PZ Myers. 2004 Nov 17. Marathon Man. <http://pharyngula.org/index/weblog/marathon_man/>. Accessed 2008 Dec 01.

Posted on M00o93H7pQ09L8X1t49cHY01Z5j4TT91fGfr on Wednesday, November 17, 2004

Marathon Man

Human beings are actually rather peculiar mammals, with an unusual bipedal posture that makes them different from not only quadrupedal mammals, but also from our most closely related primate relatives. It doesn't seem to be a particularly efficient mode of locomotion, either; we can't sprint as fast as four-legged animals of the same size, and our running has a higher energetic cost. So why are people built the way they are? What advantage did it give us during our evolution?

One possibility is that our posture is a reasonable compromise, a way to derive a relatively efficient terrestrial mode from an ape-like body. We evolved this way because it allows us to walk long distances. Another possibility described in a new paper by Bramble and Lieberman is that our posture is an adaptation for high-performance endurance running, and that really we're a species of lopers, joggers, and marathon runners.

The top speed for a human sprinters is about 10.2 m s^-1 for less than 15 seconds, while horses and greyhounds can hit 15-20 m s^-1 for several minutes—in other words, we're pathetic sprinters. Endurance running (ER) is different, though. ER involves sustained running over long distances and long times, and is carried out aerobically; that is, we only burn oxygen during the run as rapidly as our respiratory system can deliver it to the tissues. We actually seem to be able to hold our own in this activity. Human ER speeds fall between 2.3 m s^-1 (I must be somewhere around there) and 6.5 m s^-1 (for an Olympic class marathoner), with typical speeds for a moderately fit jogger of 3.2-4.2 m s^-1. In comparison, the trotting speed of a horse is about 3.1 m s^-1, and once they hit 4.4 m s^-1, they break into an anaerobic gallop. Over long distances, the average speed sustained by a horse is about 5.8 m s^-1—which means that a well-trained, conditioned human being can keep up with or even outrun a horse if the race is sustained long enough. This range of speeds is illustrated diagrammatically below.

Range of speeds for human ER and sprinting, and minimum trot (Tm), preferred trot (Tp), trot-gallop transition (T-G), preferred gallop (Gp), and maximum sustained gallop (Gms) for ponies, and predicted for quadrupeds of 65 and 500 kg. Also indicated is Gld, the optimal long distance (approx. 20 km), daytime galloping speed for horses. Note that quadrupeds sprint at speeds above Gms.

What this is saying is that we can't compete with these other animals at the high end, in the short range sprint. We don't even have a gait comparable to the quadrupedal gallop (the orange bars), which is an efficient medium range running rate. What we have done, though, is pushed that long-range, aerobic gait, the blue bars, to a greater speed than quadrupeds can match.

The paper then goes into the details of precisely how we accomplish that. They examine features of human anatomy and physiology that contribute to four broad parameters of running performance: energetics, skeletal strength, stabilization, and thermoregulation.

Energetics refers to those features that economize energy use during the activity. For instance, we have built-in 'springs' in leg tendons and skeletal features like the bony arch of the foot that store the energy of elastic recoil. We maximize energy use by increasing stride length rather than rate, so long legs are a benefit. One cost of long legs is that we're swinging a lot of weight, so reduction of foot mass is another advantage to runners.

Running is a relatively high-impact activity, sending shock waves up through the skeletal system every time a foot hits the ground. We lower joint stress by increasing the surface area of joint surfaces and by using those springy shock absorbers, our feet.

Just walking bipedally is a precarious exercise, and running amplifies the problem. These big heads bobbing on the end of a stalk have to be stabilized, both by reducing mass and by structures such as our nuchal ligament along the cervical vertebrae. Alternately swinging massive legs back and forth generates a substantial amount of torque, which is opposed by swinging the upper body to compensate—our relatively narrow waists are an adaptation to allow greater upper body mobility.

As we all know, sustained jogging is a great way to overheat, so we have many thermoregulatory adaptations: extensive sweat glands, reduced body hair, intricate cranial circulation, and elongate morphology. The authors mention that mouth-breathing during strenuous activity, which increases the rate of respiratory ventilation, is another feature humans exhibit which is unusual for an ape.

