Tuesday, 18 October 2011

Persistence hunting and a hypothesis about human evolution

English version of Chasse à l'épuisement, running, & évolution de l'homme

Persistence hunting by a Kalahari bushman:
This video is part of David Attenborough's The Life of Mammals (2002), a nature documentary produced by the BBC Natural History unit with Discovery Channel. 
When I first saw this documentary all sort of things came to my mind. I already knew that persistence hunting existed, thanks to Christopher McDougall's book Born to run and Bernd Heinrich's Why we run. But when I saw it, confused feelings and thoughts about running became focused. 
  • I don't just run. I don't go around a track, I go everywhere, I try to find obstacles (anything in my environment), I give myself an imaginary or actual goal, that has something to do with real-life situation: going somewhere, finding someone or something, etc. I can't run if I don't have a practical goal. Not a time, a heart rate, a distance, or an energy consumption, I care not about them. But I need to give myself something to do. The hunter doesn't run randomly, he has a purpose.
  • I assume many of you have watched Avatar. Remember the moment where Jake Sully says that he felt he was borned to fly the banshees/ikran ? I get exactly the same feeling when I run. That I was born to do this. I feel right in place.  
  • In a less subjective note, some things about what we are as a species made sense. I knew that we were built to run: long legs, knees to absorbe shocks, heart's ability to change its rythm, etc. I knew that if we had those, it must have been for a good reason. But there was the answer: it's a survival tool. Nobody can run like us, that's what gives us an advantage. 
  • I remembered some playful tricks I usually do when I run, e.g., be silent while running, so silent even a dog can't hear me coming until I'm right behind him, so close I could catch him with my bare hands. 
  • The transe of the hunter reminds of mystical and religious feelings and thoughts while running (e.g., when running in harsh conditions, I can't help but thinking that I'm doing a Man versus Nature contest; or the sensation of floating, as it is described by Marshall Ulrich in Running on Empty; etc).
  • I could understand my dislike of listening to music when I run or of anything that can cut me from my environment. Running is an interaction between your body and the world. Your nervous system gives information about the world through the nerves implantation in your feet, and your central system gives commands to your body to adapt to your environment. It's an harmony. Why would I want to interfere with that ? I need to be with myself when I run. 
  • I understood right to the point a fundamental law of nutrition and metabolic functions: you don't need to eat before running. Starving has been (and is still in some part of the world) the normal state of our metabolic system. Hunters ran and still run (when their territory isn't destroyed or confiscated by whatever criminal groups or States), because they need to eat, not because they had some superflous energy to spend or because they craved the health benefits of running. After running comes the feast. While fasting, we use fats as an energy source. That's what we were designed by natural evolution to do. We don't need to eat that much and certainly don't need sport drinks or a specific athlete diet. Even in harsh conditions, we can survive and be a lethal weapon.

What is persistence hunting ? 
Persistence hunting is a human hunting technique. It's the oldest known to man way to get fresh meat. Hominids seem to do persistence hunt since 2 millions years. We weren't scavenger (well sometimes we were, but very occasionally) because we weren't the biggest cat in town. And weapons came very late (spears around 400 000 years ago; bow and arrow 30 000) and were too unaccurate to be really useful. So we did persistence hunt. It's a combination of running and tracking. Tracking allows the hunters to keep track of the prey and to isolate it from the group. Running is not only to get close to the prey, but to exhaust it. That's the whole point of persistence hunting: run an animal to death. We can do that, we're the only species on earth that can run an animal to death. If you have seen the video, it's a 50% mental and 50% physical prowess. The hunter uses his perspiration and free hands's advantage. That's the physical part. But it's also a mental game. The hunter breaks the will to live of the animal.
As far as our knowledge goes, only two tribes seem currently to still practice persistence hunting: the Kalahari bushmen of the southern part of Africa (as seen in the video) and the Raramuri (also known as the Tarahumaras) of the Northern Mexico. (In the photo on the right, ultramarathoner Scott Jurek and the famous Raramuri Arnulfo Quimare.)

How to hunt and why can we ?
There is no persistence hunting manual. This knowledge is almost extinct. But some contemporary researchers and runners tried it. There are some online testimonies: Fair Chase, Persistence hunting part one, part two, part three, part four by John Durant. You can also find some description in Christopher McDougall's Born to Run, and Scott Carriers's Running after the antelope (an audio version of Carrier's book can be found here), Heinrich's Why we run (p. 128-132). 

