Why We Run: A Natural History - Bernd Heinrich (2002)
Chapter 9. The Antelope’s Running Prowess
To the farthest limit he searches out….
Our world is full of countless mythical antelopes that one could race forever, chase, and never catch. Yet even those fleet-footed ones of hide, bone, flesh, blood, and guts that appear to be invincible are mortal. One legendary animal that seems ambiguous, hovering as it does in between the real that you can touch and the humanly unattainable, is the pronghorn antelope of the American plains. It has been clocked running at 61 miles per hour—almost twice as fast as a racehorse—and not just in a short sprint. It can reputedly cover 7 miles in 10 minutes. The Hopi tribe believed the antelope to be a spirit messenger and a powerful medicine. In a recent issue of the international journal Nature, the pronghorn was declared the world’s premier ultrarunning animal, the best distance runner that muscle and bone and blood could produce. It is, of course, a mammal, and to the tiniest detail of our anatomy and biochemistry, we are also mammals. What exactly does the pronghorn antelope have that we don’t, and how did it become such a superb runner?
For over at least 4 million years, the pronghorn (Antilocapra americana) has coexisted with predators on the open plains of North America. It has evolved in a habitat that offers long views in many directions, and it has survived not by hiding from its predators but by outrunning them. In turn, the predators—most likely saber-toothed tigers, wolves, cheetahs, giant short-faced bears, dire wolves, dholes, and hyenas—have had to come close to matching its running performance. In the “arms race” for speed and endurance that was waged for millions of years, the slowest pronghorn in many a chase got eaten. Weaknesses were exposed and culled out of the gene pool. John A. Byers, at the University of Idaho, points out that at the present time, “pronghorn are ridiculously too fast for any modern predator,” and their running prowess is a “ghost” of that previous selective pressure that was greatly relaxed about ten thousand years ago after the late Pleistocene extinctions that decimated the North American fauna, at about the same time that humans arrived in America from Asia across the Bering land bridge.
One key to the pronghorn antelope’s unique performance is its extraordinarily high maximum rate of power output (the previously mentioned aerobic capacity, or O2 max).
Rate of oxygen uptake sets a limit on the sustained exercise level. Experimentally, the maximum O2, or maximum aerobic work capacity, is determined by gradually increasing the animal’s workload (for example, by forcing it to run on a treadmill at increasingly greater speeds or steeper inclines) until the rate of oxygen uptake reaches a ceiling. The workload can then be increased still further, but only for a very short time—seconds—at the cost of the buildup of lactic acid in the blood. In sprinters running all out, the quick buildup of lactic acid is subjectively felt as “dying,” when the muscles seem to congeal. The extra oxygen that must be taken in after the exercise to oxidize the lactic acid produced during the exercise is called the oxygen debt. The increased speed bought by running for a few seconds beyond the O2 max always costs dearly later. The cost of that speed is worth it only if the chase is reliably short and yields results.
In one study by Stan Lindstedt and colleagues, pronghorns were galloped on a treadmill at 10 meters per second wearing polyethylene masks to collect air for measuring aerobic work output. The incline of the treadmill was then increased to 11 percent, and the antelopes then registered an impressive O2 max of 300 milliliters of oxygen per kilogram of body weight per minute. This is only half that of a budgerigar and a fourth that of a sphinx moth in flight, but it’s impressive when compared to that of an elite human distance runner such as Olympian Frank Shorter: about 71 milliliters per kilogram per minute. Aside from sampling the air from the mask, blood was withdrawn from an artery within three to four minutes of running at O2 max to examine blood gas content and also to check for lactate to verify that the animals were indeed running at their O2max and not beyond it.
Comparisons of an animal’s relative power output must be made by taking body mass into account. Smaller animals generally have far greater rates of power output per unit of body mass, as the above comparison of a moth, a bird, and a human indicated. But taking the effect of body mass into account, the maximum aerobic capacity of the antelopes was still about three times greater than predicted for their approximately 71-pound body mass. Deviation from the predicted is called adaptive deviation, and the huge deviation (300 percent) in the antelopes’ predicted O2 max indicates that these animals indeed have unique athletic prowess with respect to aerobic metabolic specialization. (A sprinter’s athletic prowess is the opposite—to run anaerobically, that is, without oxygen uptake, and to be able to accumulate a huge oxygen debt rather than to avoid one.)
What does the antelope get from its extraordinarily high. VO2 max? The answer is, the same as human athletes do. A high rate of power output converts to the potential for high sustained running speed. For a given speed, however, the antelopes’ oxygen uptake is similar to that found in other species. Antelopes’ running speed can therefore not be explained by lower cost of transport (that is, great efficiency), and thus their high O2 max corresponds directly to aerobic running performance.
