Doctor Man-Lun Ng estimated about 300,000 men in China have mistresses. In 1995, 40% of extramarital affairs in Hong Kong involved a stable partner.
Period drama and historical novels frequently refer to the former culture of polygamy (usually polygyny). An example is the Wuxia novel The Deer and the Cauldron by Hong Kong writer Louis Cha, in which the protagonist Wei Xiaobao has seven wives (In new edition of the novel, Princess Jianning was assigned as the wife, while others are concubines).
A proposal to decriminalize polygamy was heard by the Kyrgyz parliament. It was supported by the Justice Minister, the country's ombudsman, and the Muslim Women's organization Mutakalim, which had gathered 40,000 signatures in favour of polygamy. But, on March 26, 2007, parliament rejected the bill. President Kurmanbek Bakiyev is known to oppose legalizing polygyny. Despite his opposition, he legally has two wives: Tatyana, with whom he has two sons; and Nazgul Tolomusheva, who gave birth for son and daughter.
Due to an increase in the number of polygamous marriages, proposals were made in Tajikistan to re-legalize polygamy. Tajik women who want to be second wives particularly support decriminalizing polygyny. Mukhiddin Kabiri, the Deputy Chairman of the Islamic Renaissance Party of Tajikistan, says that legislation is unlikely to stop the growth in polygyny. He criticizes the ruling élite for speaking out against the practice while taking more than one wife themselves.
The Muslim communities of Bosnia and Herzegovina traditionally practiced polygamy but the practice was last observed in Cazinska Krajina in the early 1950s. Although illegal in the country, polygamy is encouraged by certain religious circles, and the number of practitioners has increased. This trend appears linked with the advent of fundamentalist Wahhabism in the Balkans.
The Bosniak population in neighbouring Raška, Serbia, has also been influenced by this trend in Bosnia. They have suggested creating an entire Islamic jurisdiction including polygamy, but these proposals have been rejected by Serbia. The top cleric, the Mufti of Novi Pazar, Muamer Zukorlić, has taken a second wife.
Factual polygamy and sexual relationships with several adult partners are not punishable in accordance with current revisions of Criminal Code of Russia and Code of the Russian Federation on Administrative Offenses. But multiple marriage can't be registered and officially recognised by Russian authorities because Family Code of Russia (section 14 and others) prohibits registration of marriage if one of person is in another registered marriage in Russia or another country. Polygamy is tolerated in predominantly Muslim republics such as Chechnya, Ingushetia, and Dagestan.
Polygyny was legalized and documented in unrecognised Chechen Republic of Ichkeria but Russian authorities had annulled these polygynous marriages after they regained control over territory of Ichkeria. Later Ramzan Kadyrov, President of the Chechen Republic, has been quoted on radio as saying that the depopulation of Chechnya by war justifies legalizing polygamy. Kadyrov has been supported by Nafigallah Ashirov, the Chairman of the Council of Grand Muftis of Russia, who has said that polygamy is already widespread among Muslim communities of the country.
In Ingushetia in July, 1999 polygyny was officially recognised and allowed by edict of president of Ingushetia Ruslan Aushev and registration of polygyny marriages had been started. But this edict had been formally suspended soon by edict of President of Russia Boris Yeltsin. One year later this edict of Aushev had been cancelled by the Supreme Court of Ingushetia because of contradiction with Family Code of Russia.
Although non-Muslim Russian populations have historically practiced monogamy, Russian politician Vladimir Zhirinovsky offered to legalize polygyny to encourage population growth and correct the demographic crisis of Russians. Zhirinovsky first proposed to legalize polygyny in 1993, after Kadyrov's declaration that he would introduce an amendment to legalize polygyny for all Russian citizens.
Polygyny is illegal in the United States and Canada.
Mormon fundamentalism believes in the validity of selected fundamental aspects of Mormonism as taught and practiced in the nineteenth century. Fundamentalist Latter-Day Saints' teachings include plural marriage, a form of polygyny first taught by Joseph Smith, the founder of the Latter Day Saint movement.
In the 21st century, several sources have claimed as many as 60,000 fundamentalist Latter-day Saints in the United States, with fewer than half of them living in polygamous households. Others have suggested that there may be as few as 20,000 Mormon fundamentalists with only 8,000 to 15,000 practicing polygamy. The largest Mormon fundamentalist groups are the Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS Church) and the Apostolic United Brethren (AUB). The FLDS Church is estimated to have 10,000 members residing in the sister cities of Hildale, Utah and Colorado City, Arizona; Eldorado, Texas; Westcliffe, Colorado; Mancos, Colorado; Creston and Bountiful, British Columbia; and Pringle, South Dakota.
