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Journal ArticleDOI

The arboreal origins of human bipedalism

01 Sep 2014-Antiquity (Cambridge University Press)-Vol. 88, Iss: 341, pp 906-914
TL;DR: The evidence is set out for the existence of a much earlier origin for bipedalism in a Miocene primate ancestor that was still predominantly tree-dwelling, and the notion that the common ancestor of great apes and humans was a knuckle-walking terrestrial species, as are gorillas and chimpanzees today is rejected.
Abstract: Almost a century and a half ago, Charles Darwin in The Descent of Man (1871: 141) highlighted the evolution of bipedalism as one of the key features of the human lineage, freeing the hands for carrying and for using and making tools. But how did it arise? The famous footprints from Laetoli in Tanzania show that hominin ancestors were walking upright by at least 3.65 million years ago. Recent work, however, suggests a much earlier origin for bipedalism, in a Miocene primate ancestor that was still predominantly tree-dwelling. Here Susannah Thorpe, Juliet McClymont and Robin Crompton set out the evidence for that hypothesis and reject the notion that the common ancestor of great apes and humans was a knuckle-walking terrestrial species, as are gorillas and chimpanzees today. The article is followed by a series of comments, rounded off by a reply from the authors.

Summary (3 min read)

A. Board Composition and the Firm’s External Environment

  • An operating assumption of much of the corporate governance literature is that boards are endogenously determined institutions.
  • On the basis of this premise, much of this literature focuses on the proportion of outside directors and the link between performance and corporate governance.
  • It is possible that political directors are neither more effective monitors than other types of directors nor involved in rent-seeking activities but are on the boards of regulated industries because there is less market pressure to appoint more effective monitors and greater opportunities for shirking by the CEOs of regulated companies.
  • In effect, regulated firms need or simply have less effective monitoring by their boards than firms that are not regulated.

B. From Market to Political Competition: A Primer on Natural Gas Regulation

  • The business environment of natural gas companies has changed dramatically over the history of the industry.
  • 20 This section draws heavily on the discussion of the natural gas industry found in Robert L. Bradley, Oil, Gas, and Government: The U.S. Experience (1996); Stephen Breyer, Regulation and Its Reform (1982); and M. Elizabeth Sanders, The Regulation of Natural Gas: Policy and Politics 1938–78 (1981).
  • At several points during the late 1940s, the FPC commissioners tried to expand their regulatory authority to include producer prices.
  • Producer states in the late 1940s grew concerned, and on two occasions tried to enact legislation that would clarify that the FPC did not have the authority to regulate the prices charged by independent producers.
  • Finally, all extraction was deregulated in 1986 by Federal Energy Regulatory Commission (FERC) Order 451, which set the regulated price above the marketclearing price.

C. Defining Regulation

  • Given the different types and durations of regulatory regimes in the natural gas industry, the authors must be careful to clearly identify the particular regulatory events on which they focus.
  • Thus, for the Moody’s sample, the authors define a firm as regulated in a given year if (1) it lists one of its lines of business as owning a pipeline in any year after 1938 and/ or (2) it lists production as a line of business in the 1955–80 period.
  • Note that this definition biases their results toward zero; pipeline ownership does not necessarily mean the firm is regulated, since the pipeline may not cross state boundaries.
  • Clearly, the 1978 act deregulated some portion of production.
  • The oil industry was also subject to regulatory expansion during their sample period.

B. The Proxy Statement Sample

  • Given the limitations of the Moody’s-Marquis data, the authors supplement their analysis with an additional sample that consists of 96 natural gas firms.
  • Table 3 gives the breakdown by firm-year and total number of directors.
  • The authors fall short of this total because (1) several firms have missing proxy statements for several years, making it impossible to construct the board, and (2) the majority of firms operated only for a subset of the sample period.
  • The proxy data set has several advantages over the Moody’s-Marquis sample and one major disadvantage.
  • The major disadvantage is that the data extend back only to 1977.

C. Preliminary Data Analysis

  • Figure 1 presents the proportion of directors that are Washington lawyers by year and industry segment.
  • 38 Although proxy statements exist prior to 1978, their efforts to obtain them from the SEC met with limited success.
  • For pipeline companies, the number of Washington lawyers rises dramatically in 1940 and remains around 8 percent throughout the remainder of the sample period.
  • Given that production companies are deregulated beginning in 1978, this rise and fall is consistent with the external environment hypothesis that regulation requires firms to focus attention on the political process.
  • The trends for regulators and the composite indices are similar.

A. Control Variables for the Moody’s Data Set

  • Moody’s provides firm-specific data that the authors use as controls given previous findings in the literature.
  • The authors also include the size of the board, as the opportunity cost of a given director type is likely to change as the board size grows.
  • These variables control for the general economic environment common to all firms in a specific segment of the industry.
  • The authors have far better performance measures for their proxy statement sample.
  • As noted above, for holding companies or firms with pipeline operations, the authors code the regulation variable as one after 1938.

