Tuesday, July 14, 2015

Monogamous Pair-Bonding in the Lockean State of Nature

Unlike Jean-Jacques Rousseau, John Locke believed that our human ancestors in the state of nature were social animals, because the "first society" was the conjugal society of husband and wife and the familial society of parents and children.  Modern evolutionary anthropology supports Locke over Rousseau by providing evidence that the evolution of monogamous pair-bonding among our prehistoric foraging ancestors gave birth to the unique structure of human society.

In the Two Treatises, Locke gives both religious and natural explanations for human familial bonding.  It shows the "wisdom of the great Creator" that He has created human beings with inclinations for monogamous marrying and for mothers and fathers caring jointly for their children (FT, 86-89; ST, 77-80).  This can also be explained through the natural history of animal reproduction.  For some animals, whose offspring can survive on their own without much parental care shortly after birth, Locke explains, mothers care for the offspring with no need for fathers to provide any care, and consequently there is no need for any enduring bond between the sexual mates.  But for those animals whose offspring cannot survive without extensive and prolonged care from both parents, there is a natural need for an enduring pair-bonding of the sexual mates to provide biparental care.  If mothers cannot feed themselves and their offspring without the help of males, because they need the meat provided by male hunting, or if birth-spacing is so short that mothers can often have multiple dependent offspring requiring prolonged care from both parents, then these animals will have a more enduring conjugal bond; and this is true for human beings.  As compared with other animals, human offspring are dependent on adult care for a long period during which the offspring must not only be nourished but also educated, because complex human social life requires a prolonged period of social learning.

In contrast to Locke, Rousseau argued that human beings in the "pure state of nature" were asocial and almost completely solitary animals.  Men and women encountered one another by accident and engaged in sexual intercourse whenever the desire moved them, but they immediately left each other and felt no tie to one another.  Mothers nursed their children for a short period.  But as soon as the children could feed themselves, they left their mother, and they soon would no longer recognize one another.  So while the maternal attachment to children was the one social bond in the state of nature, it was only a momentary bond that created no enduring social recognition (SD, 108, 112, 120-21, 130-31, 137, 142, 147, 216, 219).

In one of the longest notes in the Second Discourse (213-20)--note l--Rousseau quotes the entirety of sections 79-80 of Locke's Second Treatise, where Locke lays out his reasoning for monogamous pair-bonding and biparental care in the state of nature.  Rousseau denies the factual truth of Locke's claims about animal reproduction and parental care, and accuses him of making the same mistake that Hobbes made in projecting what we see in human beings today back into the state of nature.  Today, human beings develop romantic attachments so that they prefer one sexual mate over another, and this can develop into a conjugal bond.  When children are conceived, parents become attached to them and care for them.  But there is no reason to believe that people in the state of nature felt this, Rousseau insists.  In the state of nature, once a man and a woman had satisfied their sexual appetite, they would have separated, with no enduring passion of love.  If the woman conceived a child, there would be no reason for the father to see this as his child.  Thus, in the state of nature, sexual mating was so indiscriminately promiscuous that fathers never recognized their children, and mothers recognized their children only for a short time.  Marriage and family life did not appear until the second stage of human evolution, which Rousseau calls the "nascent society" of the "sociable savage" (SD, 146-52).

Claiming that savage human beings began with "purely animal functions," Rousseau adds a note (note j)--the longest note in the Second Discourse--on the reports of European travelers about the strange variety in the animals and human beings that they have seen around the world (115, 203-13).  They have seen "anthropomorphic animals" that are called orangutans, pongos, or mandrills.  Although these animals have many human traits, most travelers identify them as beasts, but Rousseau suspects that more precise research might conclude that they are remnants of the earliest savage humans.  He thus implies the idea of human evolution from nonhuman animals.  He was the first thinker in the eighteenth century to suggest that humans evolved from apes, and thus he anticipating modern evolutionary theory (Wokler 1976, 1978; Frayling and Wokler 1982).

