The most common form of niyoga "... is that of a brother or kinsman siring sons in his dead brother's name with his widow." (SUTHERLAND 77) The new husband was a brother or a close relative or a distant relative of the deceased husband (or merely a member of the same caste). Niyoga is the same as English 'levirate' (from Latin levir = brother of the husband). The word niyoga stands for 'assignation,' i.e. for assigning or appointing a new husband to the widow. JOLLY 70; THIEME 453, footnote 3; SUTHERLAND 83. -- Refer for the widow in general to § 12.
Considering the enormous importance of male offspring in India (§ 4, § 8.6) it became inevitable to make an arrangement for wives who became widows without having a son. Niyoga meant that a surrogate father had to father a son who performed the funerary rites (shraddha) for the deceased husband of the widow. Refer also to Manu 9.167 for niyoga in the case that the husband is dead, impotent or sick (§ 3, Son-2). A drastic description of the horrors of lack of sons is given in an old narrative mentioned by SUTHERLAND (80: childless ascetic Jaratkaru).
A humanitarian aspect of the situation is the widow. The possibility that a widow (in particular a widow without sons) returned to her family is nowhere mentioned, but it may have existed (perhaps in all varnas). Remarriage in one form or another is apparently sanctioned in early law-books (§ 9.5), but it was probably soon a thing of the past (not recommended by Manu). Niyoga alone persisted up to the first millennium A.D. (circa 'fourth c. A.D.') when it became kalivarjya.
Considering the importance of a son one wonders why remarriage (in whatever form) became something of a problem, even if the widow had no son. There must have been an ascetic ideology which put more value on the ritual status of the widow than on the birth of a son.
SUTHERLAND says about niyoga in the Mahabharata: "In the Mahabharata, historical information about the practice of niyoga is interwoven with the use of niyoga as a mythical narrative device." (101) He also mentions that Brahmans often (myth and reality) father sons with Kshatriya women. We quote an example from the Mahabharata:
King Vicitravirya (wives Ambika and Ambalika) died without offspring. His mother Satyavati (husband: Shantanu) asked her son Vyasa (Brahman, famous rishi), half-brother of Vicitravirya, to father sons (one each) with the two widows of Vicitravirya (Kshatriya women). Ambika bore Dhritarashtra, Ambalika bore Pandu, and a maid servant (Amba) bore Vidura (birth by way of a ruse). Pandu became (through Kunti and Madri) the father of the three-plus-two Pandavas, Dhritarashtra became (through Gandhari) the father of a hundred sons (the Kauravas) and a daughter. Vidura (righteous, wise, impartial) had no sons.
In short: Vyasa (mythical author of the Mahabharata) became by niyoga the father of the central figures of the Mahabharata: Dhritarashtra´s family and Pandu´s family, both estranged.
ALTEKAR supports the orthodox criticism of niyoga, calling it "a relic of barbarism," but accentuates its relative justification: "It cannot be, however, gainsaid that Niyoga served a useful purpose in its own days.... The custom of Niyoga solved the widow's difficulty to some extent by permitting the brother-in-law to raise issues on his sister-in-law under certain circumstances. Niyoga served as a half-way house between a formal remarriage and an absolute celibacy, especially in earlier days when three sons were allowed to be raised under it. Of course it indirectly encouraged polygamy [?], but we should not forget that society was already tolerating it [?]. It also helped in improving the economic condition of the widow. When she had no son, she could get no share in the family property. When she got a son by Niyoga, she could get a share, if not as an heiress, at least as the guardian of her minor son." (149) ALTEKAR does not say what he thought was the social reality in the early days of niyoga. Was it correct by contemporary standards or was it institutionalized moral looseness?
There are special rules for sexual intercourse of niyoga partners. "Let him [the surrogate husband] approach the widow... [... three quarters of an hour before sunrise]... without dallying with her and without abusing or ill-treating her." (THIEME 447, SUTHERLAND 81). The ordinary and normal time for sexual intercourse is after sunset (LESLIE 239). The later law-books expect that the surrogate father does not engender more than one son (originally one or two, if not three). Correct niyoga was close to celibate, but correct niyoga was probably rare. Little if anything is said about ritualization.
SUTHERLAND accentuates the moral aspect (83): "Against the obviously strong and natural inclination to assign ownership of the son to his begetter..., the dead man's surviving family took every precaution, in consulting family elders and seeking to control the nature of the assignation.... The strict official and ritualistic nature of the sexual relationship [in niyoga unions] had to be adhered to in order to avoid public charges of adultery or incest, the Scylla and Charybdis governing all contact between members of the opposite sex in an Indian household who were not married to each other." SUTHERLAND also compares niyoga (as determined by emotional detachment) with the "ritualised sexuality of medieval Tantrism" (83). But Tantrism is historically different.
The male partner of the widow was married or not (ALTEKAR 151, CHEN 86). As indicated by ALTEKAR, sexual life in the days before the prohibition of niyoga must have been unconventional.
At a later time niyoga fell into disrepute, and it became kalivarjya (as mentioned repeatedly). Already in the Manu Smriti (infra) celibacy of widows and celibacy of (pious) men were praised side by side, while niyoga was criticized:
Manu 5.157. After her husband is dead, she may voluntarily emaciate her body by eating pure flowers, roots, and fruits; but she must never mention even the name of another man.
5.159. Untold thousands of Brahmins who have remained celibate [brahmacharins] from their youth have gone to heaven without producing offspring to continue their family line.
5.160. Just like these celibates, a good woman, though she be sonless, will go to heaven when she steadfastly adheres to the celibate life after her husband's death.
The abolition of niyoga was not the last word. Tryambaka insisted that niyoga was a sin, but he also insisted on the necessity of a son. Tryambaka squares the circle: The problem is solved when the husband in his lifetime desires a son (traditional emphasis on the son). LESLIE 302.
SUTHERLAND emphasizes in connection with niyoga the usefulness of Brahmans as "surrogate fathers." "Because of their being usually unpropertied, mobile, and dependent on patronage, Brahmans make ideal surrogate fathers, who are unlikely to obtrude or make claims upon the heirship procedures of the non-Brahmanical family they serve.” (101)
Niyoga is not a monolithic custom but subject to historical changes. It is almost a standard example for the introduction of kalivarjya rules. "Eventually [niyoga being no longer in keeping with the Zeitgeist], niyoga was given up as being inconsistent with increasingly pristinised and Brahmanised standards for marital chastity and devotion." (SUTHERLAND 78) According to KANE Ka 218, the kalivarjya rules started in the 4th century A.D.
Manu 9.57-70; JOLLY (70-71); ALTEKAR 143-150; KANE 599-607; LESLIE 300-302, 309-310, 324; SUTHERLAND; BROCKINGTON 221-222.