B. Control Variables for the Proxy Data Set

  • The independent variables for the proxy data set come from both the firms’ proxy statements and COMPUSTAT.
  • In general, the authors follow the existing literature on board composition in choosing their controls.
  • Finally, the authors include the firm’s debt-to-asset ratio to account for external financial pressures and sales as a proxy for firm size.
  • As before, the firm’s regulation variable is coded one if any of its lines of business is regulated in the observation year.
  • The lower section of Table 4 contains summary statistics of the sample.

C. Estimation Procedure

  • Because the dependant variable is a count of the number of directors of each type on the board, ordinary least squares will be biased and inconsistent.
  • Following Benjamin Hermalin and Michael Weisbach,42 the authors estimate a Poisson model.
  • 41 The proxy statements and COMPUSTAT SIC codes do not identify companies that hold leases for other production companies or holding companies independently from the other categories.

D. Results from the Moody’s Data

  • The cross-sectional results of the regulation effect for the Moody’s-Marquis sample are presented in the top section of Table 5.
  • Former regulators are also more common on the boards of regulated companies.
  • Only composite 3 (former regulators and politicians) is not statistically significant.
  • The last rows of Table 5 present results of the new-director model using firm-specific fixed effects.

E. Proxy Statement Sample

  • Table 7 presents results of the models using the proxy statement data for the period 1978–98.
  • In addition, composites 1 and 4 are statistically significant, which indicates between .259 and .752 additional political directors depending on the measure.
  • Nevertheless, the authors find that Washington lawyers are more common on boards of regulated companies.
  • Finally, the last rows present results for the model examining only newly appointed directors.
  • In general, the results indicate little difference between the boards of regulated companies and unregulated companies in the numbers of other director types.

V. Conclusions

  • The authors examine the role of political directors on the boards of regulated companies.
  • The first explanation is that these directors play an advisory role, providing information, expertise, and/or political access to resources relative to the firm’s external environment.
  • The authors examine the regulation of natural gas pipelines in 1938 and natural gas producers in 1954 and the 1986 deregulation of natural gas wellhead prices.
  • The authors do find evidence of broader changes in the composition of corporate boards in the 1930–90 sample period.
  • The authors examine the possibility that regulated firms are simply less effectively monitored and hence have more directors with political backgrounds simply because they are less effective monitors than other types of directors.

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The arboreal origins of human
bipedalism
Susannah K.S. Thorpe
1
, Juliet M. McClymont
2
&
Robin H. Crompton
2
Almost a century and a half ago, Charles Darwin in The Descent of Man (1871: 141)
highlighted the evolution of bipedalism as one of the key features of the human lineage, freeing the
hands for carrying and for using and making tools. But how did it arise? The famous footprints
from Laetoli in Tanzania show that hominin ancestors were walking upright by at least 3.65
million years ago. Recent work, however, suggests a much earlier origin for bipedalism, in a
Miocene primate ancestor that was still predominantly tree-dwelling. Here Susannah Thorpe,
Juliet McClymont and Robin Crompton set out the evidence for that hypothesis and reject the
notion that the common ancestor of great apes and humans was a knuckle-walking terrestrial
species, as are gorillas and chimpanzees today. The article is followed by a series of comments,
rounded off by a reply from the authors.
Theories regarding the origins of hominin bipedalism have spent some considerable time
on the ground’ as a result of the knuckle-walking hypothesis, which postulates that our
earliest bipedal ancestor evolved from an ape that knuckle-walked on the ground in a way
similar to modern chimpanzees or gorillas. By contrast, we argue that there is compelling
and unequivocal evidence that bipedalism has arboreal origins.
The concept of an arboreal origin for habitual human bipedalism was first proposed over a
century ago. The arboreal behaviour that was considered to be exaptive (i.e. to have prepared’
the body) for bipedalism has, however, changed fundamentally with the gradual discoveries
of new fossil evidence, and with the development of new approaches to reconstructing
the ecology and locomotion of extinct species. In particular, study of the ecology and
biomechanics of living apes has transformed our understanding of how bipedalism could
have evolved. Living apes offer broad models for how the dynamic between habitat and
morphology may combine to influence locomotor behaviour. Sir Arthur Keith (1903) was
the first to suggest that the arboreal locomotion of apes was important in understanding
the process by which upright posture evolved in human ancestors. His studies of primate
anatomy and behaviour led to the paradigm that an ape that moved by brachiating (arm-
swinging) underneath branches (suspension) later evolved into a habitual biped (e.g. Morton
1922; Keith 1923). Morphological and locomotor observations continued to be proffered
in support of this hypothesis for many decades (see Tuttle 1974 for a review). However,
1
Locomotor Ecology and Biomechanics L aboratory, School of Biosciences, University of Birmingham, Edgbaston,
Birmingham B15 2TT, UK (Author for correspondence; Email: s.k.thorpe@bham.ac.uk)
2
Department of Musculoskeletal Biology, Institute of Aging and Chronic Disease, University of Liverpool, Ashton
Street, Liverpool L69 3GE, UK
C
Antiquity Publications Ltd.
ANTIQUITY 88 (2014): 906–926 http://antiquity.ac.uk/ant/088/ant0880906.htm
906
https://doi.org/10.1017/S0003598X00050778 Published online by Cambridge University Press

