Shadows of Forgotten Ancestors

by Carl Sagan

  [Menzel] maintained four to six young chimpanzees in a large outdoor enclosure that was also connected to a smaller holding cage. He restrained all but one animal in the holding cage, while showing this chosen “leader” the hidden location of either an amount of food or an aversive stimulus such as a stuffed snake. The leader was then returned to the holding cage, and the whole group was released. According to Menzel’s reports, the variable behavior of the animals indicated that they “seemed to know approximately where the object was, and what sort of object it was, long before the leader reached the spot where it had been hidden” … If the goal was food, they ran ahead looking in possible hiding places; if it was a stuffed alligator or snake, they emerged from their cage showing piloerection [their hair standing on end] and staying close to their companions. If the hidden item was an alligator or snake, they became very cautious in their approach and often mobbed the area, hooting in the direction of the hidden item and hitting at it with sticks. If the hidden item was food, the animals searched the area intensively and showed little fear or distress. The behaviors occurred even if the aversive stimulus had been removed before the animals were released from the holding cage, so it was not the item itself that produced these reactions.

  In the food tests, one male (Rocky) began to monopolize the food supply when it was located. When Belle, a female, served as leader, she attempted to avoid indicating the location of the food cache, but Rocky could often extrapolate from her line of orientation and find the food. If Belle were shown two caches, one large and one small, she would lead Rocky to the small one and, while he was busy eating, run to the larger one which she would share with other individuals. Menzel concluded that chimpanzees could communicate the direction, amount, quality, and nature of the goal, as well as attempt to conceal at least some of this information, but precisely how chimpanzees achieve such communication is still not known.27

  The only possibilities seem to be gestures and speech.

  Chimps have hundreds of different kinds of food and crave dietary variety. They eat fruit, leaves, seeds, insects, and larger animals, sometimes dead ones. Caterpillars are delicacies, and the discovery of an infestation of caterpillars becomes a memorable gastronomic event. They’re known to eat soil from cliff faces, presumably to provide mineral nutrients such as salt. Mothers will offer choice tidbits of food to their infants and will snatch unusual, possibly dangerous, foods from their mouths. In the wild, adults share food occasionally, often in response to begging. There are no set mealtimes; they snack throughout the day. As a foraging party moves on, one of its members may carry a branch still laden with berries or leaves to munch as she rambles.

  When in the middle of the night, in their beds of leaves in the high branches, they are awakened by the cries of predators, they clutch each other in fright, their urine and feces raining down on the forest floor below.

  They love to play, children (whose energy is prodigious) more than adults, but even adult play is common—especially when there’s enough to eat and large numbers of chimps gather together. Play often involves, but is not restricted to, mock fighting.

  Chimp males are protective toward females and the young. They will readily risk their own lives to protect “women and children” from attack, or to rescue a youngster in trouble. Goodall writes, “Often it seems that a male cannot resist reaching out to draw an infant into a close embrace, to pat him, or to initiate gentle play.”28 When a male is discovered in flagrante delicto with a female, which is often, an infant may rush up to punch the male in the mouth or jump on the back of the female, most often his mother.* In such situations the male’s tolerance frequently exceeds human limits.

  But in a display competition for dominance, all this good-natured equanimity vanishes, and a male who ordinarily is protective of infants may pick up a small, innocent bystander and slam it to the ground in his rage. When an unfamiliar female is discovered in their territory, chimps are known to seize her infant by the ankles and smash it against the rocks.29

  Chimps tend to pick on the runt of the litter, and to displace their own anger away from higher-ranking chimps (who might do them harm) to those who are milder-tempered, younger, weaker, and female. At Gombe in 1966 there was a polio epidemic which resulted in the partial paralysis of full-fledged members of the group. Crippled by their disease, they were forced to move in odd ways, dragging limbs. Other chimps were at first afraid; then they threatened the afflicted, and then attacked them.

  Because aggression is episodic and friendly relations so much more common, some early field observers were tempted by the notion that chimps in a state of nature (that is, unimprisoned) are non-violent and peace-loving. This is not the case. In hunting other animals, in working the dominance hierarchy, in hustling the females, in peevish moments, and in skirmishes with other groups of chimps (the Strangers, in our narrative), they show themselves capable of great violence.

  Meat contains essential amino acids and other molecular building blocks more difficult to acquire from plants. Both sexes are ravenous for meat. On rare occasions, females will attack other females in their group and steal and eat their infants. Once the little one is in hand, there are no ill feelings directed to the mother of the tiny victim. In one case, a female approached those who were eating her baby; one of the diners responded by putting out her arms to embrace and comfort the grieving mother. Chimps are known to hunt mice, rats, small birds, a twenty-kilogram adolescent bush pig, monkeys such as baboons and colubuses, and other chimps.

