Shadows of Forgotten Ancestors

by Carl Sagan

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  With occasional exceptions, animals do not seem consciously to work out what to do in a given situation and then, weighing alternatives, opt for aggression. It’s too slow a process to survive the hurly-burly of the biological world. Instead, the animal senses threat or prey, and a tenth of a second later it responds A complex set of physiological reactions begins—adrenaline pours into the bloodstream, limbs begin to flex—reactions that are ordinarily sitting there in the animal on ready standby, awaiting the release signals

  In the neural architecture of mammals there is hardwired circuitry for aggression and predation. When a certain region in the brain of a solitary cat is electrically stimulated, she begins to stalk imaginary prey. Turn the current off and she stretches and licks her paws; the hallucination has vanished. Rats that do not look twice at a mouse will, when an electric current is made to pass through the appropriate parts of their brains, become crazed killers—dedicated, implacable mouse-murdering machines. The stimulated neural circuits are present for a reason; in the ordinary course of the animal’s life, they will be excited by some cue from the outside world—a motion, a smell, a sound, causing an electrical stimulation—and the brain machinery for aggression or predation is set into motion. When given a juicy bone still covered with meat, even puppies as young as two weeks old will growl and bark. Dry dog food does not trigger the same hardwired and impassioned response. Humans have such machinery too. Sometimes a misfiring or miswired circuit can set it into motion with very little stimulus from the outside world, or even none at all.

  It’s as if all of us birds and mammals—but especially the males—are walking around wearing a control panel with a set of push buttons on it. The panels are prominently displayed, easy for others to get to (or even for us to get to—so we can pump ourselves up on our own, a skill of professional athletes). When pressed, the buttons disinhibit a set of powerful, passionate, and sometimes deadly responses that are ordinarily kept under tight controls. Put this way, it may seem odd that Nature has made the buttons so easy to push, so readily available, so vulnerable to exploitation.13

  A cannibalistic species of firefly simulates the color and frequency of the come-hither flashes of another, country bumpkin species of firefly. The love buttons have been pushed on the naive insects; they see visions of sultry females where there is only a gaping mouth. To lure uninterested or recalcitrant females into mating, males of many species are often ready to press buttons designed for quite different purposes,

  such as feeding, defense, timidity in the face of aggression, or brood care. They may give a brief threatening lunge, cry like a baby, mimic an alarm call, hop on one leg as if wounded, or (as in peacocks) peck at the ground as if food has been found.14

  Undeterred by scruple, they will use any method that works. In many cultures, young men try to press all available buttons for sex, perhaps offering wholly insincere promises of fidelity and devotion; or they taunt each other into fighting by casting aspersions on another’s courage, say, or his mother’s sexual behavior. The benefits of having these buttons so readily available must outweigh the risks. The inflexibility of such hair-trigger responses might be a cause for worry, though.

  These behavior patterns also are encoded in the nucleic acids. Every deterrent flourish, every postural hint of submission, is meticulously written down in the ACGT language. That being the case, you might expect variations in the style or intensity of aggression from animal to animal within a given species, as is indeed the case. If you take a population of mice and breed the aggressive ones with each other and the peaceful ones with each other, eventually you produce two strains of markedly different temperament. This isn’t due to pup-rearing practices, because the young of aggressive parents, when raised by peaceful mothers, are aggressive, and vice versa. It’s a commonplace that through artificial selection dog breeders have produced nervous, high-strung, ferocious breeds—for example, rottweilers or pit bulls—and friendly, peaceful strains, often useless as watchdogs, such as cocker spaniels. In mouse and dog aggression, heredity often seems to take precedence over home environment. (It might be the other way around in humans, or the two influences might be evenly matched.)

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  Nearly all the social mammals are organized as groups of females (often relatives) with their offspring. Males, otherwise absent, are conspicuously present when the females are in heat They may be busy dominating, fighting, or mating, but in terms of basic social structure and the bringing up of the young, they are often a shadowy presence. Usually, the young are raised by single mothers. Among the exceptions to this rule are chimpanzees, gorillas, gibbons, wild dogs, perhaps wolves. And, more than occasionally, humans.

  In temperate and polar climates, there’s a good reason for the young to be born in the spring—so they may have the rest of spring and all of summer and autumn to grow up before having to face the rigors of winter. If the gestation period is short (or alternatively around a year), then mating will also occur in the spring. To arrange for biological clocks to be built into animals, to stimulate the reproductive machinery at the right moment in springtime and to inhibit it at other times of the year, must have occupied great vistas of evolutionary time.

