Evolution of the Cannibalism Taboo 1

RUNNING HEAD: Evolution of the Cannibalism Taboo

Evolution of the Cannibalism Taboo

Steven J. Scher, Chris M. White, & Matthew Vlasak

Eastern IllinoisUniversity

KEYWORDS: Cannibalism, Evolutionary Psychology, Disgust

Abstract

Four hypotheses about the evolution of the cannibalism taboo in humans are tested. Each makes different predictions about the functional design of the taboo. The inclusive fitness hypothesis proposes that cannibalism is taboo because of the risk of eating genetic relatives. The mate pool hypothesis proposes that the taboo evolved because of the risk of eating potential mates. The predation avoidance hypothesis proposes that cannibalism is taboo because of the risk that one will become the prey of the other human he or she is trying to cannibalize. Finally, the disease avoidance hypothesis proposes that cannibalism is taboo because it presents a greater risk of disease than the consumption of other foods. This latter hypothesis was supported: Participants found it more disgusting to eat someone who died from a disease, more disgusting to eat unattractive people, and more disgusting to eat relatives. Discussion includes comparison of the cannibalism taboo to taboos about incest and other types of sexual behavior, as well as discussion of the relationship between cannibalism and the general evolution of disgust.
Evolution of the Cannibalism Taboo

Hannibal Lecter.The Donner Party.Jeffrey Dahmer…Whether real or fictional, cannibals hold a fascination for humans.Despite this fascination, the cannibalism taboo appears to be one of the most widespread of taboos.The mere mention of cannibalism arouses feelings of disgust, even repulsion, in most people.In the current paper, we apply the logic of evolutionary psychology to try and identify the factors that led to this taboo.

There is no inherently obvious reason why we should have evolved so strong an impediment to eating our own species.Humans regularly eat the flesh of other mammals, and human flesh would provide a nutritional benefit roughly equivalent to these other types of meat.Moreover, by eating a member of one’s own species, a cannibal gains the additional benefit of eliminating a potential competitor for resources within their niche (Fox, 1975; Pfennig, 1997).

Cannibalism in Non-Human Animals

There have,in fact, been reports of cannibalism among as many as 1300 animal species (Polis, 1981), including 75 species of mammals (Polis, Myers, & Hess, 1984).The examples of cannibalism come from a taxonomically broad distribution of species, including protozoa, mollusks, insects, and primates (Fox, 1975; Polis, 1981; the volume by Elgar and Crespi, 1992a collects a series of reviews on cannibalism across a variety of taxa).On the other hand, cannibalism is rare in most species.This suggests that some evolutionary disadvantage also exists, which likely led to selection against cannibalism.

Cannibalism in Humans

There are many reported cases of cannibalism among humans (see Askenasy, 1994; Petrinovich, 2000; Sanday, 1986).Most of the non-disputed cases of cannibalism involve survival cannibalism – cannibalism practiced under conditions of extreme hunger.The most famous casesare the Donner Party, who were trapped in the mountains of the Sierra Nevada in California in 1846 (cf., Hardesty, 1997; Johnson, 1996; Rarick, 2008[EIU1]), and the case of the Uruguayan soccer team that was stranded after a plane crash in the Andes mountains – a case captured in the popular book (and later movie) Alive (Read, 1974; see also Lopez, 1973).

These, however, are behaviors occurring in unusual circumstances where immediate survival needs would be expected to outweigh any adaptive disadvantages of cannibalism (cf., Petrinovich, 2000). The available evidence does not support the notion that any human society engaged in regular consumption of human flesh for nutritional benefit.Rather, cannibalism among humans has mainly taken the form of symbolic, ritual practices.

While it is conceivable that the symbolic meanings of cannibalism are psychological/cultural mechanisms that motivate members of cultures to eat additional proteins, it is extremely rare for individuals or cultures to include human flesh as a regular, ordinary part of the diet, outside of the symbolic or ritual context; moreover, the ritual practice of cannibalism does not seem to covary with the availability of other protein sources (Conklin, 2001; Sanday, 1986; although, see Dornstreich & Morren, 1974).