Debate
Susannah K.S. Thorpe, Juliet M. McClymont & Robin H. Crompton
one of the most important lines of evidence to emerge relatively recently from new fossil
discoveries is that adaptations to suspension and arm-swinging must have evolved not once
only but convergently, across several millions of years, in multiple fossil ape species (e.g.
Almecija et al. 2009).
During the 1970s and ‘80s, Russell H. Tuttle (1974, 1981) proposed that the arboreal
ancestor of modern hominins would have been small-bodied—around the size of living
gibbons (9–13.5kg)—and would have engaged extensively in vertical climbing (that is,
climbing up and down vertical tree trunks with the torso in an upright position), an activity
that he considered to be functionally associated with bipedalism. The biomechanical link
was defined by Prost (1980) from apparent similarities in the range of joint angles exhibited
in vertical climbing by chimpanzees and in human bipedalism, and by Fleagle et al. (1981)
from joint movements and muscle activity in these behaviours in New World monkeys. But
recent work has undermined this hypothesis by showing that gorillas and orangutans have
more extended hip joint angles when moving bipedally than when they are using vertical
climbing (Crompton et al. 2003; Watson et al. 2009).
By the early 2000s the fossil record of the Eurasian and East African Miocene (23–5 million
years ago (Ma)) was burgeoning and revealing the body form of early crown hominoids
(‘crown hominoids being the direct ancestors of all living apes, including humans). These
included fossils of species such as Morotopithecus bishopi (from approximately 18–22 Ma),
Pierolapithecus catalaunicus (c. 12 Ma), Hispanopithecus (Dryopithecus) laietanus (c.10Ma)
and Orrorin tugenensis (6 Ma). These fossils suggested that, contrary to expectations and
fossil evidence from Proconsul hesoloni and associated species, the early crown hominoids
stood and moved with an orthograde (upright) posture. Thus features such as their broad,
shallow trunks; scapulae positioned on the back rather than side of their bodies, and lumbar
vertebral bodies that increased in size towards the lower end of the spine all indicated that
these species were frequently upright (MacLatchy 2004; Moy
`
a-Sol
`
a et al. 2004; Nakatsukasa
et al. 2007; reviewed in Crompton et al. 2008). In addition, since they are estimated
to have weighed between 30 and 50kg, they were also at least as large as adult female
great apes (MacLatchy 2004; Moy
`
a-Sol
`
a et al. 2004; Nakatsukasa et al. 2007), a finding
which casts doubt on the validity of Tuttle’s (1981) model of a small-bodied gibbon-like
ancestor.
The fact that orthograde (upright) body postures had been evolving and diversifying
in our hominoid ancestry for in excess of 15 million years pushed study of the origins of
bipedalism back from the Pliocene into the early Miocene. It also challenged the commonly
held concept that the acquisition of habitual bipedalism is an appropriate marker of the
separation of the hominins from the panins (bonobos and chimpanzees), a separation
that is estimated to have occurred only 5–8 million years ago. It pushed the context
of bipedal origins back into the forest canopy from the ground (Senut 2011) where it
had spent some considerable time as a result of the knuckle-walking hypothesis. This
latter paradigm, that has dominated our vision of the evolution of bipedalism since the
1960s, held that because chimpanzees and gorillas move on the ground by quadrupedal
horizontal-trunked knuckle-walking, the pre-bipedal ancestor of hominins must also
have passed through a terrestrial knuckle-walking phase (e.g. Gebo 1996; Richmond &
Strait 2000).
C
Antiquity Publications Ltd.
907
https://doi.org/10.1017/S0003598X00050778 Published online by Cambridge University Press

