I remember going off to college. I was so nervous and excited that I had the runs for a week beforehand. What if they had made a mistake by admitting me? Suppose I never made any friends? Would these really turn out to be the best years of my life? Queasy and vertiginous, I packed my bags onto a Greyhound bus, squirreling a bottle of Kaopectate into my knapsack.
Actually, getting my bowels into such an uproar proved to be quite justified, given the momentous freshman-year events that awaited me: the epiphany when I knew I was never going to understand photosynthesis and should give up on being a biology major (I switched to bioanthropology); the realization, as I contemplated four years of purple yogurt and Polynesian meatless meatballs in the cafeteria, that my mother was a fabulous cook; my first lesson in political correctness--I learned that I was now surrounded by women and not by girls; the infinitely pleasant discovery that some of those women were willing to talk to me now and then; the wonder of watching older guys suavely work references to Claude Lévi- Strauss and Buckminster Fuller into casual conversation; the giddy pleasure at finding that a joke that worked in high school worked equally well here too; the calming ritual of fighting with my roommate every evening over whether to open or close the window.
Growing up, and growing away. Off to college, off to war, off to work in the city, off to settle in a new world--home is never the same again, and sometimes home is never even seen again. What is striking about this maturational event is that it is central not only to us humans but to many of our primate relatives as well. The process of growing up and growing away has a remarkably familiar look of excitement and discovery and challenge.
Some primates, such as orangutans, lead solitary lives, meeting only for the occasional mating. But the average group of primates is supremely social, whether it is a family of a dozen gorillas living in a mountain rain forest, a band of 20 langur monkeys on the outskirts of an Indian village, or a troop of 100 baboons in the African grasslands. In such groups an infant is born into a world filled with relatives, friends, and adversaries, surrounded by intrigue, double-dealing, trysts, and heroics--the staples of great small-town gossip. Pretty heady stuff for the kid that’s learning who it can trust and what the rules are, along with its species’ equivalent of table manners.
Most young primates get socialized in this way quite effectively, and home must seem homier all the time. Then, inevitably, a lot of the young must leave the group and set out on their own. It is a simple fact driven by genetics and evolution: if everyone stayed on, matured, and reproduced there, and if their kids stayed on, and their kids’ kids too, then ultimately everyone would be pretty closely related. You would have the classic problems of inbreeding--lots of funny-looking kids with six fingers and two tails (as well as more serious genetic problems).
Thus essentially all social primates have evolved mechanisms for adolescent emigration from one group to another. Not all adolescents have to leave. The problem of inbreeding is typically solved so long as all the adolescents of one sex go and make their fortune elsewhere; the members of the other sex can remain at home and mate with the newcomers immigrating to the group. In chimpanzees and gorillas, it is typically the females who leave for new groups, while the males stay home with their mothers. But among most Old World monkeys--baboons, macaques, langurs--it is the males who make the transfer. Why one sex transfers in one species but not in another is a complete mystery, the sort that keeps primatologists arguing with each other ad nauseam.
This pattern of adolescent transfer solves the specter of inbreeding. But to look at it just as a solution to an evolutionary problem is absurdly mechanistic. You can’t lose sight of the fact that those are real animals going through the harrowing process. It is a remarkable thing to observe: every day, in the world of primates, someone young and frightened picks up, leaves Mommy and everyone it knows, and heads off into the unknown.
The transfer pattern I know best is the one among the baboons I study in the grasslands of East Africa. Two troops encounter each other at midday at some sort of natural boundary--a river, for example. As is the baboon propensity in such settings, the males of the two troops carry on with a variety of aggressive displays, hooting and hollering with what they no doubt hope is a great air of menace. Eventually everyone gets bored and goes back to eating and lounging, ignoring the interlopers on the other side of the river. Suddenly you spot the kid--some adolescent in your troop. He stands there at the river’s edge, absolutely riveted. New baboons, a whole bunch of ’em! He runs five steps toward them, runs four back, searches among the other members of his troop to see why no one else seems mesmerized by the strangers. After endless contemplation, he gingerly crosses the river and sits on the very edge of the other bank, scampering back down in a panic should any new baboon so much as glance at him.
A week later, when the troops run into each other again, the kid repeats the pattern. Except this time he spends the afternoon sitting at the edge of the new troop. At the next encounter he follows them for a short distance before the anxiety becomes too much and he turns back. Finally, one brave night, he stays with them. He may vacillate awhile longer, perhaps even ultimately settling on a third troop, but he has begun his transfer into adulthood.