The issue boils down to the question, what unique features account for the antelopes’ high O2 max, which is necessary to support their sustained high running speeds? To answer that question, researchers made comparisons with a similar-sized ruminant mammal, the goat. Goats are neither swift nor long runners. They are instead good climbers, and they evade predators not by outrunning them but by inhabiting inaccessible mountain ledges. Being safe up on ledges, they don’t need to run, and they have only one-fifth the aerobic power capacity of the antelope.
In all structural aspects relating to physiology that were examined and that relate to rate of oxygen use, the antelopes were superior to the goats. Antelopes have more massive windpipes, three times larger lung volumes, greater gas diffusion capacity through lung tissue, an oversized heart, more cardiac output, greater amounts of hemoglobin concentration in the blood, more muscle mass, and greater numbers of mitochondria and hence more oxidative enzymes in their muscles. They also regulate their muscle temperature 2.6°C higher than goats do. If we recall the beetles’ running speed as a function of body temperature, such a temperature difference should alone result in a 35 percent greater metabolic rate. In short, the antelopes’ superb running capacity relative to goats’ does not depend on any novel mechanism. There is no magic. Instead, the antelopes’ unique capacity is achieved by enhancing a specific suite of many of their normal mammalian features. There are no tricks. No one adaptation by itself makes the difference. Pronghorns are just better at everything that affects sustained running speed. That is as expected. There is no use in having any one link in the system with extra capacity relative to any other—there is no point, for example, to have an oxygen delivery system to the muscles that greatly exceeds the capacity of those muscles to utilize the oxygen. Aside from that, the antelope is more than the sum of its parts, and no dissection will ever isolate the greatest of all antelope attributes, the antelope’s spirit and enthusiasm for running. As Gary Turbak says in his loving treatment of this magnificent creature:
History is full of accounts of antelope apparently choosing to race a steed, car, train, or whatever just for the sport of it…. Is it too much to think when the prairie air hangs cool and crisp that pronghorns do not rise from their beds, stretch, and race off across the dewy morning grass at top speed…just because it feels good? Why would a sleek pronghorn in its prime not want the wind to whistle by its ears as it flies along at fifty or sixty miles per hour? Or want to hear the rhythmic pounding of its hooves on the prairie sod? Or to burst with bestial pride at being the best there is? Biologists may scoff at this, but as surely as sunrise, this happens. It has to.
Most biologists would not scoff at the message in this quote at all. Play serves a vital function in many animals. It serves the ultimate function of practice, and it is motivated by pleasure. Pleasure is a proximate mechanism for achieving many ultimate benefits.
John A. Byers, who has made a detailed study of play, has found that to the fawns of pronghorn antelopes and other ungulates that require speed to survive, play is fast running that may be interspersed with twists and leaps. It has long been argued that such exorbitant, apparently useless expenditure of energy is a survival cost. Contrary to this supposition, Byers found that those pronghorn fawns who played more had a greater chance of surviving the first month of life than those who played less. Similarly, carnivores’ main play is mock predation, as it is in us, and it ultimately makes them better predators. We’re the world’s only hunters who will voluntarily handicap ourselves in the hunt if we are not dependent on the meat. We may hunt by choice using less effective weapons, such as antique guns and even bows and arrows, when we could use high-powered rifles with telescope sights instead. For us, hunting is not (now) always a necessity. It is also play.
Young pronghorn at play
If the antelopes’ spectacularly high work capacity is adaptive (to them), why don’t we find it also in the goat or in ourselves? Why shouldn’t a goat be able to climb and run like an antelope? The answer evolutionary biologists usually give to this question is that everything has a cost. One potential cost of a high O2 max could be that it results in an elevated basal metabolic rate. That is, having a large muscle mass packed with mitochondria might mean that (as in a car with eight cylinders that can never be shut off and must always at least idle, when compared to a car with only four cylinders) more is squandered in the long run. However, goats are not known to be picky or finicky eaters, and it turns out that antelopes at rest eat less food than similar-sized goats.
Another plausible hypothesis that has been proposed for the cost of the antelopes’ high aerobic capacity, which is achieved in part by having a high percentage of metabolically active muscles but little mass of metabolically inert fat, is that this ratio makes them very vulnerable to food shortages. Like human marathoners, antelopes need to be and are very lean, and the antelopes’ leanness or lack of energy reserves can sometimes have a high price. It makes them vulnerable to periods of cold and snow, when energy expenditure must rise for heat production but food may be scarce.
