Primate Privacy

Thomas Hales (Pittsburgh)

Governments and Silicon Valley are becoming brazen in their denial of privacy. Vint Cerf, a father of the internet and Google’s chief internet evangelist, has gone so far as to claim that privacy was a temporary by-product of the industrial revolution and urban growth [11]. If privacy is a recent accident, mere fumes from an industrial smokestack, then we might conclude that its loss means naught.

Science supports a grander view of privacy, giving it an integral place in our evolutionary history, extending throughout the animal kingdom, and culminating in the unique capabilities of our species and other great apes.

My exposure to animal behavior came through my ex-wife Kerri, a University of Chicago trained primatologist. For years, she told me stories of the regular agonisms of the baboons of Brookfield Zoo and Amboseli, Kenya. Listening to her stories did not turn me into an expert, yet they attuned me to a divide separating primatology research from Silicon Valley fictions.

What I write might be obvious to ethologists and attentive animal lovers. But to my dismay, privacy debates are often formulated abstractly, without reference to biology. I see this as a fatal mistake. A notable exception is Westin’s classic work, which connects the animal’s defense of home territory with human privacy, viewed as a protected domestic space [18]. Scholarly works typically trace the concept of privacy only as far back as Aristotle. This truncated perspective disregards anthropological evidence — perhaps after a quick nod to Mead’s Coming of Age in Samoa — and neglects millions of years of evolutionary history [13]. Long before Aristotle and pointing to a distant past, our early epic literature described widespread practices of secrecy, disguises, and anonymity in the pursuit of autonomy.

A definition of privacy

Setting aside moral, legal, and political theories, let us turn to privacy as a biological capacity, especially among primates, and even more especially among great apes.

Following Moglen, privacy can be defined to have three components: (1) secrecy – our ability to selectively hide the content of messages; (2) anonymity – our ability to selectively hide the identity of the sender and receiver of messages; and (3) autonomy — our freedom to advance plans without coercion that might result from the violation of our secrecy and anonymity [16]. We extend Moglen’s definition to other species.

In this definition, messages are broadly construed in the sense of information theory: “A message need not be the result of a conscious human effort for the transmission of ideas. For example, the records of current and voltage kept on the instruments of an automatic substation are as truly messages as a telephone conversation” [20].

Secrecy and anonymity are abilities to act, rather than the actual performance of the act. The hiding must be selective in the sense that an organism may switch it on or off. So by this definition, genetically invariable camouflage in a species does not qualify as privacy. However, the hiding need not be intentional, permitting examples like the Kallima butterfly, which is richly colored when in flight but which hides itself by imitating a dead leaf when at rest with its wings folded [7,p.47].

As we will see, the practice of secrecy is well documented in primates, especially chimpanzees, including hiding or feigning injury, the masking of emotions, concealing sexual interest and arousal, furtive mating, misdirecting attention, and concealing objects behind the back, in the mouth, or between the fingers. Primate communities can be hierarchical with tremendous advantages for those that dominate, and far fewer freedoms for subordinates. We will give numerous examples of secrecy as an enabler of autonomy among subordinates.

Biological precedents of anonymity can be found in camouflage and mimicry, and in the safety of the herd. In interspecific mimicry, the kingsnake mimics the coral snake and the swallowtail butterfly mimics other butterflies. Although various forms of mimicry are prevalent in the animal kingdom, I find that anonymity is the part of the definition of privacy that extends least readily to primates. I will leave it to others to develop the appropriate concept. In this post, privacy will be defined narrowly as a combination of secrecy and autonomy.

Evolutionary sociobiology

The next several paragraphs explain my assumptions and perspective. The impatient reader may jump ahead to the examples of primate privacy. This post adopts the perspective of evolutionary sociobiology as described by biologists such as E. O. Wilson and Goldsmith [8], [21], [22].

Evolution can produce what is called behavioral scaling, which is a flexible behavioral capacity. This fits nicely with privacy as a behavioral capacity. In this view, behavior is not a deterministic response to a simple identifiable stimulus in a fixed action pattern. Rather, behavioral flexibly depends on a large number of deterministic and random input variables from the environment.

