Cruelty’s Rewards: The Gratifications of Perpetrators and Spectators: V.Nell (preprint)

Keywords: compassion; cruelty; entertainment industry; evolutionary psychology; intraspecific killing; pain; predation; punishment; torture; violence prevention

Abstract: Cruelty is the deliberate infliction of physical or psychological pain on other living creatures, sometimes indifferently, but often with delight. Though cruelty is an overwhelming presence in the world, there is no neurobiological or psychological explanation for its ubiquity and reward value. This paper attempts to provide such explanations by describing three stages in the development of cruelty. Stage 1 is the development of the predatory adaptation from the Palaeozoic to the ethology of predation in canids, felids, and primates. Stage 2, through palaeontological and anthropological evidence, traces the emergence of the hunting adaptation in the Pliocene, its development in early hominids and its emotional loading in surviving forager societies. This adaptation provides an explanation for the powerful emotions—high arousal and strong affect—evoked by the pain-blood-death complex. Stage 3 is the emergence of cruelty about 1.5 million years ago as a hominid behavioural repertoire that promoted fitness through the maintenance of personal and social power. The resulting cultural elaborations of cruelty in war, in sacrificial rites, and as entertainment are examined to show the historical and cross-cultural stability of the uses of cruelty for punishment, amusement, and social control.

Effective violence prevention must begin with perpetrators, not victims. If the upstream approaches to violence prevention advocated by the public health model are to be effective, psychologists must be able to provide violence prevention workers with a fine-grained understanding of perpetrator gratifications. This is a distasteful task that will compel researchers to interact with torturers and abusers, and to acknowledge that their gratifications are rooted in a common human past. It is nonetheless an essential step in developing effective strategies for the primary prevention of violence.

1. Introduction

Cruelty (from the Latin crudelem, morally rough) is the deliberate infliction of physical or psychological pain on a living creature; its most repugnant and puzzling feature is the frequently evident delight of the perpetrators. Cruelty is an overwhelming presence in the world—in wars and massacres, in the routine work of police and military interrogators, in children’s play, in the dealings of men with women, and of adults with children. Though the ease with which situations can overwhelm values and elicit cruelty in hitherto irreproachable individuals is empirically (Haney, Banks, & Zimbardo, 1973; Milgram, 1974; Zimbardo, 2003) and observationally (Browning, 1993; Grossman, 1996; Tester, 1996) well-established, there is no motivational or neurobiological explanation for cruelty’s prevalence or fascination.

This paper argues that reinforcement value of pain and bloodshed derives from the predatory adaptation from the middle Cambrian to the Pleistocene. The argument is therefore

1. that cruelty is a behavioural by-product of predation;

2. that it is driven by reinforcers that derive from this adaptation;

3. that, since cruelty presupposes the intention to inflict pain, and is therefore exclusively a hominid behaviour, it dates to no earlier than H. erectus, about 1.5 million years ago (Ma);

4. that cruelty has fitness benefits in solving problems of survival and reproduction in forager, pastoral, and urban societies;

5. and that the enjoyment of cruelty is a culturally elaborated manifestation of the predatory adaptation.

These hypotheses generate a research agenda for affective neuroscience, for social psychology, and for violence prevention. They also provide a heuristic for understanding why media violence is attractive, why men find war beautiful, why homicide has been a fixed feature of human societies from prehistoric times to the present, and why, despite the human capacity for compassion, atrocities continue.

1.1 Three stages in the emergence of cruelty

Predation. The predatory adaptation derives from resource competition between and within species, which, in the Cambrian, becomes predation, the killing and consumption of one living creature by another. Predation is hard work: the evidence reviewed in Section 3 is that it is powerfully reinforced in mammalian carnivores and in the hunting apes by a set of linked conditioned stimuli that are carried over to the hunting adaptation in hominids. The stimuli driving predation and hunting are the pain-blood-death (PBD) complex—the prey’s terror and struggles to escape as it is brought down, the shedding of its blood, and its vocalisations as it is wounded and eaten, often while it is still alive. A range of anticipatory and consummatory reinforcers is triggered by the PBD complex, which is also active in intraspecific killing, and strikingly so in chimpanzees. The material in Section 3 on the neurobiology of predation suggests that predation is dopaminergic, affectively positive, and distinct from rage.