On the other hand, there is evidence that cannibalism was a regular ritual practice throughout time and around the world.Numerous archeological (e.g., Degusta, 1999;Turner & Turner, 1999; White, 1992) and ethnographic (e.g., Conklin, 2001; Poole, 1983; Whitehead, 2000) studies present evidence of human cannibalism.Sanday (1986) found enough information to determine whether or not cannibalism existed in 109 societies ranging from Babylonia (circa 1750 B.C.E.) to societies as recently as the 1960s. Cannibalism appeared to have been practiced in 37 (33.9%) of these societies.

Cannibalism practiced as a regular cultural practice can be classified into at least three categories (Salmon, 1995): medicinal cannibalism, where the consumption of human flesh is viewed as a way to cure or ward off disease; mortuary cannibalism, which involves the consumption of humans as part of the funerary ritual after their death; and sacrificial cannibalism, consumption for the appeasement of the gods or for revenge against one’s enemies.

This incorporation of cannibalism into the cultural rituals of a society raises questions about the taboo nature of cannibalism.If cannibalism is a universal human taboo, it would seem surprising to find societies where the eating of human flesh was a regular cultural practice.

Even in cultures where cannibalism is socially sanctioned in some circumstances, however, it is unpleasant and perhaps even avoided.For example, Barth (1975, cited by Whitehead, 2000, p. 82) reported that children of the Baktaman society of Papua New Guinea “often to their surprise and disappointment vomit when they first try eating it [human flesh], and even some of the greatest warriors among the Baktaman admit somewhat shamefacedly that they are still unable to eat it, or more non-commitally, do not like it.”Similarly, Poole (1983), who witnessed some examples of mortuary

cannibalism among the Biman-Kuskusmin (also of New Guinea), wrote that “manyBimin-Kuskusmin men and women whom I interviewed and who admitted to socially proper cannibalistic practices acknowledged considerable ambivalence, horror, and disgust at their own acts.Many persons noted that they had been unable to engage in the act, had not completed it, had vomited or even fainted, or had hidden the prescribed morsel and lied about consuming it” (p. 9n).Likewise, Conklin (2001), who lived among the Wari’ of Brazil in a time after they had ceased practicing (mortuary) cannibalism,

wrote that her older informants reported that “eating the dead was quite unpleasant” (p. 94).

These accounts suggest that where cannibalism has developed as a cultural practice, the cultural norms are enforcing a behavior which is counter to the preferences or natural tendencies of the members of the culture.This is consistent with our assumption that the disgust we feel regarding cannibalism is a manifestation of an evolved taboo.Any full account of the evolution of this taboo will eventually have to confront the question of how these cultural systems developed in interaction with other evolved tendencies.However, such a model goes far beyond the scope of the present paper.

Disgust and the Cannibalism Taboo

Our review of the literature on cannibalism suggests that cannibalism has and does occur among humans and other species.Moreover, there appear to be at least some evolutionary benefits that could be gained from the practice.Nevertheless, the behavior is rare in all species.

The taboo among humans seems to be enforced by an emotional mechanism which makes the concept of eating human flesh disgusting or unpleasant.Rozin, Haidt, and their colleagues have designated the emotion originating in the actual or imagined oralincorporation of a contaminated object core disgust (see Rozin, Haidt, & McCauley, 2008[EIU2] for a recent review). They point out that the physiological and expressive components of disgust all revolve around actions related to expelling the contaminant (e.g., nausea, facial gape) or avoiding ingestion in the first place (e.g., wrinkling of the

nose).

Disgust seems to have generalized from the oral/food domain into areas apparently far removed from the mouth.Rozin et al. (2008; Haidt et al., 1997) suggest that disgust evolves further, into a reaction to anything which reminds humans of our animal nature, and therefore reminds us of our eventual death (elicited by reminders of the functions we share with non-human animals such as eating, excretion, and sex; see also Goldenberg et al., 1999, 2001). Disgust further generalizes to interpersonal disgust (elicited by contact with undesirable others) and to moral disgust (elicited by violation of normative codes of behavior).

The act of cannibalism has the potential to span all four of these disgust domains: It involves the consumption of an unpleasant food substance, it involves behavior associated with death, it involves contact with other people (potentially undesirable others – although see Conklin, 2001), and it frequently involves violation of moral restrictions. An exploration, therefore, of the evolution of the disgust elicited by the idea of cannibalism seems to provide an opportunity to study a uniquely complex disgust elicitor.