The idea that evolution has produced behavioral capacities that can accommodate themselves to a range of environmental contingencies is commonly accepted by contemporary ethologists. — Goldsmith [8,p.110]

Goldsmith goes on to call the behavioral flexibility of the vertebrate brain “the complete antithesis of genetic determinism” [8,p.123]. Yet, this antithesis of determinism is not an absolute freedom. “For a biologist the idea of infinite cultural flexibility is unacceptable” [4,p.259]. The behavioral scaling itself (that is, the contingent range of possible outputs) is determined by our evolutionary history and cannot be renegotiated by culture. Herein lies human nature.

Evolutionary continuity between humans and great apes

A basic assumption is our evolutionary continuity with great apes.

We live in a time of increasing acceptance of our kinship with the apes. True, humanity never runs out of claims of what sets us apart, but it is a rare uniqueness claim that holds up for over a decade. If we consider our species without letting ourselves be blinded by the technological advances of the last few millennia, we see a creature of flesh and blood with a brain that, albeit three times larger than a chimpanzee’s, doesn’t contain any new parts. Even our vaunted prefrontal cortex turns out to be of rather typical size compared with that of other primates. No one doubts the superiority of our intellect, but we have no basic wants or needs that are not also present in our close relatives. Just like us, monkeys and apes strive for power, enjoy sex, want security and affection, kill over territory, and value trust and cooperation. Yes, we have computers and airplanes, but our psychological makeup remains that of a social primate. — de Waal [6,p.16]

We share with other great apes a long evolutionary history; a large fraction of our DNA; brain structure; sense organs; and a range of emotions including happiness, sadness, anger, and fear that are all evoked in similar contexts. Staying on guard against false anthropomorphisms, many researchers nonetheless accept a principle of evolutionary continuity. When, for example, a chimpanzee responds in the same way that a human responds in a given context, we may infer a probable underlying agreement of cognitive processes. I recommend Tomasello’s recent book for a particularly careful comparative analysis of how human thinking agrees and differs from that of other great apes [17].

Deception unravelled

There is one other potential misconception to clear up before turning to the biological evidence of privacy.

Research on animal secrecy is generally classified as a subfield of research on Machiavellian intelligence and deception. I was surprised to find so much privacy research buried here. By this classification, it might seem that biologists condemn the practice of secrecy. But in fact, no moral judgment is intended by this classification, and the terms deception and Machiavellian intelligence must be read in a scientifically neutral way. In the evolutionary literature, Machiavellian intelligence is used counterintuitively in a broad technical sense for many forms of social intelligence, even those encompassing cooperative behavior [19,p.12].

From an evolutionary, comparative perspective, ‘Machiavellian’ intelligence is an expression used instead for contrast with simpler social repertoires widespread in the animal kingdom (as well as with non-social uses of intelligence). It is the complex, indirect nature of the strategies we wish to highlight, and this usage seems to have become commonplace in our discipline. — Byrne and Whiten [19,p.13]

Mitchell, editor of the book Deception, describes the use of the word “deceit” as an umbrella term “to include both deception and hiding,” notably even when hiding involves no deception [14]. Deception may get higher billing than secrecy in the academic literature, but following our interest in privacy, we extract the secrecy research and set deception aside.

This post makes no judgments about the morality of the practice of privacy among humans or other primates. We do not touch theories of the evolutionary basis of human morality. However, I recommend Greene’s Moral Tribes [10].

Also, by making privacy the exclusive focus of this post, we in no way deny the broader context of primate behavior. We and our primate cousins can be both selfish and altruistic, both solitary and social, and both competitive and cooperative. Privacy can be used to promote both selfish and altruistic goals (the sage who through seclusion finds wisdom to benefit humanity, or the mother who withholds developmentally harmful messages from her child). However, this is not our focus here.

Finally, I acknowledge the enormous variations that exist in the practice of privacy among different species, and within our own species, as anthropologists document. That is material for another essay. With all this background out of the way, let us turn to examples of privacy-related behaviors among primates.

Sexual privacy among primates

Secret sexual liaisons are not solely a human invention. De Waal describes secret matings between low-ranking male chimpanzees and females in oestrus.