Hunting. Nutritional killing by hominids is also hard work: the palaeontological and anthropological evidence reviewed below suggests that hunting in hominids, as with predation in canids, felids, and primates, is reinforced by the PBD complex, and that the non-nutritional “other end” of hunting, for which anthropologists have sought, derives from these reinforcers.

Power. Cruelty requires a sufficient cognitive basis for intentionality, and a sufficient social basis for its disciplinary elaboration (Section 5). Once these foundations have been laid, there are florid social and cultural elaborations of cruelty as punishment, for amusement, and for social control. Each of these modalities affirms the power of the perpetrator–this may be an individual acting alone or as the agent of a collective–over the victim. In hierarchical states with centralised power, cruelty becomes a vehicle for public entertainments that buttress the power of the state and heroise war. The affective loading of these elaborations is described in order to identify parallels between blood as a principle reinforcer of predators and hunters on the one hand, and, on the other, of the audiences that delight in spectacles of pain and bloodshed.

In Stage 3, the use of cruelty is a strongly male gendered and contextually sensitive adaptation, which “could remain dormant for the entire life of an individual, if the relevant contexts are not encountered” (Buss, 1999, p. 284), promoting inclusive fitness by augmenting the personal power, survival, and sexual access of cruel individuals. Historically, the enjoyment of cruelty has been sufficiently powerful to have channelled huge social resources into cruel rites and spectacles, and remains a primary driver of the modern entertainment industry. The distinction between use and enjoyment has behavioural and neurobehavioral implications that may have animal parallels with quiet-biting predation on the one hand and aggressive rage on the other. However, as with all behavioural states, the boundaries between instrumentality and affectivity are permeable: for example, hunters may inflict pain on the prey beyond that which is instrumentally necessary, and the hunt may slip into surplus killing that continues beyond the satisfaction of nutritional needs (as with Actaeon in Ovid’s Metamorphoses, c. 8 AD/1997, p. 105). Violence is a significant by-product of cruelty (Section 6).

Evidence for the continued salience of the predatory adaptation for human behaviour is derived from palaeontology and taphonomy (Brain, 1981), predator ethology; primatology, with special reference to chimpanzee predation and intraspecific killing; cognitive evolution with special reference to language; the psychology of motivation and learning; the anthropology of provisioning; societal evolution; cultural history; and the psychology of individual differences.

The reinforcers of cruelty feed into violence, defined by the World Health Organisation as the intentional use of physical force or power against oneself, another individual or group that causes injury, death, or psychological harm (Krug, Dahlberg, Mercy, Zwi, & Lozano, 2002, p. 5): one of the paper’s purposes is to show cruelty’s relevance to the initiation and escalation of high-volume everyday violence such as drunken brawls, child beating, and sexual assault.

The study of cruelty, which is one of the manifestations of evil, is dangerous on three counts: first, because of the fear that evil is contagious, and that those who deal with it become tainted (as for example in The Problem of Evil in Coetzee, 2003); second, because to probe the psychology of perpetrators fails to condemn, casting a shadow over the researcher’s rectitude; and third, because rooting cruelty in the human evolutionary past appears to naturalise it, absolving perpetrators and their audiences of moral responsibility. The study of cruelty neither contaminates nor condones, and the purpose of this paper is compassionate and preventive. Cruelty will not be contained through obscurantism. Its reinforcers must be understood, and if these have evolutionary origins, effective prevention requires that they be revealed.

2. A Taxonomy of Cruelty

The preconditions for cruelty are a mental state, namely the intention to inflict pain, which in turn presupposes a theory of mind; and an action, which is the deliberate infliction of physical or psychological1 pain on another living creature, or on the self2.

Punishment is cruel if its purpose is not to vanquish or disable the victim, but to inflict pain; if the victim has no control over the intensity or duration of the pain; and if the victim is physically restrained or otherwise rendered helpless. Punishment may also be used for social control and discipline: here, the preconditions are that the reason for the punishment is communicated to the victim, that the punishment is derived from a penal code, is imposed by a higher authority, and is implemented by agents of that authority.