The Hindu scriptures acknowledge numerous occasions of polygyny; it was the norm among kings, the nobility and the extremely wealthy. Pandu, the father of the Pandavas in Mahabharata, had two wives Kunti and Madri. Krishna, considered one of the incarnations of Vishnu, had eight chief wives and sixteen thousand junior wives. Many other personalities including Rama had only one wife, and while this was regarded as morally exemplary, polygyny remained customary and acceptable among Hindus. It was legally abolished for Hindus in India by the Hindu Marriage Act of 1956.
The Torah, the Five Books of Moses; Genesis-Deuteronomy, includes specific regulations on the practice of polygyny. Exodus 21:10 states that multiple marriages are not to diminish the status of the first wife, while Deuteronomy 21:15-17 states that a man must award the inheritance due to a first-born son to the son who was born first, even if he hates that son's mother and likes another wife more; and Deuteronomy 17:17 states that the king shall not have too many wives.
According to Michael Coogan, "[p]olygyny continued to be practiced well into the biblical period, and it is attested among Jews as late as the second century CE." The incidence was limited, however, and it was likely largely restricted to the wealthy. By the first century, both the expense and the practical problems associated with maintaining multiple wives were barriers to the practice, especially for the less wealthy. Since the 11th century, Ashkenazi Jews have followed Rabbenu Gershom's ban on polygyny (except in rare circumstances).
Some Mizrahi (Mideast) Jewish communities (particularly Yemenite Jews and Persian Jews) discontinued polygyny more recently, after they immigrated to countries where it was forbidden or illegal. Israel prohibits polygamy by law. In practice, however, the law is loosely enforced, primarily to avoid interference with Bedouin culture, where polygyny is practiced. Pre-existing polygynous unions among Jews from Arab countries (or other countries where the practice was not prohibited by their tradition and was not illegal) are not subject to this Israeli law. But Mizrahi Jews are not permitted to enter into new polygamous marriages in Israel. However polygamy may still occur in non-European Jewish communities that exist in countries where it is not forbidden, such as Jewish communities in Yemen and the Arab world.
Karaite Jews, who do not adhere to Rabbinic interpretations of the Torah, do not practice polygyny. Karaites interpret Leviticus 18:18 to mean that a man can only take a second wife if his first wife gives her consent and Exodus 21:10 to mean that a man can only take a second wife if he is capable of maintaining the same level of marital duties due to his first wife: namely, food, clothing, and sexual gratification.
Polygamy is not forbidden in the Old Testament. The New Testament is largely silent on polygamy, however, some point to Jesus's repetition of the earlier scriptures, noting that a man and a wife "shall become one flesh". However, some look to Paul's writings to the Corinthians: "Do you not know that he who is joined to a prostitute becomes one body with her? For, as it is written, 'The two will become one flesh.'" Supporters of polygamy claim this indicates that the term refers to a physical, rather than spiritual, union.
Have ye not read, that he which made them at the beginning made them male and female, And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?
Jesus also tells the Parable of the Ten Virgins going to meet the bridegroom, without making any explicit criticism or other comment on the practice of polygamy.
The Bible states in the New Testament that polygamy should not be practiced by certain church leaders. 1 Timothy states that certain Church leaders should have but one wife: "A bishop then must be blameless, the husband of one wife, vigilant, sober, of good behavior, given to hospitality, apt to teach" (chapter 3, verse 2; see also verse 12 regarding deacons having only one wife). Similar counsel is repeated in the first chapter of the Epistle to Titus.
Periodically, Christian reform movements that have aimed at rebuilding Christian doctrine based on the Bible alone (sola scriptura) have at least temporarily accepted polygyny as a Biblical practice. For example, during the Protestant Reformation, in a document referred to simply as "Der Beichtrat" (or "The Confessional Advice" ), Martin Luther granted the Landgrave Philip of Hesse, who, for many years, had been living "constantly in a state of adultery and fornication", a dispensation to take a second wife. The double marriage was to be done in secret, however, to avoid public scandal. Some fifteen years earlier, in a letter to the Saxon Chancellor Gregor Brück, Luther stated that he could not "forbid a person to marry several wives, for it does not contradict Scripture." ("Ego sane fateor, me non posse prohibere, si quis plures velit uxores ducere, nec repugnat sacris literis.")
"On February 14, 1650, the parliament at Nürnberg decreed that, because so many men were killed during the Thirty Years' War, the churches for the following ten years could not admit any man under the age of 60 into a monastery. Priests and ministers not bound by any monastery were allowed to marry. Lastly, the decree stated that every man was allowed to marry up to ten women. The men were admonished to behave honorably, provide for their wives properly, and prevent animosity among them."
In Sub-Saharan Africa, there has often been a tension between the Christian insistence on monogamy and traditional polygamy. In some instances in recent times there have been moves for accommodation; in other instances, churches have resisted such moves strongly. African Independent Churches have sometimes referred to those parts of the Old Testament that describe polygamy in defending the practice.