For a long time we thought that sexual preferences of oestrus females for particular males could be inferred from the frequency with which they followed, groomed or presented to males. The limited value of such measurements were discovered by watching the colony enter the night cages. Oestrus females who had not paid any attention, not even by means of looking up, to a male who had repeatedly made sexual advances during the daytime, would sometimes rush up to the same male’s cage to quickly mate through the bars. After observing many of these sequences, it became clear that these hurried matings only occurred with low-ranking males in the absence of high-ranking ones. The observations implied that females are capable of fully concealing sexual interests, presumably in order to forestall aggressive interference by dominant males. For the same reason, females learn to suppress screams during the climax of copulation. They may still utter a high-pitched scream during a “public” mating with the alpha male, but by the end of adolescence females do not scream anymore during furtive matings with subordinate males. — De Waal [15,p.229]

A male chimpanzee, named Dandy, was not allowed by the alpha male to mate with adult females. Nevertheless, Dandy successfully mated with females by making dates with them on the sly, arranged through surreptitious glances. He and his partner would independently walk away from the group, as if unaware of the other, then meet in rendezvous behind tree trunks [2,p.124].

Male chimpanzees sometimes make sexual advances to females by displaying their erections. At the same time, they try to hide their erections from dominant males, “who watch over the sexual contacts of other males.” The chimpanzee penis is a “bright pink color, which strongly contrasts with the dark fur.” It is not easily hidden. A male chimpanzee will sometimes try to expose his erection to a female while simultaneously hiding it from a nearby dominant male by positioning his body and arms in the right way. When a dominant male approaches, a subordinate might turn his back until his erection is lost [15,p.233].

Secretive mating also occurs among rhesus monkeys and among baboons. Observations at the Wisconsin Primate Center indicate that the alpha rhesus monkey, Spickles, “does all the ‘public’ mating. He copulates in full view of everybody, uttering a series of loud barks at the climax.” By contrast, the number two male does all his mating on the sly, out of view of Spickles [4,p.131]. With baboons, “the alpha male accounts for the vast majority of matings, particularly those that occur around the time of ovulation.” Yet, there is “also often a considerable amount of `sneaky’ mating” that gives non-alpha males some reproductive success [3,p.56], [1].

Concealing injury and fear

Primates have a general tendency to hide injuries, especially from aggressors. A chimp Amos had an enlarged liver and several cancerous growths that he kept a secret until the end.

Amos must have felt miserable for months, but any sign of vulnerability would have meant loss of status. Chimps seem to realize this. A limping male in the wild was seen to isolate himself for weeks to nurse his injuries, yet would show up now and then in the midst of the community to give a charging display full of vigor and strength, after which he’d withdraw again. That way, no one would get any ideas. Amos didn’t betray his condition until the day before his death. — De Waal [6,p.26]

Selectivity is part of our definition of privacy In fact, primates are selective in hiding injuries. After describing the gentle care that a female named Daisy gave to Amos the day before his death, De Waal comments,

The incident illustrated two contrasting sides of primate social life. First, primates live in a cut-throat world, which forces a male to conceal physical impairment for as long as possible in order to keep up a tough facade. But second, they are part of a tight community, in which they can count on affection and assistance from others, including nonrelatives. Such dualities are hard to grasp. Popular writers tend to simplify things. — De Waal [6,p.27]

For chimpanzees, teeth-baring grins and yelping sounds are signs of fear and nervousness. Males attempt to avoid revealing these signs to opponents during bluff displays. They may largely suppress their yelps. However, they lack the facial motor control to suppress their teeth-baring directly. Instead they resort to other means such as turning their back to hide signs of fear. De Waal writes of one male who turned his back to hide the grin that betrayed his fear, then used his fingers to force his lips back in place. “The manipulation occurred three times before the grin ceased to appear. After that, the male turned around to bluff back at his rival” [15,p.233].

Hiding resources

We extend our discussion for a moment beyond primates. Food caching is practiced by many species. For example, crows and ravens hide food, but they do so selectively. They have the intelligence to distinguish between their social partners and potential thieves. Ravens adopt intricate strategies to mislead pilferers. They create false stashes, going through the motions of creating a stash, but without depositing the goods. Or they shuttle the goods from one cache to another, to further confuse competitors [12,pp.45,227,230].

We now return to chimpanzees. They selectively hide food resources. We have already met Dandy when we discussed his secret dates. Here he is again.

