The bipédie is the fact of being driven on two rear limbs, therefore “upright”. An animal or a species is not biped that if they pass as much or more time to go on two rear limbs than by any other means. An animal which is held on its two legs five seconds even an hour per day will not be regarded as a biped .

The Homme is the most widespread biped on Ground. It has common origins with the Singe S (known as Hominidé S like the Orang-outan, the Gorille…), which is also able to be driven on their two rear limbs.

The debate on the bipédie enters within the framework of that broader on the missing link , the passage of Hominoïde to Hominidé - and by discrepancy on what differentiates us from the other animals. In this context one opposes generally biped to Quadrupède S.

The generally allowed period nowadays for the separation of the monkey and the man, is that between 7 and 5 million years. Few fossils of this period were put at the day. The transition was much faster (less a-half million years) than one thought it for a long time.

Biped animals

Origin (S) of the human bipédie

Assumption of savanna

To date this theory still is most usually taught and accepted. One often connects it to that of the Main Tool .

The ancestor of the man would have learned how to walk because the forest moved back with the profit of savanna. Put aside the fact that there more would have been trees on which to climb, the station upright would then have had multiple advantages:

  • monitoring of the territory above tall grasses.
  • better temperature control of the body. The position upright has less surface to the sun, and more surface with the wind.
  • the absence of pilosity would have also come to help with the temperature control (less cover for the body)
  • transport of tools and/or weapons, imposed by the nomadism of the life of savanna ( Hypothèse of the Hand Tool ).

Certain arguments were advanced against this theory: if the distinctive features of human come from the adaptation to savanna, one should find at least some of these adaptations in other mammals of savanna. However, one finds none of it among these, even at the other descendants of common ancestors, like the vervets, baboons or others. No other animal of savanna adopted the apilosity “to refresh itself”: the hairs provide on the contrary a protection against the sun. Who more is the hairs are essential for the primates whatever their environment: the young people in low-age cling to them while their mother is occupied with her occupations.

The bipédie learned in the trees?

Many observations corroborate the facts: the Chimpanzé S ( Pan troglodytes ), which pass less than 3% of their time upright according to a long study of Kevin Hunt (published in 1994), even do it mainly on the large branches in the trees. He sought examples of bipédie optional in the monkeys. Its article initiated a school of thought according to which the bipédie can be learned in the trees. Other studies since showed that the Orang-outan S show the same tendencies, as well as other monkeys. The scientists indicate that the life in the trees is specific to develop balance necessary to the bipédie.

Initial theory of Bipédie

The bipédie learned in water?

Published for the first time in 1960 by Sir Alister Hardy FRS, the Théorie of the Watery Primate was recently given to the day order by the accumulation of several studies and obviousnesses (photographs, films) of varied sources, showing monkeys going in water preferably with the stroke.

The majority of the characteristics of human physiology would be current in the watery mammals although very rare at those terrestrial. Our ancestors would thus have lived in habitat flooded for a long time, semi-watery - what would solve the major part of the questions of human physiology remained until there unanswered.

The beginning of these evolutions would be contemporary divergence between the large monkeys and the human ones.

However this assumption remains discussed and is far from achieving the unanimity among paleoanthropologists.

Who is the first biped?

The skeleton of one hominidé old from 3,8 to 4 My has just been discovered in Ethiopia. That made of this known oldest last if one excludes Orrorin tugenensis and/or " Toumaï ". This discovery was announced by the team of the Paléontologue American Bruce Latimer.

The place of the discovery is to 60 km of that where in 1974 had been found celebrates it Lucy, in the Ethiopian North-East. This place was flooded there are 7 My, becoming the Sea of Afar. One found with Lucy of the fossils of crocodiles, of crab grip and turtles, the whole at the edge of an easily flooded plain close of what at the time was the coast of Africa. The inhabitants would have found themselves suddenly in varied semi-watery environments: flooded forests, marsh, mangroves, lagoons,…

Later, their descendants, having acquired characteristics adapted to the aquatic life, would be turned over on the continent and would have gone up the Nile towards the south. One found more in the south of the fossils of others Australopithèque S, more recent and almost always close to aquatic environments.

On another side, Richmond and Détroit affirm to prove that Lucy was still quadruped:

Here we bring the proof that fossils allotted to Australopithecus anamensis (KNM-ER 20419) and Australopithecus afarensis (AL-288-1 or Lucy) preserves a specialized morphology of the wrist associated with a form with quadrupédie. The distal morphology of the Radius differs from that of the last hominiens and the Primate S anthropoïdes not " quadrupèdes" , suggesting that the quadrupédie with support on the joints is a characteristic derived from the large African monkeys and human Clade. This removes the morphological arguments for the existence of a clade Chimpanzé S Gorille, and suggests that biped hominiens developed starting from an ancestor going " to four pattes" and which was already partly terrestrial|B.G. Richmond and D.S. Détroit|A proof that the man comes from an ancestor " quadrupède"
.

In the same newspaper having published this article, Collard & Aiello (2000) these results discuss. The dilemma is the following:

  • A. afarensis could have had vestiges of walk on the joints (of the forelimbs) while having already become biped. But of recent research showed that one could not grant credit as much than one thought it of the philogenetic inférences drawn from the fossils. Others recall that the bones are relatively plastic during a life. One is not explained either that Australopithecus africanus , a possible descendant of Australopithecus afarensis , lost this feature if this one were philogenetic. It thus seems well that Lucy went on the joints.

However it shows also the deformation of the radius implied by the bipédie, as well as other features in the same direction.

Curiosities

In exceptional circumstances, certain animals quadrupeds can also become biped, here a dog.

A French biped robot, Rabbit, were conceived especially for the study of walk and the race.

The Suricate, some American Dogs of meadow, can be held upright in a prolonged way… The lizard Jesus-Christ or basil (Basiliscus will plumifrons), is even able to run on water! (of short distances). Video:]

Sources

  • '' Aquatic Ape Theory '', Elaine Morgan (English site)

  • '' Wading for Food: Does The Driving Force the Evolution off Bipedalism off? '', Algis Kuliukas MSc (Human Evolution & Behavior, UCL, 2001). Article subjected to Nutrition and Health, August 2002. Abstract. (English site)

  • '' New Insights into Chimpanzees, Tools, and Termites from the Congo Basin '', (“New horizons on the chimpanzees, Tools and Termites in the Basin of Congo”), by Crickette Sanz, Dave Morgan and Steve Gulick. Amndt Nat. 2004. Vol. 164, pp. 567-581. © 2004, University off Chicago. (using English site on the primates of the tools)

  • '' Stride lengths, speed and energy costs in walking off Australopithecus afarensis: using evolutionary robotics to predict locomotion off early human ancestors '', William I. Sellers, Gemmated Mr. Cain, Weijie Wang, Robin H. Crompton. Royal The Society (English site on the bipédie of Lucy)

  • a proof that the man comes from an ancestor " quadrupède" , according to Brian G. Richmond and David S. Détroit, Nature, 2000,404,382-385, article on the quadripédie of Lucy.

  • Mutant: One Genetic Variety and the Human Body ('Mutant: on the genetic variety and the human body ), by Armand Marie Leroi. (delivers in English on the changes, and the speed with which they can occur (and a race to evolve/move))

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