Many of these adaptations are manifest in the skeleton, and so we have a record of their appearance in our evolutionary history. The table below lists a series of these features, along with their functional role, whether they assist in walking (W), running (R), or both, with more advantage to running (R>W).

Now look at these diagrams of a few primates that illustrate these features. At the top left is us, and top right is Homo erectus; despite the smaller brainpan, H. erectus has virtually all of the features for endurance running that we have. The lower left image is a chimpanzee, which can run short distances at a rapid sprint, but has no endurance at all. Compare that to Australopithecus afarensis at the lower right—it's intermediate between our chimp cousins and ourselves.

Anatomical comparisons of human, chimpanzee, H. erectus and A. afarensis. a, c, Anterior and posterior views of human, enumerating features related to endurance running listed in previous table. b, d, Anterior and posterior views of chimpanzee. Labelled muscles connect the head and neck to the pectoral girdle and are reduced or absent in humans. e, Reconstruction of H. erectus based primarily on KNM-WT 15000; f, reconstruction of A. afarensis based primarily on AL-288.

In the two middle pictures, you'll also notice a key difference between us and chimpanzees; we have a massively bunched gluteus maximus, while the chimp has a mere strap of muscle. That muscle is used relatively little in walking, but is crucial at higher running speeds. A firm plump butt is actually a cursorial adaptation.

There are still some major evolutionary questions: did walking evolve first, or was it concurrent with the evolution of endurance running? What behaviors drove this feature—pursuing prey to exhaustion, rapid exploitaton of carrion, tracking injured prey, or just getting early man close enough to use projectile weapons? And what were the consequences?

Additional research will help to clarify and test when and how ER capabilities evolved in humans, and to examine more thoroughly their implications for human evolution. For example, it is known that major increases in encephalization occurred only after the appearance of early Homo. The hypothesis that ER evolved in Homo for scavenging or even hunting therefore suggests that ER may have made possible a diet rich in fats and proteins thought to account for the unique human combination of large bodies, small guts, big brains and small teeth. Today, ER is primarily a form of exercise and recreation, but its roots may be as ancient as the origin of the human genus, and its demands a major contributing factor to the human body form.

These physical adaptations to a walking/running lifestyle came first, and our big brains may be a consequent side effect.

Bramble DM, Lieberman DE (2004) Endurance running and the evolution of Homo. Nature 432:345-352.

1. Interesting stuff. Science had an article a few months back, just before the Olympics, on human distance runners. It referred to some of the same anatomical features that this one does, but specifically was looking into why about half of the world's top distance runners are from one area in Kenya. The suspicion is that it's part body shape and part extra-efficient metabolism.
   
   PZ, your citation's incomplete. Is it in Nature?
   #: Posted by  on  11/17  at  09:15 PM
2. After hearing a piece on this on NPR this afternoon, I have been hoping for additional details and anaylsis here.
   
   For those of us at the 'hobby' end of the biology and evolution interest group, it is great to know that Pharyngula will expand on popular science information and educate us further.
   
   As I once told PZ, he does the best popular science writing I have found since the passing of Gould.
   #: Posted by  on  11/17  at  09:16 PM
3. Errm, uh, would you believe it is in that famous biology journal, 432?
   
   I don't know how that slipped by me. Fixed it now.
   #: Posted by PZ Myers  on  11/17  at  09:18 PM
4. William Least Heat Moon in the book Prairyerth used the concept of upright locomotion to postulate that humans were best adapted to prairie environments due the ability to see just above the grasses while hunting and traveling. Adding endurance speed into that equation makes a certain amount of sense.
   #: Posted by  on  11/17  at  09:33 PM
5. Another more personal connection to this concept occurs to me.
   