And what an awful experience it is--a painfully lonely, peripheralized stage of life. There are no freshman orientation weeks, no cohorts of newcomers banding together and covering their nervousness with bravado. There is just a baboon kid, all alone on the edge of a new group, and no one there could care less about him. Actually, that is not true-- there are often members of the new troop who pay quite a lot of attention, displaying some of the least charming behavior seen among social primates, and most reminiscent of that of their human cousins. Suppose you are a low- ranking member of that troop: perhaps a puny kid a year or so after your own transfer, or an aging male in decline. You spend most of your time losing fights, being pushed around, having food taken from you by someone of higher rank. You have a list of grievances a mile long and there’s little you can do about it. Sure there are youngsters in the troop that you could harass pretty successfully, but if they are pretransfer age, their mothers--and maybe their fathers and their whole extended family--will descend on you like a ton of bricks. Then suddenly, like a gift from heaven, a new, even punier kid shows up: someone to take it out on. (Among chimps, where females do the transferring, the same thing occurs; resident females are brutally aggressive toward the new female living on the group’s edge.)
Yet that’s only the beginning of a transfer animal’s problems. When, as part of my studies of disease patterns among baboons, I anesthetize and examine transfer males, I find that these young animals are just teeming with parasites. There is no longer anyone to groom them, to sit with them and methodically clean their fur, half for hygiene, half for friendship. And if no one is interested in grooming a recent transfer animal, certainly no one is interested in anything more intimate than that- -in short, it is a time of life filled with masturbation. The young males suffer all the indignities of being certified primate geeks.
They are also highly vulnerable. If a predator attacks, the transfer animal--who is typically peripheral and exposed to begin with--is not likely to recognize the group’s signals and has no one to count on for his defense. I witnessed an incident like this during one of my first research stints in Africa. The unfortunate animal was so new to my group that he rated only a number, 273, instead of a name. The troop was meandering in the midday heat and descended down the bank of a dry streambed into some bad luck: a half-asleep lioness. Panic ensued, with animals running every which way as the lioness stirred--while Male 273 stood bewildered and terribly visible. He was badly mauled and, in a poignant act, crawled for miles to return to his former home troop and die near his mother.
In short, the transfer period is one of the most dangerous and miserable times in a primate’s life. Yet, almost inconceivably, life gets better. One day an adolescent female will sit beside our transfer male and briefly groom him. Some afternoon everyone hungrily descends on a tree in fruit and the older adolescent males forget to chase the newcomer away. One morning the adolescent and an adult male exchange greetings (which, among male baboons, consists of yanking on each other’s penises, a social gesture predicated on trust if ever I saw one). And someday, inevitably, a terrified new transfer male appears on the scene, and our hero, to his perpetual shame perhaps, indulges in the aggressive pleasures of finding someone lower on the ladder to bully.
In a gradual process of assimilation, the transfer animal makes a friend, finds an ally, mates, and rises in the hierarchy of the troop. It can take years. Which is why Hobbes was such an extraordinary beast.
Three years ago my wife and I were spending the summer working with a baboon troop at Amboseli National Park in Kenya, a research site run by the behavioral biologists Jeanne and Stuart Altmann from the University of Chicago. I study the relationships between a baboon’s rank and personality, how its body responds to stress, and what sorts of stress- related diseases it gets. In order to get the physiological data--blood samples to gauge an animal’s stress hormone levels, immune system function, and so on--you have to anesthetize the baboon for a few hours with the aid of a small aluminum blowgun and drug-filled darts. Fill the dart with the right amount of anesthetic, walk up to a baboon, aim, and blow, and he is snoozing five minutes later. Naturally it’s not quite that simple--you can dart only in the mornings (to control for the effect of circadian rhythms on the animal’s hormones). You must ensure there are no predators around to shred the guy, and you must make certain he doesn’t climb a tree before passing out. And most of all, you have to dart and remove him from the troop when none of the other baboons are looking so that you don’t alarm them and disrupt their habituation to the scientists. So essentially, what I do with my college education is creep around in the bushes after a bunch of baboons, waiting for the instant when they are all looking the other way so that I can zip a dart into someone’s tush.
It was about halfway through the season. We were just beginning to get to know the baboons in our troop (named Hook’s troop, for a long- deceased matriarch) and were becoming familiar with their daily routine. Each night they slept in their favorite grove of trees; each morning they rolled out of bed to forage for food in an open savanna strewn with volcanic rocks tossed up eons ago by nearby Mount Kilimanjaro. It was the dry season, which meant the baboons had to do a bit more walking than usual to find food and water, but there was still plenty of both, and the troop had time to lounge around in the shade during the afternoon heat. Dominating the social hierarchy among the males was an imposing character named Ruto, who had joined the troop a few years before and had risen relatively quickly in the ranks. Number two was a male named Fatso, who had had the misfortune of being a rotund adolescent when he’d transferred into the troop years before and was named by a callous researcher. Fat he was no longer. Now a muscular prime-age male, he was Ruto’s most obvious competitor, though still clearly subordinate. It was a fairly peaceful period for the troop; mail was delivered regularly and the trains ran on time.