Affectivity. Cruelty’s affective state is ferocity (from the Latin ferox, fierce, now in the sense of savage violence). Cruel acts arouse strong positive or negative emotions in the perpetrator and the audience, though habituation and instrumentality may attenuate them. Whether or not the conditions for punishment are met, an act is cruel if the perpetrator or the audience experiences physiological or psychological arousal triggered by the victim’s pain. Entertainment is cruel if the audience is aroused by the intentional shedding of blood or infliction of pain; the infliction of pain for amusement is always cruel.

These definitions hold regardless of the perpetrator’s position on a continuum ranging from instrumental cruelty, marked by the perpetrator’s emotional coldness and distance from the victim, to expressive or affective cruelty, marked by the perpetrator’s escalating arousal.

Exclusions. These definitions of cruelty exclude pain that results from fighting, killing, and war3, in which the goal is not to inflict pain but to cause the adversary’s flight, submission, or death; and pain that is a by-product of treatment intended to cure or heal.

3. Stage 1: The Predatory Adaptation

3.1 Antecedents of predation

Predation’s precursor is competitive aggression, which confers fitness by solving an animal’s problems in relation to self-preservation, protection of the young, and resource competition (Archer, 1988, p. ix); this competition began 3 billion years ago with the first primordial cell, a benthic procaryote, which, “outreproducing its competitors, took the lead in the process of cell division and evolution” and made the world we know (Alberts, Bray, Lewis, Raff, Roberts, & Watson, 1989, p. 10). Organisms at a primitive level of neural organisation and without specialised effector organs are capable of aggression. Thus, intertidal molluscs such as limpets and chitons show spatial aggression by crawling over a rival conspecific and trying to dislodge it from its rock crevice by backward and forward movements; and the nematocysts of the solitary anemone, Actinia equina, are used for offence against conspecifics, with the loser detaching from the substrate (Archer, 1988, pp. 18-19).

The earliest evidence of predation in the fossil record is from the terminal Proterozoic, 600 Ma, from which Cloudina fossils with tiny rounded holes have been recovered, suggesting that the attacking organism was a predator, selecting its prey for size (Brain, 2001). With the middle Cambrian explosion of animal life, 540-523 Ma, the first effective predators emerged, with sense organs to locate prey, and the ability to pursue and overpower it. The largest and most fearsome of these was Anomalocaris, an active swimmer growing up to 50 cm with two large eyes; Opabinia, another Burgess Shale organism, “had five large eyes at the front of the head and a long flexible proboscis that ended in an array of grasping spines” (Brain, 2001, p. 23).

3.2 The Ethology of Predation

Predation is widespread in the animal kingdom. Salticids, the largest family of spiders, have elaborate, vision-mediated predatory behaviour that is prey-specific, with behavioural flexibility that includes conditional predatory strategies, trial-and-error to solve predatory problems, and detours to reach prey (Jackson & Pollard, 1996); there is similar flexibility in the predatory behaviour of Pacific white sharks (Klimley, 1994) and electric rays (Lowe, Bray, & Nelson, 1994).

The ethology of mammalian predation is now reviewed in relation to the arousal level, sensory feedback, and biochemical neurobiological drivers of the search-swoop-kill-feed cycle. Photographic evidence and the field observations reported below show that this cycle is accompanied by a range of auditory, visual, olfactory, tactile, gustatory and visceral stimuli which together make up the PBD complex.

Hyenas and lions

In his Serengeti notebook, Kruuk describes an adult male wildebeest turning to confront four spotted hyenas who have pursued it at speeds of 40-50 km/h over a 3 km distance:

The hyenas tried to bite him in the hindquarters, sides, and especially the testicles, while he in turn struggled to horn his attackers.... All four [hyenas] bit simultaneously at the loins, testicles, and anal region of the wildebeest, paying little attention to his horns. The mobility of the victim was much impaired by the four pursuers hanging onto his hindquarters. Another two minutes later the wildebeest had a large gash in the right loin, the testicles had been bitten off, and he stood as if in a state of shock. Occasionally he made some frantic movements and was able to struggle free from the hyenas, but then some member of the pack would renew the attack.... Eight minutes after the wildebeest had stopped running he went down and the hyenas stood over him pulling out his insides. Another two minutes later, the wildebeest died (Kruuk, 1972, p. 149).