The arboreal origins of human bipedalism
In parallel to the burgeoning fossil record, significant progress was being made in quanti-
fying the locomotor ecology of modern wild apes (i.e. the relative proportions of bipedalism
and other forms of movement exhibited by a given species in a given setting). Hunt and
colleagues (1996) advocated much-needed uniformity in the language used to describe loco-
motion across primate clades. They wished primarily to avoid the ubiquitous term climbing
to describe a wide range of locomotor behaviours that conflated pronograde (horizontal)
and orthograde (upright) body postures, and travelling in vertical and horizontal directions.
In the event, this has been adhered to more closely by the literature on living primates
than that on fossil forms. The significance of the approach was that it allowed comparative
quantification of the ecological context of locomotion (how much time a particular species
spent in knuckle-walking, brachiating, vertical climbing, etc.; in what kinds of setting—
e.g. forest canopy, forest floor, open grassland—and an indication of the stresses different
behaviours placed on the body). Thus it made it possible to quantify the adaptive advantages
of arboreal behaviours, a factor that was lacking from many earlier studies of locomotion that
were restricted to studies of captive animals or qualitative observations of wild-living taxa.
The approach revealed that all great apes occasionally choose to engage in arboreal
bipedalism—walking along and between branches on two legs (e.g. Hunt 1992; Remis
1995; Thorpe & Crompton 2005, 2006). It was from this that Hunt (1996) and Stanford
(2006) developed the arboreal foraging hypothesis. They showed that in chimpanzees, hand-
assisted bipedal posture (as opposed to bipedal locomotion) was associated with arboreal
feeding on relatively stable branches >100mm in diameter, and suggested such behaviour
might have been exaptive for terrestrial bipedalism. Postures are, however, less energetically
demanding to maintain than locomotion, and standing on large-diameter branches does
not pose the safety risks that are associated with balancing on thin, flexible branches. In
contrast we studied Sumatran orangutans (Pongo abelii), as they exhibit strong similarity to
humans in the extended-leg bipedal kinematics (joint angles) and kinetics (forces exerted
on the ground during locomotion) (Crompton et al. 2003; Crompton & Thorpe 2007).
Furthermore, they are the only exclusively arboreal great ape. We found that Sumatran
orangutans use extended-leg bipedal locomotion on highly flexible branches, <40mm in
diameter (Thorpe et al. 2007a) (Figure 1). This result countered traditional hypotheses
that had suggested that movement along flexible branches should be either via orthograde
suspension in which the animal gains stability by hanging with its centre of mass directly
under the branch; or by compliant quadrupedalism, in which stability is maximised in
part by bending the knees and elbows substantially to reduce the movements of the branch
caused by the animal’s weight.
We also found that in 75 per cent of our observations of orangutan bipedal locomotion
along branches, they used their hands for stabilisation, as do chimpanzees (Hunt 1996;
Stanford 2006). Hand assistance ensures maximum safety while the bipedalism enables a
free hand to reach out for feeding, weight transfer, or balance in the peripheral branches
of trees, where the majority of preferred foods are situated and where primates must cross
between tree crowns. Being able to access these peripheral branches effectively is highly
advantageous because it allows large-bodied apes to cross more gaps between trees. Crossing
rather than circumventing gaps in the canopy can dramatically reduce the energy costs of
travel, especially where a change of height would otherwise be required (Thorpe et al. 2007b).
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Antiquity Publications Ltd.
908
https://doi.org/10.1017/S0003598X00050778 Published online by Cambridge University Press

Debate
Susannah K.S. Thorpe, Juliet M. McClymont & Robin H. Crompton
Figure 1. Standardised cell residuals (SCRs) to demonstrate the primary results in the Log linear model of Thorpe et al.
2007a. The left-hand diagram shows the relationship between locomotion and the number of supports used and the right
shows the relationship between locomotion and the diameters of the supports used. SCRs indicate by their sign whether an
interaction is more (positive values) or less (negative values) common than predicted by the model and, by their size, to what
degree. SCRs greater than
+
2.0 indicate a lack of fit. The graphs show that quadrupedalism is strongly associated with
locomotion on single, large, stable supports >200mm in diameter; orthograde suspension is mostly associated with locomotion
on supports between 40–100mm in diameter. In contrast bipedalism is strongly associated with locomotion on multiple
supports and those that are <40mm in diameter.
We concluded that hand-assisted arboreal bipedalism as part of a smooth continuum of
orthograde behaviours ranging from suspending underneath branches to standing on top of
them confers a major selective advantage on orangutans and argued that arboreal bipedalism
would have been equally advantageous for ancestral crown hominoids (Figure 2).
We are convinced that the accumulating evidence for the arboreal origins of human
bipedalism is strong. Inevitably, some do not share our conviction. As part of a more general
critique on the use of ‘living referential models to understand fossil taxa, Sayers and Lovejoy
(2008) argued that our use of orangutan data was based on false premises. First, they
suggested that we studied bipedal posture and not bipedal locomotion. This indicates that
they didnt read our paper well; even the title alluded to locomotion rather than posture. They
also suggested that orangutans are an unsuitable model because they have feet that are highly
specialised for gripping, such as very long toes that cannot therefore have been exaptations
for bipedality; and that they are rarely terrestrial, and when they are terrestrial they use
knuckle- or fist-walking (citing Tuttle & Beck 1972). We agree that the feet of orangutans
are highly specialised—but even then our recent work (Bates et al. 2013) shows that foot
pressures in the bipedalism of orangutans (and bonobos) overlap substantially with those
of humans, particularly under the middle of the foot. Nevertheless, orangutan footprint
morphology does not need to be exaptive for bipedality for the purposes of our model.
We studied Sumatran orangutans because, unlike Bornean orangutans (Pongo pygmaeus sp.)
and other great apes, they very rarely descend to the ground and should therefore be a
good model for arboreal locomotor ecology. If Sumatran orangutans did (hypothetically)
descend to the forest floor they probably would move quadrupedally because palmigrade
quadrupedalism is strongly associated with travel on broad, stable tree boughs (Figure 1)
(Thorpe & Crompton 2006; Thorpe et al. 2007a). Furthermore, anecdotal evidence suggests
wild Bornean orangutans generally use quadrupedalism when terrestrial. To our knowledge,
C
Antiquity Publications Ltd.
909
https://doi.org/10.1017/S0003598X00050778 Published online by Cambridge University Press