In the harsh winter of 1984, thousands of antelopes died in Wyoming. In the South Dakota winter of 1985–86, 80 percent of the state’s fifty thousand antelopes perished from cold, heavy snow, and wind. And fences. The animals were unable to escape the weather by migration, and piled up dead in droves behind fences. They have powerful jumping capability, but they have not evolved, like forest-dwelling deer, the behavior of making vertical jumps. Although the task would be trivial for its body, its mind does not reach that high. The mind leads, the body follows. A pronghorn antelope can’t conceive of jumping over a fence.
No studies are available, but I suspect that the antelopes may be more compromised than is assumed with respect to ultrarunning endurance as well, and for the same basic reason that they are susceptible to periods of cold and snow. Pronghorn antelopes reduce body weight not only by having little fat but also by having a very small stomach—about half the size of comparable slower grazers. They are therefore compromised for endurance, because to continue to run fast for long durations they are forced to refuel at frequent intervals, and on high-energy-containing food at that. Pronghorns are picky eaters, choosing broad-leafed plants generally growing best where herds of bison have grazed off the grass.
Although the pronghorn antelopes, because of their exceptionally high aerobic capacity, have been touted as the ultimate mammalian endurance athletes, nobody has yet put the endurance of the pronghorn antelope to a serious scientific test. At least two human runners have tried. Dave Carrier, who works on the biomechanics of locomotion at the University of Utah biology department, and his brother, Scott Carrier, had heard tales of how in the old days Navajos and Paiute hunters had chased antelopes to exhaustion. The brothers, working as a team, tried to do the same, but Dave told me, “We failed miserably.” The antelopes, who travel in groups, would dash off over a hill and “use the terrain to ditch us.” The brothers would follow, and when they came over a rise, they’d see where the chased antelopes had joined others. By joining others who were still fresh, these animals were essentially using relays to outrun their pursuers. As part of a herd, an antelope also uses the others as a shield. Then it no longer needs to be able to outrun the predator, only the slowest member of its group. Running in herds may indeed be an antelope strategy that has worked in the past with pursuing wolves. (Humans arrived too recently in America to have been a strong selective pressure on their performance.) I suspect that a fair test of human versus antelope runningperformance would be to release a pronghorn in unfamiliar and open terrain, after painting it fluorescent orange. This might be a new and even more interesting running challenge for humans than a currently popular one of running around a quarter-mile track for 24 hours.
I consulted my friend the folklorist Barre Toelken at Utah State University (who had lived with and married into the Navajo tribe during the 1950s), trying to find out if the practice of running down deers and antelopes, in the days before long-range killing by rifles, might be referred to in folklore.
“I saw it done in the 1950s,” he wrote me.
But it’s deer rather than pronghorns. What I saw was my friend Yellowman (in the 1950s he was about forty or forty-five) jogging along on the trail of a deer in semi-open desert country. The deer runs in bursts and then stops, listens, and then sprints again. The hunter, by consistently jogging along the trail left by the animal, eventually tires it out. Then, approaching the exhausted deer, he slowly puts an arm-lock on it and holds his hand over the mouth and nose of the deer, smothering it. His hand is supposed to have corn-pollen in it, which is considered sacred. The deer dies while breathing the sacred substance, and then its hide can be used as a sacred deer hide, unblemished because it’s from an animal who was not punctured when it was killed. I never heard of the Paiutes doing it, but I know very little about them. I don’t personally know of anyone who still does it, but there must be some people, since sacred hides are still in demand for ceremonies, and they’re still obtainable. It usually took Yellowman all afternoon to run down a deer.
Yellowman, unlike most other predators, was undoubtedly not fooled by the deer’s tactic of trying to avoid a race. Most predators are very selective and try to chase only what they stand a chance of getting in a short race. Deer exploit that tactic either by trying to get a headstart or by blasting off waving their white tail flag, thus showing they’ve got a headstart and a fast one at that, so that they won’t be followed.
As I later learned—from Indian Running by Peter Nabokov (1981)—many Native American tribes highly prized running ability for hunting and for war. Many tribes had traditions of chasing down animals directly or indirectly on foot. In the Great Basin, antelopes were hunted after being chased on foot into V-shaped corrals. Before the Omahas of the central plains acquired horses, they had buffalo runners, who scanned the skies for ravens that signaled the location of bison herds, and then they ran back to the camp to recruit hunters for the attack. Hopi prized black-tailed jackrabbits and ran them down by following their fresh tracks in the snow. Both Pueblo and Yuki hunters ran deer to exhaustion, as did Papagos and Pimas.
