In his famous monologue, Hamlet marvels at what mankind has become. “What a piece of work is a man! how noble in reason! how infinite in faculty! in form and moving how express and admirable! in action how like an angel! in apprehension how like a god! the beauty of the world! the paragon of animals!” But what if Hamlet had the causation backwards? What if it is precisely our admirable “form and moving” - our bodies - that enabled our “noble reason” and “infinite faculties”? Specifically, could distance running be what made human cognition possible?
There are an estimated 6.5 million terrestrial animals. Roughly 2/3 of these are predators. But of the millions of predators on land, just 5 are classified as persistence pursuit predators — meaning instead of ambushing prey, they engage in prolonged pursuit, running their quarry to exhaustion over miles and hours. In this sense, we really are the paragon of animals.
The argument is that that running and intelligence are not merely correlated. The same biological adaptations that made us exceptional endurance hunters created the physical substrate that a large, metabolically expensive brain requires; running built the hardware that enabled our superior wetware.
The Body Built for Running
Bramble & Lieberman (2004) identified approximately 26 features in Homo anatomy specifically adapted for endurance running: the nuchal ligament — a thick band at the back of the neck that stabilizes the head during a running stride, enlarged gluteus maximus, shortened toes, arched foot, narrow waist, and semicircular canal enlargement for gaze stabilization. These features appear in Homo erectus — the same lineage showing significant encephalization — the evolutionary process by which our brains grew disproportionately large relative to our body size.
The timing is significant. These skeletal changes appear in the fossil record roughly 1.5 to 2 million years ago, in concert with the first substantial increases in brain size. This is unlikely to be mere coincidence. The Endurance Running Hypothesis posits that the many of the skeletal adaptations that differentiate Homo from other primates were based on running. What if these anatomical changes enabled the cognitive changes?
Running Built the Brain’s Infrastructure
The human brain is metabolically extraordinary, consuming approximately 20% of resting cardiac output despite being just 2% of body mass. Sustaining an organ this hungry requires an exceptional circulatory system. The human cardiovascular system has several unusual features: relatively large heart-to-body ratio, high stroke volume capacity, and crucially the ability to maintain some cerebral perfusion even during near-maximal exertion. These were perhaps initially adaptations for our unusual hunting style (e.g., keeping tissues oxygenated during a two hour pursuit), but they may have become essential for our enlarging brains to function.
The eccrine sweating system and loss of body hair that enable persistence hunting also protect a large brain from heat damage. Neurons are fragile at high temperatures; the brain begins to malfunction above roughly 104°F (40°C). Most large mammals solve this problem with panting, but that limits simultaneous breathing during sustained exertion. Humans solved the cooling problem differently. The selective brain cooling mechanism, via the cavernous sinus and cooled venous blood returning from facial evaporation, is unusually well developed in humans. It is plausible this thermoregulatory system was selected for distance running, but incidentally enabled a large brain to operate safely for sustained periods in the hot African savanna.
Effective hunting also improved the availability of calories and the quality of food. Being able to take down large ungulates (antelope, wildebeest, and early horses) provided a stable supply of nutrition, including nutrients and micronutrients essential for brain development. Hunting provided early humans with dense animal fat, critical for brain lipid composition: DHA, arachidonic acid, and organ meats with micronutrients (B12, zinc, iron) that are limiting for neural development. A brain that cannot be fed cannot grow. Running gave us the means to feed it.
The Hunt Demanded More Than Legs
The relationship between running and cognition was almost certainly not one-directional. The demands of persistence hunting likely created selection pressure for greater intelligence in its own right. Persistence hunting is cognitively demanding in ways that pure ambush hunting is not. It requires tracking and interpreting spoor over hours, mental modeling of prey behavior and terrain, sustained goal-directed attention over long timeframes, prospective memory and planning (“the animal will head toward water when it overheats”), and coordination within a group. Perhaps the need to convey these more complex ideas was even the genesis of language.
The anthropologist Louis Liebenberg has argued extensively that tracking is one of the most cognitively complex tasks hunter-gatherers perform, functionally equivalent to scientific reasoning: forming hypotheses about an unseen animal’s behavior, testing them against evidence in the environment, and revising them in real time. If persistence hunting created selection pressure for these cognitive capacities, brain size could follow as a consequence. If running built the hardware, hunting refined the software.
The Company We Keep
Our choice of best friends supports the hypothesis that persistence pursuit was important. Perhaps it is not a coincidence that the wolf, the first species we domesticated, is another of the 5 persistence pursuit predators, and has a VO2max among the highest in the animal kingdom. (Sled dogs, a close relative of wolves, have a VO2max of 175-300 ml/kg/min!)
Dogs are a profound outlier in the history of domestication. They were the first species we domesticated, and by a lot! Studies suggest dogs were domesticated 15,000 to 40,000 years ago, at least 5,000 and perhaps as much as 30,000 years before the goat. Dog domestication precedes the agricultural revolution by at least 5,000 years and possibly much more, occurring during the Upper Paleolithic, by hunter-gatherers, before any other animal or plant. This strongly supports the hypothesis that dog domestication was driven by hunting utility rather than pastoral or agricultural need. We did not recruit the wolf because we needed a companion around a fire. We recruited it because it could run and keep up with us.
In choosing the wolf, we reveal what we understood ourselves to be: persistence hunters, defined by the chase. We recognized a kindred physiology and made it our companion.
Too Good to Last
Indeed, it is likely that early humans were too good at hunting. In the Late Pleistocene, the majority of megafauna (animals over 44 kg, roughly the size of a large dog) went extinct in a remarkably short period of time. Roughly 50,000 years ago, there was an extinction of megafauna in Australia and Europe. 13,000 years ago in North America, over 70% of megafauna — including mammoths, mastodons, and saber-toothed cats — vanished in less than 3,000 years. Each of these extinctions coincided with the arrival of humans.
This is the dark epilogue to the persistence hunting story. The same cognitive and physical capacities that evolution had spent millions of years refining turned out to be so effective that we systematically eliminated the megafauna that had shaped them. We outran the evolutionary niche that had built us. The prey disappeared; eventually, so did the hunter’s niche. Within a few thousand years of the North American extinctions, the agricultural revolution had begun. Running had made us intelligent enough to eliminate our own ecological role.
The Paragon of Animals
So what made us the paragon of animals? Not, as Hamlet implies, some ineffable divine spark. Rather, the physiologic adaptations that enabled our endurance played a critical role in the growth of our intelligence. The cardiovascular system that could sustain a two-hour pursuit also delivered oxygen to an enlarging brain. The thermoregulatory system that kept a hunter cool on the savanna also protected neurons from heat damage. The caloric windfall from taking down large ungulates provided the raw materials for neural tissue. And the cognitive demands of the hunt itself created selection pressure for the very faculties Hamlet was celebrating. Put another way: we did not become intelligent and then become hunters; we became intelligent because we hunted and because our bodies were built to run.
Fascinating work!
Very nice!