So why can we run a animal to death ? As I said, first because we possess the finest thermoregulation on earth, second, because our hands are free, third, because we are fast on long distance, fourth because we are a social species, fifth because our respiration is disconnected from our running movements. 
Perspiration is the production of fluid that consists primarily of water and some chlorids. They are execreted by sweat glands in the skin of mammals. In the human species, perspiration is a thermoregulation system: as the water evaporate, the skin is cooled down. Other species thermoregulate using their glands in their mouth by panting. They evaporate the water in the oral cavity, which decreases the body temperature. So why can we run a animal to death? Because, in persistence hunting, we constantly increase his body temperature while reducing is recovery/panting time. At the end, his body cannot cope with the effort. They die of heatstroke. A lot of people are not comfortable with sweating during an effort. I would say to them that there is no reason to, because it's a matchless advantage. Some argue (it's an hypothesis amongst others) that the reason why we are alive and Homo neandertalis (a species, with strong, huge and highly sophisticated from a cultural viewpoint individuals) disappeared is that they could not cope with the global warming of Earth 50 000 years ago, because their thermoregulation system was not efficient enough. In an endurance running competition with Homo sapiens, we would run a lot faster than they were in long distance. We would get our prey long before they could. 
Our hands are free, contrary to quadrupedes, thus we can carry thing, like water. Quadrupeds are faster than we are on short distance, we have an advantage with the ability to carry things. With water, we can refresh, replenish our stock of body-water. We can run an animal to death, because other animals can't cover the loss of water, they drain water faster than they can replenish their stock. We can stop this depletion.  
We're fast on long distance thanks to our pace. See (Bramble & Lieberman 2004) They compared the stride lengths of humans and horses (quadruped <500kg). Horses are really fast when they gallop. They can cover up to 11m per second, while humans can cover up to 10m per second in a sprint. But the point is that horses can't sustain over a long time speed gallop. When they can't gallop anymore, they trot. When they trot, they cover up to 6m per second. We can't run as fast as horses, but at an average jog, that we can sustain for hours, we can cover up to 7m per second (see the graphic from Bramble & Lieberman 2004). You see the tactics: the horse is frightened and run for his life for a few kilometers. We run not fast enough to stay at his level, but to keep him in sight and compell him to gallop regularly. Then, meters after meters, we get closer and closer until he is tired enough not to be able to gallop anymore. Another point on Bramble & Lieberman paper: we are faster than quadrupeds >65kg (e.g. chimpanzees) at this game.  
We're a social species. Alone, persistence hunting is a losing game. As Scott Carrier says it, animals are professional preys. They know their stuff. They will struggle against our will to isolate them, they will go in the middle of the tribe so that no one can recognize them, and that hunters' efforts are nothing but a waste of time and energy. That's why we need other humans. They will keep the prey isolated, carry some extra-water, etc, so that the runner can carry on his duty at the final point of the hunt (the last two or four hours of running). We can run an animal to death because we're an extra-organized species.  

Our breathing technique is different from other species (Bramble & Carrier 1983). Have you ever seen a rabbit or a cat running? First, they anterior legs touch the ground, then the posterior. While they're doing so, their back is round. At this point, the guts are pushing against their rib cage and lungs, forcing the air to go out, the animal to exhalate. Second, they elongate, the guts are stretched, pushed back against the pelvis and pressure against the lungs stops. At this point, a call for air is provoked and inhalation begins. The faster the movement of the guts, the faster they can breath. (See Heinrich 2001, p. 98, 99, 111-119; McDougall 2009, pp. 214-). As McDougall puts it, it's a "take-a-step, take-a-breath" coordination. Well it's not the case for us. Our breathing is disconnected from our stride. We can do several strides while inhaling. The whole point of other species breathing is that they save energy, their technique does not require a specific movement for breathing, as we do. But because they cool down by panting, their thermoregulation is entirely locked to their breathing system. It's more economic but less efficient. Indeed, if their temperature is skyrocketting during an effort, it means that for decreasing the temperature, they have to pant more. But to pant more, they have to run faster. But if they run faster, their temperature increases! Thus, it's less efficient than the functioning of our breathing/thermoregulation system. Once a cheetah reaches 40 degrees (celsius), it refuses to continue. The system shut down, it stops running. If not it dies. Well, for us, as long as we sweat, we can continue breathing at heart content.