  A successful hunt is accompanied by enormous excitement. The spectators scream, hug, kiss, and pat one another reassuringly. Those actually involved in the kill immediately begin feeding, or attempt to carry off tasty body parts. The forest is filled with screeches, barks, pants, and hoots—which attract additional chimps, sometimes from a considerable distance. Generally males help themselves to bigger portions than females. Those of high rank are more likely to distribute the spoils, and one way or another most who are actually present at the kill gain a share. Newcomers plead for morsels. Pieces will be stolen, and the chimp whose prize has been taken will be furious, perhaps indulging in a temper tantrum. Portions of meat are taken to bed for midnight snacks.

  A rat may be eaten head first. A monkey or young antelope is often killed by having its head smashed against a rock or tree trunk, or by giving it a vampirish bite in the back of the neck. Almost always the brains are eaten first. This is often the prize of the hunter who performs the actual kill. Other tasty body parts include the genitals of male victims and the fetuses of pregnant female victims. Goodall reports the final, attenuated, scream of a young bush pig as a chimp, like some ancient Aztec priest, tore out its living heart. Cooking has not yet been invented, nor flatware, nor table manners, nor squeamishness. This is a world of red blood and raw meat.

  Janis Carter describes30 a juvenile chimp and a colubus monkey, about its own size, grooming one another; but when the colubus is seized by the tail and killed by a passing adult chimp, who bashes its head against a tree, the juvenile readily enough joins in devouring its erstwhile playmate. Most of the monkey (and small mammal) victims of chimp predation are infants and juveniles, often snatched from their mothers’ arms. Sometimes the mother tries to rescue the infant and is herself eaten.

  In this world there is no mercy shown to food, even if it’s still ambulatory. Food is for eating. Those who are moved to mercy eat less and leave fewer offspring. Clearly the chimps do not recognize monkeys, or chimps of other groups, or even members of their own group as deserving of mercy or other moral considerations. They may be heroic in defending their own young, but they do not show the least compassion for the young of other groups of species. Perhaps they consider them “animals.”

  Hunting is a cooperative endeavor. Cooperation is essential for making the larger kills—and also for avoiding their dangers, such as an enraged bush pig charging, tusks first, to save its young. The hunters exhibit real teamwork. One chimp may softly call to anot
her when it has detected prey in the underbrush. They smile to one another. The victim is flushed out of its cover toward other chimps who are lying in wait. Escape routes are blocked off. Ambushes are refined. Plays are called. The chimps—so passionate after the kill—were coolly planning it all out beforehand.

  ——

  In densely forested habitats, the territory controlled by a given chimpanzee group is only a few kilometers wide. In sparsely wooded regions, it can be as much as thirty kilometers across. These are the territories that a chimp group considers its turf, its home, its fatherland or motherland, to which something like patriotic sentiments are owed. It is not to be trespassed by strangers. It’s a jungle out there. The typical day range of a chimp combat patrol is a few kilometers. So if they live in heavy forest, they can fairly readily patrol a good portion of the border in a single day. But if the vegetation and food supply are more sparse and their territory accordingly larger, it may be a few days’ journey from one end to the other, and longer if they go around the perimeter.

  A patrol is typified by cautious, silent travel during which the members of the party tend to move in a compact group. There are many pauses as the chimpanzees gaze around and listen. Sometimes they climb tall trees and sit quietly for an hour or more, gazing out over the “unsafe” area of a neighboring community. They are very tense and at a sudden sound (a twig cracking in the undergrowth or the rustling of leaves) may grin and reach out to touch or embrace one another.

  During a patrol the males, and occasionally a female, may sniff the ground, treetrunks, or other vegetation. They may pick up and smell leaves, and pay particular attention to discarded food wadges, feces, or abandoned tools on termite heaps. If a fairly fresh sleeping nest is seen, one or more of the adult males may climb up to inspect it and then display around it so that the branches are pulled apart and it is partially or totally destroyed.

  Perhaps the most striking aspect of patrolling behavior is the silence of those taking part. They avoid treading on dry leaves and rustling the vegetation. On one occasion vocal silence was maintained for more than three hours … [When] patrolling chimpanzees return once more to familiar areas, there is often an outburst of loud calling, drumming displays, hurling of rocks, and even some chasing and mild aggression between individuals … Possibly this noisy and vigorous behavior serves as an outlet for the suppressed tension and social excitement engendered by journeying silently into unsafe areas.31

  In this description by Jane Goodall of a patrol at Gombe, we are taken by the ability of the chimps to overcome their fear, to exercise self-control by inhibiting their usual noisy interchanges, but particularly by their deductive abilities. These chimps are tracking. They are weighing the evidence of branches, footprints, droppings, artifacts. We might expect that, when food is in short supply, group differences in tracking skills help determine who lives and who dies. Not just strength and aggressiveness are being selected here, but something akin to reasoning and quick-wittedness. And stealth. When one human who lived with a troop for a long time tried to accompany a patrol as it set out, they looked at him reprovingly. He was just too clumsy. He could not, as they do, slip silently through the forest.

