Monogamy

Monogamy describes a partnership between two people who form a mutual, exclusive intimate bond. It involves having only one partner at a time—either for life or in a series of exclusive relationships (serial monogamy)—and stands in contrast to non-monogamous arrangements like polygamy or polyamory. The word comes from the Greek for "one marriage," but its meaning shifts depending on context: genetic, sexual, social, and marital definitions all exist, and interpretations vary widely across cultures and academic fields, making the term complex and frequently debated.

In biology, monogamy often refers to animal mating systems where an individual has only one mate at a time. In human societies, it typically means a sexually exclusive commitment between two people, regardless of orientation. However, human monogamy is far from uniform. Only a minority of societies are strictly monogamous; many permit serial monogamy or tolerate extramarital sex. Genetic monogamy—where DNA evidence confirms exclusive paternity—is relatively understudied and often contradicted by cases of extrapair paternity. The evolution of monogamy in humans likely stems from a mix of biological factors, such as the need for paternal care and ecological pressures, along with cultural developments like agriculture, property inheritance, and religious or social norms that promote stability.

Biologists distinguish between social, sexual, and genetic monogamy to capture how animal pairings may involve cohabitation, sexual exclusivity, and reproductive fidelity in different combinations. Serial monogamy refers to successive exclusive relationships over time. The term itself can be broken into four intersecting definitions: genetic monogamy (sexually exclusive with genetic proof of paternity), sexual monogamy (partners remain sexually exclusive with no outside partners), social monogamy (two people cohabitate, share resources like shelter and food, and raise children together), and marital monogamy (marriage involving only two people). Biologists and behavioral ecologists often use monogamy in the sense of sexual or genetic exclusivity, while social scientists typically mean social or marital monogamy. Marital monogamy can be further split into classical monogamy (a single relationship where partners marry as virgins, remain sexually exclusive for life, and become celibate after a partner’s death) and serial monogamy (marriage to only one person at a time, as opposed to bigamy or polygamy).

Cultural assumptions complicate the definition. Some societies require lifelong sexual exclusivity; others accept premarital sex or even extramarital sex and spouse swapping. Some consider a relationship monogamous even if partners separate and enter new exclusive relationships through death, divorce, or dissolution—regardless of the relationship’s length. A 2012 study highlighted this need for precise definitions by identifying 53 communities between 1912 and 2010 that practiced polyandry (women with multiple male partners), suggesting it was more common than previously thought. Terminology also affects how data on polygamy is interpreted. Genetic records show that genetic monogamy increased in the last 5,000–10,000 years, but the form of prehistoric non-monogamy remains unclear; a lack of genetic monogamy could be mistaken for polygamy when other explanations exist. Anthropological observations reveal that even in societies where polygyny is accepted, most relationships are monogamous in practice—couples stay together for a time, though not necessarily for life. So in both prehistoric and polygamous communities, short- or long-term serial monogamy may be the norm rather than a lifelong bond.

According to the Ethnographic Atlas, out of 1,231 societies studied, 186 were monogamous, 453 had occasional polygyny, 588 had more frequent polygyny, and 4 had polyandry. This count does not account for population size; in societies that tolerate polygamy, actual practice may be low, with most people in de facto monogamous marriages. Divorce and remarriage create serial monogamy—multiple marriages but only one legal spouse at a time—which can be seen as a form of plural mating. This pattern also appears in societies with frequent rotation of unmarried partners, such as in parts of the Caribbean, Mauritius, and Brazil, accounting for 16 to 24% of the "monogamous" category. The prevalence of sexual monogamy can be roughly estimated by the percentage of married people who avoid extramarital sex, as measured by the Standard Cross-Cultural Sample.