Travelers have described the characters and customs of the foreign peoples they have seen, but Rousseau suspects that they have not accurately reported how different these foreign cultures are from European culture.  Rousseau complains that these travel reports are coming mostly from sailors, soldiers, merchants, and missionaries, who are not motivated by the intellectual curiosity that would produce precise studies of these foreign animals and human beings.  Rousseau hopes that soon some rich philanthropists will provide the money to support some philosophic scientists who could devote at least ten years of their lives to voyaging around the world and studying the animals and humans they find, and then they could return to write "the natural, moral, and political history" of the animal and human world.

Beginning in the first half of the nineteenth century, scientific travelers like Alexander von Humboldt, Alfred Russel Wallace, and Charles Darwin began the world-wide scientific research that Rousseau had hoped to see (Carroll 2009).  Now, after two centuries of anthropological research and almost a century of primatological research, we now have, for the first time, the scientific knowledge required for clarifying and perhaps resolving the debate between Hobbes, Locke, and Rousseau over what human ancestors looked like in the state of nature.  Through the comparative study of behavioral primatology and social anthropology grounded in evolutionary biology, we can reconstruct the natural evolutionary history of human social life from our nonhuman primate ancestors to our prehistoric hunter-gatherer ancestors.

The conclusion that emerges from that study, I argue, is that in their accounts of the state of nature, Locke was mostly right, Rousseau was mostly wrong, and Hobbes was partly right and partly wrong.

Here I will concentrate on the question of whether and how monogamous pair-bonding evolved in the human state of nature as the fundamental element in the universal deep structure of human sociality.  The best single survey of the evidence and argumentation for answering this question is in the work of Bernard Chapais (2008, 2011a, 2011b, 2013), who has shown how the primate evolution of reciprocal exogamy--the exchange of women for marriage between kin groups--made human societies unique among primate societies by integrating local groups through bonds of biological kinship and affinal kinship (the kinship of in-laws).

Despite the diversity of marital arrangements in different human cultures, there is an underlying unity in that all types of marital unions are cultural offshoots of the same biologically natural stem pattern--enduring pair-bonds.  Monogamous, polygynous, polyandrous, and even homosexual marriages are all based on enduring pair-bonds.  In a polygynous marriage, a single man maintains pair-bonds with two or more women.  In a polyandrous marriage, a single woman maintains pair-bonds with two or more men.  Homosexual marriage is same-sex pair-bonding.  In most human societies (over 80%), polygynous marriage has been permitted, although most marriages (over 90%) are monogamous even in societies that permit polygyny.  Thus, most human marriages have been monogamous.

Of course, sexual promiscuity and adultery has been common in all human societies.  But in no human society has promiscuity been the only or the main form of sexual mating.  This separates us from the primate species most closely related to us by evolutionary descent--chimpanzees and bonobos--because they are totally promiscuous, with no enduring pair-bonding.  Other primate species do show enduring pair-bonding--in single monogamous pairs, single polygynous units, single polyandrous units, or multiharem groups of several polygynous units assembled together.  But human pair-bonding mating systems are unique in their bilateral kin recognition (recognizing kin on both the mother's and the father's side) and bilateral affinity (both spouses recognizing their respective in-laws).

Rousseau was wrong in asserting that in the state of nature, savage human beings were solitary animals who mated promiscuously with no enduring social bonds.  Locke was right in recognizing that the earliest human beings were hunter-gatherers who lived in bands of families based on pair-bonded  monogamous or polygynous mating and extensive parental care of children by both mothers and fathers.

Archaeologist anthropologists Kent Flannery and Joyce Marcus argue that the evidence generally supports Rousseau's history of human social evolution.  But in making this argument, they silently throw out Rousseau's first stage of human evolution--living as solitary animals--because they begin with what Rousseau saw as the second stage that arose with the establishment of families (Flannery and Marcus 2012, 19-39).

One defense of Rousseau would be to point to his intimation that the savages in the "pure state of nature" were actually orangutans or chimpanzees, from which human hunter-gatherers evolved.  The hunter-gatherer bands studied by anthropologists are organized around families with conjugal love and parental love, but these belong to the second phase of human evolution, according to Rousseau, which he calls "nascent society" (SD, 146-52).

