Bipedalism

Bipedalism is the fact of moving preferentially on two hind legs. It is one of the physical characteristics of Homo sapiens but he shares with other species. An animal or a species that is bipedal or if he spends much more time to walk on two hind legs than by any other means.

The bipedal animals

An ostrich, one of the fastest two-legged animals.

Bipedalism characterized also birds and some dinosaurs. It is also envisaged for some marsupials such as kangaroos and kangaroo rats , although these two legged animals use their tails as well as support points.

A form of bipedalism quite strange was also observed in two species of octopus , Octopus marginatus and Octopus aculeatus. These animals appear to walk on the bottom of the water on two of their tentacles, the other being bent to deceive predators by simulating the appearance of algae or coconut .

In certain circumstances, quadrupeds may also adopt a bipedal station . The meerkat and some prairie dogs American can stand for long periods. The Jesus Christ lizard or basil ( Basiliscus plumifrons ) is likely to run on water over short distances .

The human bipedalism and its origin

Homo sapiens is the most common biped on Earth. It has common origins with the great apes today as the orang-utan or gorilla , which are also capable of moving on their two hind legs.

The debate on the origin of bipedalism is part of the wider on the " missing link "- passage from hominoid to hominid - and contradiction about what differentiates us from other animals. In this context, it generally opposes bipeds to quadrupeds.

The generally accepted date for the separation between the ancestors of monkeys and humans is between 9 and 7 million years. Few fossils of this period have been unearthed. The transition was much faster (less than half a million years) than has been thought for a long time.

Savannah hypothesis

To date, this theory is the most commonly taught and accepted. It is often linked to the Hand Tool.

The ancestor of man had learned to walk because the forest gives way to savannah. Apart from the fact that there have been any more trees on which to climb, standing would have had multiple benefits:

• surveillance of the territory above the tall grass;
• better regulation of body temperature, standing with less sun and more surface area to the wind;
• the lack of hair would also appeared to help regulate the temperature (under cover for the body);
• carrying tools and / or weapons, imposed by the nomadic life of Savannah (Hypothesis Hand Tool). The jaw in man is not enough to carry food and shelter as in some cats.

Some arguments have been advanced against this theory: if the distinctive features of humans are adapting to the savannah, you should find at least some of these adaptations in other mammals of the savanna. However, we do not find among those, even among the other descendants of common ancestors, like vervets , and baboons or other. No other animal of the savannah has evolved to a lack of hairiness to regulate its temperature: the hairs on the contrary provide protection against the sun. They are vital for primates regardless of their environment: young toddlers clinging to them while their mother goes about her business.

Another objection is that standing in open area more exposed to potential predators.

The learned bipedalism in the trees?

Many observations corroborate the facts: the chimpanzee (Pan troglodytes), who spend less than 3% of their time standing on a long study of Kevin Hunt published in 1994 ^{The theory of supply in crouch}

This theory was advanced in 2003 by zoologist Jonathan Kingdon. Anatomical changes would have appeared originally in another goal that bipedalism. This pre-adaptation to bipedalism is primarily related to the facilitation of food in a crouched position (collection of insects, worms ...) by the change of the feet become more flat .

The theory of sexual selection

This theory was proposed by Maxine Sheets-Johnstone .

Theory of initial bipedalism

Proponents of the theory of initial bipedalism consider that early mammals were bipeds. This anatomical character would have been maintained in the human lineage, while most other lines, including that of apes , developed a mode of quadrupedal locomotion. The common ancestor was bipedal and linked to a marine habitat.

Unlike the current dominant paradigm, based on data of paleontology , the theory of initial bipedalism is based mainly on the embryology and on the comparative anatomy. It is a theory zoological as well as the theory of constructions of Professor Wolfgang F. Gutmann.

This theory is now a radical concept that most scientists do not share .

The energy saving in bipedal

Some believe that bipedalism saves energy when walking in search of food ^{The learned bipedalism in the water?}

First published in 1960 by Sir Alister Hardy FRS, the Primate of the Aquatic Theory has been recently relaunched by the accumulation of studies and evidence (photos, movies) varied provenance, showing monkeys walking in water. Most features of human physiology are common in aquatic mammals and very rare among those on land. Our ancestors have lived for so long in flooded habitat, semi-aquatic, which would solve most of the issues of human physiology so far remained unanswered. The beginning of these developments would be contemporaneous with the divergence between apes and humans.

However, this hypothesis remains controversial and is far from unanimous among paleoanthropologists.

What is the first bipedal hominid?

The skeleton of a hominid dating back 3.8 to 4 Ma was discovered in Ethiopia. This makes it the oldest known if we exclude Orrorin tugenensis and Sahelanthropus tchadensis. The discovery was announced by the team of paleontologists American Bruce Latimer "

In the same issue of Nature, Mr. Collard, LC Aiello discuss these results A. afarensis could have had traces running on the knuckles (forelimb) while already become bipedal. Recent research has shown that we could not give as much credit as we thought phylogenetic inferences based on fossils. Others recall that the bones are relatively plastic in a lifetime. It can not be explained any more than Australopithecus africanus , a descendant of possible Australopithecus afarensis , has lost this trait if it was phylogenetic. If Lucy was walking on the knuckles, his bones are also the deformation of the radius implied by bipedalism and other features along the same lines.

Robotics

A biped French was designed specifically for the study of walking and running . The company Honda has also shown in the realization of biped robots including the project ASIMO.

Notes

Sources

• (In) Aquatic Ape Theory , Elaine Morgan
• (In) Wading for Food: The Driving Force of the Evolution of Bipedalism? , Algis Kuliukas MSc (Human Evolution & Behaviour, UCL, 2001). Article submitted to Nutrition and Health, August 2002. Abstract.
• (In) Stride lengths, speed and Energy Costs in walking of Australopithecus afarensis: using evolutionary robotics to predict locomotion of early human ancestors , William I. Sellers, Gemma M. Cain, Weijie Wang, Robin H. Crompton. The Royal Society
• Mutants: On Genetic Variety and the Human Body ("Mutants: on genetic variety and the human body), by Armand Marie Leroi. (English book on the changes, and how quickly they can produce (and evolve a race))

• Portal Prehistory

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