Simopoulos AP (ed): Nutrition and Fitness: Evolutionary Aspects, Children’s Health,
Programs and Policies. World Rev Nutr Diet. Basel, Karger, 1997, vol 81, pp 49–60
...........................
Evolutionary Aspects of Exercise
Loren Cordain a, Robert W. Gotshall a, S. Boyd Eaton b
a
Department of Exercise and Sport Science, Colorado State University,
Fort Collins, Colo.;
b
Department of Radiology, Emory University School of Medicine, Atlanta, Ga., USA
As a species, human work (exercise) capacities and limitations are a
result of our species-specific anatomical and physiological characteristics,
which in turn are defined by our genetic constitution. Similar to all other
organisms, the human genome was shaped by environmental selective pres-
sures over eons of evolutionary experience. As hominids evolved and became
separate from pongids between 6.3 and 7.7 million years ago (MYA), in
response to selective pressures, they developed specific structural and func-
tional characteristics which allowed them to exploit environmental niches
which were previously unavailable to their pongid ancestors. Consequently,
the selective pressures of the ecological niche which hominids occupied were
responsible for shaping those genetic characteristics which are unique to our
species (including anatomical and physiological parameters influencing our
exercise capacities, limitations and requirements). Examination of both the
hominid fossil record and structural and functional differences between mod-
ern humans and primates provides insight into the evolutionary changes
which occurred in human anatomy and physiology which directly influenced
the exercise capacities of contemporary men and women. Further, by studying
modern-day hunter-gatherer societies, it is possible to not only develop models
of optimal exercise patterns for fitness, but to evaluate how the discordance
between the activity patterns of modern sedentary societies and hunter-
gatherer societies is implicated in a wide variety of chronic degenerative
diseases which plague contemporary man.
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Table 1. The main events of human evolution [adapted from ref. 1]
Years ago Epoch Development
7,500,000 hominid-pongid divergence
late Miocene
4,200,000 Pliocene bipedal Australopithecus anamensis present
3,900,000 Australopithecus afarensis present
Australopithecine divergence
2,000,000 Homo habilis present
1,700,000 early Pleistocene Homo erectus present
400,000 archaic Homo sapiens appears
230,000 Homo sapiens neanderthalensis appears
late Pleistocene
45,000 Homo sapiens sapiens (anatomically modern) appears
latest Pleistocene
10,000 agricultural revolution
Holocene
200 industrial revolution
Changes in Hominid Anatomy/Physiology Impacting
Exercise Capacities
The evolution of the human species can ultimately be traced to the origin
of life itself. However, the distinctive structural and functional features which
characterize our species have occurred following the evolutionary split between
pongids (apes) and hominids (upright, bipedal primates) 6.3–7.7 MYA
(table 1) [1]. Evolutionary changes in hominid anatomy/physiology which have
had the greatest impact upon our present day exercise capacities include the
development of an upright bipedal gait; increases in cranial capacity and body
size associated with changes in dietary quality; the attenuation of body hair
and the subsequent development of a highly efficient sweat gland system. In
conjunction with these basic anatomical and functional alterations were
changes in behavioral complexity which led to increased tool use which in
turn is associated with a decreased upper and lower limb robustness [2] (fig. 1).
Bipedalism
The first hominids to walk fully upright (Australopithecus anamensis)
appear in the fossil record between 3.9 and 4.2 MYA [3] in East Africa
coincident with climatic changes in which large areas of the tropical rain forest
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Fig. 1. Changes in percent femoral cortical area [(cortical area/periosteal area)¶100]
relative to changes in cranial volume over the course of the evolution of the genus Homo.
Adapted from Ruff et al. [2].
were replaced by a more open woodland [4]. A. anamenis perhaps represents
the ancestral species of the better known Australopithecine, Australopithecus
afarensis (table 1). A. afarensis exhibited sexual dimorphism (weight: 30–70 kg,
height 1–1.5 m) and had a cranial capacity of 400–500 ml [5]. A. afarensis did
not make stone tools and because they maintained a more ape-like body with
relatively longer arms and shorter legs than contemporary men, these hominids
may have been well adapted to both arboreal and terrestrial environments [6].