And yet, Rousseau's account of the original state of nature is not even true for chimpanzees or orangutans.  These primates are sexually promiscuous, with no enduring pair-bonding of sexual mates.  But they are not solitary animals, because they show enduring mother-child bonding and other social bonds.  Rousseau is wrong in claiming that when offspring leave their mothers, they no longer recognize one another.  Maternal care and bonding extends beyond weaning.  In most primate species, females stay in their natal group, and males migrate to another group when they reach puberty.  In these species, mother-daughter bonds can extend throughout the lifespan.  With chimpanzees and bonobos, most females leave their natal group at puberty, and males stay.  Here the bond between mothers and their resident sons extend for long periods beyond weaning.

Of all the apes, orangutans are the most solitary, in the sense that most individuals spend most of their time alone.  So they might be the one primate species that most resembles the solitary savage of Rousseau's pure state of nature.  But even they show a social organization.  Mothers care for their offspring, even after weaning.  Orangutans live in loose communities organized around a dominant male.  Mature females tend to settle close to their mothers and sisters.  This social life allows for social learning, which creates cultural traditions that distinguish one orangutan community from another.  Various skills (such as tool use and nest building) and communication signals seem to be passed from generation to generation through social learning.

But while apes are social animals, they do not show the complexity and flexibility of human social structure because they lack the enduring pair-bonding that makes human society possible.  Locke rightly saw the importance of pair-bonding in human hunter-gatherer societies, and he also rightly saw that a major adaptive function of human pair-bonding is the collaboration of mothers and fathers in the parental care of children.  Among hunter-gatherers, pair-bonds are parental partnerships.

Locke recognized the high costs of maternity--in pregnancy, lactation, post-weaning care, and the short birth intervals that make it necessary for mothers to feed more than one child at a time--and that these costs were higher for human beings than other species.  He also recognized that fathers could reduce these costs by helping mothers in caring for their children, particularly through male hunting and sharing of meat with mothers.  Modern anthropological studies of hunter-gatherer bands have confirmed the importance of parental cooperation, which suggests that this was the original evolutionary function of human pair-bonding, as it evolved in the earliest hominid ancestors, such as Australopithecus afarensis (Fisher 1992, 2006; Lovejoy 1981).  High sexual dimorphism (males being much larger than females) is correlated with polygynous mating systems in which males fight with other males in the attempt to monopolize access to females.  Low sexual dimorphism, as is shown by human beings,  is correlated with monogamous mating.  Some paleoanthropologists see evidence that the fossil skeletons of Australopithecus afarensis show low sexual dimorphism comparable to that of human beings, which they interpret as evidence that the earliest hominid ancestors of human beings had turned to monogamous pair-bonding and parental care (Reno et al. 2003; Reno et al. 2010).  This would support Locke's claim that humans in the original state of nature were organized in families of pair-bonded mates cooperating in caring for their children.

Other anthropologists, however, offer a different evolutionary scenario.  They argue that there is growing evidence and argumentation for an evolutionary history of pair-bonding in which stable breeding bonds did not originally evolve for parental care, although that is their present-day adaptive function (Chapais 2008, 157-84).  They assume that our earliest common ancestor with chimpanzees had a chimpanzee-like social structure--the promiscuous multimale-multifemale group.  The question then is what were the evolutionary steps required to reach the present human social structure--the multifamily human group in which most families are monogamous, and a few are polygynous.  Comparison with primate species suggests that there must have been an intermediate stage--the multiharem group in which all families are polygynous, and some males have no mates, which is the social structure of hamadryas and gelada baboons.  This evolutionary history requires two steps.  The first step is from sexual promiscuity to the multiharem group.  The second step is from the multiharem group to the multimonogamous family group (Chapais 2008, 171-84).

The general consensus among paleoanthropologists is that the fossil evidence of Australopithecus afarensis shows high sexual dimorphism, which suggests a polygynous mating system like that of hamadryas and gelada baboons (Gordon et al. 2008; Lockwood et al. 1996; Plavcan et al. 2005).  But in polygynous primate systems, fathers do not help the mothers care for their children.  For males, the benefit of polygynous mating is in guarding their mates from other males.  In fact, for most mammals and primates, both monogamous and polygynous, pair-bonding is primarily a mating arrangement rather than a parental partnership.  In most monogamous species that show cooperative parenting, paternal care has evolved after monogamy was already established (Brotherton and Komers 2003).  Among monogamous primate species, some show direct paternal care (in callitrichids, siamangs, and titi monkeys); but paternal care is not shown in other species (such as gibbons, tarsiers, and lemurs) (van Schaik and Kappeler 2003).

