Incest taboo
Universal cultural norm prohibiting sexual relations between close relatives.
The incest taboo refers to any cultural rule or norm that forbids sexual relations among specific family members, particularly those linked by blood. Every known human society has rules that exclude certain close relatives from being acceptable sexual or marriage partners, marking such unions as taboo. However, cultures vary widely in which blood relatives are considered off-limits.
Some cultures prohibit sexual relations between members of the same clan, even if no biological connection can be traced, while allowing such relations with members of other clans, regardless of actual genetic ties. In many societies, certain types of cousin relationships are preferred for marriage or sex, whereas in others, these same relationships are taboo. Some cultures permit sexual and marital bonds between aunts or uncles and their nieces or nephews. In certain cases, brother–sister marriages have been practiced regularly among elite groups. Parent–child and sibling–sibling unions are almost universally forbidden.
**Origin**
Debate over the origin of the incest taboo often centers on whether it stems from nature or nurture. One explanation views it as a cultural expression of a biologically evolved preference for partners unlikely to share one’s genes, since inbreeding can have harmful effects. The most widely accepted hypothesis suggests the Westermarck effect discourages adults from sexual relations with those they grew up with, and this effect has some empirical support.
Another school of thought argues that the incest prohibition is a cultural construct arising as a side effect of a general human preference for marrying outside one’s group. This preference emerges because intermarriage between groups builds valuable alliances that help both groups thrive. According to this view, the incest taboo is not necessarily universal but is likely to become stricter in cultures that favor exogamy over endogamy, and more relaxed in cultures that favor endogamy. This hypothesis also has some empirical support.
**Limits to biological evolution of taboo**
Although natural selection might theoretically favor individuals who instinctively avoid mating with close relatives under certain genetic conditions, incest still persists in the gene pool. Even genetically weakened, inbred individuals serve as better watchposts against predators than none at all, and weaker individuals can
- field
- Cultural anthropology, sociology
- known_for
- Universal cultural prohibition of sexual relations between close relatives, with variations across societies
- key_debate
- Whether the taboo is based in nature (biological evolution) or nurture (cultural construct)
Lore & Background
Debate about the origin of the incest taboo has often been framed as a question of whether it is based in nature or nurture. One explanation sees the incest taboo as a cultural implementation of a biologically evolved preference for sexual partners with whom one is unlikely to share genes, since inbreeding may have detrimental outcomes. The most widely held hypothesis proposes that the Westermarck effect discourages adults from engaging in sexual relations with individuals with whom they grew up, and this effect has achieved some empirical support. Another school argues that the incest prohibition is a cultural construct arising as a side effect of a general human preference for group exogamy, which builds valuable alliances between groups; this hypothesis has also achieved some empirical support.
Reader's Guide
The incest taboo is significant because it is a universal feature of human societies, yet its specific prohibitions vary widely across cultures. Some cultures proscribe sexual relations between clan-members even without biological relationship, while others permit certain cousin relations or even aunt/uncle–nephew/niece unions. Parent–child and sibling–sibling unions are almost universally taboo. The taboo's origin remains debated: biological explanations point to the Westermarck effect and inbreeding avoidance, while cultural explanations emphasize exogamy's role in forming intergroup alliances. Anthropological research shows that societies distinguish between prohibitions on sexual intercourse and marriage, and that penalties and definitions differ. The Trobriand Islanders, for example, prohibit brother–sister relations as incestuous but encourage flirtatious or marital relations between a man and his father's sister. The taboo thus serves as a lens for understanding kinship, social structure, and the interplay of biology and culture.
Did You Know?
- All known human cultures have norms that exclude certain close relatives from permissible sexual or marriage partners.
- The Westermarck effect, which discourages sexual relations among those who grew up together, has achieved some empirical support.
- Some cultures permit sexual and marital relations between aunts/uncles and nephews/nieces.
- In Trobriand society, a man and his father's sister are encouraged to have sexual relations or marry.
More in Taboo 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record