Analysis of both fossil footprints and pelvic/leg bone structure indicate that
A. afarensis walked/ran with a mechanical efficiency similar or superior to
modern humans [7].
Although it is not entirely clear which specific environmental pressures
were ultimately responsible for the evolution of bipedal locomotion, a number
of potential advantages have been identified. An upright, bipedal gait raises
the level of the head and provides for a greater visual field for location of food,
water and predators in a more open woodland environment [8]. Additionally,
bipedalism frees the hands to carry food and other objects during locomotion
[7].
More importantly, from an exercise standpoint, bipedalism may be more
energy efficient than a comparable quadrupedal posture for standing/walking
but not for running. Whereas the oxygen cost of running in man (0.212 ml/
g/km) is approximately twice that of other mammals [9], the oxygen cost of
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human walking is at least as economical as the walking of typical mammalian
quadrupeds [10, 11]. Moreover, the difference in energy expenditure for adult
humans between their erect and resting (supine) postures is less than that
for a quadrupedal animal [12]. Collectively, these data suggest that bipedalism
for the most frequent hominid posture (standing/walking) resulted in an
energy savings which may have produced a slight but meaningful selective
advantage.
Thermoregulation
An upright posture would have had selective advantage for an exercising,
diurnal hominid in a hot, sunny woodland or savanna environment because
it would reduce the surface area of the body exposed to the sun and thereby
reduce the thermal load [13]. Because A. afarensis was a biomechanically
efficient walker and runner [7] and because their daily range increased substan-
tially with the evolution of bipedalism [14], it has been argued that they may
have begun to evolve a more complex eccrine sweat gland system which would
have allowed them to run considerable distances under a hot tropical sun
without overheating [15]. Further, the evolution of a ‘naked’ skin (attenuation
of body hair size) would have increased the rate at which sweat could be
evaporated from the surface of the skin and therefore would have increased
the evaporative cooling efficiency of the cutaneous sweat glands [15].
The adaptive value of man’s elaborate eccrine system has been largely
attributed to its facilitation of heat dissipation during running [16]. The ability
to rapidly run considerable distances without overheating would have had
obvious survival advantages for bipedal hominids during locomotion in more
open woodland and savanna environments. Escape from predators and location
and transport of food, infants and other objects would have been facilitated
by an efficient evaporative cooling system.
Cranial Capacity and Body Enlargement
The first hominids likely to have made stone tools, Homo habilis, had
body dimensions similar to A. afarensis, but a slightly larger cranial capacity
(~750 ml). Increasingly, it has been recognized that in order for a larger, more
metabolically active brain to have evolved, an increase in dietary quality
(caloric density) had to occur [17–19].
Throughout evolutionary history, carnivorous mammals have always
maintained a proportionately larger brain size relative to body size when
compared to their herbivorous prey [20]. Because proportionately larger brains
are more metabolically active, in order to fuel their increased energetic demands
they either require an increase in dietary quality, a reduction in the size and
metabolic rate of another tissue, or both [17]. Carnivores have evolved their
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Table 2. Metabolic parameters in primates [adapted from ref. 21]
Species Sex Weight RMR TEE Ratio PA-EE Day range
kg kcal kcal (TEE/ kcal km
RMR)
Nonhuman primate
Pan troglodytes M 39.5 1,036 1,510 1.46 474 4.8
F 29.8 839 1,144 1.36 305 3.0
Fossil hominids
Australopithecus 37.1 1,149 1,824 1.59 675
afarensis
Homo habilis 48.0 1,404 2,387 1.70 983
Homo erectus 53.0 1,517 2,731 1.80 1,214
Homo sapiens (early) 57.0 1,605 2,889 1.80 1,284
Modern
hunters-gatherers
Kung M 46.0 1,275 2,178 1.71 903 14.9
F 41.0 1,170 1,770 1.51 600 9.1
Ache M 59.6 1,549 3,327 2.15 1,778 19.2
Acculturated
modern humans
Homo sapiens M 70.0 1,694 2,000 1.18 306 0
(office worker)1
F 55.0 1,448 1,679 1.16 231 0
Homo sapiens M 70.0 1,694 2,888 1.70 1,194 12.1
(runner)2
RMR>Resting metabolic rate; TEE>total energy expenditure; PA-EE>energy expendi-
ture attributed to physical activity.