Not drawing attention to oneself or not paying attention to another are everyday tactics of the chimpanzee. These tactics are performed with… great sophistication…. A young male, Dandy, was seen walking over a place where some grapefruits had been hidden under the sand. Since he did not react at all, not even by stopping or looking around, we assumed that he had not noticed anything. More than three hours later, however, when most other chimpanzees (including the dominant males) were asleep, Dandy made a bee-line to the spot, where he calmly and without hesitation dug up and devoured the grapefruits. The size of the enclosure, and his controlled deliberate manners, exclude the possibility of his accidentally finding the fruits. — De Waal [15,p.228]

De Waal tells the following story about an adolescent female chimp, named Zwart, who saw someone throw an apple into her enclosure at the zoo. Rather than attract the attention of other chimps by rushing to pick it up, she kept her composure, and casually approached it, after only briefly glancing at it. She sat near the apple and inconspicuously groped for it without looking. After taking hold of the apple, she walked off using a stride that is generally not used when food is grasped. (“Chimpanzees usually walk on two or three extremities when carrying food.”) Safely out of sight behind a pile of tires, she finally ate the apple [15,p.228].

These examples show that some chimpanzees go to great lengths to hide food. On the other hand, sharing can be a way for chimpanzees to boost their influence within the group. Males can be “surprisingly generous [except with rivals] when it comes to material things” [5,p.204]. They even cooperate with a special scream that signals to others the capture of fresh meat [6,p.226].

Kanzi is a pygmy chimpanzee at the Language Research Center, who regularly hides objects. The purpose of the secrets often seems to be to increase autonomy from his human caretaker. Once, suspecting foul play, Kanzi’s caretaker made a thorough search of the enclosure, but found nothing. Kanzi even (deceptively) joined in search. The suspicions were confirmed when the caretaker looked away, and Kanzi quickly produced a door key “from nowhere” and escaped the enclosure [2,p.226].

Kanzi loves to eat wild mushrooms, but his caretakers do not allow it. He “has devised many ways to hide them. Often he will secretively conceal them between his thumb and forefinger as he walks, never breaking stride.” When his human companion looks away, “Kanzi will quickly pop the mushroom into his mouth…. The only tell-tale sign is the distinct mushroom odour which lingers upon his breath” [2,p.231].

Chimps sometimes conceal rocks that are hurled as weapons. During charging displays, a chimpanzee Nikkie “almost always carries a weapon in his hand, often holding it behind his back” [15,p.235]. Santino is a “male chimp at a Swedish zoo. Every morning, before the visitors arrived, he’d leisurely collect rocks from the moat around his enclosure, stacking them up into neat piles hidden from view. This way he’d have an arsenal of weapons when the zoo opened its gates” [6,p.205].

The safety of silence

Chimpanzee mothers are known to silence their children by holding a finger or hand over their mouths in situations where noise might provoke the aggression of a nearby adult male chimpanzee.

Most of the examples I have quoted are concerned with privacy of an individual within a community. Privacy also matters between different groups. Goodall describes how male chimpanzees form border patrols to safeguard their territory from intruders from different groups. When on patrol, they maintain silence to conceal their presence, but when they return to the safety of home base, they may let loose with hoots and drumming [15,p.234], [9].

Challenges to autonomy

The pursuit of autonomy can be a desperate undertaking in a hierarchical community. Here are some examples of dominant animals forcibly searching subordinates for contraband.

When a low-ranking female baboon discovers a clutch of bird eggs, she looks furtively around her and then stuffs as many eggs into her mouth as fast as she can. If she is detected she runs away, averting her face from any onlookers. If another baboon catches up to her, she resolutely keeps her mouth firmly closed, even when the other attempts to pry it open. But if a high-ranking female stumbles onto a similar trove, she calmly and deliberately eats the eggs in plain view of others. The inescapable impression is that the low-ranking female is trying to conceal her discovery from others in order to avoid theft. For high-ranking animals, such subterfuge is unnecessary. — Cheney and Seyfarth [3,p.153]

In a related example, De Waal shows a picture of a dominant rhesus monkey inspecting the cheek pouches of a juvenile for hidden food [4,p.128].