If our hominid ancestors lived in multiharem societies like hamadryas baboons, then we would have to wonder why and how our ancestors eventually moved to the mating system of human hunter-gatherers, with mostly monogamous mating and cooperative parenting.  Chapais points out that hamadryas males differ in their competitive abilities, so that some have big harems, others have smaller harems, and many have none.  If they had roughly the same fighting abilities, fighting would be so costly for them that they would have to give up their harem system.  Chapais (2008, 176-79) suggests that that is what happened when hominid males began to make tools that could be used as weapons.  If all males can use weapons, and perhaps form coalitions, for fighting, this would have a leveling effect that would favor the egalitarianism of monogamy.  This would not completely eliminate polygynous inclinations, but it would constrain those inclinations.  And, indeed, that is what we see in human mating systems.  Many men will seek polygynous mating when they have the power and resources to do this successfully, but most men will have to settle for monogamy.

But why should these hominid males care for their children?  Chapais's answer is that pair-bonding was a preadaptation for the evolution of paternal care.  Once males were monogamously pair-bonded with their mates, then they would probably share food with the family; and as the feeding and caring for the children exceeded the abilities of the mothers, fathers could specialize in hunting large animals, while mothers could gather plants and small animals.

As a consequence of that deep evolutionary history, we can now see the biochemistry of monogamy and parental cooperation in the human brain and endocrine system (Fisher 2006; Brizendine 2006, 2010).

If the human state of nature is identified as the life of the earliest members of Homo sapiens, then all of this research in evolutionary anthropology confirms Locke's account of humans in the state of nature as egalitarian hunter-gatherers living in pair-bonded monogamous families where mothers and fathers cooperated in caring for their children.  But if the human state of nature is identified as the life of  hominids who evolved prior to the emergence of Homo sapiens, then there is disagreement about whether the human pattern of pair-bonded families with parental cooperation can be found in those earliest hominid species.  The crucial debate over whether the hominid fossil record shows a human-like pattern of sexual dimorphism in hominid species, which would suggest monogamous pair-bonding and parental cooperation, cannot be resolved because the fossil record is too fragmentary and sparse.  Another problem is that the causes and functions of sexual dimorphism are so complex that they are hard to interpret.  For example, sexual dimorphism depends on both male traits and female traits, and so it's hard to know whether dimorphism has arisen from male traits, from female traits, or from both (Plavcan 2011, 2012).


Brizendine, Louann. 2006. The Female Brain. New York: Morgan Road Books.

Brizendine, Louann. 2010. The Male Brain. New York: Harmony Books.

Brotherton, Peter, and Komers, Petr. 2003. "Mate Guarding and the Evolution of Social Monogamy in Mammals," in Ulrich Reichard and Christophe Boesch, eds., Monogamy: Mating Strategies and Partnerships in Birds, Humans, and Other Mammals (Cambridge: Cambridge University Press), 42-58.

Carroll, Sean B. 2009. Remarkable Creatures: Epic Adventures in the Search for the Origins of Species (Boston: Houghten Mifflin Harcourt).

Chapais, Bernard. 2008. Primeval Kinship: How Pair-Bonding Gave Birth to Human Society (Cambridge, MA: Harvard University Press.

Chapais, Bernard. 2011a. "Understanding Dimorphism as a Function of Changes in Male and Female Traits," Evolutionary Anthropology 20: 143-55.

Chapais, Bernard. 2011b. "The Deep Social Structure of Humankind." Science 331: 1276-1277.

Chapais, Bernard 2012. "Sexual Size Dimorphism, Canine Dimorphism, and Male-Male Competition in Primates: Where Do Humans Fit In?" Human Nature 23: 45-67.