   As a teenage motocross racer I used to train by running on coyote/rabbit trails through the desert of central Oregon. At 5 - 6' tall a human can easily navigate at speed weaving between sage (3-5' tall) and similar obstacles while maintaining running speed on moderately firm sandy soil.
   #: Posted by  on  11/17  at  09:52 PM
6. Another advantage of bipedalism for long-distance running is that it affords the runner the ability to carry food and/or water and refuel on the run -- quadrupeds can't do that.
   #: Posted by  on  11/17  at  10:21 PM
7. Or a rock or a stick or a spear. Or if you're scavenging, the ability to grab a nice gooey greasy bit from the carcass and run elsewhere to consume it away from the hyenas.
   #: Posted by PZ Myers  on  11/17  at  10:34 PM
8. Oh, wonderful. Before, I was just being lazy and ignoring my cardiovascular health if I blew off a run to watch TV. Now, I'm going against millions of years of evolution. That's just great.
   #: Posted by Chris Clarke  on  11/17  at  11:18 PM
9. Yeah, me too. I read the bit about "slender waists" and reasonable rates of running and felt like a traitor to my whole species.
   
   Do you think they'll kick us out?
   #: Posted by PZ Myers  on  11/17  at  11:23 PM
10. It doesnt take millions of years. 30 is enough ....
    
    My current profile bears little resemblance to that youngster running through the sagebrush I mentioned earlier.
    #: Posted by  on  11/17  at  11:36 PM
11. PZ Meyers wrote: Or a rock or a stick or a spear.
    
    I was wondering about that. Is freeing up the hands for tool use while moving thought to be a co-occuring selection pressure, or is it a bonus feature that we exploited after the fact?
    
    Erm, that could be worded better, but you hopefully get the point.
    #: Posted by  on  11/17  at  11:46 PM

12. I was wondering about that. Is freeing up the hands for tool use while moving thought to be a co-occuring selection pressure, or is it a bonus feature that we exploited after the fact?

    
    
    I just went out and ran a couple miles on unlit rough trail - strictly in the spirit of scientific inquiry, you understand - and noticed how useful my arms were in counterbalance on the uneven terrain. Hard to imagine that wasn't part of the original spec.
    
    Still, our close non-cursorial cousins carry tools when walking bipedally.
    
    

    Yeah, me too. I read the bit about “slender waists” and reasonable rates of running and felt like a traitor to my whole species. Do you think they’ll kick us out?

    
    
    Silverbacks R Us.
    #: Posted by Chris Clarke  on  11/18  at  12:29 AM
13. Damn Chris, if only my committment to science were as strong as yours, I might weigh 15 pounds less
    #: Posted by  on  11/18  at  12:32 AM

14. Is freeing up the hands for tool use while moving thought to be a co-occuring selection pressure, or is it a bonus feature that we exploited after the fact?

    
    
    Tool use was once considered as a pressure for bipedalism, but in light of this possibility, it certainly might be just a secondary result, even if tool use is much more important to later selection.
    #: Posted by mattH  on  11/18  at  01:40 AM
15. I can't remember the details, but I assume you're familiar with the hunting methods of some African tribes: run down the animal by keeping it on the move for a long time - tens of hours. We can't catch an antelope, but we can wear it out, then kill it. It's the same technique wolves use when hunting animals too big to kill with their teeth.
    #: Posted by  on  11/18  at  02:21 AM
16. Yes, the paper talks about that, but mentions that it is considered a very rare and unusual strategy that modern hunters don't typically follow —technology gives us much less exhausting ways of bringing down game.
    #: Posted by PZ Myers  on  11/18  at  07:30 AM
17. Tool use was once considered as a pressure for bipedalism, but in light of this possibility, it certainly might be just a secondary result, even if tool use is much more important to later selection.
    
    Tool use (mode 1 technologies) are known before the shift to the modern post-cranial body form (so, used by early Homo: habilis and rudolfensis, and perhaps Paranthropus).
    
    Modern post-cranial body form is first known from the Nariokotome Boy (H. ergaster), which I think is dated at 1.6 mya. (This date is off the top of my head, tho).
    #: Posted by  on  11/18  at  07:31 AM
18. One aspect I didn't see mentioned is that for some runners (or former runners like me), the act of running long distances is actually pleasurable. I loved a long run through the woods and now, since my knees have sidelined me, I look longingly at the trails I pass. It seems that humans aren't intended to do long distance running much past early middle age. I guess we are supposed to have reproduced and brought our offspring to maturity by then. So much for us late bloomers.
    #: Posted by  on  11/18  at  08:22 AM
19. PZ, you mentioned that
    

    ER involves sustained running over long distances and long times, and is carried out aerobically; that is, we only burn oxygen during the run as rapidly as our respiratory system can deliver it to the tissues.

