Why We Run: A Natural History - Bernd Heinrich (2002)
Chapter 13. Evolution of Intelligent Running Ape People
When you experience the run, you…relive the hunt. Running is about thirty miles of chasing prey that can outrun you in a sprint, and tracking it down and bringing life back to your village. It’s a beautiful thing.
the 2000 American national champion at 25 kilometers
The apelike creatures that were our ancestors were a strange breed. They were perhaps at first awkward scavengers on the African plains, who later became bipedal predators. They were neither big nor swift and had to make up for it with sociality and smarts.
The above scenario of our evolution as bipedal savanna hunting apes and ultimately people is like a large house with many rooms in various stages of construction, from rough to nearly finished. It is the result of constant restructuring and elaboration by many builders of a great range of expertise. The various parts were contributed or built by paleontologists, anthropologists, behavioral field biologists, ecologists, physiologists, and anatomists. I will here try to show some of the evidence and logic for the construction of the main frame of the house that contains so much. I will then explore what I think are ramifications relative to our psychological and physiological capacities as endurance predators. In this limited space I cannot here argue all the pros and cons of each specific point. I can only review the scenario as it seems to me to make the most sense. And a central part of that scenario is, I think, our endurance. Furthermore, the key to endurance, as all distance runners know, is not just a matter of sweat glands. It’s vision. To endure is to have a clear goal and the ability to extrapolate to it with the mind—the ability to keep in mind what is not before the eye. Vision allows us to reach into the future, whether it’s to kill an antelope or to achieve a record time in a race.
Our specialty as bipedal runners spans a history of at least 6 million years. It probably began in Africa, when open or semiopen plains were replacing forests and our ancestors began to diverge from other apelike creatures to venture out of the forests and feed on the vast assemblage of herbivores supported by the growing seas of grass. There were many other predators out there and little safety from them in trees. Nor was it easy to hide.
Life on the plains generates arms races between predators and prey. Here we find such sprint champions as the cheetah and the various species of antelopes it hunts. Also on the plains were (and still are) such cooperative predators as pack-running canids and hyenas, which catch prey by capitalizing on the weakness that sprint speed produces, namely compromised endurance. In turn, the sprinting prey species sought and found some measure of safety in numbers. Antelopes are consummate herd animals.
The very first bipedal hominids were undoubtedly not superb runners and they needed alternatives to raw running speed for survival. They would have cooperated to hunt, as some monkeys and apes do today. On the plains, even some normally solitary predators became social in order to hunt. Lions, who live in groups unlike all other felines, are a prime example.
Speed was useful, and necessary as well. We’d never run 60 miles an hour like a cheetah, but a cheetah doesn’t need to run for an hour. It needs to run only for a half minute, and it can’t run much farther before it runs head-on into the problem of overheating and lactic acid buildup, and must stop. The speed-disadvantaged hominids had other advantages beyond their already existing sociality. Not only did they have grasping hands useful for climbing and throwing, and ultimately for tool use, plus an edge on intelligence, they also developed running endurance while remaining upright.
Human bipedalism in running has been thought enigmatic because it is energetically expensive relative to quadrupedal running. Nevertheless, when used for traveling long distances on the plains, bipedalism was likely a great improvement over the knuckle-walking of hominids’ ancestors. In evolution, almost every solution is the result of compromises. Energy efficiency was sacrificed in favor of freeing the hands for other use. For instance, hands were useful not only for throwing rocks and sticks, and later for making, carrying, and using weapons, but also for carrying our babies and prey to our safe campsites. Our progenitors, like chimps today, could likely hurl objects. By standing upright, they could see farther and defend themselves, when necessary, in several directions at once.