1
Sedentary office worker [22].
2
Runner running 12.1 km/h [22].
larger, more metabolically active brains at the expense of a smaller gut. This
adaptation can occur because less digestive energy is required to extract food
energy from the nutrient dense lipids and proteins in animal foods than from
plant foods of low digestibility.
As hominids increasingly included animal foods in their diet, there was
a relative increase in brain size and a reduction in their gut size [17] similar
to carnivores. These changes were associated with increased behavioral com-
plexity which in turn led to an increased daily range and an increased total
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energy expenditure (TEE) (table 2). By 1.7 MYA, H. habilis was succeeded
by Homo erectus who stood as tall as contemporary humans [23, 24] and
based upon cortical bone thicknesses and diameters [2] was quite heavily
muscled and therefore was likely stronger than most modern humans.
Besides being powerfully muscled, H. erectus likely had aerobic capacities
similar to modern men. Pongids and Australopithecines have rib cages which
narrow as they move upward in order to accommodate the extremely powerful
muscle groups of the pectoral girdle which are used during arboreal locomotion
[17]. Therefore, ventilation of the lungs was probably mainly dependent upon
the movements of the diaphragm and would have been less effective than in
H. erectus, in which the upper part of the rib could have been raised to enlarge
the thorax during inspiration [17].
With the appearance of H. erectus, hominids not only became taller, but
there was a relative decrease in maximal pelvic breadth relative to stature [24].
This relative increase in body linearity would have allowed the (surface area/
body mass) ratio to remain favorable for heat dissipation during aerobic activi-
ties such as running even though absolute body size had increased from earlier
hominids. A relative increase in body linearity may have also facilitated a
greater stride length [16] for greater efficiency during running. Regardless of
the mechanisms involved, it is clear that the wider rib cages of H. erectus
and their tall slender physiques facilitated high level aerobic activities in hot
climates.
H. erectus (the Kenyan version is sometimes referred to as H. ergaster)
walked out of Africa by at least 1 MYA or perhaps earlier and colonized
eastern Asia but not Europe. Archaic Homo sapiens (Homo heidelbergensis)
inhabited Europe by 400,000–500,000 thousand years ago or perhaps even
much earlier [25] and probably represents ancestors of the well-known Nean-
derthals (Homo sapiens neanderthalensis) [26]. Anatomically, modern human
beings first appear in the fossil record 90,000–100,000 years ago in the Near
East and Africa, and the first truly modern humans, complete with art,
culture and sophisticated tools are recognizable 40,000 years ago. Until the
agricultural revolution 10,000 years ago, all hominids occupied the hunter-
gatherer niche, and regular daily activity utilizing both endurance and strength
pathways was essential for all but the most infirm individuals. Consequently,
by studying living groups of hunters-gatherers, it is possible to examine the
physical activity patterns to which we are genetically adapted so that insight
can be gained in determining optimal exercise levels for modern, sedentary
societies.