    
    Is there evidence for evolutionary changes (respiration, circulation) that would favor long-term aerobic work (over our quadripedal ancestors)?
    
    e.g. Hemoglobin structure, gas exchange mechanism, rbc/mitochondrial differences, respiratory membrane characteristics, etc.
    
    If so, were these specific building blocks already in place before we took to the plains, or did we "acquire" them out of need (I know, bad choice of words)?
    #: Posted by  on  11/18  at  08:45 AM
20. This avenue of speculation is at least twenty years old. See Carrier, D. R. 1984. The energetic paradox of human running and hominid evolution. Cur. Anthro. 25:483-495.
    
    David Carrier's brother Scott is a writer, who wrote a book that is partially concerned with David's speculations about hominid evolution, and their attempts to replicate the legendary trick of running down an antelope; the book is Running after antelope, Counterpoint, ISBN 1582431116.
    #: Posted by  on  11/18  at  08:50 AM

21. Or if you’re scavenging, the ability to grab a nice gooey greasy bit from the carcass and run elsewhere to consume it away from the hyenas.

    
    
    All I know of this is what I see on nature shows, but isn't sprinting more important than endurance running if you're a scavenger? The top predator's not going to spend time chasing you down when they've got their nice carcass there, but they will make a dash and snap if you get too close and piss 'em off.
    
    Jackals spend their time lurking, grabbing bites until the lion/hyena/whatever goes after them, and sprinting maybe 20 feet away until the predator gives up and heads back to the carcass. Ditto for vultures, which take to the air just long enough for the predator's attention to drift. A hominid trying the same stunt--especially one of those adorable four-foot-tall australopithecines--would be dead before they could run six feet.
    
    Seems to me the only way for hominids to successfully scavenge carcasses would be to approach en masse, tossing rocks or waving torches or whatever, and actually run the predator off. That doesn't mean marathoner adaptations wouldn't be useful for getting to the kill in the first place, though--the faster you get there, the more meat's left--and that's what Bramble and Lieberman suggest in the Nature article.
    #: Posted by  on  11/18  at  11:28 AM
22. From my reading, it seems to be a tad more complex. A group of hominids, using their slightly larger brains, could communicate a group strategy. Then, using hairless, heat-shedding bodies to move out to great distance, could position themselves for the extended chase/drive. Once the game was slain, the carcass could be carried back on extra-wide shoulders to the fire-circle to feed offspring.
    
    It's a lot easier though to manage a herd of 8th graders and take the cash to buy tri-tip.
    
    Again, it speaks to why primitive man prefers a bigger, less thermoefficient quarry. Also, what was said about head height has merit. Other animals have solved the problem differently in the long grass—meerkats do it by building a mound and then standing upright on it, most others by putting a head on the end of a long, flexible neck. But notice that our cultural brethren, the big quadroped carnivores, have neither long necks nor do they stand on hind legs for a better view. Hmmmm...
    #: Posted by  on  11/18  at  11:33 AM
23. Knees are horrible malfunctional things. I'll be quite happy when medical science gives us real replacements. Running can ruin knees in a few short years. For the more expert runners here I have a question. How much running is too much, in terms of knee damage buildup? If I jog for 30 mins, 3x per week, what are the odds I'll be unable to do that in a decade? two decades? Is it worth it? Are things like elliptical trainers (which I love) good substitutes which reduce impact?
    
    Maybe I should just switch to swimming. 'Course, the chlorine has been known to cause athsma...
    #: Posted by  on  11/18  at  11:57 AM
24. "technology gives us much less exhausting ways of bringing down game."
    True, but wasn't it Abebe Bikela, the marathoner in the 1960's, that did all his early training as one of Haile Selassie's bodyguards? He'd chase whatever the Emporer was hunting that day back toward His Highness's gun, barefoot across Ethiopia. And went on to get an Olympic gold medal, also barefoot.
    #: Posted by  on  11/18  at  12:27 PM

25. technology gives us much less exhausting ways of bringing down game.

    
    
    I'd phrase now that as "technology gives us much less disgusting ways of scavenging carrion," actually. A vanishingly small percentage of us bring down game anymore, and most of those who do raise it in fenced-off habitat.
    #: Posted by Chris Clarke  on  11/18  at  12:51 PM
26. Steve spake:
    
    

    
    Running can ruin knees in a few short years...
    