The arboreal origins of human bipedalism
Figure 2. A reconstruction of the arboreal bipedalism hypothesis depicting the evolution of modern great apes including
humans from an orthograde ancestral ape, capable of hand-assisted, arboreal bipedalism with extended lower limbs (from
O’Higgins & Elton 2007). Orangutan ancestors became a rboreal specialists, whereas the ancestors of gorillas and chimpanzees,
in response to changing and variable habitats, climbed vertically in and out of trees, and independently acquired knuckle-
walking. Hominins retained existing adaptations for extended-limb bipedalism and eventually became committed terrestrial
bipeds. Reprinted with permission from AAAS.
however, orangutan hand postures in terrestrial locomotion in the wild have never been
quantified because hands are difficult to see in the clutter of the forest floor from the distance
required for following orangutans in the wild. The hand postures are likely, however, to be
something akin to fist-walking simply because of the length of the digits.
The Tuttle and Beck (1972) paper that Sayers and Lovejoy (2008) reference as evidence
for orangutans employing knuckle-walking when terrestrial is based primarily on the mostly
postural descriptions of the behaviour of a single, captive, very obese male orangutan called
Felix. Tuttle and Beck (1972: 33–34) conclude that although Felix often places his hands
in knuckle-walking postures, he rarely supports a major portion of his body weight on
C
Antiquity Publications Ltd.
910
https://doi.org/10.1017/S0003598X00050778 Published online by Cambridge University Press

Citations
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Journal ArticleDOI
TL;DR: For instance, it has been accepted that hominids emerged during the Pliocene in a savanna environment in which a terrestrial quadruped gradually developed bipedal adaptations as mentioned in this paper.
Abstract: It has long been accepted that hominids emerged during the Pliocene in a savannah environment in which a terrestrial quadruped gradually developed bipedal adaptations. However, data from the Late M...

31 citations


Cites background from "The arboreal origins of human biped..."

  • ...…al. 2001; Haile-Selassie 2001; White et al. 2009; Brunet et al. 2002; Schmid 1983; Stern 2000, Alemseged et al. 2006; Green and Alemseged 2012; Nakatsukasa 2004; Galik et al. 2004; Pickford 2006; Pickford et al. 2002; Crompton et al. 2008; Senut 2012a, 2012b, 2014, 2016; Thorpe et al. 2007, 2014)....

    [...]

  • ...The structure of the woodland environment is important in relation to the weight of the animal and the flexibility of the substrates (Thorpe et al. 2007, 2014)....

    [...]

  • ...…knuckle- walkerlike chimpanzee or a vertical climber (Keith 1923; Gregory 1930; Morton 1935; Washburn 1967; Tuttle 1969, 1977, 1981; Stern 1975, Prost 1980; Fleagle et al. 1981; Coppens & Senut 1991 for comprehensive articles; Richmond et al. 2001; Thorpe et al. 2014 for an historical perspective)....

    [...]

Journal ArticleDOI
TL;DR: The data suggest that the evolutionary development of modern biomechanical locomotion pre-dates the earliest human tracks and also the transition from the genus Australopithecus to Homo, which involved the development of anatomy and physiology better-suited to endurance running and walking.

18 citations


Cites background from "The arboreal origins of human biped..."

  • ...335  This speaks to recent debates about the origins of hominin bipedalism and the importance of complex 336  topography (Winder et al., 2013, 2014) which challenges the more conventional arboreal hypotheses 337  (Thorpe et al., 2007, 2014a, b; Crompton et al., 2010)....

    [...]

