Warfare and reproductive success in a tribal population

Ethnographic Background

The Nyangatom are nomadic agro-pastoralists numbering ∼30,000 who inhabit a remote region along the southern border of Ethiopia and South Sudan. This region is one of the few remaining areas of the world in which warfare continues to occur largely free from commercial or state agendas.

The Nyangatom are members of the larger Ateker or Karamojong cluster, which includes the more populous and well-known Karamojong, Turkana, and Toposa (19, 20).

The Nyangatom have the social organization of a small-scale society. Many Nyangatom reside in mobile encampments ranging from a few families to several hundred individuals. There are also semipermanent villages in agriculturally productive areas, although membership is dynamic, as many individuals move between these villages and the temporary encampments. Local environmental conditions or the threat of conflict sometimes forces villages to relocate or disintegrate entirely, causing large areas of their territory to be uninhabited.

The Nyangatom have ongoing conflict with several neighboring ethnic groups including the Turkana, Dassanetch, and Suri, as well as occasional conflicts with other groups (21). Automatic weapons were introduced into the area in the late 1980s and are used throughout the region. Similar to neighboring pastoralist groups such as the Turkana (22), the Nyangatom have two types of offensive raids: stealth raids and battle raids. Stealth raids (sing. emojirimónu) are composed of a small number of men, usually 4–25, who attempt to capture poorly guarded livestock by stealth or sneak into an enemy village at night and steal livestock undetected. They may also opportunistically attack and kill individuals they encounter. Stealth raids are conducted primarily by young to middle-aged males and sometimes have informal leadership. Because warriors on stealth raids seek to minimize their risks and engage in livestock theft only when they are unlikely to be detected, stealth raids have a low casualty rate (22).

Battle raids (sing. ajoré) frequently include hundreds of participants and are intended to forcibly capture livestock or attack the enemy with overwhelming numerical superiority. Because they primarily rely on violent force instead of stealth, deaths for attackers are not uncommon. They commonly have leaders, which we here call “battle raid leaders.” Battle raid leaders appear to take an especially active role in the conflict, coordinate participants, and provide tactical advice. However, as in stealth raids, participation in battle raids is not compulsory, and there are no chains of command or explicit sanctions for desertion or cowardice.

Similar to the neighboring Dassanetch, warriors commonly give livestock to their older paternal relatives after capturing them in stealth and battle raids (23). In such exchanges, the warrior is frequently reluctant to make the transfer, but succumbs to pressure from his relatives. The ethnographic context creates a lag between capturing livestock in a raid and accessing them for personal use. Because captured livestock are generally given to paternal male relatives, the successful raider is unlikely to be able to use them for his own purposes over the short term.

The basic unit of social organization is the nawi, which refers to both the family and the settlement, which are commonly coextensive (19), although many villages are composed of multiple families. The nawi includes monogamous or polygynous families including the children of such marriages, adult offspring, and their wives and children. It may also include other adults such as the brothers of the family head, their wives and children, as well as other relatives and friends. Families are usually headed by an elder male who makes most decisions affecting the family, such as where and when to migrate. The family head is usually the owner of all of the livestock on which the family depends, although adults within the family sometimes own a few livestock individually. However, individuals commonly have stock rights to livestock owned by a family head. Stock rights are culturally recognized claims on livestock that allow the holder to claim livestock for certain reasons, including marriage and subsistence.

The Nyangatom are polygynous, with some men having as many as five or more wives. Marriage order within a family usually follows birth order, such that older sons marry before their younger brothers. Typically this applies across polygynous marriages, but the sons of first wives are sometimes favored above older brothers from the wives of subsequent marriages. Marriages, including cases of bride capture and elopement, do not occur without an eventual transfer of bridewealth, no matter how well regarded the groom is. When the bride’s family accepts an offer of marriage, a few livestock may be transferred at once, but the majority of the bridewealth is usually given up to a decade later. Elders who marry polygynously commonly exchange bridewealth earlier than nonelders. The primary claims for bridewealth are usually against the family head of the groom and not the groom himself, unless he is the family head or owns a significant number of livestock. The amount of bridewealth required for marriage is not negotiated at the time of marriage but depends on several variables that may change before bridewealth is eventually paid. The number of livestock eventually transferred depends on the relative size of the herds belonging to the groom’s paternal kin, the number and sex of the children produced by the marriage, and the number of the bride’s male kin. It involves an exchange of more than 30 cattle and may reach up to 100 cattle. Such a transfer can seriously deplete the herds of the groom’s family, so men are expected to use a variety of means to obtain access to livestock to use for bridewealth, including raiding.

Acquiring bridewealth is complex and delays the age at first marriage until the late 20s to mid-30s, during which time virtually all men are married. For first marriages, males acquire bridewealth through accessing any livestock they personally own and by appealing to relatives and friends, although in practice men receive nearly all of their bridewealth allocations from their father and paternal uncles who are family heads.

Obtaining livestock for bridewealth for polygynous marriages is generally more difficult than for first marriages because relatives are less willing to provide livestock to the groom. Thus, to obtain additional wives after his first marriage, the prospective groom must own a herd of livestock or have significant stock rights on livestock owned by kin. Thus, the possibility of polygynous marriage is severely constrained for young men.

Men commonly generate stock rights through the marriage of a female relative. When females marry, their marriage generates incoming bridewealth in the form of livestock, although unmarried men usually cannot receive these livestock. Rather, they receive stock rights to a share of the livestock that they may claim later in life when they desire to marry. The number of livestock to which these stock rights pertain depends on the man’s relatedness to the female who was married, with maternal brothers having the strongest claims to incoming bridewealth generated by their sister’s marriage. Thus, men with few sisters are called “sister-poor,” whereas men with several sisters are called “sister-rich” (18). In the same way, older brothers may use up much of a family’s livestock through bridewealth payments, leaving younger brothers with little access to bridewealth. We call such men “brother-biased.” Individuals who face shortages of bridewealth may seek strategies such as raiding to increase their access to livestock.

Stock rights are also generated through the compulsory gifts of captured livestock that men make to their elder relatives after a successful raid. Although young men “give” cattle they capture to their relatives, they may later invoke these gifts as stock rights. Commonly claimees resist fulfilling these stock rights due to their desire to use the livestock for their personal benefit, either for bridewealth or subsistence.

The death of a family head provides a means for the holder of stock rights to inherit livestock. Married men who have stock rights on livestock owned by the deceased can claim a share of the inheritance, and the stock rights held by unmarried individuals can transfer to the inheritors and be claimed later. Thus, the gifts of livestock to relatives that occur after a successful raid result in the possibility of a delayed return of livestock.

Here we evaluate the hypothesis that raiding provides reproductive benefits to warriors over the lifetime by testing four predictions: (i) among nonelders, increased raiding is associated with a greater number of wives and children; (ii) elders who were more active raiders in their youth have a greater number of wives and children; (iii) battle raid leadership is associated with a greater number of wives and children; and (iv) among nonelders, being sister-poor or brother-biased is associated with increased raid participation. We then use quantitative and qualitative ethnographic data to propose possible pathways between raiding and reproductive success.