    Maybe I should just switch to swimming. ‘Course, the chlorine has been known to cause athsma...
    

    
    
    How very timely. I'm reading this on my 40th birthday. I can no longer run due to ruined knees and can't swim because the chlorine causes my athsma to flare up. I could swim in a lake, but that's only an option three months out of the year in northern Michigan.
    
    In high school, I ran nearly constantly. It was my default mode of transportation. City streets, trails, the woods behind the family farm, wherever. Sometimes to get someplace, sometimes to just run. When my knees started giving me trouble in my early 30's, I tried swimming (until the athsma thing), biking, running on rubber tracks, every mechanical contraption imaginable, but they were all just pointless ways to raise a sweat. Running was fun!
    
    So. My point? A couple.
    
    First: yea, running will wreck your knees in pretty short order although I know people who seem to last far longer. It probably has a lot to do with a person's mass. I'm (mostly) northern European; tall, large-boned, carry substantial weight even when I'm not fat. I know people in their 60's that still run marathons; on windy days, they carry heavy objects as anchors. So the answer as to how long you can get away with running without destroying knees is probably, "It depends."
    
    Second: Stephen Baxter in Evolution, speculates on running evolving partially from the enjoyment of running. Reading that section of the book describing the pleasure of simply running certainly resonated with me. Not to discount any of the other factors at play here, but could distance running be partially the result of a feedback loop of sorts?
    #: Posted by Ric Frost  on  11/18  at  04:19 PM
27. Steve, you have my sincere sympathies. I have communion wafers masquerading as disks, so I know from which you speak. Most of the bad-knee thing comes from concrete. Zulu warriors ran supra-marathon distances up into their 60s, but barefoot across soft earth. Most barefoot runners run on the balls of their feet, not the heels. I used to run down-hill backwards: It looked weird, but it got me to the gym without blowing out my joints.
    
    Bikela must have trusted Tafari Makonen's aim. One would bet the emperor was using a classic 1903 Mannlicher-Schoenauer, probably in 6.5.
    #: Posted by  on  11/18  at  04:54 PM
28. Right, concrete is not the distance runner's friend, Steve. Which is why if you are like me and spend a good part of your free time running upwards of 70+ miles a week you do most of it on soft trails. The elite marathoners can run over twice my base mileage.
    Also a medical student was telling me that the stress on one's knees scales as something like 5 times your weight. I'm not sure if this is true but it remains true that if you're overweight and not carefull when running it is easier to get knee injuries.
    #: Posted by Steven S.  on  11/18  at  06:30 PM
29. Trail running is most definitely the way to go if you want to extend your running career. Next is asphalt. Don't run on concrete unless your life depends on it. Even with my bad knees I can occasionally manage a run on trails. If you want to extend your running career, you might also consider alternating other types of exercise, like bicycling, swimming, non-impact trainers, rowing machines, and even (dammit) walking at a good pace.
    #: Posted by  on  11/19  at  10:12 AM
30. I have a friend on the NCSU cycling team. He also told me that he can cycle forever with no joint problems. I think I'll switch to biking, swimming, and the elliptical trainer. Knee pain is for the birds.
    #: Posted by  on  11/19  at  10:49 AM
31. Let me tell you about my first job: I was 13 years old. It was with the Parks Department. The job was in developing a couple of new parks, and involved the fat middle-aged guy driving a tractor and plowing up the field, and then we would move in and rake up the rocks (this was glacial till) into large piles before the area would be seeded.
    
    Then we'd get shovels and scoop and heave heaps of rocks over our heads into a dump truck. I'm thinking now that this was insane, back-breaking labor to subject young kids to, but back then we didn't know better.
    
    Anyway, after a couple of weeks of this, one day my left knee just sorta disintegrated. There I was, sweating in the sun and hoisting up 10 pounds of rocks, and pop, the knee cap flies over this way, the joint buckles that way, I fall over towards the dump truck and am supporting myself on it with one leg looking all cock-eyed. I got fired and got to spend the rest of my summer in a hip-to-ankle cast.
    