Four Hypotheses for the Evolution of the Cannibalism Taboo

We began this research with several hypotheses about the origin of the cannibalism taboo. Therefore, we developed several different models of how the modern psychology of the taboo should be designed. The studies that follow test these predictions in an attempt to identify what pressure or pressures led to preferential selection for such a strong taboo against cannibalism. As the first research on the evolutionary psychology of the cannibalism taboo, we have no preconceived prejudices about which pressures actually drove the evolution of the taboo; we expect some of our hypotheses to be wrong, and some to be right, thus eliminating some hypothesized evolutionary histories, and supporting others.

Hypothesis One: Predation Avoidance.Under the first hypothesis, cannibalism is infrequentbecause attempts to kill and consume a member of one’s own species present a greater risk to an organism than attacking members of species that are smaller, weaker, slower, or have less effective protective mechanisms (Dawkins 1989 [1976]; Holmes, 1977; Jackson, 1979; Polis, 1981). If fear of becoming prey – rather than preying on a conspecific – was the adaptive disadvantage that led to the cannibalism taboo, two predictions follow about the design of the taboo. Firstly, it should be most disgusting to cannibalize those who have to be hunted to be eaten (Prediction 1a). Individuals who died from other causes (e.g., illness or accident) die without intervention from a potential cannibal, and therefore do not pose a predation risk. Secondly, since juveniles present less of a threat than adults, people should find it more disgusting to eat an adult who was hunted to be eaten than to eat a child who was hunted to be eaten (Prediction 1b). This is consistent with the fact that most cases of cannibalism in nonhuman species involve adults eating juveniles (Elgar & Crespi, 1992b; Polis, 1981).

Hypothesis Two: Disease Avoidance. Our second hypothesis proposes that the cannibalism taboo evolved as a means of protection against disease transmission. In general, disease transmission seems to be primarily a product of contact with other animals, and as a result, core disgust reactions are primarily related tocontact with animals and animal products (Rozin & Fallon, 1980).Moreover, disease avoidance processes seem to play an important part in the evolution of a number of human psychological processes, including mate perceptions (Gangested & Buss, 1993[EIU3]), prejudice (Schaller, Park, & Faulkner, 2003), and cultural variation (Fincher, Thornhill, Murray & Schaller, 2008[EIU4]).

Cannibalism is, among other things, a form of social interaction. And, as Kurzban and Leary (2001; see also Faulkner, Schaller, Park & Duncan, 2004; Park, Faulkner, & Schaller, 2003) have suggested, a variety of evidence suggests that although humans are a highly social species, we have a tendency to reject contact with those who show evidence that they may be contaminated with infectious parasites. Cannibalism should, in fact, provide an extreme case of this type of behavior, because the consumption of a conspecific provides an even greater risk of contagion than mere contact does.

Pathogens that have evolved to attack a specific host would be more dangerous to others of the same species, who share most of the physical/genetic makeup of the original host (Freedland, 1983).The consumption of conspecifics should therefore present an especially high risk of disease transmission. The greater the genetic similarity between the consumer and the consumed, the greater the risk of disease faced by the consumer. Pfennig, Ho, & Hoffman (1998) provide experimental evidence that tiger salamanders were at greater risk of disease from cannibalism than from consumption of other, related species.

Further support for the disease avoidance hypothesis comes from evidence that bovine spongiform encephalopathy (BSE), otherwise known as Mad Cow Disease, was spread among cattle in Britain because cattle were fed the ground remains of conspecifics who had already died from BSE (see Lindenbaum, 2001).The related human disease, Kuru, most likely spread among the Fore of New Guinea as a result of cannibalism(Mathews, Glasse, & Lindenbaum, 1968; cf., Lindenbaum 1979, 2001; Nelson, 1996. Goodfield, 1997, argues that Kuru came not from the consumption of infected victims, but from contact while preparing the corpses).

Based on the disease avoidance hypothesis, therefore, we predicted that people would find it more disgusting to eat those who died from an illness (especially a virus) than those who died by other means (e.g., hunted to be eaten or by accident) [Prediction 2a].