Journal ArticleDOI
TL;DR: Bearded capuchin monkeys' behavior supports the suggestion from anatomical analysis that S. libidinosus is morphologically better adapted than its congeners to adopt orthograde postures, and the influence of sex on positional behavior and substrate use is tested.
Abstract: Natural selection for positional behavior (posture and locomotion) has at least partially driven the evolution of anatomical form and function in the order Primates. Examination of bipedal behaviors associated with daily activity patterns, foraging, and terrestrial habitat use in nonhuman primates, particularly those that adopt bipedal postures and use bipedal locomotion, allows us to refine hypotheses concerning the evolution of bipedalism in humans. This study describes the positional behavior of wild bearded capuchins (Sapajus libidinosus), a species that is known for its use of terrestrial substrates and its habitual use of stones as tools. Here, we test the association of terrestrial substrate use with bipedal posture and locomotion, and the influence of sex (which co-varies with body mass in adults of this species) on positional behavior and substrate use. Behavior and location of 16 wild adult bearded capuchins from two groups were sampled systematically at 15 s intervals for 2 min periods for 1 year (10,244 samples). Despite their different body masses, adult males (average 3.5 kg) and females (average 2.1 kg) in this study did not differ substantially in their positional behaviors, postures, or use of substrates for particular activities. The monkeys used terrestrial substrates in 27% of samples. Bipedal postures and behaviors, while not a prominent feature of their behavior, occurred in different forms on the two substrates. The monkeys crouched bipedally in trees, but did not use other bipedal postures in trees. While on terrestrial substrates, they also crouched bipedally but occasionally stood upright and moved bipedally with orthograde posture. Bearded capuchin monkeys' behavior supports the suggestion from anatomical analysis that S. libidinosus is morphologically better adapted than its congeners to adopt orthograde postures.

13 citations

Journal ArticleDOI

11 citations

Journal ArticleDOI
TL;DR: The first 3-D kinematic data of the wrist, hand and metacarpophalangeal joints during knuckle-walking in chimpanzees and in macaques using digitigrade and palmigrade hand postures are presented.
Abstract: The origin and evolution of knuckle-walking has long been a key focus in understanding African ape, including human, origins Yet, despite numerous studies documenting morphological characteristics potentially associated with knuckle-walking, little quantitative three-dimensional (3-D) data exist of forelimb motion during knuckle-walking Nor does any comparative 3-D data exist for hand postures used during quadrupedalism in monkeys This lack of data has limited the testability of proposed adaptations for knuckle-walking in African apes This study presents the first 3-D kinematic data of the wrist, hand, and metacarpophalangeal joints during knuckle-walking in chimpanzees and in macaques using digitigrade and palmigrade hand postures These results clarify the unique characteristics of, and commonalities between, knuckle-walking and digitigrady/palmigrady in multiple planes of motion Notably, chimpanzees utilized more wrist ulnar deviation than any macaque hand posture Maximum extension of the chimpanzee wrist was slight (5–20°) and generally overlapped with macaque digitigrady Metacarpophalangeal joint motion displayed distinct differences between digits in both species, likely related to the timing of force application These data also reveal that maximum metacarpophalangeal extension angles during knuckle-walking (26–59°) were generally higher than previously considered In macaques, maximum metacarpophalangeal extension during digitigrady and palmigrady overlapped for most digits, highlighting additional complexity in the interpretation of skeletal features that may be related to limiting metacarpophalangeal motion Most importantly however, these new 3-D data serve as a fundamental dataset with which evaluation of proposed musculoskeletal adaptations for knuckle-walking can be tested

10 citations


Cites methods from "The arboreal origins of human biped..."

  • ...This suggestion, based on carpal morphology, has been widely adopted in the human evolution literature (e.g. Le Maître et al., 2017; Macho et al., 2010; Saunders et al., 2016; Schilling et al., 2014; Simpson et al., 2018; Thorpe et al., 2014)....

    [...]

  • ...This hypothetical postural difference has since been relatively well adopted within the literature, and has subsequently been upheld as kinematic evidence of fundamentally different forms of knucklewalking (Le Maître et al., 2017; Macho et al., 2010; Saunders et al., 2016; Schilling et al., 2014; Simpson et al., 2018; Thorpe et al., 2014)....

    [...]

References
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24 Feb 1871
TL;DR: In this paper, secondary sexual characters of fishes, amphibians and reptiles are presented. But the authors focus on the secondary sexual characteristics of fishes and amphibians rather than the primary sexual characters.
Abstract: Part II. Sexual Selection (continued): 12. Secondary sexual characters of fishes, amphibians and reptiles 13. Secondary sexual characters of birds 14. Birds (continued) 15. Birds (continued) 16. Birds (concluded) 17. Secondary sexual characters of mammals 18. Secondary sexual characters of mammals (continued) 19. Secondary sexual characters of man 20. Secondary sexual characters of man (continued) 21. General summary and conclusion Index.