British physiologist Peter Wheeler has proposed that our bipedalism evolved in part for thermoregulation under exposure to the blazing tropical sun. As the examples of the hawk moths, bees, and camels demonstrated, reducing heat input or increasing heat loss translates to greater endurance. Wheeler photographed a model humanoid in either bipedal versus quadrupedal posture and found that in the bipedal posture it experienced 60 percent less direct solar radiation. In addition, in that posture the body is better situated to take advantage of breezes for convective cooling. As I’ve discussed (Chapter 12), bipedalism can enhance speed, but even if it did not, and even if it is more energetically costly, it was still a better bargain than giving up our tool-using hands, reducing our visual range, and compromising our endurance in the heat. So, on balance, human bipedalism is not enigmatic at all.
The hominid line to which we belong likely diverged from apelike creatures about 5 to 8 million years ago. The first fossil traces of that hominid line have been found in 4.4-million-year-old rocks from Ethiopia that contain a creature called Ardipithecus ramidus. The australopithecines, or “southern apes” (after their discovery in Southern Africa), which were derived from Ardipithecus, were small brained relative to us, but as determined from skeletal remains and from footprints, they already walked upright. Australopithecus afarensis, of Lucy fame—the three-and-a-half-foot-tall female, was discovered in Ethiopia in 1974—is one of the best-known australopithecine fossils found. Australopithecines were bipedal intermediaries between the apelike and the subsequent Homo-like forms and were unlikely to have been able to outrun most large predators. Australopithecines needed other defenses. The endurance running capability that subsequently evolved in humans and that was derived from australopithecines must have been under some selective pressure other than avoiding predation.
Most likely, the australopithecines diverged from forest dwellers to occupy the dangerous plains not to avoid predation but to seek food there, despite, and perhaps because of, the predation there. Meat was in abundance on the plains for those who could catch it, for those who could take it from such other carnivores as leopards, cheetahs, and lions, and for those who could compete for it against hyenas, jackals, and vultures.
Given the reasonable assumption that the australopithecines were group-living as most present-day apes, it is not difficult to envision a plausible scenario for how they got their food. Traveling in groups and coming upon a predator-killed carcass, they might have chased off the owner with sticks and rocks. Takeovers would have been difficult at night, and it would have been easiest in the middle of the day when the predator had retired into the shade, leaving carcasses untended or at least less vigorously defended.
Intelligent hominids would have quickly learned how to find carcasses. Some years ago, I dropped off a dead horse near my mother’s house in Maine to feed ravens. Her two dogs found the carcass with the raven crowd. Ever since then, the dogs have become eager raven watchers. Early plains hominids would have been no less able than circling vultures, my mother’s dogs, and myself to recognize and heed signs of a recent kill.
On the African veldt, most predators need to kill frequently, because what they don’t eat almost immediately is consumed by scavengers or spoils quickly. There is great competition for scavengers to be there first after a kill has been made, and the fastest come on the wing. In an intact northern ecosystem, Yellowstone Park, it is the same, only there the scavengers that come within a minute or so of wolves’ making a kill are ravens, not vultures. Eagles, bears, and coyotes then use the ravens’ activity as a cue that indicates the kill, and they also rush in. In Yellowstone, within about seven hours after wolves kill an elk there is nothing left but the bones. In Africa even the bones are eaten (by hyenas), and the carcasses are consumed even quicker.
During my year in Tanganyika (now Tanzania), I found one morning an unattended freshly dead cow in a deep streambed. By noon, when I came by again, there were well over a hundred vultures there feeding, and more were still streaming in all the time from all directions at once. Vultures, too, find carcasses by watching others, and their mobility allows these birds to exploit the diurnal niche of predator-provided meat. Similar competition for predator-killed carcasses would have existed on the grass savannas where our anthropoid ancestors evolved. Then as now, traveling fast and long would have been a great premium for getting to predator-killed carcasses before the competitors devoured it. Ultimately, the hominids’ mobility in the heat could have been transferred to getting their own fresh meat, by hunting.
Although the earliest australopithecine-like hominids were probably not swift enough to run down healthy adult antelopes, there were undoubtedly many advantages for them to become ever faster. The races against scavengers and against others of their own species, that is, their closest competitors, could have become the bridge to races with formidable live prey. Once hominids were fast enough, they potentially could run down such weaker prey as calves, the old, and the injured.
