Books and Arts

Nature 454, 29-30 (3 July 2008) | doi:10.1038/454029a; Published online 2 July 2008

Bonding as key to hominid origins

Monique Borgerhoff Mulder1

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Primatology meets socio-cultural analysis in a controversial account of human evolution.

BOOK REVIEWEDPrimeval Kinship: How Pair-Bonding Gave Birth To Human Society

by Bernard Chapais

Harvard University Press: 2008. 368 pp. $39.95, £25.95, euro dollar30.00

Bonding as key to hominid origins

P. BOWATER/ALAMY

A father in Papua New Guinea displays his marriageable daughters.

Over the centuries answers to the question of what makes us uniquely human have varied. The Greek philosophers emphasized reason, Enlightenment scholars pointed to our political nature, and nineteenth-century historical evolutionists prioritized our complex social organization. After Charles Darwin and Sigmund Freud, answers became increasingly psychological, and in recent decades attention has turned to the genome and cognition. For the most part, modern social scientists eschew grand debates over human origins, fearful of becoming tarred with the brush of nineteenth- century social Darwinism.

Primeval Kinship returns to the big questions about ancient society that mesmerized the prominent social theorists of the Victorian era such as Edward Tylor, Lewis Henry Morgan and Friedrich Engels. The author, primatologist Bernard Chapais, offers a powerful and controversial new account of hominid origins. The root of humanity, he argues, lies in pair bonding (the strong affinity that can develop in a breeding couple), the brother–sister tie, and the transfer of females between groups. Imagine a violent chimp-like encounter between two groups of early humans. An attacking dad in one group recognizes his daughter in the other and thinks twice about killing her baby. Meanwhile the daughter's bonded mate recognizes his sister in the attacking group, and refrains from a counterattack. We might even see some reconciliatory grooming. Both males have a vested interest in the same mother–offspring pairs, and hence, to cut Chapais' intricately woven argument short, females act as peacemakers between groups.

A unique feature of human society is the largely peaceful relations between tribes. Chapais reiterates and builds upon the central claim in anthropologist Claude Lévi-Strauss' 1949 classic treatise Les Structures Élémentaires de la Parenté about what makes us human. Namely, that men exchange daughters and sisters between kin groups to form alliances. The idea goes back to Tylor's aphorism "marry-out or be killed-out". Placing the story in its phylogenetic context, Chapais radically reorders some of Lévi-Strauss' logic and develops a more fully fledged thesis. For instance, in contrast to Lévi-Strauss' claim, hominids did not invent incest taboos to achieve marital exchange, but inherited them from much deeper animal roots; outmigration of one sex (exogamy) was already in place when the last common ancestor of humans and chimpanzees stalked the forests.

Chapais' key contribution is to ask how hominids could recognize relatives who had transferred to other groups. He presents evidence from macaques and other primates that mother–child recognition, and cognizance of other mother–child dyads, can exist without the long-term establishment of sexual bonds between mates. Father–offspring recognition, by contrast, requires relatively durable pair bonds. Individuals who can identify a father–child relationship in others can more confidently identify their own siblings. Then, his logic goes, if one sex migrates to other groups, these long-distance sibling links will form the kernel of peaceable intergroup relations. Chapais stands apart from his eminent anthropological forebears, such as Leslie White and Robin Fox, all of whom posited that language was the key to exogamy.

Primeval Kinship makes several claims that will upset biological anthropologists. Chapais' model requires that ancestral hominids lived in male-centred kinship groups. Essentially he proposes a nuanced homology between several systems in which males stay in their natal groups and females transfer — in chimps or bonobos and in hunter–gatherers. A common objection to this is that contemporary hunter–gatherers show variable residence patterns, even cases in which men preferentially reside with their wife's kin.

This for Chapais is irrelevant, as his argument is about origins, not contemporary adaptations to socioecological constraints. Many will contest the assumption of male philopatry, especially adherents to the idea that humans evolved as cooperative breeders. These scholars argue that women's extended post-reproductive lifespans, short intervals between births and the extreme and extended helplessness of our children evolved because of the aid of maternal grandmothers and other kin in rearing children.

Other contentious claims include the irrelevance of infanticide and parental investment in the evolution of pair bonds. The book's treatment of proposed alternatives for pair-bond origins — a pact among individuals to reduce the costs of a physical scramble for mates — is dissatisfying because Chapais fails to consider sexual size dimorphism, brain expansion and changes in life-history traits across the paleoanthropological record. He also argues that food sharing arose from bipedalism, not from male specialization in hunting. Moreover he dismisses language as an important step in our becoming human, a position that will alienate many social scientists. The answer to the perennial question — why did this suite of traits arise only in hominids — is not fully dealt with, despite deft intellectual fencing.

Refreshingly, Chapais does not seek specific selective pressures for every trait. He conceives of evolution occurring under the constraints of prior adaptations and producing novel features from pre-existing parts. He abhors unsubstantiated evolutionary narratives and nimbly marshals evidence from primatological studies to sociocultural analyses to support his case. In the end, his book offers us one more scenario of our human trajectory, but it is a scholarly one. Chapais' thesis urges us to consider very carefully why humans are so different.

  1. Monique Borgerhoff Mulder is professor at the Department of Anthropology, Graduate Group in Ecology, and Center for Population Biology at the University of California, Davis, 1 Shields Avenue, Davis, CA 95616. She is co-author of Conservation: Linking Ecology, Economics and Culture.