  So the long-range combat patrol wends its way toward the borders of their turf If it’s more than a day’s walk, they’ll set up camp at night and continue on their way tomorrow. What happens if they encounter members of another group, Strangers from the adjacent territory? If it’s just one or two intruders, they’ll attempt to attack and kill them. There’s much less disposition here toward threat displays and intimidation. But if two parties of roughly equal strength encounter one another, now there are a great many threat displays, rocks and sticks are thrown, trees are drummed. “Somebody hold me back, I’m gonna break his knees,” you can almost hear them saying. They practice threat assessment If the patrol senses an obviously larger number of Strangers, it is likely to beat a hasty retreat. At other times chimp patrols may penetrate enemy territory or even raid its populated core area—for many purposes, including copulating with unfamiliar females. The combination of tracking, stealth, danger, teamwork, fighting hated enemies, and the opportunity for sex with strange females is enormously attractive to the males.

  The delight shown by the members of a patrol after having successfully returned from dangerous—perhaps enemy-held—territory is little different from what happens when chimps unexpectedly encounter a substantial cache of food. They screech, kiss, hug, hold hands, pat one another on the shoulders and the rump, and jump up and down. Their camaraderie is reminiscent of teammates in mutual embrace just after winning the national title At the start of a heavy rain, male chimps often perform a spectacular dance. On coming upon a stream or waterfall they display, seize vines, swing from one tree to another, and cavort high above the water in a breathtaking acrobatic performance that may last for ten minutes or more. Perhaps they are awed by the natural beauty or entranced by the white noise. Their evident joy sheds a revealing light on the eighteenth-century doctrine32 that humans are right to enslave other animals because we are unmatched in our capacity to be happy.

  The prescription offered by Sewall Wright for a successful evolutionary response to a changing environment closely matches many aspects of chimp society. The species is divided into free-ranging groups, generally comprising between ten and one hundred individuals. They have different territorial ranges, so that if the environment alters the impact will be at least slightly different from group to group. A staple food at one end of a vast tropical forest may be a rare delicacy at the other. A blight or infestation that might result in serious malnutrition or famine for chimps in one part of the forest might have negligible consequences in another. Each territorial group is enough inbred that the gene frequencies differ systematically, group to group. And yet the pattern of inbreeding is relieved by exogamy (outbreeding). There are key sexual encounters with chimps from adjacent territories, initiated either when a patrol penetrates into alien territory or when a foreign female wanders over. These unions provide genetic communication, group to group, so that if in an adaptive crisis one group were more fit than the others, the adaptation would rapidly spread to the entire chimpanzee population through a sequence of sexual contacts—perhaps hundreds of copulations in a chain linking the remotest groups of a vast tropical forest. If there’s a modest environmental crisis, the chimpanzees are ready.

  If this is indeed the explanation, at least in part, of the territoriality, ethnocentrism, xenophobia, and occasional exogamy that characterize chimpanzee society, we do not imagine that individual chimps understand the reasons for their behavior. They simply can’t stand the sight of strangers, find them hateful and deserving of attack—except, of course, for the chimps of the opposite sex, who are unaccountably exciting. The females occasionally run away with strange males, no matter what crimes they may earlier have committed against their land and kin. Perhaps they feel something of what Euripides makes Helen of Troy feel:

  What was there in my heart, that I forgot

  My home and land and all I loved, to run away

  With a strange man?…

  Ah, husband still, how shall thy hand be bent

  To slay me? Nay, if Right be come at last,

  What shalt thou bring but comfort for pains past,

  And harbour for a woman storm-driven:

  A woman borne away by violent men …33

  Mothers know who their sons are and so can preferentially resist their (very rare) sexual advances. But fathers are not sure who their daughters are, and vice versa. Thus, when a female comes of age in a small group, there’s a significant chance of an incestuous union, further inbreeding, more infant mortality, and fewer of their genetic sequences passed on to future generations. So around the time of first ovulation, a female often feels an inexplicable urge to visit the neighboring territory. This can be a dangerous undertaking, as she probably understands full well. The compulsion, then, must be strong, which in turn underscores the evoluti
onary importance of her mission. Combine this not uncommon itch to wander at first ovulation with the rarity of brother-sister and, especially, mother-son unions and it’s clear that a high-priority, well-functioning incest taboo is operating among the chimps.

  There’s one aspect of chimpanzee territoriality not shared by other apes—all of whom are divided into territorial, xenophobic groups, with a little exogamy thrown in: Unlike encounters within the group, where bluff and intimidation play major roles and only rarely does anyone get seriously hurt, when two chimp groups interact there can be real violence. No main force combat has ever been observed. They prefer guerrilla tactics. One group will pick off the members of the other in ones and twos until there’s no longer a viable force left to defend the adjacent territory. Chimpanzee groups are constantly skirmishing to see if it’s possible to annex more turf. If the penalty for failure in combat is death for the males and alien sexual bondage for the females, the males soon find themselves caught up in a powerful selection for military skills. Genes for those skills must have been racing through the tropical forests, by exogamous mating, until nearly all chimps had them. If they didn’t, they died.

  Moreover, the skills that make you good on patrol and good in skirmishes also make you good in the hunt. If your combat skills are honed, you can also supply your friends, loved ones, and concubines—to say nothing of yourself—with more of that delicious red meat. Except for the part about the good eating, being a male chimp is a little like being in the army.