Persistence hunting and evolution
Persistence hunting and the endurance running hypothesis
The endurance running hypothesis states that some human features can be explained as adaptation for long-distance running. What are those features ? In Wikipedia's entry Endurance running hypothesis, you can find the following:
  • Hairlessness and an abundance of sweat glands, as a heat loss mechanism.
  • Short toes. (See Campbell et al 2008).
  • Large gluteal muscles.
  • Human aptitude for endurance events such as ultramarathon
  • Increased bodyfat.
  • Long legs with springy tendons (no tendons in walking species, like chimpanzees).
  • Intolerance of sedentary lifestyle, regarding obesity and diabetes related pathologies

I deleted the last one (ability to breath through the mouth while running), because it doesn't make sense. Maybe they meant that homo sapiens has an aerobic capacity (capacity to use oxygen to burn fuel during physical activities), that asks for breathing, required for any effort covering a long period (unlike anaerobic capacity -also possessed by hominids-, where the organism fuels on a biological process -anaerobic metabolism- by which saccharids -sugars- in the body are converted into fuel and lactate through a fermentation, in the absence of oxygen). And there's more to it (Bramble & Lieberman 2004):
  • The nuchal ligament. This ligament is used to stabilize the head when an animal is running fast. It's attached to the posterior tubercule of the atlas and to the spinous processes of the cervical vertebrae. Dogs and horses got this one. Walking species, like chimpanzees, don't. This ligament typically identifes a species as a running one (thus, not a walking species).

The brainy advantage of persistence hunting
If you study the evolution of the brain of hominids, you know that the size of the brain increased suddenly 2 millions years ago. An increase means that i) the individual with an increased brain size has to find new supplies to provide energy resources (because the brain requires high amount of energy); ii) some aeras of the brain are more developped in this individual (requiring perhaps a reorganisation of the brain) than in the brain of the members of the species from which it derives.
2 millions years ago, the hominids pertained to the australopithecus genus (who appears 3 millions years before, i.e., 5 millions years ago). His features were, among others, giant jaws, tiny brain, and very long intestines. What for? To digest fibrous plants. But 2 millions years ago, it's the transition between australopithecus genus and homo genus, via homo ergaster and homo erectus. What happened? Their intestines were shorter, they standed up, they had tearing teeth, and their brain became bigger. Why? Because they found a new energy source. Which one? Fresh meat. It's easier and faster to digest, and per unit, it contains more energy resources than plants (which differed strongly from the domestic species we know). How did we get fresh meat? Persistence hunting.
With persistence hunting, we could supply more energy resource to feed our brain. And the benefits were increased sophistication of our mind. (Liebenberg 1990) boldly ties up hunting and the evolution of modern culture, e.g. science and art, but I never actually read it. So I won't venture any statements on that subject. However, a study (Brower 2006; Leakey 1992, pp. 257-258) shows that, contrary to members of australophitecus genus, homo erectus and his most direct descendants possessed the Broca's area (region of the brain required for sophisticated and articulated language ability) and another (Boehm 1999) that they were the first to live in small band societies similar to modern hunter-gatherer groups .


Bramble, Dennis M., and Carrier, David R. (1983). Running and Breathing in Mammals. Science 219: 251-256.
Bramble, Dennis M. & Lieberman, Daniel E. (2004). Endurance running and the evolution of Homo. Nature, 432: 345-353. 
Boehm, Christopher (1999). Hierarchy in the forest: the evolution of egalitarian behavior. Cambridge Mass.: Harvard University Press.
Bower, Bruce (2006). "Evolutionary Back Story: Thoroughly Modern Spine Supported Human Ancestor". Science News Online 169 (15): 275. 
Campbell, Rolian, Lieberman, Daniel E., Hamill, Joseph, Scott, John W., Werbel, William (2009) Walking, running and the evolution of short toes in humans. The Journal of experimental biology, 212, 713-721.
Carrier, David, R.(1984). The energetic paradox of human running and hominid evolution. Current Anthropology, 25:4. 
Carrier, Scott (2001). Running after Antelope. Counterpoint Press.
Heinrich, Bernd (2002). Why we run. A Natural History. New York: HarperCollins Publishers.
Leakey, Richard (1992). Origins Reconsidered. New York: Anchor.  
Liebenberg, Louis 1990. The Art of Tracking: The Origin of Science. David Philip.
Liebenberg, Louis (2006). Persistence Hunting by Modern Hunter-Gatherers. Current Anthropology, 47:6.
Liebenberg, Louis (2008). The relevance of persistence hunting to human evolution. Journal of Human Evolution, 55: 1156-1159.
McDougall, Christopher (2009). Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen. New York: Knopf.

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