Endurance running and the evolution of HomoDennis M. Bramble1& Daniel E. Lieberman21Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA2Peabody Museum, Harvard University, Cambridge, Massachusetts 02138, USA...........................................................................................................................................................................................................................Striding bipedalism is a key derived behaviour of hominids that possibly originated soon after the divergence of the chimpanzeeand human lineages. Although bipedal gaits include walking and running, running is generally considered to have played no majorrole in human evolution because humans, like apes, are poor sprinters compared to most quadrupeds. Here we assess how wellhumans perform at sustained long-distance running, and review the physiological and anatomical bases of endurance runningcapabilities in humans and other mammals. Judged by several criteria, humans perform remarkably well at endurance running,thanks to a diverse array of features, many of which leave traces in the skeleton. The fossil evidence of these features suggests thatendurance running is a derived capability of the genus Homo, originating about 2 million years ago, and may have beeninstrumental in the evolution of the human body form.Most research on the evolution of human locomotionhas focused on walking. There are a few indicationsthat the earliest-known hominids were bipeds1,2,and there is abundant fossil evidence that australo-pithecines habitually walked by at least 4.4 millionyears (Myr) ago3,4. Many researchers interpret the evolution of anessentially modern human-like body shape, first apparent in earlyHomo erectus, as evidence for improved walking performance inmore open habitats that came at the expense of retained adaptationsin the australopithecine postcranium for arboreal locomotion (forexample, refs 5–8). Althou gh the biomechanics of running, theother human gait, is well studied, only a few researchers (see refs 9,10 for example) have considered whether running was a mode oflocomotion that influenced human evolution. This lack of attentionis largely because humans are mediocre runners in several respects.Even elite human sprinters are comparatively slow, capable ofsustaining maximum speeds of only 10.2 m s21for less than 15 s.In contrast, mammalian cursorial specialists such as horses, grey-hounds and pronghorn antelopes can maintain maximum gallop-ing speeds of 15–20 m s21for several minutes11. Moreover, runningis more costly for humans than for most mammals, demandingroughly twice as much metabolic energy per distance travelled thanis typical for a mammal of equal body mass12. Finally, humanrunners are less manoeuvrable and lack many structural modifi-cations characteristic of most quadrupedal cursors such as elongatedigitigrade feet and short proximal limb segments.However, although humans are comparatively poor sprinters,they also engage in a different type of running, endurance running(ER), defined as run ning many kilometres over extended timeperiods using aerobic metabolism. Althoug h not extensively studiedin non-humans, ER is unique to humans among primates, anduncommon among quadrupedal mammals other than social carni-vores (such as dogs and hyenas) and migratory ungulates (such aswildebeest and horses)13,14. Here, we review the evidence for andimpact of ER in human evolution. We begin with a discussion of themechanical differences between walking and running, and how wellhumans perform at ER compared to other mammals. We thenreview what is know n about the key structural specia lizationsthought to underlie human ER capabilities, the extent to whichthey may be features that evolved originally for bipedal walking, andthe evidence for their appearance in the hominid fossil record. Weconclude by outlining some hypotheses for why ER capabilitiesinitially arose in the genus Homo, and the significance of thisbehaviour for human evolution.How well do humans run long distances ?In considering human running, it helps to start from the perspectiveof the basic biomechanical differences that distinguish running andwalking gaits in all mammals, including human bipeds. Thesedifferences are well characterized. Walking uses an ‘inverted pen-dulum’ in which the centre of mass vaults over a relatively extendedleg during the stance phase, efficiently exchanging potential andkinetic energy out-of-phase with every step (Fig. 1a, b). The meta-bolic cost of transport (COT) for human walking, like that of othermammals, is a ‘U’-shaped curve, in which optimal speed, approxi-mately 1.3 m s21, is largely a function of leg length15. Most humansvoluntarily switch to running at approximately 2. 3–2.5 m s21,which corresponds closely to the intersection of the COT curvesfor walking and running in humans (Fig. 2b)16,17. At these higherspeeds running becomes less costly than walking by exploiting amass-spring mechanism that exchanges kinetic and potential energyvery differently (Fig. 1b). Collagen-rich tendons and ligaments inthe leg store elastic strain energy during the initial, braking par t ofthe support phase, and then release the energy through recoil duringthe subsequent propulsive phase18,19. To use these springs effectively,the legs flex more in running than in walking: flexing and thenextending at the knee and ankle during the support phase (Fig. 1a).Limb stiffness relative to body mass in running humans is similar tothat of other mammalian cursors20.Although extensive data on endurance capabilities are not avail-able for most quadrupedal mammals, several lines of evidenceindicate that humans, using criteria such as speed and sustainabledistance, are much better endurance runners than has generallybeen appreciated. Human ER speeds range from approximately 2.3to as much as 6.5 m s21in elite athletes. Average ER speeds forrecreational joggers range between 3.2–4.2 m s21(ref. 21). From anevolutionary perspective, it is important to note that human ERspeeds are exceptional compared to non-human primates. Apessuch as chimpanzees, and other primates, such as patas monkeys,can sprint rapidly, but they do so rarely and only for shortdistances22,23. No primates other than humans are capable of ER.Quadrupedal cursors easily sprint faster than humans over shortdistances, but sustainable ER speeds of humans are surprisinglycomparable to specialized