Ultimately, what early hominids did routinely may have been less significant than what they could do in the times of greatest need, such as when no dead or injured animals were available. Running ability would have become ever-more valuable on the plains after meat became an important part of the diet. By about 2 to 3 million years ago, the bipedal plains hominids already had a leg and foot structure almost identical to our own. The fossilized footprints that Mary Leakey discovered show that they walked like us. It is reasonable to suppose that they could also run even before they evolved to several species of Homo, of which H. erectus was the first to leave Africa.
Another theory, one recently proposed by Richard W. Wrangham and colleagues, is that the big evolutionary change from australopithecines to Homo occurred after the invention of cooking, primarily of energy-rich underground tubers. Cooked food, being easier to digest than raw, increased the available energy supply and freed us up to hunt. If so, then the cooking hypothesis is not an alternate to the hunting hypothesis. Rather, it is one complementary to it; both cooking and meat eating would have promoted reduction of gut size, improved speed, and range of movement, and permitted even more hunting.
At this point in the argument, there will surely be skeptics who will doubt that our ancient hominid ancestors could become specialized enough as endurance predators to outrun swift prey that had already evolved to outsprint the world’s swiftest predators. To elaborate the hypothesis, it is now necessary first to examine what some present-day apes do routinely, and then to consider the evolution of our uniquely human physiology, social structure, and psychology.
Chimps are generally considered to be frugivores. Nevertheless, they prize meat and hunt monkeys, young antelopes, and other mammals. Studying hunting parties of male chimps at Gombe in 1995, Craig Stanford found them depleting one-fifth of their prey population of colobus monkeys each year. Group hunts are effective. In just a half day of observing olive baboons in Kenya’s Amboseli Park, I once saw a troupe of about fifty individuals catch a hare, tear it apart, and eat it with great gusto. Only two or three individuals of the dispersed troupe chased the hare, but the panicked animal was intercepted by others.
Hunting by chimps and baboons is largely secondary to other foraging, but prey is almost routinely taken as opportunity affords. These primates do not rely on meat, nor do they travel long distances in pursuit, yet they eat meat when they can, and sometimes they even hunt systematically and with great vigor. In short, even hominids that are unspecialized for a meat diet are willing and able not only to eat meat but also to hunt.
If our hominid ancestors millions of years ago on the hot open African grass plains relied on meat, they would presumably have evolved physiological adaptations to help them obtain it. Animals evolve unique features and capacities when they face unique situations. Of all the insects, for example, only the Apache desert cicada, Diceroprocta apacha, has evolved a sweating response. This insect has water available for use because it sucks plant juice, and sweating not only permits it to be active at noon on the hottest days in the hottest season of the year, it also chooses that time to be active, when it escapes its avian predators, because they are forced to yield the field. Similarly, the uniquely heat-tolerant Saharan desert ants, Cataglyphis bambycina, become active only when their major predators (lizards) retire from the heat. A similar scenario of taking to the field when the great predators were forced to lie low, and were less able to vigorously defend their kills, likely applies to our hominid ancestors. Humans are unique, as I will show, in having an ample sweating response that allows them to engage in sustained running in the heat, even under direct sun. Furthermore, our 3 million sweat glands excrete not only water for cooling but also toxic metabolic wastes, such as the ammonia and uric acid that are produced when we eat meat.
During my year on the bird-hunting expedition of Tanganyika, I experienced what ancient hunters were up against. I shall never forget my feelings of dreary claustrophobia during the months we spent in wet, dense, dripping mountain forests. These times contrasted with feelings of glorious exhilaration when I was out on the open savanna steppe with its scattered acacia trees and large vistas. On the savanna, to catch even small birds, I had to wander extensively. I wandered half of each day until it was time to return to camp, where my mother cooked our meals and prepared the day’s specimens. I never carried water with me, to avoid being encumbered, but I was often forced to slow down or rest due to the heat. Although the heat often made my bird hunting difficult at midday, I could still travel freely. I could cope because I sweat copiously.
