When European travelers first encountered the Warlpiri of Australia’s Outback or the Kalapalo of the Amazon Basin in the 19th century, at least one institution would have been familiar amid the welter of cultural differences. As in the West, life among the Warlpiri and Kalapalo is profoundly shaped by marriage. In their own ways, the members of both of these societies strive to attract desirable spouses and then to raise children and forge a life together. As anthropologist Joseph Henrich observes, despite important variation in its form across cultures, “marriage represents the keystone institution for most (not all) societies, and may be the most primeval of human institutions.”Marriage might be nearly ubiquitous, but does it still matter today? As reliable contraception has lowered the stakes of sex, and women have achieved political and, in some cases, economic equality with men, perhaps marriage has now become merely optional, a capstone rather than a cornerstone of a successful life.

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