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Metabolic Considerations in Primates, Hunters-Gatherers and
Contemporary Humans
Activity Patterns in Primates, Hominids and Modern Hunters-Gatherers
Table 2 contrasts the metabolic rates and activity patterns of primates,
fossil hominids, modern hunters-gatherers, sedentary office workers and a
modern runner. It can be seen that as body weight increases, resting metabolic
rate (RMR) increases proportionately. This relationship is well established
across mammalian species such that RMR scales to the 3/4th power of body
weight [27]. As hominids evolved, they became larger; consequently RMR
increased [21]. Additionally, as the tropical forest gave way to more open
woodland and savanna environments, caused by prolonged drying periods
[4, 28], food resources became less abundant and more dispersed [29]. There-
fore, it is probable that early members of the genus Homo would have had
to increase their daily range [14] and thereby increase the physical activity
component (PA-EE) of their total daily energy expenditure (TEE). Since hu-
man body size has remained essentially constant since the first appearance of
H. erectus [24], then the ratio of TEE/RMR in table 2 reflects (ignoring the
small thermic effect of food ~5–10% TEE) changes in activity levels which
have occurred during the evolution of hominids. The mean estimated (TEE/
RMR) ratio (1.87) for hominids since the appearance of full-sized humans
(H. erectus) represents the activity level for which our species is genetically
adapted. The TEE/RMR ratio of sedentary office workers (1.18) denotes
activity levels which have previously not been encountered in our species and
which are clearly discordant with our genetic requirements.
From table 2, it can be seen that hunter-gatherer males typically spend
between 19.6–24.7 kcal/kg/day in physical activity whereas the sedentary office
worker would expend only 4.4 kcal/kg/day. Even if a 3.0-mile walk (minimal
health benefits suggested by the American College of Sports Medicine [30])
were added to the office workers activities, the resulting value of 8.7 kcal/kg/
day would be significantly lower than that which would be normal for our
pre-agricultural ancestors. Only when higher level activities are engaged in
(say running 12.1 km/h for 60 min) do modern sedentary workers simulate
the energy expenditures of our stone age ancestors.
‘Primitive’ Physical Fitness and Acculturation
Previous studies of modern hunters-gatherers have been compiled by
Eaton et al. [31], and mean estimates of maximal oxygen consumption
(VO2max) in young men (52 ml/kg/min) would place them in either the excellent
to superior fitness classifications as established by Cooper [32] for modern
industrialized populations, whereas comparably aged modern men would only
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have ‘fair’ fitness levels (Vo2 max>40.8 ml/kg/min) [31]. Clearly, the normal
day-to-day activities of hunters-gatherers, even without the benefit of specific
exercises designed to improve cardiorespiratory fitness, produce high levels of
endurance.
Rode and Shepherd [33] recently completed a 20-year study (1970–1990)
of an Inuit community and were able to document the changes in fitness
levels as these hunters-gatherers adopted a more modern, sedentary existence.
Not only did activity levels decrease substantially with the adoption of
mechanized tools and equipment, but the native diet changed so that it
approximated the typical diet of industrialized populations [34]. Associated
with these lifestyle changes were increases in body fat, a loss of muscular
strength and a decrease in aerobic fitness levels. This native Inuit community
is now threatened with ‘diseases of civilization’ (such as hypertension, cardio-
vascular disease, and diabetes mellitus) which have been rare until recently
[33].
Evolutionary Insights into Exercise, Health and Disease
With the exception of H. sapiens, mammals have to work in order to
eat: food procurement depends directly upon energy expenditure. Because
technological achievement and social organization have disrupted this basic
relationship for contemporary humans, low levels of physical exertion have
become unprecedentedly common in western, industrialized societies. This
departure from exercise patterns which prevailed throughout our evolutionary
history has been implicated in the etiology of many chronic degenerative
diseases which plague modern-man including diseases of insulin resistance
(obesity, non-insulin-dependent diabetes mellitus (NIDDM), hypertension and
coronary artery disease) and bone demineralization and fractures.
Diseases of Insulin Resistance
Increasingly it is being recognized that insulin resistance/hyperinsulinemia
may be a primary factor in the development of three major diseases (hyperten-
sion, NIDDM, coronary artery disease – collectively referred to as ‘syndrome
X’) as well as obesity [35, 36]. These diseases are so epidemic in modern,
industrialized societies as to be designated ‘diseases of civilizations’, since they
are rare to nonexistent in less-acculturated societies [31]. The extent to which
environmental and genetic factors play in disposing people to these diseases
is not clear, however both dietary [37] and exercise [38] patterns seem to play
an essential role in the development of syndrome X via their long-term influ-
ence upon insulin metabolism.