Internally generated heat in an animal forced to keep moving or exercising in the heat on the open plains under the African equatorial sun is one of the most potent factors limiting endurance. I could literally feel that fact, and I had shown experimentally that hawk moths, even without solar heat input, are limited to about two minutes of exercise even at modest room temperatures if their mechanism for getting rid of metabolic heat is disrupted. Similarly, jackrabbits, kangaroos, and cheetahs, even without experimental disruption of their heat-dissipating ability, are limited to only a few minutes of running under common field conditions. It is a reasonable assumption that our ancestors would also have experienced selective pressure not only to get rid of body heat by sweating, but also to reduce heat input from the sun in order to maintain sustained physical activity at a time when they had perhaps the most to gain.
Different animals have evolved diverse means of dealing with often debilitating direct solar radiation. In New Guinea, close to the equator as in Central Africa, I found that butterflies heat to lethal body temperatures in as little as one minute if subjected to direct sunshine and prevented from using their wings for shading.
Our erect posture (with our consequent bipedal locomotion) would have been a preadaptation for us in the equatorial sun, both reducing the total amount of direct exposure to solar input and simultaneously increasing the area of exposure of skin to moving and cooling air. The tops of our heads would have been the area where solar input is focused to, potentially endangering the extremely heat-sensitive brain because of its already high internal heat load from metabolism. Thus, although bipedalism reduced overall heat input, it would have accentuated local heating of the most heat-sensitive body part.
A solution to this problem evolved. The human brain has a special network of veins that acts as a heat radiator to dissipate the extra heat load. Vein tracks on fossil skull bones indicate that the gracile australopithecines already had the same blood circulating network; this indicates that they had experienced strong selective pressure to prevent overheating.
Insects have analogous solutions. I heated honeybees on the head and discovered they not only regurgitated liquid for cooling, they also pumped more blood through the head to help carry the heat away. As in other animals subjected to potential overheating from the sun, upright hominids on the open equatorial plains likely would have evolved heat shields to reduce the solar heat input to the brain. Desert ground squirrels shield themselves with their bushy tail, desert beetles use their wing covers, camels have humps and thick dorsal hair—and we are unique in having bushy head hair that covers both head and shoulders from the sun’s rays. Head hair probably evolved in part for the very purpose that it now can still serve, although it later could also have become a sexually selected trait. Later still it would also have served as insulation to reduce body heat loss, after Homo erectus left Africa and invaded the mammoth steppes of the north and became ever more reliant on a meat diet. That latter invasion occurred recently, only about sixty thousand years ago, and it may have coincided with the inventions of spear throwing and clothing.
Our nakedness and exceptionally numerous and well-developed sweat glands are potent features that contribute to running speed under external and internal heat. Because of sweating, we can tolerate very high heat loads derived from internal metabolism and the exterior environment. But the endurance that capacity buys costs us much water. On a continuous run of over 60 miles on a moderate to cool day, an ultramarathoner may lose nearly 20 pounds of water by sweating alone. Without sweating, running speed and range would be dramatically reduced. Most arid-land animals are compromised in endurance because they are highly adapted to conserve water. The fact that we, as savanna-adapted animals, have such a hypertrophied sweating response implies that if we are naturally so profligate with water, it can only be because of some very big advantage. The most likely advantage was that it permitted us to perform prolonged exercise in the heat. We don’t need a sweating response to outrun predators, because that requires relatively short, fast sprinting, where accumulating a heat load is, like a lactic acid load, acceptable. What we do need sweating for is to sustain running in the heat of the day—the time when most predators retire into the shade.
