Over the past few years, something like a perfect storm has been brewing over human pair bonding and the profound impacts it has wrought on human social structure. This is a welcome development in a field that has long been dominated by those who wish to root the relatively modern idea of marriage in ancient evolutionary soil. Such a desire usually stems from the notion, metaphysical in nature, that marriage is a timeless and sacred institution. Given this animating impulse, much of the evolutionary literature on pair bonding and “marriage” has been a fact and fossil free zone where just about anything goes, and what goes usually serves the sub rosa interests of institutionalized religions. This has begun to change.
In 2008, Bernard Chapais published Primeval Kinship: How Pair-Bonding Gave Birth to Human Society. Chapais observes that primate sexual practices limit the recognition of kinship. When kinship is recognized, it does not extend far. This in turn constrains group size, composition, and alliances. Humans are obviously different, but how did it happen? Commenting on a recent study of hunter-gatherer group composition and kinship that appeared in Science, Chapais explains:
A key event might have been the advent of pair bonding in the human lineage. Our closest relatives, chimpanzees and bonobos, live in large mixed-sex groups [and] mate promiscuously, with both sexes having multiple short-term partners. [This results in a genealogical structure that] is to a large extent “socially silent.” Now suppose that pair bonding evolved in this type of social structure. This brought the multifamily composition of human groups, with enduring associations between mothers and fathers enabling children to recognize their fathers. This, in turn, made it possible for children to recognize their father’s relatives; that is, pair bonding would reveal the underlying genealogical structure and create bilateral kinship.
In the nascent “tribe,” males were now able to circulate freely between groups in which they had kin and in-laws, cross-sex kin maintained lifetime bonds, and between group alliances were ensured by kinship bonds, “marital” ties, and the ensuing extensive networks of bonds between in-laws. [T]he dramatic and fortuitous extension of kin recognition brought about by pair bonding would have launched the evolution of supragroup social structures in which a large proportion of individuals were now distantly related.
Pair bonding, in other words, triggered a cascade of kinship effects that irrevocably altered human social structure. Groups would have become larger, more cooperative, and more cohesive. Networks resulting from pair bonding and bilateral kinship would have enabled between group cooperation and “multilevel alliance structures.” These effects are mathematically unassailable and ethnographically observed.
Chapais was not, however, the first to suggest that pair bonding is a key hominid adaptation. In his 1981 article “The Origin of Man,” C. Owen Lovejoy proposed that pair bonding was the “breakthrough” adaptation for hominids. While intriguing, Lovejoy’s hypothesis was largely referential (depending heavily on primate models) and theoretical (grounded extensively in life history analytics). It was short on evidence, whether from fossils or people. Two decades later, there is now some evidence from both.
In 2009, Lovejoy was part of the team that unveiled the 4.4 million year old Ardipithecus ramidus or “Ardi” in a special issue of Science. The team argued that Ardipithecus is an ancestral hominid and the genus that spawned Australopithecus. Lovejoy’s contribution, “Reexamining Human Origins in Light of Ardipithecus ramidus,” re-states his case for pair bonding as a breakthrough adaptation and places it within a suite of adaptations that uniquely altered the course of hominid evolution. It is a densely packed and impressive argument that hangs almost entirely on the slender thread of canine reduction in Ardipithecus.
Although Lovejoy’s paean to proto-marriage has the distinct feel of an umbrella hypothesis, this does not make it untrue. In fact, the recent study of hunter-gatherer group composition by Kim Hill and colleagues provides additional support for the idea that pair bonding is the key to extended kinship. While we currently have no way of knowing when hominids began pair bonding, there seems to be little doubt that it played a critical role in human evolution.
Given this fact, it is not surprising that nearly all organized religions sanctify this key evolutionary adaptation. It is important to realize, however, that the pair bond has not always been subject to supernatural sanction or ritual blessing. In many pre-state societies where shamanic practices prevail, pair bonding or “marriage” is a rather low key affair detached from the spirit world. Hunter-gatherers “marry” and “divorce” with relative ease and without the kinds of rituals or covenants that arose in conjunction with the earliest organized religions. The metaphysics of modern marriage are a post-Neolithic invention.
Chapais, B. (2011). The Deep Social Structure of Humankind. Science, 331 (6022), 1276-1277 DOI: 10.1126/science.1203281
Hill, K., Walker, R., Bozicevic, M., Eder, J., Headland, T., Hewlett, B., Hurtado, A., Marlowe, F., Wiessner, P., & Wood, B. (2011). Co-Residence Patterns in Hunter-Gatherer Societies Show Unique Human Social Structure. Science, 331 (6022), 1286-1289 DOI: 10.1126/science.1199071
Lovejoy, C. (1981). The Origin of Man. Science, 211 (4480), 341-350 DOI: 10.1126/science.211.4480.341
Lovejoy, C. (2009). Reexamining Human Origins in Light of Ardipithecus ramidus. Science, 326 (5949), 74-74 DOI: 10.1126/science.1175834
Langdon, J. (1997). Umbrella hypotheses and parsimony in human evolution: a critique of the Aquatic Ape Hypothesis. Journal of Human Evolution, 33 (4), 479-494 DOI: 10.1006/jhev.1997.0146