Routes to Language

Habitual Bipedalism

Precursors: Beyond scope of model

Possible Emergence: Ardipithecus ramidus About 4.5 million years ago

Products: Increased Dexterity Phonology

References and other reading

Biewener, A.A. (1990). Biomechanics of mammalian terrestrial locomotion. In Science, 250, 1097–1103.

Carrier, D. (2011). The Advantage of Standing Up to Fight and the Evolution of Habitual Bipedalism in Hominins. In PLoS ONE 6:5, e19630.

Lovejoy, C. O. (1981). The Origin of Man. In Science 211:4480.

Pontzer, H. (2017). Economy and endurance in human evolution. In Current Biology 27, R613–R621.

Discussion

Habitual Bipedalism refers to locomotion on two legs as primary means of movement and the regular use of a bipedal gait. Habitual bipedalism is a defining characteristic of modern humans and we stand alone amid over 200 extant primate species as obligate bipeds, such a uniquely human feature that skeletal adaptations to obligate bipedalism are used in tracing the development of our extinct hominid ancestors. Whilst skeletal adaptions are documented in early hominids there are varying accounts explaining the success of the bipedal gait in humans. This is opposed to Facultative bipedalism observed in animals today, which is performed on a temporary basis, usually in response to exceptional circumstances

Pontzer (2017) postulates that habitual bipedalism facilitates economy and endurance in early Hominins; particularly benefits to walking economically that allowed greater range of hunting without increased calorie costs. This allowed energy to be redirected to reproductive efforts; increased brain size and longer life spans, all metabolically expensive traits unique to humans. Pontzer’s (2017) approach builds on Biewener’s (1990) research showing how well-equipped humans are for long distance running compared to our Chimpanzees relatives. Benefits to hunting and scavenging from endurance running lead to the hypothesis those endurance capabilities were the drive for the dramatic anatomical changes brought about by Habitual Bipedalism.

Carrier (2011) proposes the evidence of numerous quadruped species using their forelimbs to fight is evidence that a bipedal posture offers a range of motion that is advantageous to fighting. The bipedal gait orientates forelimbs from pronograde (horizontal) to orthograde (upright) and repositioning the bodily axis allows quadrupeds to grapple, strike and defend with greater capacity, as the range of motion now produces the most force. Striking downward increases power in retractor muscles, which produce positive movement associated with acceleration as opposed to protractor muscles primarily responsible for ‘braking’. These observations lead to Carrier’s (2011) prediction that mammals strike with greater capacity from a bipedal posture, particularly striking upwards and that humans developed Habitual Bipedalism due to its efficiency in performing aggressive acts.

Lovejoy (1981) traces bipedalism to its social origins, claiming how males supplied food to females to gain mating access and this component of social behaviour requires use of the hands.

Considerable debate persists regarding the timing and ecological context surrounding bipedalism, with discussion becoming ‘fossil driven’ and focused on mapping taxa. Reconciling physical adaptions with environmental and social changes will further explain the how and why of human bipedalism.

Nicholas Papadopoullos, 2019