Our ancient legacy as endurance predators is now, in “Western” cultures, effectively masked by recent changes in our ways of living. The Khoisan people of Southern Africa (Hottentots and Bushmen) were well known for being able to run down swift prey, including steenboks, gemsboks, wildebeests, and zebras, provided they could hunt in the heat of the day. The Tarahumara Indians of northern Mexico chase down deer till the animals are exhausted, then throttle them to death by hand. The Paiutes and Navajos were reported to do the same with pronghorn antelopes. Australian Aborigines chase down kangaroos, but only by forcing them to reach lethal body temperatures.
Each predator capitalizes on its strengths, brought to bear on the prey’s weakness. Most predators catch their prey by a combination of surprise and sprint, or by singling out the young, old, or weak. In turn, prey escape by sprinting. Since they usually will not be pursued for very long, it pays prey animals to sprint fast, a behavioral trait that the human predator can exploit. As the previously mentioned anecdotes from my friend Barre Toelken have suggested, chased deer have little sense of pace. The sprints cost them dearly in the end. If the predator is not induced to give up after seeing the deer’s brilliant sprint exhibition, then the accumulated lactic acid and body heat can be exploited. Humans who capitalize on the deer’s weaknesses by having a longer vision—a view further into the future—can be a superpredator through the agency of mind power.
It is a truism that animals have evolved to match their morphology and physiology, along with their behavior, creating a coherent unit that fits them to their environment. In Africa, one can distinguish the European migrant birds from the residents by their longer, narrower wings, which in turn indicate greater flight endurance and their behavioral responses of launching themselves biannually on migration. Owls have eyes and ears tuned to detect mice, the unique behavior of hunting by sitting still at night and then pouncing to grasp prey with their feet, and hooked bills for tearing flesh. Kingfishers have sharp, long bills for catching fish, the physiology to digest fish and be nourished by fish proteins, and perhaps more important, the very specific behavior of diving down from a perch at moving objects underwater. Our behavioral and psychological tendencies are also matched to the structure of our bodies, to adapt us to the environment we faced in the past.
The early pack-hunting hominids likely would have been at least as flexible in their hunting behavior as packs of African wild dogs and wolves are today. Specialized skills are required to kill zebras and bison, and learned skills in these canid groups are handed down over the generations. The more learning, the more possible diversity, so we can’t draw absolute conclusions.
We are behaviorally much more flexible than most other animals. Proximally we are now so flexible that we get food in any way that we have to; that obscures our innate tendencies. We probably don’t work on an assembly line or as a bank teller because that is what we prefer doing above all else in the world. We may not really know what might suit us most of all, because we don’t get the exposure to find out and we become culturally biased. I had the opportunity to be out in free, wild nature to hunt. Of course, I no longer shoot little birds with a shotgun, though I still marvel at the excitement I used to feel, and that ornithologists almost universally felt at the turn of the century when they discovered new birds.
I grew up in Maine hunting deer, and that seemed to me the most absorbing activity humanly possible. I still participate in the Maine deer hunt in the fall. Getting my meat from an animal that is wild and has a chance to escape, rather than from one confined in a factory pen and raised for slaughter only, is just part of the reason. Aside from moral considerations, I hunt because of the allure. I wander the woods for days, searching for clues, hoping to see signs, and getting excited by every track. But I’m rarely “successful.” Every fall, I hope that I’ll get that big buck, but it eludes me. Why do so many of us bother to hunt when the chances of success are so slim? The answer came to me on a recent trip to Yellowstone Park. I saw elk, bison, bighorn sheep, and mule deer from within several yards. As I saw these beautiful animals that were tame, I knew that even if hunting them were allowed, I would have not the slightest desire to do so. The very idea was repulsive. Why? Because simply shooting animals is not hunting at all. Not even close.
It is not killing that motivates, nor is it the prize as such. The allure is in being out in the woods, in having all senses on edge, and in the chase. The white-tailed deer in the Maine woods are alert to scent, sound, and sight. They are shy, swift, wily.
The qualities that attract us to hunting are precisely the ones that dissuade the other great predators, those that do not have to chase their prey very far. Those great cats and hunting dogs take not that which is most difficult, but that which is easiest—they are very selective, trying to take the old, the young, the weak, the diseased; and the most preferred of all are the already deceased.