    And ever since, I've had this gimpy knee that doesn't take well to stress. I don't run much, I'm afraid. Good thing I don't have to hunt wildebeest for a living.
    #: Posted by PZ Myers  on  11/19  at  11:01 AM
32. But the good gnus is that you went on to teach science instead of manage a hockey team.
    #: Posted by  on  11/19  at  04:51 PM
33. Who says WE were hunting down antelopes on the savanna and stealing food from cheetahs, lions and hyenas? I daresay we evolved our comic way of running to avoid becoming bushmeat. Lions may run faster than we do for a short while but they can never keep up with us. Being rather tall, we can see far in the savanna and keep prudent distance from those shopping for Homo spp. steaks, and they would never had a chance to catch us. And arms - the fantasies of your (paunchy) selves carrying spears and rocks (and firearms) to kill big animals, it is pathetic. Arms are, probably, to carry children.
    #: Posted by  on  11/20  at  12:48 AM
34. "Arms are, probably, to carry children."
    
    From what I've heard, many cultures have spent considerable time inventing slings, carriers, strollers, and other ways to avoid using the arms to carry children.
    
    You bring up a good point, though: Baby gorillas and chimpanzees travel by clinging to their parents' fur. Us H. sapiens, being a little skimpy on the fuzzy stuff, would've needed an alternate method. I suppose it's possible that we lost our hair before we became bipedal, which forced us to use our arms to carry babies, which gave an advantage to individuals who could walk on only two limbs...
    #: Posted by  on  11/20  at  12:20 PM
35. I don't think our mode of locomotion evolved to enable escape from predators for the simple reason that it doesn't work. For that, we'd need to be fast, short distance sprinters -- it does no good to be capable of jogging along at 4 m/s for hours if a leopard can run 10 m/s for one minute.
    
    I don't think of our ancestors as mighty hunters as much as flexible opportunists, taking down an occasional antelope with a volley of rocks, working as a social group, or snatching up a scrap from another animal's kill.
    #: Posted by PZ Myers  on  11/20  at  01:23 PM
36. Arms is for arms. We got smart and learned about fire-hardening wood and flaking stone, an suddenly they didn't include us on the shopping list as much.
    #: Posted by  on  11/20  at  01:44 PM
37. Sorry, I cannot visualize taking down an antelope with a volley of rocks in the savanna. Not even in a canyon.
    
    A leopard makes 300 m in a 30 seconds (and lies down exhausted), and a Homo spp. makes 120 m in the same time and keeps running, we need to identify the leopard at a distance of 200 m. Even in the savanna, that is not easy. Leopards, in fact, are dangerous. However, it is known that humans can and sometines do kill lions and other big cats barehanded. But cats have no chance against a cooperative group, like baboons.
    
    It was no picnic, that's for sure.
    #: Posted by  on  11/20  at  11:12 PM
38. Jaim: There is a term in hunting called a 'drive'. One group forces the quarry (the term 'game' is reserved for when you have other food) into another, sited on favorable ground or in concealment. On the steppe you can still find wadis/gullies/dongas, tall grass and tree lines which will help channel game or conceal hunters. But it is not the talent or endurance of a single hunter but of several working as a team (communications skills) and capable of carrying the meat home that makes the difference.
    
    Also, it is easy to discount rocks as weapons. Get hit by one the size of fist thrown by an adult and see if you ever forget the experience.
    
    
    One thing we modern projectile diletantes discount is practice. In a primitive situation where the most fascinating thing you can do with your time is hit things with a rock, you'll do it quite frequently. All day long. The accuracy of people in simple cultures with thrown stones, slings, atl-atls and with bows and arrows, is astounding. A Piute Indian child could usually take out a bunny with a thrown rock to about 25 yards. Mongols became completely automatic in their archery. Muscle memory is a powerful thing and few of us today invest the time to become as proficient at anything we do.
    
    This may be difficult for a person of refined sensitivities, but pick up a hunting video by Ted Nugent and see what muscle memory can do. Nugent has applied the amount of practice usually only found in symphonic musicians and applied it to his archery. It is scary how fast his mind can compute a firing solution and his body translate it and apply it perfectly under stress.
    
    I guess your last comment is particularly accurate in Wisconsin.
    #: Posted by  on  11/24  at  09:03 AM