However, in the EEA we would not expect awareness of disease to be conscious. Rather, we would expect people to evolve mechanisms to avoid cannibalism (and other forms of social contact) with people who show manifest signs of disease. In particular, unattractiveness may be a sign of parasite infection (Fink & Penton-Voak, 2002[c5]; Gangestad & Buss, 1993; Thornhill & Gangestad, 2006). We can therefore predict that people will find it more disgusting to eat unattractive people, compared to attractive people (Prediction 2b).

Furthermore, while humans share a larger portion of their genetic material with other humans than they do with other animal species, the amount of overlap in genotype is not identical for all humans. Specifically, the more closely related we are to someone, the greater their genetic similarity. As mentioned, the greater the genetic similarity between the consumer and the consumed, the greater risk of disease. Therefore, we would expect the cannibalism avoidance mechanism to incorporate kin rejection in its design: people should find eating relatives more disgusting than eating non-relatives (Prediction 2c).

Hypothesis Three: Mate Pool Reduction.Paine (1965) and Fox (1975), addressing existing cases of cannibalism among non-human animals, both suggested that one cost associated with cannibalism is the elimination of potential mates. In the environment of evolutionary adaptedness (EEA), our ancestors generally lived in small, closely connected groups. Killing members of the group for cannibalism would almost certainly eliminate potential mates.

Under this hypothesis, people should be most disgusted by imagining eating someone who would be a desirable mate. Specifically, we reasoned that people would be most disgusted eating members of the opposite sex, especially if the target is more desirable (Prediciton 3a). We predicted that physically attractive opposite sex people should be more disgusting as cannibalistic food – especially for male participants, because males indicate that physical attractiveness is more important to them in mate selection (e.g., Buss, 1989) [Prediction 3b]. Females, on the other hand, seem to value status more in a mate (e.g., Buss, 1989); therefore, they should find it more disgusting to eat a high status male than to eat a low status male (Prediction 3c).

The prediction that people will be more disgusted eating physically attractive others is similar to a prediction we made regarding the disease avoidance hypothesis. However, note that the mate pool reduction hypothesis predicts that this preference for the physically attractive should be limited to opposite sex others. Physical attractiveness is a marker of disease for both males and females, and therefore its affect on cannibalism should not differ by sex under the disease avoidance hypothesis.

We also predicted that people would be more disgusted eating an opposite sex target if that target was hunted to be eaten, compared to if that target had died accidentally. Individuals who die accidentally are removed from the mate pool in any event. It is only when someone is deliberately killed to be eaten that they represent an additional reduction in potential mates (Prediction 3d).

Hypothesis Four: Inclusive Fitness.Another potential cost to cannibalism grows out of threats to inclusive fitness: Eating members of one’s own species presents the risk of eating a genetic relative (Fox, 1975).This hypothesis is supported by the fact that many non-human cannibals avoid the consumption of close kin (Pfennig, 1997).

Accounts of human cannibalism also provide examples of the avoidance of genetic kin.Many cases of cannibalism involve exocannibalism – the consumption of individuals captured from outside one’s own community.This presents little risk of eating one’s relatives.However, even in cases of endocannibalism, there are examples of kin avoidance.For example, the Wari’ of the Amazon practiced mortuary cannibalism. This form of cannibalism was meant to be an expression of compassion for the close relatives who had died.However, the actual consumption of the dead was completed not by the blood relatives of the deceased, but by the affinal relatives (i.e., relatives by marriage; Conklin, 2001).

We therefore predicted that people would find it more disgusting to eat a relative than to eat a friend of the family. This prediction should be especially true for victims who were hunted to be eaten, because those who died by other means (e.g., accidentally) are already dead, and the cannibalism does not add to the decrease in inclusive fitness (Prediction 4a).

We also predicted that it would be more disgusting to eat a relative who was of reproductive age, compared to an older target who was beyond reproductive potential. The consumption of older relatives does not lower inclusive fitness substantially, since their reproductive years are over. On the other hand, the reproductive potential of friends, and therefore the age of friends, should not make a difference in the disgust level of cannibalism with friends (Prediction 4b).