We are a different sort of predator. We can’t outsprint most prey. We are psychologically evolved to pursue long-range goals, because through millions of years that is what we on average had to do in order to eat. To us, even an old deer that had not yet been caught would have required a very long chase. It would have required strategy, knowledge, and persistence. Those hominids who didn’t have the taste for the long hunt, as such, perhaps for its own sake, would very seldom have been successful. They left fewer descendants.
Our ancient type of hunting—where we were superior relative to other predators—required us to maintain long-term vision that both rewarded us by the chase itself and that held the prize in our imagination even when it was out of sight, smell, and hearing. It was not just sweat glands that made us premier endurance predators. It was also our minds fueled by passion. Our enthusiasm for the chase had to be like the migratory birds’ passion to fly off on their great journeys, as if propelled by dreams.
A quick pounce-and-kill requires no dream. Dreams are the beacons that carry us far ahead into the hunt, into the future, and into a marathon. We can visualize far ahead. We see our quarry even as it recedes over the hills and into the mists. It is still in our mind’s eye, still a target, and imagination becomes the main motivator. It is the pull that allows us to reach into the future, whether it is to kill a mammoth or an antelope, or to write a book, or to achieve record time in a race. Other things being equal, those hunters who had the most love of nature would be the ones who sought out all its allures. They were the ones who persisted the longest on the trail. They derived pleasure from being out, exploring, and traveling afar. When they felt fatigue and pain, they did not stop, because their dream carried them still forward. They were our ancestors.
Sometimes I wonder if this ability to have long-range vision, if not also the drive to explore, might not also have been the boost that gave us our unique brain power to extrapolate. The currently popular explanation of our unique intelligence is thought to be related to deception in the social context. Deception indeed tweaks capacities for mental visualization, and there is little debate that social interactions involve keeping track of individuals, trading favors, pay-backs, and possibly deceiving. In support of this idea of intelligence based on sociality, brain size in animals correlates with group size. Did, then, Homo erectus live in super-large groups relative to other animals? That’s unlikely; these archaic humans were hunters, likely living in small groups, and their brain size already overlapped with that of moderns. Another hypothesis, also a nonexclusive one, is that sexual selection was a driving force in the hunting syndrome. There is no either-or answer; all factors likely acted in concert, but I’ll briefly examine the last hypothesis.
The mere fact that we can run down some of the swiftest ungulates, animals that have evolved to outrun the swiftest predators, indicates that we are indeed highly specialized, physiologically and psychologically, for that particular task. But there is a sexual difference. Curiously, in all human cultures that have been examined, as well as in baboons and chimpanzees, hunting is largely a male activity. Sexual specialization is common in animals. In some hawks, for example, females are larger than males and catch the larger prey, while the males specialize in the smaller prey. As a consequence, the sexes in effect achieve a division of labor in foraging, causing less depletion of the food supply near the nest.
For the protohominid females, pregnant or burdened by offspring who needed to be carried along, hunting for large animal prey requiring long pursuit was even more difficult than it is for present-day apes. Having become naked to increase heat loss, the young could no longer hang on to their mothers’ fur but rather had to be held. Through food sharing, a multifaceted male-female symbiosis evolved. Adult men were free to hunt, but women foraged and chose mates. On what basis did they choose?
The females with young could not readily take part in long exhaustive hunts, and they needed to enlist the aid of males to provide them and their families food. Hunters killing large animals had a temporary superabundance of meat, which could not be stored. How could it be used? It was brought home, to be shared in mutual obligations with other hunters, and to trade for sex. Sleeping together and eating together became interrelated. It is an old formula. Chimps trade sex for food routinely, as do baboons. Craig Stanford, who studied the hunting practices of chimps at Gombe, says, “Chimps use meat not only for nutrition; they also share it with their allies, withhold it from their rivals. Meat is thus a social, political, and even a reproductive tool.” Similarly, among the Aché of South America, women prefer successful hunters, the meat providers. Similar correlations between reproductive choices and resources exist in most societies where the limiting factor to reproduction in females with young is resources. For males, the limitation is more commonly sex.