Then one morning we arrived to find the baboons in complete turmoil. It is not an anthropomorphism to say that everyone was mightily frazzled. There was a new transfer male, and not someone meekly scurrying about the periphery. He was in the middle of the troop, raising hell-- threatening, chasing, and whacking everyone in sight. This nasty, brutish animal was soon named Hobbes (in deference to the seventeenth-century English philosopher who described the life of man as solitary, poor, nasty, brutish, and short).
This is an extremely rare, though not unheard of, event among baboons. The transfer male in such cases is usually a big, muscular, intimidating kid. Maybe he is older than the average seven-year-old transfer male, or perhaps this is his second transfer and he picked up confidence from his first emigration. Maybe he is the son of a high-ranking female in his old troop, raised to feel cocky. In any case, the rare animal with these traits comes on like a truck. And he often gets away with it for a time. As long as he keeps pushing, it will be a while before any of the resident males works up the nerve to confront him. Nobody knows him yet; thus no one knows if he is asking for a fatal injury by being the first fool to challenge this aggressive maniac.
And this was Hobbes’s style. The intimidated males stood around helplessly. Fatso discovered all sorts of errands he had to run elsewhere. Ruto hid behind females. No one else was going to take a stand. Hobbes rose to the number one rank in the troop within a week.
Despite his sudden ascendancy, Hobbes’s success wasn’t going to last forever. He was still a relatively inexperienced kid, and eventually one of the bigger males was bound to cut him down to size. Hobbes had about a month’s free ride. At this point he did something brutally violent but which made a certain grim evolutionary sense. He began to selectively attack pregnant females. He beat and mauled them, causing three out of four to abort within a few days.
One of the great clichés of animal behavior in the context of evolution is that animals act for the good of the species. This idea was discredited in the 1960s but continues to permeate Wild Kingdom-like versions of animal behavior. The more accurate view is that animals usually behave in ways that maximize their own reproduction and the reproduction of their close relatives. This helps explain extraordinary acts of altruism and self-sacrifice in some circumstances, and sickening aggression in others. It’s in this context that Hobbes’s attacks make sense. Were those females to carry through their pregnancies and raise their offspring, they would not be likely to mate again for two years--and who knows where Hobbes would be at that point. Instead he harassed the females into aborting, and they were ovulating again a few weeks later. Although female baboons have a say in whom they mate with, in the case of someone as forceful as Hobbes they have little choice: within weeks Hobbes, still the dominant male in the troop, was mating with two of those three females. (This is not to imply that Hobbes had read his textbooks on evolution, animal behavior, and primate obstetrics and had thought through this strategy. The wording here is a convenient shorthand for the more correct way of stating that his pattern of behavior was almost certainly an unconscious, evolved one.)
As it happened, Hobbes’s arrival on the scene--just as we had darted and tested about half the animals for our studies--afforded us a rare opportunity. We could compare the physiology of the troop before and after his tumultuous transfer. And in a study recently published with Jeanne Altmann and Susan Alberts, I documented the not very surprising fact that Hobbes was stressing the bejesus out of these animals. Their blood levels of cortisol (also known as hydrocortisone), one of the hormones most reliably secreted during stress, rose significantly. At the same time, their numbers of white blood cells, or lymphocytes, the sentinel cells of the immune system that defend the body against infections, declined markedly--another highly reliable index of stress. These stress-response markers were most pronounced in the animals getting the most grief from Hobbes. Unmolested females had three times as many circulating lymphocytes as one poor female who was attacked five times during those first two weeks.
An obvious question: Why doesn’t every new transfer male try something as audaciously successful as Hobbes? For one thing, most transfer males are too small at the typical transfer age of seven years to intimidate a gazelle, let alone an 80-pound adult male baboon. (Hobbes, unusually, weighed a good 70 pounds.) Most don’t have the personality needed for this sort of unpleasantry. Moreover, it’s a risky strategy, as someone like Hobbes stands a good chance of sustaining a crippling injury early in life.
But there was another reason as well, which didn’t become apparent until later. One morning, when Hobbes was concentrating on who to hassle next and paying no attention to us, I managed to put a dart into his haunches. Months later, when examining his blood sample in the laboratory, we found that Hobbes had among the highest levels of cortisol in the troop and extremely low lymphocyte counts, less than one-quarter the troop average. (Ruto and Fatso, sitting on the sidelines now, had three and six times as many lymphocytes as Hobbes had.) The young baboon was experiencing a massive stress response himself, larger even than those of the females he was harassing, and certainly larger than is typical of the other, meek transfer males I’ve studied. In other words, it doesn’t come cheap to be a bastard 12 hours a day--a couple of months of this sort of thing is likely to exert a physiological toll.
