Chimpanzees engaged in what humans call horseplay put on a characteristic “playface” to show that their combat gymnastics are meant only as a game. Courtship displays in gulls have been described as “fear and hostility, or attack and fleeing tendencies, expressed … in a manner that denies them.”11
In cranes there’s an “appeasement ceremony” in which the male spreads his wings, exaggerates his size, raises his beak … and then, still in a threat posture, turns himself aside—presenting a vulnerable and very visibly marked part of his anatomy, perhaps the side or back of his head. The pantomime may be repeated several times and incorporate an attack on a piece of wood or something else handy. The message being communicated is clear. “I am big and threatening, but not toward you—toward the other, the other, the other.”12
Smiling may have a similar origin. Baring one’s teeth carries the message. “I think you’re food,” or at least “Watch out for me.” But in the symbolic language of animals, this signal may be softened and altered: “Even if you are food, even though I’m well-equipped to eat you, you’re safe with me” All over the world, in virtually every human culture, smiling signifies affection and good fellowship (with certain nuances conveying a touch of nervousness and deference). All over the world, in nearly every human culture, in civilian as well as military life—in handshakes, high fives, salutations among mounted Sioux, hails to Caesar and heils to Hitler, upon greeting a superior officer or waving farewell—we humans offer our right hands in greeting, demonstrating while still at a safe distance that we are unarmed and therefore pose no threat. In a species given from its earliest days to clubs, knives, spears, and axes, this is information worth having.
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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.