Like wild dogs (Van Lawick, 1977, pp. 242-3, 246-7), hyenas “kill the victim by eating it” (Kruuk, 1972, p. 153), in that the animal may be struggling and vocalising as feeding begins, dying up to a quarter hour later. The belly and loins are torn open, the fetus eaten if the prey is pregnant, the testicles or udder eaten, the stomach pulled out, the stomach wall eaten and the contents spilled on the ground (Kruuk, 1972, p. 125). Mills’ descriptions (1990, p. 103 and Fig. 3.25) and photographs (Mills & Harvey, 2001, pp. 66-69) of spotted hyenas hunting and feeding in the Kalahari, and Van Lawick’s (1977, pp. 186-187) for the Serengeti, show virtually identical behaviour.

Lions kill by slow strangulation, biting the throat of their prey: death is rapid for small prey, but may take an hour for an adult wildebeest (Schaller, 1973, p. 31) while the animal struggles to escape.

Auditory stimuli. Most prey species emit distress calls as they are wounded during the kill—zebras give a high intense scream that is quite different to their bark or snort alarm calls; wildebeest and buffalo bleat or moan, like an intensified lowing (Mills, personal communication, November 22, 2001). Schaller describes the “wild...frenzied cry of a dying zebra” (1973, p. 97), and Kruuk writes of wildebeest “moaning at the incessant...bites” inflicted by hyenas (1972, pp. 27, 29). A Thompson’s gazelle fawn pursued by a hyena “jumped, ran, bleated until the hyena’s jaws closed around its shoulders” (Kruuk, 1972, p. 25). Lions dig out a warthog burrow, the animal finally bolts, and, “amid screaming cries from the pig, the lions...tear it apart” (Mills & Harvey, 2001, p. 46).

Olfactory stimuli are equally rich. Schaller arrived at a fresh zebra kill to find “the air heavy with the odors of blood and sour rumen contents” (1973, p. 97). Visceral reinforcers operate through gastric distention and satiation. Hyenas for example gorge themselves at great speed: Kruuk describes a pack of 25 hyenas completely consuming a zebra and her foal within 40 minutes (1972, p. 16). Tactile stimuli include proprioceptive feedback as the prey is clawed and bitten, and the prey’s bucking, writhing, kicking and goring as it attempts to escape.

Arousal level. The predatory cycle is highly energised. Schaller writes that “at no other time do animals convey such a high level of mental and physical tension” (1973, p. 25). Kruuk describes hyena hunts as “wild and exciting.... there is the sudden action, the wild run, the gasps of the victim.... Then the kill, steaming in the chill air, with a hyena cacaphony over and around it” (1975, p. 23, p. 33). Lion hunts are attended by the same high arousal (Mills & Harvey, 2001, pp. 44-45).

Arousal during feeding. High arousal is maintained during the feeding phase as the predators scan for scavengers, chase them off, and jostle one another (Schaller, 1973, p. 83), while hyenas also feed in large competitive groups; a single hyena may be overwhelmed by vultures (Van Lawick, 1977, pp. 188-189). For lions, scavenging from a hyena kill (and vice versa: Van Lawick, 1977, pp. 98-99) is dangerous work accompanied by loud vocalisations.

Baboons and capuchins

One of the earliest authenticated cases of baboon predation is an eyewitness description with photographs in Dart, 1957 (Figures 11 and 12). The Gilgil baboons in Kenya hunt cooperatively and eat meat once a day—more often than any other nonhuman primate population (Strum, 1981, in Stanford, 1999). New world capuchins “hunt as avidly and successfully as chimpanzees” (Stanford, 1999, p. 30), preying on squirrels, tamarin monkeys, and immature coatis. Like chimpanzees, they have a high brain to body mass ratio.