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06 Apr 1871-Nature
TL;DR: The Descent of Man, and Selection in relation to Sex as mentioned in this paper, by Charles Darwin, &c. In two volumes. Pp. 428, 475, as mentioned in this paper.
Abstract: I. IF Mr. Darwin had closed his rich series of contributions to Science by the publication of the “Origin of Species,“he would have made an epoch in Natural History like that which Socrates made in philosophy, or Harvey in medicine. The theory identified with his name has stimulated ethnological and anatomical inquiries in every direction; it has been largely adopted and followed out by naturalists in this country and America, but most of all in the great work-room of modern science, whence a complete literature on “Darwinismus“has sprung up, and there disciples have appeared who stand in the same relation to their master as Muntzer and the Anabaptists did to Luther. Like most great advances in knowledge, the theory of Evolution found everything ripe for it. This is shown by the well-known fact that Mr. Wallace arrived at the same conclusion as to the origin of species while working in the Eastern Archipelago, and scarcely less so by the manner in which the theory has been worked out by men so distinguished as Mr. Herbert Spencer and Prof. Haeckel. But it was known when the “Origin of Species “was published, that instead of being the mere brilliant hypothesis of a man of genius, of which the proofs were to be furnished and the fruits gathered in by his successors, it was really only a summary of opinions based upon the most extensive and long-continued researches. Its author did not simply open a new province for future travellers to explore, he had already surveyed it himself, and the present volumes show him still at the head of his followers. They are written in a more popular style than those on "Animals and Plants under Domestication,“as they deal with subjects of more general interest; but all the great qualities of industry and accuracy in research, of fertility in framing hypotheses, and of impartiality in judgment, are as apparent in this as in Mr. Darwin's previous works. To one who bears in mind the too frequent tone of the controversies these works have excited, the turgid rhetoric and ignorant presumption of those "who are not of his school -or any school,“and the still more lamentable bad taste which mars the writings of Vogt and even occasionally of Haeckel, it is very admirable to see the calmness and moderation (for which philosophical would be too low an epithet) with which the author handles his subject. If prejudice can be conciliated, it will surely be by a book like this. The Descent of Man, and Selection in relation to Sex. By Charles Darwin, &c. In two volumes. Pp. 428, 475. (Murray, 1871.)

4,740 citations

Journal ArticleDOI
01 Oct 1996-Primates
TL;DR: 32 primate positional modes are defined, divided more finely into 52 postural sub-modes and 74 locomotor sub-Modes, and a nomenclature is recommended that is not dedicated to or derived from any one taxonomic subset of the primates.
Abstract: As quantitative studies on primate positional behavior accumulate the lack of a standard positional mode terminology is becoming an increasingly serious deficiency. Inconsistent use of traditional terms and inappropriate conflation of mode categories hamper interspecific and interobserver comparisons. Some workers use common terms without definition, allowing at least the possibility of misunderstanding. Other researchers coin neologisms tailored to their study species and not clearly enough defined to allow application to other species. Such neologisms may overlap, may completely encompass, or may conflate previously defined labels. The result is, at best, the proliferation of synonyms and, at worst, the creation of confusion where clarity had existed. Historical precedents have sometimes resulted in “catch-all” terms that conflate any number of kinematically different behaviors (e.g. “brachiation,” “climbing,” and “quadrumanous climbing”). We recognize three areas where distinction of positional modes has some current importance: (1) Modes that require humeral abduction should be distinguished from adducted behaviors; (2) locomotor modes that involve ascent or descent should be distinguished from horizontal locomotor modes; and (3) suspensory modes should be distinguished from supported modes. We recommend a nomenclature that is not dedicated to or derived from any one taxonomic subset of the primates. Here we define 32 primate positional modes, divided more finely into 52 postural sub-modes and 74 locomotor sub-modes.

348 citations

Journal ArticleDOI
Kevin D. Hunt1
TL;DR: Although no significant differences were found between sympatric baboons and chimpanzees in the proportion of time spent in the terminal branches, or in the mean diameter of weight-bearing strata, chimpanzees exhibited evidence of a terminal branch adaptation in that they, unlike baboons, used postures among smaller supporting strata different from those used among larger supports.
Abstract: The positional behavior of habituated adult chimpanzees and baboons was observed for 784 hr in a year-long study. Comparisons between species were made to establish the distinctiveness of chimpanzee positional behavior and habitat use. Brachiation (sensu stricto, i.e., hand-over-hand suspensory locomotion) was observed in low frequencies among chimpanzees, and its significance for chimpanzee anatomy is judged slight. Although no significant differences were found between sympatric baboons and chimpan- zees in the proportion of time spent in the terminal branches, or in the mean diameter of weight-bearing strata, chimpanzees exhibited evidence of a termi- nal branch adaptation in that they, unlike baboons, used postures among smaller supporting strata different from those used among larger supports. Among chimpanzees, unimanual arm-hanging was most common among the smallest strata and was associated with smaller mean and median support diameter than other postures. Unimanual arm-hanging was the only common behavior among chimpanzees that usually involved complete abduction of the humerus. A number of behaviors often subsumed under the label "quadruman- ous climbing" were distinguished in this study. Compared to baboons and other cercopithecoids, chimpanzees did not show increased frequencies of large-stratum vertical climbing, and their vertical climbing did not involve significant humeral abduction. Arm-hanging (i.e., unimanual suspension) and vertical climbing distinguish chimpanzee positional behavior from that of monkeys.

