the evolution of running

Hominin running

Between 5 and 7 million years ago, some African apes evolved adaptations enabling them to move about on 2 legs ("bipedalism") for short periods of time, supplementing their arboreal lifestyle. By about 1.8 million years ago, with Homo erectus (though some now say earlier), there was a second bipedal transition: these hominins had adapted to a life fully spent on the ground, covering distance with efficiency. These traits have been conserved through our own species. In fact, modern humans can run long distances, in the heat, at a variety of paces, better than almost any other animal on earth. This unique ability demands explanation.  What pressures are responsible for this evolved ability? Have humans evolved to run long distances, or is our unique running ability a byproduct of adaptations for walking or other pressures?  Either way, this conspicuous ability has an evolutionary history.  What follows are articles dealing directly or indirectly with this topic. Below are papers that explicity discuss running in extinct hominins.

Endurance running and the evolution of Homo
Outlines the argument for running as an adaptive feature of genus Homo (that is, produced by natural selection).

The energetic paradox of human running and hominid evolution
David Carrier was perhaps the first to suggest that human running is noteworthy and adaptive.

Human locomotion and heat loss: an evolutionary perspective.
Dan Lieberman's most recent summary of how endurance running may have evolved and how it is tied to thermoregulation.

Thermoregulation and endurance running in extinct hominins: Wheeler’s models revisited
Heat dissipation through sweating enables modern humans to run without overheating.  Homo erectus displays body proportions similar to us.  Could these hominins have shed heat well enough to be efficient runners?

Locomotor anatomy of Dmanisi hominins
Analyzing the locomotor abilities of the engimatic Homo erectus fossils from Dmanisi, Georgia.  These diverse, small-brained specimens have upended our understanding of the early evolution of H. erectus, but what do they tell us about the evolution of endurance running ability in this species?

Ileret footprints of Homo erectus
1.5 million year old footprints demonstrate modern human foot biomechanics. These prints are amazing; I spoke with the lead researcher at a conference and he is a rad and lucky dude.

Walking, running, and the evolution of short toes in humans co-authored by Joseph Hamill of the UMass Biomechanics Laboratory. Tests the hypothesis that short toes evolved as an adaptation for endurance running.

Calcaneus length determines running economy: Implications for endurance running performance in modern humans and Neandertals
Title says it all.

The evolution of human running: Effects of changes in lower-limb length on locomotor economy
Within human runners, longer legs mean decreased cost of transport. 

The Human Body is Built for Distance-- New York Times article summarizing current (well, 2009) research pertaining to the role of running in human evolution, including some of the primary research articles listed on this blog.

Economy and endurance in human evolution
Herman Ponzter, who mostly works on questions of metabolism and energetics, here directly addresses the question of hominin running.  My summary of this paper can be found here.

Running, ecology, and energetics

Anything an animal does, it does in the context of its surrounding environment, constrained by energy, time, and risk.  Endurance running ability likely emerged some 2 million years ago (a rough estimate and moving target), so we should view running in the ecological context of that time--the early Pleistocene--and we must ask what utility it could have had.  Not surprisingly, hypotheses for the purpose of running mostly center on food acquisition: hunting (the "persistence hunting hypothesis"), scavenging, and plant gathering.  Many researchers place especially great importance on the high energetic cost of running, and wonder if the net gain in food gathering enabled by running would be enough to offset its cost.  Testing these hypotheses requires an understanding of the environment our ancestors evolved in.  What food was available?  Was it seasonal?  How widely dispersed was it?  Paleoecologists are hard at work on these questions and the few of us interested in the evolution of human running will do our best to apply it.  Following are papers discussing ecology and energetics in human evolution in ways that bear upon the question of endurance.

The energetic paradox of human running and hominid evolution
The original paper outlining the case for evolved running capability and the persistence hunting hypothesis.

Ecological energetics of early Homo
Early Homo put into an ecological context.  How did they forage for food, and how did they physically adapt to this ecology? Key point: Early humans increased their home range through greater locomotor ability, but not necessarily economy.  In this light, the increased energetic cost of our exceptional bipedal ability makes sense. A wonderful argument from comparative biology.

Energetics and the evolution of the genus Homo
More on the interconnected adaptations that arose early in our genus.

Grandmothering and the evolution of Homo erectus
Outlines a case for a plant-based (vs. the traditional "man the hunter") dietary adaptation in Homo erectus, with surprising implications.

