Simulation model for kinship structures is ethnographically invalid

The simulation model presented in ref. 1 requires correct usage of kinship concepts. However, the two kinship concepts central to the model, the incest taboo and the clan form of social organization, are incorrectly presented.

The authors incorrectly consider the incest taboo to express preference for marriages between different social units: “marriage occurs only with a certain different cluster, resulting in the incest taboo” (ref. 1, p. 2379). The incest taboo actually refers to the cultural prohibition of sexual relations between parent and child or between siblings (2) and only affects marriages through cultural prohibition of marriages involving incestuous sexual relations.

What the authors call the incest taboo is actually a cultural marriage rule prohibiting within-group marriages, but this does not apply to all lineages. Arabian tribal societies recognize the incest taboo, yet prefer within-lineage marriage between a man and his father’s brother’s daughter, which contradicts the authors’ statement that “a father’s brother belongs to the same clan [as the father], and, thus, marriage with a father’s brother’s daughter is prohibited, when the incest taboo is organized” (ref. 1, p. 2380).

The authors incorrectly assume behavior patterns lead to cultural prohibitions (1), but the !Kung San, a hunter-gatherer group in Botswana, lack within-group marriage, yet have no rule prohibiting such marriages. Within-group marriages do not occur due to their cultural rules defining marriageable kin categories (3).

The authors mistakenly assume a clan is a cluster of interacting lineages (1). A clan, when it occurs, consists of those lineages that recognize the same apical ancestor from whom lineage members believe they are descended, either through father−child filiation (patrilineal societies) or through mother−child filiation (matrilineal societies) (4). Clans are determined conceptually, not through behavior.

The authors incorrectly assume that “siblings of the opposite sex belong to a different clan by the move of brides to husbands’ lineages” (ref. 1, p. 2380). Instead, the bride remains a member of her natal clan even after moving in with her husband. Consequently, brother and sister are always members of the same clan, regardless of marriage. Clan marriage exogamy implies a man and his wife will be in different clans both before and after marriage. A child is always in the clan of its mother or its father. The authors’ model, however, mistakenly implies “children can belong to different clans from parents by inheriting traits from both parents” (ref. 1, p. 2381).

They conclude that a distinction between cross cousins (parent’s cross-sex sibling’s children) and parallel cousins (parent’s same-sex sibling’s children) arises from the model’s incorrect implication that “women change lineages after marriage” (ref. 1, p. 2382). This cousin distinction does not derive from the processes that the authors model but from the generative logic of a kinship terminology (5–7).

Their argument (1) that generalized exchange is linked with cooperation is confounded by Leach's early work on the Kachin (8); their argument that restricted exchange is linked with conflict is not ethnographically realistic; their idea that systems “emerge” in response to cooperation or conflict is exaggerated: All systems of this sort are subject to both conflict and cooperation. In sum, their models do not correspond more than occasionally to actual ethnographic situations.