269 citations


"The arboreal origins of human biped..." refers background in this paper

  • ...Hunt and colleagues (1996) advocated much-needed uniformity in the language used to describe locomotion across primate clades....

    [...]

  • ...Hunt 1992; Remis 1995; Thorpe & Crompton 2005, 2006). It was from this that Hunt (1996) and Stanford (2006) developed the arboreal foraging hypothesis....

    [...]

  • ...The approach revealed that all great apes occasionally choose to engage in arboreal bipedalism—walking along and between branches on two legs (e.g. Hunt 1992; Remis 1995; Thorpe & Crompton 2005, 2006)....

    [...]

Journal ArticleDOI
23 Mar 2000-Nature
TL;DR: Evidence is presented that fossils attributed to Australopithecus anamensis and A. afarensis retain specialized wrist morphology associated with knuckle-walking, which removes key morphological evidence for a Pan–Gorilla clade and suggests that bipedal hominids evolved from a knuckles-walking ancestor that was already partly terrestrial.
Abstract: Bipedalism has traditionally been regarded as the fundamental adaptation that sets hominids apart from other primates. Fossil evidence demonstrates that by 4.1 million years ago1, and perhaps earlier2, hominids exhibited adaptations to bipedal walking. At present, however, the fossil record offers little information about the origin of bipedalism, and despite nearly a century of research on existing fossils and comparative anatomy, there is still no consensus concerning the mode of locomotion that preceded bipedalism3,4,5,6,7,8,9,10. Here we present evidence that fossils attributed to Australopithecus anamensis (KNM-ER 20419)11 and A. afarensis (AL 288-1)12 retain specialized wrist morphology associated with knuckle-walking. This distal radial morphology differs from that of later hominids and non-knuckle-walking anthropoid primates, suggesting that knuckle-walking is a derived feature of the African ape and human clade. This removes key morphological evidence for a Pan–Gorilla clade, and suggests that bipedal hominids evolved from a knuckle-walking ancestor that was already partly terrestrial.

259 citations

Frequently Asked Questions (11)
Q1. What are the contributions mentioned in the paper "The arboreal origins of human bipedalism" ?

The article is followed by a series of comments, rounded off by a reply from the authors. 

Published online by Cambridge University PressD ebat eone of the most important lines of evidence to emerge relatively recently from new fossil discoveries is that adaptations to suspension and arm-swinging must have evolved not once only but convergently, across several millions of years, in multiple fossil ape species (e.g. Almecija et al. 2009). 

Theories regarding the origins of hominin bipedalism have spent some considerable time ‘on the ground’ as a result of the knuckle-walking hypothesis, which postulates that their earliest bipedal ancestor evolved from an ape that knuckle-walked on the ground in a way similar to modern chimpanzees or gorillas. 

Locomotion and posture from the common hominoid ancestor to fully modern hominins, with special reference to the last common panin/hominin ancestor. 

The authors also found that in 75 per cent of their observations of orangutan bipedal locomotion along branches, they used their hands for stabilisation, as do chimpanzees (Hunt 1996; Stanford 2006). 

The significance of the approach was that it allowed comparative quantification of the ecological context of locomotion (how much time a particular species spent in knuckle-walking, brachiating, vertical climbing, etc.; in what kinds of setting— e.g. forest canopy, forest floor, open grassland—and an indication of the stresses different behaviours placed on the body). 

The famous footprints from Laetoli in Tanzania show that hominin ancestors were walking upright by at least 3.65 million years ago. 

Despite the longevity of the paradigm that derived human bipedalism from chimpanzeelike knuckle-walking, the authors conclude that the arboreal origin of bipedalism is now overwhelmingly supported by the fossil, biomechanical and ecological evidence. 

By the early 2000s the fossil record of the Eurasian and East African Miocene (23–5 million years ago (Ma)) was burgeoning and revealing the body form of early ‘crown’ hominoids (‘crown’ hominoids being the direct ancestors of all living apes, including humans). 

Explaining how their ancestors survived a locomotor transition in a relatively dangerous semi-open habitat remains a critical challenge to these hypotheses” (Winder et al. 2013: 334). 

Thus features such as their broad, shallow trunks; scapulae positioned on the back rather than side of their bodies, and lumbar vertebral bodies that increased in size towards the lower end of the spine all indicated that these species were frequently upright (MacLatchy 2004; Moyà-Solà et al.