These days, man versus animal races are sometimes devised mainly to settle bets. One of these that objectively measures the speed and endurance of humans versus another running animal is the annual “Man vs. Horse” race held at the Welsh town of Llanwrtyd Wells. This race is serious. It is sponsored by William Hill, the largest bookmaking company in Great Britain, which puts up £21,000 ($31,500) payable to the first runner who beats a horse. So far (after two decades) they haven’t had to pay up; no individual runner has beaten a horse that is paced by a human jockey (relay teams of four runners do so often).
Nevertheless, the contest is close. In the last race, Mark Croasdale, a British runner who has won the Marine Corps Marathon in 2:23, came within 80 seconds of the winning horse. Since the best human marathoners have run marathons in near 2:06, it is probably only a matter of time before one of them will beat the best horse in a long-distance race, even one as short as this one, which is four miles less than the marathon distance.
In summary, although pronghorn antelopes and horses are superb runners for moderate distances of maybe 20 to 30 miles (or possibly more), there is no evidence that they are ultramarathon distance runners. Antelopes and horses will never have to run 30 miles at a stretch from wolves. At least on the open terrain of Yellowstone Park, wolves usually catch elks within about a mile or so. If not, they give up the chase. According to Doug Smith—a wolf researcher and director of the Yellowstone Wolf Recovery Project, who routinely watches wolves hunt while observing from small aircraft—wolves seldom pursue for more than 2 miles. I suspect, therefore, that elks or pronghorns may perform poorly relative to a trained human who is motivated by the personal sense of accomplishment, such as that achieved by winning a race.
Speed is meaningless unless the distance is specified. This concept is best illustrated by human runners, among whom different running specializations are apparent. I plotted world record running speeds of both men and women (separately) as a function of distance from 100 meters to 200 kilometers. As expected, maximum running speeds by men (about 37 kilometers per hour) decrease dramatically with distances raced—about threefold as the racing distance increases two-thousandfold. However, the threefold decrease in running speed is not uniform over the whole distance. Speed decreases uniformly at first, but then plummets precipitously after about 1 kilometer; then it again decreases uniformly, before again plummeting precipitously after another break point, at about 30 kilometers. I interpreted the two transition points as a reflection of different physiological specializations, the first from anaerobic to aerobic metabolism, and the second from carbohydrate to fat metabolism. When I plotted the same curve for women, it showed the identical break points, which suggests the same physiologies as related to running specializations. However, at all distances, world record running speeds for women are slower than men’s, especially at the longer distances. A March 2000 paper published in Nature confirms (or rediscovers) some of the same points made fifteen years earlier using a different data set.
Only forty years ago, there were hardly any competitive women runners. Now there are as many female as male athletes in many sports. Running is not just biological destiny. Rather, it is a biological capacity that is now largely a cultural phenomenon. Women, it turns out, are as eager and competitive runners as men are. Nevertheless, average differences in male versus female performance are clearly visible in the outcome of almost any race today, and those differences are reflected (though they need not be) in the records, the exceptional performances. However, no matter what the records say or what the population average may be of the group that we belong to, neither says anything about what individuals may be or could become or could do. Population data are required for formulating theories that are often perceived as laws of biology. But such laws don’t dictate. They describe. Ultimately, the empirical performances of individuals create trends that are used for formulating theories, not vice versa. Each of us is unique and free to nurture their own gifts or dreams.
The reason for the statistical male running advantage is not known, although I suspect it may have something to do with average hip structure, tendency for weight distribution, and possibly different normal foot lengths. In any case, we all recognize the male-female difference, else there would be no separate male and female divisions and prizes at races. Despite the difference, women distance runners like Joan Benoit Samuelson, Utta Pippig, and Grete Waitz have bettered even Emil Zatopek’s men’s Olympic marathon record of 2:23, set in Helsinki in 1952. Men have bettered it also, by almost 16 minutes. Ann Trason wins ultramarathons outright.
Given that there are different physiologies for sprint, middle, and distance running, what would happen if the fastest men or women ultra-distance runners were to force an antelope or a horse to run 100 kilometers? Could the trained and motivated human force the animal to exhaust its fuel supplies? Until the race is run and the results are in, I’ll reserve judgment on the pronghorn’s prowess as an endurance athlete relative to both the best men and women ultraendurance athletes.
The antelopes, who have the equivalent of a V-8 engine in a VW frame, prove that aerobic capacity is absolutely crucial, as it is in human middle-distance runners, but I’ll not be running a middle-distance. I’ll be running an ultramarathon. Antelopes, like any runners, make compromises in energy reserves and in digestion in order to achieve speed in long-distance running. Those compromises are chinks in their armor that, in order to beat them in an ultramarathon race, would have to be exploited.