Chimpanzees

At the Gombe, TaV, Mahale and Kibale research sites, chimpanzees hunt red colobus monkeys as well as other primate and ungulate species (Mitani & Watts, 1999). Hunting is coalitionary (Boesch, 1994): for example, a group of Gombe chimpanzees locates a troop of red colobus, posts drivers and blockers, the trap closes, and the colobus retreat to the highest branches: “all the forest is screaming, meat is so rare and so special, there is huge excitement” (soundtrack, National Geographic, 1995). The prey is often an immature colobus “that is grasped by the hands, pinned to the branch, and bitten through the rear of the skull or the neck” (Stanford, 1999, p. 96). Chimpanzees are highly successful hunters (Wrangham & Peterson, 1996, p. 216; Stanford, Wallis, Mpongo, & Goodall, 1994; Stanford, 1999), and arousal during hunts is very high, with pant-hooting, screaming, whistling, piloerection to exaggerate body size, charge displays and the shaking of tree branches (Michael L. Wilson, personal communication, April 24, 2001). At all the sites,

the chimpanzees’ visceral reaction to a hunt and kill is intense excitement. The forest comes alive with the barks and hoots and cries of the apes, and aroused newcomers race in from several directions. The monkey may be eaten alive, shrieking as it is torn apart. Dominant males try to seize the prey, leading to fights and charges and screams of rage. For one or two hours or more, the thrilled apes tear apart and devour the monkey. This is blood lust in its rawest form (Wrangham & Peterson, 1996, p. 216; see also pp. 10-11).

Bonobos, on the other hand, do not prey on monkeys, and are socially more peaceable than their close relations, the chimpanzees: Wrangham and Peterson (1996, p.219) speculate that as predation was suppressed, so was intraspecific violence.

3.3 Intraspecific killing

The array of sensory and autonomic reinforcers that operate during nutritional hunting is also activated when conspecifics are attacked, wounded, or killed, as with Norway rats (Blanchard, Spencer, Weiss, et al., 1993) and wild rats (Niehoff, 1999, p. 61). Hyenas and lions defend their home ranges vigorously. Kruuk records four sightings of hyenas dead near the site of a kill “with clear evidence that they were killed by other hyenas” (1972, p. 256); Schaller (1973, p. 76) documents territorial killing in Serengeti lions.

Among chimpanzees, alpha-male unseating can lead to life-threatening or fatal wounds (Wrangham & Peterson, 1996, De Waal, 1989), and territorial defence may involve lethal violence. As with colobus hunts, these inter-band confrontations are marked by intense excitement that appears indistinguishable from that during predation. Goodall’s early account of such intergroup violence (1990, p. 89) has now been supplemented by Wrangham & Peterson (1996) and Wilson, Hauser, & Wrangham (2001). Though rarer than nutritional hunting, chimpanzee intraspecific killing is frequent enough to account for between 24 and 52% of Gombe male mortality (Wrangham & Peterson, 1996, pp. 271-272).

3.4 The Neurobiology of Predation

Three distinct aggressive circuits in the mammalian brain are evoked by electrical stimulation (ESB) of three slightly different brain areas, namely predatory aggression; intermale territorial and sex-related aggression; and angry aggression (RAGE in Panksepp’s terminology—1998, pp. 51 & 188).

Predatory aggression. Predatory, quiet-biting aggression is mediated by the SEEKING system, a foraging, exploration, curiosity, and expectancy system “that leads organisms to eagerly pursue the fruits of their environment.... Energy is delight” (Panksepp, 1998, p. 145, p. 164), and SEEKING is its vehicle. Predatory aggression is quiet, with methodical stalking and well-directed pouncing

ESB in the ascending dopamine pathways from midbrain nuclei through the extended lateral hypothalamic corridor from the ventral tegmental area to the nucleus accumbens, evokes the most highly energized exploratory and search behaviours of which the animal is capable (1998, p. 145). The emotional tone of affective attack is unpleasant (3.4.2), but the hunt and kill are positive emotional experiences for the predator (Panksepp, 1998, p. 188):

The most effective quiet-biting attack electrodes always evoke self-stimulation.... [self-stimulation and predatory aggression] are two behavioural expressions of SEEKING tendencies that emerge from homologous systems in the brains of different species. The species-typical expressions of this system lead to foraging in some species and predatory stalking in others (Panksepp, 1998, p. 194).