For! Kung Bushmen, meat is only a small part of the diet, but it is the food they desire most. The women bring in the bulk of the food, feeding the band from day to day on berries, bulbs, leaves, and roots. The men hunt, oftener than not having little to show at the end of the day. Still, hunting is deemed highly important. Only after a boy makes his first kill of a large antelope does his father perform the rite of the first kill, which marks his passage from adolescence to manhood. A male! Kung who does not hunt remains a child who cannot marry. He cannot expect to have a wife if he cannot bring home meat and skins for his family and parents-in-law. Bushmen males hunt from the time of adolescence until they are old. Often they travel 30 kilometers per day, come home with nothing, and by next morning are off again, impelled by their will to persist, if not their wives’ goading. They carry no food or water with them, because that hinders their ability to travel.! Kung hunters might follow a wounded giraffe for five days. This is not work that women carrying infants can perform. Division of labor, though perhaps currently not politically correct, is an ancient tradition with deep biological roots. And there is nothing wrong with diversity, either between people or between sexes. Division of labor has allowed men to rely on women to feed them, and enabled them to engage in long-range hunts after large prey that required traveling rapidly and unencumbered over long distances.
Contrary to some presumptions and misconceptions, the idea of man the hunter as a driving force in human evolution neither denigrates women nor relegates them to a passive role. Misconceptions can be minimized if we read “man” as “humankind.” Evolution has not very likely affixed the huge complement of genes that affect growth and development of the brain and human evolution onto the Y (male) chromosome. The different behavioral tendencies of men and women, at least those regarding long-term cooperation to rear children, can best be explained in terms of compromise and cooperation. If “man” is the hunter, then it is because women permitted or selected him to be. They are the other half of the same man-the-hunter syndrome. Women had to become intelligent choosers, because choice could not be trusted to appearance alone.
Sexual selection in the animal world often results in such runaway scenarios as the notorious peacock’s tail, the elaborate songs of some birds, and even balloon making in flies, which I will discuss later. If the hypothesis that hunting is, in part, also a consequence of sexual selection, rather than merely a device for the fulfillment of caloric requirements, then there are wide repercussions, because with energetics removed as the primary constraint on hunting, there are few limits. If bringing a rabbit back to the group can enhance a hunter’s sexual desirability, then just imagine if he kills a mammoth or has the ability to do so, while the woman develops the capacity to evaluate!
The strategy of supplying protein to secure mating privileges is the rule in many male birds, spiders, and insects, especially in scorpion flies (Panorpa), some grasshoppers, crickets, and cockroaches, and some beetles (Malochiidae). Among insects, the nuptial gift food offering may be prey, or in the absence of prey, protein from body secretions. In some mantids and spiders, it is the male’s own flesh.
Male mantids are legendary suitors, who regularly make the ultimate sacrifice for sex: their own bodies. They are cannibalized by the females with whom they mate. The benefits of offering themselves (usually reluctantly) may go beyond just providing a dietary supplement that ultimately provides nutrition to the eggs he has fertilized. The females first eat the male’s head. Males with intact heads mate for only four hours, but the encounters that result in decapitation last up to twenty-four hours. Maydianne Andrade, who studied Australian redback spiders, has shown that being eaten prolongs copulation and increases the amount of sperm transfer. In this spider, allowing himself to be eaten also prevents the female from mating with other males, since a satiated female spider rejects other suitors and the “victim’s” sperm thus have precedence in fertilization. Spiders die for sex, and their suicidal behavior has, ironically, evolved because it increases their individual fitness.