Optimal running speed and the evolution of hominin hunting strategies
Could hominins have performed persistence hunts at a pace that was both effective and efficient? The authors claim to demonstrate that humans do have optimal and suboptimal running speeds, contrary to conventional dogma, and they further argue that human running was therefore an unlikely activity early in our genus.  However, see "Ecological energetics" (above) for an explanation of mammal foraging efficiency, demonstrating that natural selection should not increase locomotor economy in species that already achieve high energy returns from foraging.

Ethnographic and modeled costs of big-game hunting
Optimal Foraging Theory: would hunting large animals yield enough calories to offset the energy expended from the hunt?

Persistence Hunting by Modern Hunter-Gatherers
What does a modern persistence hunt look like? Can it tell us anything about the potential role of the persistence hunt in the past?

Can persistence hunting signal male quality?
Here's a fun one: Male fetal exposure to testosterone (and subsequent "mate quality") is positively correlated with running performance. Very cool, but consider their conclusions with discretion. This isn't an energetics argument but I didn't know where else to put it!

Metabolic acceleration and the evolution of human brain size and life history
The expensive tissue hypothesis and its offshoots claim that human energy expenditure (metabolism) must have deceased to accommodate a growing brain.  Ponzter et al. argue against this zero-sum model of energy and claim that, in fact, human metabolism increased.  This thinking is important in reconciling high physical activity levels (including running and walking) hypothesized in early humans.

Several papers by Herman Pontzer outline his recent hypothesis that humans have "constrained total energy expenditure": the body seems to respond to increased exercise by reducing overall metabolic rate.  This helps explain why moderate exercise is a lousy way to lose weight, and more interesting (to me) it suggests that evolution has shaped our metabolism to conserve energy.  (It should be noted that, even in this model, exercise has a metabolic cost, and so very active athletes will indeed have very high total energy expenditure.) Here are 3 of his papers:

             Constrained total energy expenditure and metabolic adaptation to physical activity in adult humans

             Energy expenditure in humans and other primates: A new synthesis

             The crown joules: energetics, ecology, and evolution in humans and other primates

              ...and a Scientific American article summarizing much of this in a friendlier format (requires a                 subscription):

My breakdown of this paper can be found here.

My breakdown of this paper can be found here.

Biology of the modern running primate

The study of modern human exercise biology helps us investigate its evolutionary history.  Exercise physiology is a huge field of study; here I merely hope to keep a short list of papers I've found especially helpful and pertinent in thinking about the evolution of endurance.

Evolutionary Aspects of Human Exercise – Born to Run Purposefully
Skip the introduction, which summarizes several hypotheses regarding the evolution of human running in an uncritical and adaptationist fashion.  Instead move to the meat of the article which very nicely discusses the human body's protective and adaptive responses to endurance running, especially responses in the brain.

Wired to run: exercise-induced endocannabinoid signaling in humans and cursorial mammals with implications for the ‘runner’s high’
Humans and dogs are found to produce high levels of endocannabinoids in the brain after endurance running, a reward mechanism that may have evolved to encourage us to run.

Mobility as an emergent property of biological organization: Insights from experimental evolution
A fantastic overview of 20 years of selective breeding for running-loving mice.  The authors clearly summarize the genetic, biological changes associated with selection for increased voluntary endurance running and suggest how these results can inform our view of how mammal running evolves (humans too).

Training augments resistance exercise induced elevation of circulating brain derived neurotrophic factor (BDNF)
More on how the brain responds to exercise: Resistance (strength) training, in addition to running, increases BDNF, which protects brain neurons and stimulates neuron growth.

Fiber types in mammalian skeletal muscle
The current understanding of how muscle fiber type transitions (fast to slow twitch, etc.) are controlled.

Energy system interaction and relative contribution during maximal exercise
Current (as of 2012) understanding of the several "energy systems" providing energy to human skeletal muscle.

Running forward: new frontiers in exercise biology
Written for physicians, this paper gives an excellent and in-depth (to me) review of the mechanisms of muscle adaptation to endurance exercise.

The biomechanics of running
Title says it all.

The capacity of the human iliotibial band to store elastic energy during running
Demonstrates that the IT band has an important function during running, one that is not employed during walking

The human gluteus maximus and its role in running
Glutes: likely an adaptation for endurance running, not walking.
retort: Activity and functions of the human gluteal muscles in walking, running, sprinting, and climbing ; human gluteus maximus "is highly active during running, sprinting, and climbing, supporting the idea that the uniquely human muscle is functionally important for a range of rapid and powerful movements."

Optimal footfall patterns for cost minimization in running
How does foostrike (forefoot, midfoot, rearfoot) affect energy expenditure?

A quick look at biochemistry: carbohydrate metabolism
A technical but informative summary of how carbohydrates are metabolized for energy.

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