Summary and Conclusions

These examples suggest that privacy can be exercised by low-ranking primates to avoid direct conflict with dominant group members. Privacy allows individuals to pursue autonomous activities within a community. Selectively withholding and revealing secrets allows the individual to adjust to the complex, changing dynamics of the group.

Private matings break the near monopoly of the alpha male over access to oestrus females, without upsetting the social hierarchy. Food is sometimes shared, and sometimes consumed alone. Injuries are generally kept hidden when possible, but sometimes revealed when it seems safe to do so.

We form general categories of privacy-seeking behavior among primates: in sexual relations, in protecting valuable resources, and in hiding injury from others. De Waal reminds us, we too “are a hierarchical primate,” and it is hard not to draw the obvious parallels with humans that seek privacy in their sexual relations, resources, and medical histories. It is striking that we seek privacy in domains closely tied to reproduction, access to resources and survival — which are all basic to evolution.

I do not expect this post to be the final word. Anecdotal evidence is merely an early step in systematic data collection and analysis of scientific evidence. Many of my examples come from animals in confined spaces that are quite different from their natural habitats. More evidence is needed to determine whether the examples I give are representative of the various species I mention. Nevertheless, these anecdotes suggest that privacy seeking is an enduring part of primate behavior.


I thank Kerri Smith for her comments and acknowledge the significant influence of De Waal’s writings on this post.


[1] Jeanne Altmann, Susan C Alberts, Susan A Haines, Jean Dubach, Philip Muruthi, Trevor Coote, Eli Geffen, David J Cheesman, Raphael S Mututua, Serah N Saiyalel, et al. Behavior predicts genes structure in a wild primate group. Proceedings of the National Academy of Sciences, 93(12):5797–5801, 1996.

[2] Richard Byrne and Andrew Whiten, editors. Machiavellian intelligence: social expertise and the evolution of intellect in monkeys, apes, and humans. Oxford University Press, 1989.

[3] Dorothy L Cheney and Robert M Seyfarth. Baboon metaphysics: the evolution of a social mind. University of Chicago Press, 2008.

[4] Frans De Waal. Peacemaking among primates. Harvard University Press, 1990.

[5] Frans De Waal. Chimpanzee politics: Power and sex among apes. JHU Press, 2007.

[6] Frans De Waal. The bonobo and the atheist: In search of humanism among the primates. WW Norton & Company, 2013.

[7] Peter Forbes. Dazzled and deceived: mimicry and camouflage. Yale University Press, 2011.

[8] Timothy H Goldsmith. The biological roots of human nature. Oxford University Press, 1994.

[9] Jane Goodall, Adriano Bandora, Emilie Bergmann, Curt Busse, Hilali Matama, Esilom Mpongo, Ann Pierce, David Riss, et al. Intercommunity interactions in the chimpanzee population of the Gombe National Park. The great apes, 5:13–53, 1979.

[10] Joshua Greene. Moral tribes: emotion, reason and the gap between us and them. Atlantic Books Ltd, 2014.

[11] Jacob Kastrenakes. Google’s chief internet evangelist says ’privacy may actually be an anomaly’, November 20, 2013.

[12] John M Marzluff, Tony Angell, and Paul R Ehrlich. In the company of crows and ravens. Yale University Press, 2007.

[13] Margaret Mead. Coming of age in Samoa. Penguin, 1973.

[14] Robert W Mitchell. Deception and hiding in captive lowland gorillas (gorilla gorilla gorilla). Primates, 32(4):523–527, 1991.

[15] Robert W Mitchell and Nicholas S Thompson, editors. Deception: Perspectives on human and nonhuman deceit. SUNY Press, 1986.

[16] Eben Moglen. Oh, freedom, Oct 30, 2013.

[17] Michael Tomasello. A natural history of human thinking. Harvard University Press, 2014.

[18] Alan F Westin. Privacy and freedom. Atheneum, 1967.

[19] Andrew Whiten and Richard W Byrne, editors. Machiavellian intelligence II: Extensions and evaluations, volume 2. Cambridge University Press, 1997.

[20] Norbert Wiener. Extrapolation, interpolation, and smoothing of stationary time series, volume 2. MIT press Cambridge, MA, 1949.

[21] Edward O Wilson. Sociobiology. Harvard University Press, 2000.

[22] Edward O Wilson. On human nature. Harvard University Press, 2012.


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