Incest (agammagamaṇa, literally ‘going to what should not be gone to,’ or adhamma raga, ‘wrong desire’), is sexual behaviour between close relatives. Incest is sometimes thought of as sexual contact between a parent and child or between siblings, but many cultures consider even sex between second or third cousins to be incestuous. Incest between parents and children and between siblings existed in ancient India. The Vedas include several myths in which the gods commit incest; e.g. Agni, Brahma and Prajāpati.
It is occasionally mentioned in Buddhist literature too. In the Udaya Jātaka the Bodhisattva is a prince who is compelled to marry his half-sister. Although the two sleep in the same room for many years they remain celibate (Ja.IV,105). In the Dasaratha Jātaka the princes Rāma and Lakkhaṇa marry their sister (Ja.IV,130). As with many ancient peoples the Sākyans, the tribe the Buddha belonged to, had a myth about their origins which included brother-sister incest. When the Koliyans were involved in a dispute with the Sakyans they taunted them by sayings that they ‘cohabited with their sisters like dogs, jackals and other animals’ (Ja.V,413).
During the Buddha’s life there was an incident where a nun became infatuated with her son who was a monk and had sex with him, an offence entailing expulsion from the Saṅgha (Vin.III,35). When this was brought to the Buddha’s attention he said, ‘Does not this foolish man know that a mother shall not lust after her son or a son after his mother?’ (A.III,67-8). Perhaps referring to this incident the Buddha also said, ‘Shame and fear of blame, are the two states that protect the world. If they did not protect the world it would not be clear who was one’s mother or mother’s sister, one’s uncle’s wife and the world would fall into confusion. The promiscuity seen amongst goats and sheep, chickens and pigs, dogs and jackals would prevail.’ (A.I,51).