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Acute exercise bouts, either aerobic [39] or strength [40] enhance glucose
uptake by skeletal muscle, whereas chronic training is associated with increased
skeletal muscle insulin sensitivity and reduced plasma insulin levels [39]. The
net effect of an increased insulin sensitivity in conjunction with the increased
metabolism of exercise serves to beneficially influence body composition (loss
of fat), blood pressure and glucose (lower BP, glucose) and lipid metabolism
thereby reducing many of the risk factors for syndrome X.
Relative to activity levels and body composition, trained individuals are
similar to our hunter-gatherer ancestors. In response to a glucose load, they
secrete less insulin and have lower peak plasma glucose levels than do nonath-
letes [41]. Twentieth century hunters-gatherers (African San and Efe) and
isolated horticulturists (Venezuelan Yanomamo) have insulin sensitivity which
is exceptional when compared to that which is considered ‘normal’ for western-
ized, affluent individuals [42–44]. When a group of urbanized Australian Abori-
gines temporarily reverted to a foraging lifestyle, their serum insulin and
glucose levels were markedly reduced [45]. For Paleolithic humans, obesity
was rare and physical exertion the norm [31]. Accordingly, syndrome X and
diseases of hyperinsulinemia would have also been rare.
Bone Demineralization and Fractures
Osteoporosis, a major orthopedic disease (primarily in postmenopausal
women), is marked by a decalcification of bone which results in a loss of bone
tensile strength that can ultimately lead to fractures. Even though many factors
(diet, smoking, genetic and metabolic diseases) including physical activity
levels have been suggested as causes of osteoporosis [46], it is likely that the
etiology of the disease is multifaceted and no single factor is entirely responsi-
ble for its onset [47].
Although there are numerous cross-sectional studies showing that active
men and women have a higher bone mineral density (BMD) than those who
are sedentary, prospective studies have generally indicated that exercise has a
minimal influence upon the postmenopausal decline in BMD [47]. Addition-
ally, studies of BMD using dual-energy X-ray absorptiometers in archaeolo-
gical skeletons from the Bronze Age [48] and Medieval times [49], during
which there was less mechanization and humans presumably were more active,
have shown the range of BMD to be similar to modern populations.
Although the most commonly recognized index of bone integrity is BMD,
bone structural geometry may be equally, if not more important, in determining
a bone’s intrinsic strength and ability to resist mechanical stresses [2]. Since
BMD is a function of both cortical mass and volume, it is possible to have
bones of identical densities but with considerably differing volumes. The greater
long bone robustness exhibited by all pre-industrialized humans appears to
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Fig. 2. Reduction in femoral mid-shaft cross-sectional cortical area from early to recent
members of the genus Homo. % CA>[(cortical area/periosteal area)¶100]. Adapted from
Ruff et al. [2].
have occurred from relative increases in cortical volume (fig. 2) elicited by
greater activity levels [2]. Consequently, the regular loading of skeletal tissue
experienced by our pre-industrialized ancestors produced robust, fracture-
resistant bones via changes in structural geometry which may have counterbal-
anced deficiencies in bone mineral content.
Conclusions
Because of the sedentary nature of industrialized societies, exercise is
usually viewed as an activity (jogging, walking, swimming, bicycle riding,
aerobics, weight lifting, etc.) separate from daily activities, done during leisure
time to improve fitness or strength. In contrast, in living hunters-gatherers,
exercise results from the daily muscular activity needed to adequately function
within the hunter-gatherer niche. Food and water procurement, social inter-
action, escape from predators, and homeostatic maintenance evoke obligatory
movements, and these movements needed to carry out life’s functions represent
the genetically established exercise patterns of man prior to the agricultural
revolution of 10,000 years ago. Although human lifestyles have changed almost
inconceivably since the advent of the agricultural revolution and the more
recent industrial revolution, our exercise capacities, limitations and require-
ments remain the same as those selected by natural selection for our stone
age ancestors. Deviation from these intrinsic exercise patterns established long
ago inevitably results in dysfunction and disease.
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