These extremes alert us to mechanisms that might otherwise remain hidden in our species. All animals have to pay something for sex. My favorite example, because it is in some ways a caricature of the human situation while at the same time illuminating of the evolutionary process, is that of dance flies (Empididae). These European and North American flies are predators that hunt other flies. Their name is derived from their group gatherings, during which these insects fly up and down and sometimes in distinctive lines and curves, or dances. Females choose mates from among the dancers on the basis of the male’s energetic displays and the male’s offerings during those dances.
To have a chance of mating, a male must sustain himself in hovering flight while holding a nuptial offering of a fly carcass in his feet. Females size up the lineup, then pick and choose. Couples then drop to the ground, where the males transfer their offering to the females, which then eat their offered prey.
A small fly carcass suffices as a suitable mating inducement in some species of empids. Another step in the evolutionary progression is found in other species, where the male wraps the prey in a fine shiny veil that he weaves with spinning glands on his forelegs. A silk-wrapped nuptial gift is more attractive to the females than an unwrapped one, possibly because it appears larger in size and is more conspicuous than unadorned or unadvertised prey.
The next step in the evolutionary progression seems downright devious. Some males dance carrying an even larger and more conspicuous package, but one that contains a fly that is too little to eat (but easier to carry and thus show off), an inedible piece of debris, or nothing at all. For example, in Empis politea, the male carries a great white egg-shaped balloon within which he may or may not enclose a little fly. The female pays no attention to a male carrying a fly. She goes for a big, showy but empty package.
In Hilaria sartar, S. sartrix, and H. granditarsis the males have taken the final step in deception. They always carry an empty gleaming white oval balloon throughout the course of their ever more acrobatic dance. If a foolish male were to attempt to hoist a balloon containing prey, he would be badly outclassed by dancers with lightweight balloons. Hoisting heavy prey offering would be possible only at high temperatures, when the fly’s muscles could achieve the high work output required.
The flies prove the point that, as with the scenario that anthropologists have proposed for humans, it is not the nutritional value of the offering that counts. The showing off does. One difference is that human hunters can’t cheat. In the protohominids, the males had to bring home real meat, or demonstrate ability to do so, not just hoist pretty empty packages. Meat was a valued resource that was an important and necessary part of the diet.
As in the dancing flies, vigor or capability can sometimes be evaluated on the basis of physical appearance, but it is more reliably based on performance, either in hunting or in symbolic representation. Could the origin of our dances, like our athletic games that provide worthless colored ribbons and metal or fake metal trophies, be symbolic activities that show off our capacities?
A race is like a chase. Finishing a marathon, setting a record, making a scientific discovery, creating a great work of art—all, I believe, are substitute chases we submit to that require, and exhibit, the psychological tools of an endurance predator, both to do and to evaluate. When fifty thousand people line up to race a marathon, or two dozen high schoolers toe the line for a cross-country race, they are enacting a symbolic communal hunt, to be first at the kill, or at least to take part in it.
The real hunt is long out of date to most of us. Very recently (geologically) we eradicated some of the most magnificent creatures that were ever on this globe when we came, as full-fledged hunters, into contact with them in America, Australia, Madagascar…We had by then evolved the psychology, physiology, and technology to make us extraordinary hunters. In contrast to those in Africa, our homeland, our new prey did not have time to evolve effective evasive responses to our unique hunting capabilities, which combined physiology and psychology with intelligence, and ultimately also weapons.
It is fortunate that we have now invented some ecologically friendly redirections of our hunting tendencies. We can now chase one another rather than mammoths and mastodons. We can be road warriors, who will have races to run forever. Now we dream not of killing great beasts to be heroes as we provide nourishment for our social band. We may dream—and get the same psychic nourishment that was once necessary to provide bodily nourishment—of winning races or setting records or fulfilling other long-term goals. In the Olympics we witness the biggest hunt. If we can’t be part of it, then as spectators we cheer for those who represent us, who are really a part of us, since through our evolutionary time of millions of years we were (and still are) mutually interdependent. There is one main difference, though. In contrast to hunting prey animals, where there is always an end point, in chasing against one another there is no end point. Where can it end? What are the limits?