As a postscript, Hobbes did not hold on to his position. Within five months he was toppled, dropping down to number three in the hierarchy. After three years in the troop, he disappeared into the sunset, transferring out to parts unknown to try his luck in some other troop.
All this only reaffirms that transferring is awful for adolescents--whether they’re average geeks opting for the route of slow acceptance or rare animals like Hobbes who try to take a troop by storm. Either way it’s an ordeal, and the young animals pay a heavy price. The marvel is that they keep on doing it. Transferring may solve the inbreeding problem for a population; but what’s in it for the individual?
Adolescent transfer is a feature of many social mammals, not just primates, and the mechanisms can differ. Sometimes transfer can arise from intrasexual competition--a fancy way of saying that the adolescents are driven from the group by a more powerful same-sex competitor. You see this in species like gazelles and impalas, for example. The core social group consists of a single breeding male, a large collection of females, and their offspring. At any given point some of those male offspring are likely to be entering puberty. But since the breeding male typically doesn’t hold on to his precarious position for long, he is probably not the father of these adolescent males. He doesn’t view them as sons coming of age but as unrelated males becoming reproductive competitors. At their first signs of puberty he violently drives them out of the group.
In primates, however, forced dispersion almost never happens. Critically, these adolescents choose to go--even though the move seems crazy. After all, they live in a troop surrounded by family and friends. They know their home turf, which trees are fruiting at what time of year, where the local predators tend to lurk. Yet they leave these home comforts to endure parasites, predators, and loneliness. And why? To dwell among strangers who treat them terribly. It makes no sense, from the standpoint of the individual animal. Behaviorist theories state this more formally: animals, including humans, tend to do things for which they are rewarded and tend not to do things for which they get punished. Yet here they are, leaving their comfortable, rewarding world in order to be amply dumped on far away. Furthermore, animals tend to hate novelty. Put a rat in a new cage, give it a new feeding pattern, and it exhibits a stress response. Yet here young primates are risking life and limb for novelty. Old World monkeys have been known to transfer up to five times over their lifetime, or travel nearly 40 miles to a new troop. Why should any individual in its right mind want to do this?
I do not know why transfer occurs, but it is clearly very deeply rooted. Humans, in part because their diets are adaptable, are the most widely distributed mammal on Earth, inhabiting nearly every godforsaken corner of this planet. Among our primate relatives, those with the least finicky of diets, such as baboons, are also among the most widely distributed beasts on Earth (African baboons range from desert to rain forest, from mountain to savanna). Inevitably, someone had to be the first to set foot in each of those new worlds, an individual who transferred in a big way. And it is overwhelmingly likely a young individual who did that.
This love affair with risk and novelty seems to be why the young of all our primate species are the most likely to die of accidents, doing foolhardy things while their elders cluck over how they told them so. And it is also the reason that the young are most likely to discover something really new and extraordinary, whether in the physical or the intellectual realm. When the novel practice of washing food in seawater was discovered by snow monkeys in Japan, it was a youngster who did so, and it was her playmates who picked up the adaptation; hardly any of the older animals did. And when Darwin’s ideas about evolution swept through academic primates in the mid-nineteenth century, it was the new, up-and-coming generation of scientists that embraced his ideas with the greatest enthusiasm.
You don’t have to search far for other examples. Think of the tradition of near-adolescent mathematicians revolutionizing their fields, or of the young Picasso and Stravinsky galvanizing twentieth-century culture. Think about teenagers inevitably, irresistibly wanting to drive too fast, or trying out some new improvisatory sport guaranteed to break their necks, or marching off in an excited frenzy to whatever stupid war their elders have invented. Think of the endless young people leaving their homes, homes perhaps rife with poverty or oppression, but still their homes, to go off to find new worlds.
Part of the reason for the evolutionary success of primates, human or otherwise, is that we are a pretty smart collection of animals. What’s more, our thumbs work in particularly fancy and advantageous ways, and we’re more flexible about food than most. But our primate essence is more than just abstract reasoning, dexterous thumbs, and omnivorous diets. Another key to our success must have something to do with this voluntary transfer process, this primate legacy of getting an itch around adolescence. How did voluntary dispersal evolve? What is going on with that individual’s genes, hormones, and neurotransmitters to make it hit the road? We don’t know, but we do know that following this urge is one of the most resonantly primate of acts. A young male baboon stands riveted at the river’s edge; an adolescent female chimp cranes to catch a glimpse of the chimps from the next valley. New animals, a whole bunch of ’em! To hell with logic and sensible behavior, to hell with tradition and respecting your elders, to hell with this drab little town, and to hell with that knot of fear in your stomach. Curiosity, excitement, adventure--the hunger for novelty is something fundamentally daft, rash, and enriching that we share with our whole taxonomic order.