  Natural selection has provided a wide range of visual, olfactory, auditory, and other cues to inform the normally uninterested males of the otherwise indetectable fact that ovaries are releasing eggs all around them. Sexual attention at other times is generally a wasted effort (it’s used to bond male and female in species where both are needed to raise the young). So the female is designed with some internal calendar (perhaps triggered by the length of the day), and a series of signals and behaviors (alluring pheromones plus enticing postures, say). In the season of love, on cue, as if activated by some Cartesian clockwork, both sexes become mad with passion.

  If mating is to occur in the spring, then the rivalry of males for the attentions of females should also peak in the spring. If the lives of deer depend in part on their speed and their ability to fight back when cornered by predators, then intraspecific tests of strength, speed, stamina, and strategy among stags are to the benefit of the genes of the victors as well as to the deer clan. This is ritualized combat, almost never to the death. The point of the exercise becomes instantly clear as the doe gives herself to the winner. A multitude of such dramas over many generations helps deer keep pace with hereditary improvements in, for example, the hunting skills of wolves.

  In many predatory species, animals hunt together. Prey is flushed into ambush, or is exhausted by repeated feinting. Stragglers, usually the weak, the young, and the old, can be isolated. The predators may adopt a relay system, Group One performing feints only, and Group Two loping along to pick up the attack when Group One is exhausted. Cooperation makes hunting much more efficient, and the predators may now bring down animals much larger than they are.

  Members of hunting packs have a kind of ethic: Whatever rivalries they bear are put aside during the hunt. For them too, “politics stops at the water’s edge.” There’s a different set of social rules within the group than without. But it’s an easy step from attacking animals of other species to attacking strangers of the same species. This is true of dogs and lions, which hunt in packs, and of ants and penguins, which do not. They behave as if special loyalty is owed to their group only; suspicion and hostility are due all others, even though they are fellow members of the same species. And this is not restricted to hunting packs. It’s a fact of life among most sociable birds and mammals.

  Ethnocentrism is the belief that our group (whichever it happens to be) is at the focus of everything good and true, the center of the social universe. We do things the way they were meant to be done. Xenophobia is the fear and hatred of strangers. Their behavior is wrong-headed or weird or abominable. They don’t have the same respect for life that we do. And anyway they’re out to get us. “Us against them,” again. Ethnocentrism and xenophobia are extremely common among birds and mammals, although
they do not constitute an invariable rule: Flocks of migrating birds, for example, are pretty much open to all comers of the same species.

  If we’re confronted by some stranger who means harm to both of us, then we’re motivated to put aside whatever differences lie between us and together deal with the common enemy. Our chance—as individuals and as a group—of surviving an attack is greatly improved if we make common cause with our fellows. The existence of common enemies can work as a powerful unifying force. Common enemies make the social machinery purr. Those groups that incline to xenophobic paranoia might gain a cohesive advantage over groups that are initially more realistic and carefree. If you’ve exaggerated the threat, at least you’ve reduced internal tensions in your group; and if the external threat is more serious than you’ve privately estimated, your preparedness is higher. As long as the social costs stay within reasonable bounds, it may become a successful survival strategy. So there’s a kind of contagion about xenophobia.

  Even among animals that as adults have few natural enemies—dolphins, say, or wolves—the young are vulnerable. Special steps must be taken to protect them. Adult dolphins keep very close to the young. Wolf cubs are cautious and fearful in their first few months of life. Many nestlings beg for food with visual, not auditory, cues so as not to attract the unwelcome attention of predators. These measures are useful in dealing with both interspecific and intraspecific violence: Because so many group-living animals attack members of other groups who stray into their territory, the young have good reason to be wary of strangers.

  Among the wildebeests, an African antelope hunted by many predators, the calf shakily stands within a few minutes after birth. Five minutes later it can follow its mother, and in twenty-four hours it can keep up with the herd. Wildebeests grow up fast. In other animals, of which humans are the most striking example, the young are born utterly helpless. If abandoned by their parents, they would perish in a few days, predators aside. A wildebeest mother need make few concessions to her young, apart from permitting them to suckle. Human mothers (and robin, wolf, and monkey mothers, among many others) must adopt a complex behavioral repertoire in order for there to be a next generation. In higher mammals, these special activities may last years or even decades—until the youngster is nearly fully grown. For so major an investment to be made, there must be a comparably major benefit. The long childhood of the higher mammals is connected with their larger brains and with the necessity that the young be taught. This frees the youngsters from the comparative inflexibility of having preprogrammed genetic knowledge only.

  In many animals there’s a period early in life during which profound and irreversible learning occurs, a time, for example, when a duckling will follow anything nearby that moves as if it were Mom—even if it’s a bearded pioneer in animal behavior. This is called imprinting. Some imprinting goes on even before birth. Ducklings, before they hatch, memorize the voice of whoever is incubating them, and respond (by peeps from inside the egg). If it’s a human who talks to the egg during incubation, that’s the voice the duckling responds to after it’s hatched. Imprinting may involve learning a call, a song, an odor, a shape, or a food preference, and is accompanied by deep emotional bonding. The information is implanted in the memory for a lifetime.