Under Islamic marital jurisprudence, Muslim men are allowed to practice polygyny, that is, they can have more than one wife at the same time, up to a total of four. Polyandry, the practice of a woman having more than one husband, is not permitted.
Based on verse 30:21 of Quran the ideal relationship is the comfort that a couple find in each other's embrace:
And one of His signs is that He created for you spouses from among yourselves so that you may find comfort in them. And He has placed between you compassion and mercy. Surely in this are signs for people who reflect.
The polygyny that is allowed in the Quran is for special situations; however, it advises monogamy if a man fears he can't deal justly with them. This is based on verse 4:3 of Quran which says:
If you fear you might fail to give orphan women their ˹due˺ rights ˹if you were to marry them˺, then marry other women of your choice—two, three, or four. But if you are afraid you will fail to maintain justice, then ˹content yourselves with˺ one or those ˹bondwomen˺ in your possession. This way you are less likely to commit injustice.
There are strict requirements to marrying more than one woman, as the man must treat them equally financially and in terms of support given to each wife, according to Islamic law.
Muslim women aren't allowed to marry more than one husband at once. However, in the case of a divorce or their husbands' death they can remarry after the completion of Iddah, as divorce is legal in Islamic law. A non-Muslim woman who flees from her non-Muslim husband and accepts Islam can remarry without divorce from her previous husband, as her marriage with non-Muslim husband is Islamically dissolved on her fleeing. A non-Muslim woman captured during war by Muslims, can also remarry, as her marriage with her non-Muslim husband is Islamically dissolved at capture by Muslim soldiers.This permission is given to such women in verse 4:24 of Quran. The verse also emphasizes on transparency, mutual agreement and financial compensation as prerequisites for matrimonial relationship as opposed to prostitution; it says:
Also ˹forbidden are˺ married women—except ˹female˺ captives in your possession. This is God's commandment to you. Lawful to you are all beyond these—as long as you seek them with your wealth in a legal marriage, not in fornication. Give those you have consummated marriage with their due dowries. It is permissible to be mutually gracious regarding the set dowry. Surely God is All-Knowing, All-Wise.
Muhammad was monogamously married to Khadija, his first wife, for 25 years, until she died. After her death, he married multiple women, mostly widows, for social and political reasons. He had a total of nine wives, but not all at the same time, depending on the sources in his lifetime. The Qur'an does not give preference in marrying more than one wife. One reason cited for polygyny is that it allows a man to give financial protection to multiple women, who might otherwise not have any support (e.g. widows). However, the wife can set a condition, in the marriage contract, that the husband cannot marry another woman during their marriage. In such a case, the husband cannot marry another woman as long as he is married to his wife. According to traditional Islamic law, each of those wives keeps their property and assets separate; and are paid mahar and maintenance separately by their husband. Usually the wives have little to no contact with each other and lead separate, individual lives in their own houses, and sometimes in different cities, though they all share the same husband.
In most Muslim-majority countries, polygyny is legal with Kuwait being the only one where no restrictions are imposed on it. The practice is illegal in Muslim-majority Turkey, Tunisia, Albania, Kosovo and Central Asian countries.
Countries that allow polygyny typically also require a man to obtain permission from his previous wives before marrying another, and require the man to prove that he can financially support multiple wives. In Malaysia and Morocco, a man must justify taking an additional wife at a court hearing before he is allowed to do so. In Sudan, the government encouraged polygyny in 2001 to increase the population.
In zoology the term polygyny is used for to a pattern of mating in which a male animal has more than one female mate in a breeding season. Males get their mates by defending the females directly or holding resources that the females want and need. This is known as resource defense polygyny and males of the bee species Anthidium manicatum (also known as the European wool carder bee) exhibit this behavior. Males claim patches of floral plants, ward off conspecific males and other resource competitors, and mate with the multiple females who forage in their territories. Males of many species attract females to their territory by either gathering in a lek or going out in search of dispersed females. In polygyny relationships in animals, the female is the one who provides most of the parental care for the offspring.
Polygyny in eusocial insects means that some insects living in colonies have not only one queen, but several queens. Solitary species of insects take part in this practice in order to maximize their reproductive success of the widely dispersed females, such as the bee species Anthidium maculosum. Insects such as red flour beetles use polygyny to reduce inbreeding depression and thus maximize reproductive success.
There is primary polygyny (several queens join to found a new colony, but after the hatching of the first workers the queens fight each other until only one queen survives and the colony becomes monogynous) and secondary polygyny (a well-established colony continues to have several queens).
...encoraged their husbands to marry other wives so that they may engage themselves and bestow their affection upon the co-wives' children.
Content from Wikipedia