Fisher, Helen. 1992. Anatomy of Love: The Natural History of Monogamy, Adultery, and Divorce. New York: Norton.

Fisher, Helen. 2006. Why We Love: The Nature and Chemistry of Romantic Love. New York: Henry Holt.

Flannery, Kent, and Marcus, Joyce. 2012. The Creation of Inequality: How Our Prehistoric Ancestors Set the Stage for Monarchy, Slavery, and Empire (Cambridge, MA: Harvard University Press).

Frayling, Christopher, and Wokler, Robert. 1982. "From the Orangutan to the Vampire: Towards an Anthropology of Rousseau," in R. A. Leigh, ed., Rousseau After 200 Years (Cambridge: Cambridge University Press), 109-29.

Gordon, A. D., Green, D. J., and Richmond, B. G. 2008. "Strong Postcranial Size Dimorphism in Australopithecus afarensis: Results from Two New Resampling Methods for Multivariate Data Sets with Missing Data." American Journal of Physical Anthropology 135: 311-28.

Lockwood, C. A., Richmond, B. G., Jungers, W. L., and Kimbel, W. H. 1996. "Randomization Procedures and Sexual Dimorphism in Australopithecus afarensis." Journal of Human Evolution 31: 537-48.

Lovejoy, C. O. 1981. "The Origin of Man." Science 211: 341-50.

Plavcan, J. Michael. 2011. "Understanding Dimorphism as a Function of Changes in Male and Female Traits." Evolutionary Anthropology 20: 143-55.

Plavcan, J. Michael. 2012. "Sexual Size Dimorphism, Canine Dimorphism, and Male-Male Competition in Primates: Where Do Humans Fit In?" Human Nature 23: 45-67.

Plavcan, J. Michael, Lockwood, C. A., Kimbel, W. H., Lague, M. R., and Harmon, E. H. 2005. "Sexual Dimorphism in Australopithecus afarensis Revisited: How Strong is the Case for a Human-Like Pattern of Dimorphism?" Journal of Human Evolution 48: 313-20.

Reno, P. L., Meindl, R. S., McCollum, M. A., and Lovejoy, C. O. 2003. "Sexual Dimorphism in Australopithecus afarensis Was Similar to that of Modern Humans." Proceedings of the National Academy of Sciences USA, 100: 9404-9409.

Reno, P. L., McCollum, M. A., Meindl, R. S., and Lovejoy, C. O. 2010. "An Enlarged Postcranial Sample Confirms Australopithecus afarensis Dimorphism Was Similar to Modern Humans." Philosophical Transactions of the Royal Society B. 365: 3355-3363.

van Schaik, Carel P, and Kappeler, Peter M. 2003. "The Evolution of Social Monogamy in Primates." In Ulrich H. Reichard and Christophe Boesch, eds., Monogamy: Mating Strategies and Partnerships in Birds, Humans, and Other Mammals, 59-80. Cambridge: Cambridge University Press.

Wokler, Robert. 1976. "Tyson and Buffon on the Orangutan."  Studies on Voltaire and the Eighteenth Century 155: 2301-2319.

Wokler, Robert. 1978. "Perfectible Apes in Decadent Cultures: Rousseau's Anthropology Revisited." Daedalus 107: 111-17.

Some of these points have been developed in other posts here, here, here, here, and here.


byff said...

Excellent read. It helps round out some of my arguments regarding human nature, particularly with respect to the paleoanthropological origins of marriage.

Anonymous said...


You seem to attract a readership (just based off blog comments) with a strong, perhaps even radical, libertarian bent. Philosophically, in fact, many of these readers appear much more at home with Ayn Rand than your touchstone, Aristotle.

I know you've written on why "Conservatism" is the most appropriate way to describe your take on Darwin, but do you think your readers intuit your arguments through this lens?

Larry Arnhart said...

I understand Darwinian conservatism as a fusion of traditionalist conservatism and classical liberalism. So my conservatism is a very liberal conservatism. I have also written some posts on "Aristotelian liberalism"--like that defended by Douglas Rasmussen and Douglas Den Uyl. I have no way of knowing how many of my readers agree with this.