  These sounds, smells, and sights are associated with food, warmth, love, and safety in an often-hostile world. Lambs, chicks, and goslings must reliably recognize and follow their perambulatory mothers; failure to do so is punishable by death. It’s no wonder imprinting lasts for life. The predisposition to be imprinted is programmed in the DNA and subject to very strict constraints (in some cases imprinting can occur only in a specific one- or two-day period over an entire lifetime). But the specific information that is so indelibly etched is conditioned by environment and experience, and differs from animal to animal. In this way the youngster can learn, generally from its parents, wisdom too recent to have been inscribed in the latest edition of the nucleic acids.

  An unfocused inclination towards ethnocentrism and xenophobia can be particularized as needed in each generation. The groups to which loyalty is owed and the ones deserving special hatred and contempt may change from generation to generation. Imprinting is a means for fitting general proclivities to practical politics, and is a form of education. The machinery stands ready for those who know how to use it. The young animals have a nearly eidetic memory. But they have no critical faculties. They’ll believe anything—whatever they’re taught. As the example of the parade of ducklings waddling adoringly after the ethologist reminds us, imprinting might lead, in unscrupulous higher animals, to misuse. The young are so ready to learn who to love and who to hate.

  If the nipples and vaginas of nursing rats (“suckling dams,” the scientists call them) are regularly swabbed with the scent of lemon, the male pups, when grown, are preferentially attracted to lemon-scented females—foreswearing the naturally aromatic, accessible, and nubile alternatives.15 This odor imprinting suggests how powerfully early experiences can affect later sexual preference and performance. It’s something like the line in the song that goes, “I want a girl just like the girl that married dear old Dad.” But humans are not rats.

  With long childhoods and efficient imprinting, animals can make wholesale changes in their behavior to adapt to a changing environment—taking only a few lifetimes instead of a geological age. In turn, this bonds mothers and offspring together still more closely. It creates something akin to love. It also means that different communities of the same species may have different patterns of behavior that are passed down the generations—even if the groups are, genetically, essentially identical. The strategy of long childhoods and early learning introduces a new element: culture.

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  Human life begins in a race of one against hundreds of millions The stampeding sperm cells are competitive from the start. But the whole point of the-rivalry is cooperation of the most intimate sort. The two cells wholly merge. They combine their genetic material. Two very different beings become one. The act of making a human being involves an almost bizarre mix of opposites—desperate competition against all odds, and cooperation so perfect that the partners’ separate identities vanish. It would be inconsistent for beings who arise out of intense rivalry and begin in perfect cooperation to decry either.

  “In the ways of Nature,” said Marcus Aurelius, “there is no evil to be found”16 Animals are aggressive not because they are savage, or bestial, or evil—those are words with very little explanatory power—but because such behavior provides food and defense against predators, because it spaces out the population and avoids overcrowding, because it has adaptive value. Aggression is a survival strategy, evolved to serve life. It coexists, especially in the primates, with compassion, altruism, heroism, and tender, self-sacrificing love for the young. These are also survival strategies. Eliminating aggression would be a foolish as well as an unachievable goal—it’s built too deeply into us. The evolutionary process has worked to achieve the right level of aggression—not too much, not too little—and the right inhibitors and disinhibitors.

  We emerge out of a turbulent mix of contradictory inclinations. It should be no surprise that in our psychology and our politics a similar tension of opposites should prevail.

  * A very nice test of these ideas are the observations by the animal behavior expert Stephen Emlen He thought to examine jacanas, birds in which the usual sex roles are reversed: Males do all the parenting and the females compete vigorously for something like a harem of males Those females who don’t possess a harem don’t reproduce, so the dominant females are often challenged by lower-ranking females When a takeover attempt succeeds, the incoming female routinely destroys the eggs and kills the chicks She then sexually solicits the males, who now have no young to distract them—and so are able to attend to propagating the genetic sequences of the incoming female The genetic strategy of infanticide is situational, not gender-based

  * Another aspect of the gestural voca
bulary of appeasement is infantile behavior in adults, including begging. It’s a little like human lovers using baby talk and calling each other “baby.” They’re applying a lexicon established in infancy to another purpose

  Chapter 11

  DOMINANCE AND SUBMISSION

  When we no longer look at an organic being as

  a savage looks at a ship, as something wholly

  beyond his comprehension; when we regard

  every production of nature as one which has

  had a long history; when we contemplate every

  complex structure and instinct as the summing

  up of many contrivances, each useful to the

  possessor, in the same way as any great

  mechanical invention is the summing up of the

  labour, the experience, the reason, and even

  the blunders of numerous workmen; when we

  thus view each organic being, how far more

  interesting—I speak from experience—does the