Though SEEKING is dopaminergic, the pleasures of the consummatory processes (feeding, sex) diminish arousal in the SEEKING system (1998, p. 147) and are strongly linked to brain opioid systems which “may participate in every pleasure, serving as a general neurochemical signal that the body is returning to homeostasis” (1998, p. 184).

Affective aggression. RAGE circuits run from the medial areas of the amygdala through the hypothalamus and down to the dorsal PAG. Affective attack sites yield escape behaviours (p. 195), and most animals soon learn to turn off rage-inducing ESB (p. 194). High testosterone, high MAO-A and low serotonin potentiate aggression; in “tournament species,” testosterone is highest in the breeding season (p. 189).

Affective attack, whether offensive or defensive (this latter is a mix of RAGE and FEAR), has marked display features—piloerection with noisy hissing and growling (the chimpanzee vocalisation during affective attack is the pant-hoot). Both quiet-biting attack and self-stimulation are evoked by ESB to the ventral periaqueductal grey (PAG) of the midbrain, while the dorsal PAG evokes affective attack and aversive response.

Predation in relation to aggression. It has been customary to make a clear distinction between predation and aggression. Archer (1988) holds that “so-called predatory aggression is so motivationally and neurally different from other forms of aggression that it is most usefully considered as a separate form of behaviour” (p. 25; also Lorenz, 1963 and Niehoff, 1999).

Panksepp’s model accords more parsimoniously with the above behavioural accounts of predation and intraspecific killing, which suggest that predation and aggression are closely interwoven (see also Wilson, 1975, p. 243), with quiet stalking (felids) or observation (canids and hyenids) alternating with noisy defence of the kill. It also provides a neurobehavioural basis for predation’s distinctiveness, in that, first, predation and affective attack have separate circuits in the brain; second, the RAGE and SEEKING circuits have mutually inhibitory interactions and cannot therefore co-occur; third, predatory attack is endogenously generated because the predatory cycle usually begins before the stimulus is present—unlike affective attack, which is triggered by the presence of the target; and fourth, it is accompanied by positive affect, even though the energising contribution made by hunger may be aversive, and, “from the animal’s point of view, there is no apparent anger involved in this food-seeking response” (p. 198).

Endogenous opioids. The literature on the role of the neuropeptides in predation, especially endorphin and the enkephalins, is sparse and contradictory, for example that microinjection of naloxone at PAG sites at which ESB evoked quiet-biting attack in cats blocked predatory behaviour (Weiner, Shaikh, Shaikh, & Siegel, 1991); a later study (Manchanda, Poddar, Saha, Bhatia, Kumar, & Nayar, 1995) showed on the other hand that microinjection of an enkephalin at excitatory PAG sites suppressed both the somatomotor and affective display components of predatory attack.

On the other hand, there is a copious literature on opioid release under predatory threat, which entrains a sequence of defensive responses in prey that include hypoalgesia (in mice exposed to a cat, Kavaliers & Colwell, 1994, and to insect stings, Kavaliers, Colwell, & Choleris, 1994), and, as a final-stage response, tonic immobility (Gargaglioni, Pereira, & Hoffmann, 2001). Predator odours are highly salient in eliciting innate defensive analgesia (Williams, 1999). In humans, the release of endogenous opioids in acute traumatic injuries correlates significantly with physician pain ratings and scores on an injury severity scale (Bernstein, Garzone, Rudy, Kramer, Stiff, & Peitzman, 1995), suggesting that anecdotal accounts of spontaneous analgesia in soldiers wounded in combat have a physiological basis.

The hunt and kill are a dangerous time for predators. The prey butts, kicks and gores, and scavengers must be repulsed. If the predator is the scavenger—as often happens with hyenas and lions—the risk of injury increases. The known links between consummatory processes and brain opioid systems may therefore be augmented during the killing-feeding cycle by further opioid release in response to injuries: an aspect of the predatory adaptation may thus be an opioid “high” that is further augmented by injury.

