Incest/Inbreeding Taboos

The incest taboo is better understood when examined in the context of the sociocultural development of human systems (Leavitt 1989). This development is best understood in light of the general organizational framework of human kinship groups (or descent systems) that comprise a fundamental component of many human communities.

In general, descent systems are either bilateral or unilineal. Bilateral systems, like American society, are diffused and include equally the relatives of both an individual's parents. In this system, a person is not usually acquainted with relatives beyond first or second cousins, and ritual or formal activities beyond the most immediate family are typically absent.

In a unilineal kinship system, all members of the kinship group trace their ancestry to a common ancestor (either mythical or actual). If this founder was male, descent is traced through the male line (patrilineal); if the founder was female, ancestry is traced through the female line (matrilineal). In a few rare instances, there are societies of double or dual descent in which each individual inherits two descent group memberships. Because membership in unilineal descent groups is determined by an individual's descendancy from a single ancestor, only some of a person's relatives will belong to their kinship group.

Societies with unilineal descent systems are commonly organized around lineages or clans, in other words, kinship organizations, which include hundreds of people recognized as blood relatives. These groups are the organizational backbone of the society and orchestrate most societal activities, including political, economic, military, religious, and educational functions.

The earliest, simplest societies (hunting and gathering or foraging societies) typically consisted of a tribe incorporating a number of small nomadic bands organized through bilateral descent. Band exogamy was practiced to ensure that the bands remained unified, even though they ranged far apart and saw each other only occasionally. This meant that a person had to marry and have sex with a partner outside of the immediate family and band. Thus, the survival of the tribe was ensured through bonds of blood and marriage ( Johnson and Earle 1987). When bands, which consisted normally of twenty-five to fifty people, found themselves in trouble their marriage and blood ties ensured that they could seek aid from other groups.

At the end of the Ice Age (10,000 B.C.E.), the earth's climate, flora, and fauna changed sufficiently to begin moving human communities toward agriculture (Harris 1977). With this change came a need for more sophisticated social structures, especially for politico-military and economic activities. As life became increasingly sedentary and communities grew in size, access to resources became increasingly crucial, as did the need to defend relatively scarce fertile farmland. These structural and institutional changes encouraged the appearance of unilineal descent groups.

By extending the incest taboo to encompass lineage or clan members, the kinship group compelled its children into marriages of alliance with other descent groups. Such marriages carried reciprocal obligations for economic and military assistance essential for survival. These marriage bonds were so important that parents and other kin commonly determined whom their young would marry (arranged marriage). Frequently, kin group associations were made strong and stable through an exchange of gifts between family groups (bride price, dowry, groom wealth) and the encouragement of the couple to have many children ( Johnson and Earle 1987).

As human societies continued to grow and evolve technologically and structurally (including larger settlements), the incest taboo began to contract, encompassing fewer relatives. New organizational structures not based on kinship ties or descent became increasingly common, and these structures were more efficient for operating larger, more complex societies. These new institutions were part of the development of the state, which ensured political and economic alliances through its own bureaucratic agencies.

With the appearance of modern industrial societies, the incest taboo contracted to encompass only the nuclear family and a few other immediate relatives (Cohen 1978). Punishments for violating the incest taboo have followed a similar evolutionary path. Where the incest taboo has been extended to ensure survival, its violation has generally been punished more severely. As the incest prohibition became less essential for enhancing alliances, it contracted to include fewer categories of relatives, and sanctions for violations of the incest proscriptions have become less severe (Leavitt 1989).

By understanding human sociocultural and environmental conditions, it is possible to understand the incest taboo, as well as its many variations, without tortuous allusions to genetic evolution.