Pain and pleasure in predation, hunting and sexuality. The predatory cycle makes massive energy demands of the predator, among them a sustained high level of autonomic arousal, the physical exertion of what may be a prolonged high-speed chase, the act of killing, during which the predator must overcome the last highly energised struggle of the prey and the close-in hazards of the kill, followed by scavenger threats. The aversive stimuli of physical exertion to the point of exhaustion are augmented by this final struggle. Yet the dopaminergic biochemistry of the predatory cycle and ESB evidence of its reward value indicate that far from being aversive, predation is a powerfully rewarding experience even before satiation occurs.

One may thus hypothesise that a necessary condition for the success of the predatory and hunting adaptations is the conjunction of pain—the stress of exertion and the pain of injury—with a high level of pleasurable reward intermixed with sexual arousal, and that this is also true of fighting in its various forms—single combat, assaults by individuals or groups on rivals, and war: though fighting is by definition not cruel, pain is inseparable from combat.

It is incomprehensible that the infliction of pain on the self is both pleasurable and also sexually arousing. This unlikely conjunction has long puzzled moral philosophers and psychologists. In a famous passage, Freud wrote that “the existence of a masochistic trend in the instinctual life of human beings may justly be described as mysterious from an economic point of view” (1924/1985, p. 413). Yet using functional magnetic resonance imaging (fMRI), Becerra, Breiter, Wise, Gonzalez, and Borsook (2001) report that a pain stimulus (a probe heated to 46^NC applied to the skin) activated the brain’s reward circuitry, following a pathway similar to that of the pleasure response: protein from the cfos gene shows “that many neurons in the amygdala that are aroused by aggressive encounters are also aroused by sexual activity” (Panksepp, 1998, p. 199): the underlying motivation may be the seeking of safety.

The intertwining of aggression and sexuality is linguistically and ethologically apparent. The term for the !Kung hunting bow, n!au, is “a bawdy metaphor for the penis” (Lee, 1979, p. 207), and !Kung hunters say that “when one’s heart is sweet with the thought of the kill, intercourse is particularly good” (Lee, 1979, p. 220). In primates and humans, intermale territorial and dominance-seeking aggression is driven by reproductive fitness needs, with females responding positively to aggressive success so that the most vigorous males get preferential access to reproductive opportunities (Panksepp, 1998). Men with absolute power may father several hundred children (Wrangham & Peterson, 1996, p. 234; Ridley, 1993).

4 Stage 2: The Hunting Adaptation

Despite its high costs, the hunting adaptation mediates powerful social and psychological rewards, and is “the most successful and persistent... man has ever achieved” (Lee & DeVore, 1968, p. 3). It remains so in 58 surviving forager societies from the equator to latitudes above 60^", in which the contribution of hunting to annual food intake converges on 35% (Lee, 1968). The following sections review the emergence of hominid hunting, and then, in two forager societies, the Dobe !Kung of Botswana (Lee, 1979, 1984) and the Yanomamö of southern Venezuela (Chagnon, 1983), consider the reinforcements that support the expenditure of large time and energy resources on meat procurement.

4.1 Early Hominid hunting

As hominids moved into the dry savannas of the Pliocene, the evolutionary shift from gathering to meat eating required major changes in sociality, brain size, and weapons (Stanford, 1999). The nutritional accommodation of a big brain is by shrinking the gut, which can only be done if there has been a switch to easily digested and highly nutritious foods (Aiello & Wheeler, 1995) such as meat and tubers, with pre-consumption processing of chemically or mechanically protected tubers (O’Connell, Hawkes, & Blurton Jones, 1999).

The earliest fossil evidence of hominid meat eating is the appearance of crude stone tools in east Africa in the mid-Pliocene about 2.5 Ma, probably representing an overlay of large mammal scavenging on a tradition of small mammal hunting (Plummer & Stanford, 2000); killing or meat scavenging without tools may be much earlier, but would not have left fossil evidence (Stanford, 1999). O’Connell et al. (1999) argue that the earliest hominid meat eating is considerably later, contemporaneous with the appearance of African H. erectus about 1.8 Ma. Changes driven by “grandmothering”—foraging by post-menopausal women—would have promoted larger group size, which in turn brought advantages in defendi