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, one of the fastest of living bipeds]] ]] DIVERSITY AND EVOLUTION OF BIPEDALISM Types of bipedal movement There are are a number of states of movement commonly associated with bipedalism. 1. Standing . Staying still on both legs. In most bipeds this is an active process, requiring constant adjustment of balance. 2. Walking . One foot in front of another, with at least one foot on the ground at any time. 3. Running . One foot in front of another, with periods where both feet are off the ground. 4. Hopping . Moving by a series of jumps with both feet moving together. Bipedal animals Bipedal movement has evolved a number of times other than in s are interesting birds with regard to bipedality as they tend to hold their bodies upright, rather than horizontal as in other birds. Bipedal movement is less common among Mammal s, most being Quadraped al. The largest mammalian group using bipedal movement are the Kangaroo s and their relatives. However these tend to move mostly by hopping, which is quite different from humans, and also from birds and theropods. There are also various groups of hopping rodents, such as the Kangaroo Rat s. A primate, the Sifaka , also moves by hopping when on the ground. Possibly the only mammal other than humans that commonly moves bipedally by an alternating gait rather than hopping is the Giant Pangolin . Limited examples of bipedalism are found in some other mammals. One exception is found among some Primate s who live in forests that are often flooded, the Bonobo ape and Proboscis Monkey . These primates will wade through water in a bipedal stance. On occasion bonobos and proboscis monkeys, and less frequently some other primates, will also walk or stand bipedely on land. The Raccoon also often stands erect also or squats in water to use its hands to manipulate food and rocks/sticks. Some animals, such as the Bear , may raise up and move bipedally during physical confrontation, so as to better be able to use their forelegs as weapons. Also a number of mammals, such as Ground Squirrel s or Meerkat s will stand on their hind legs, but not walk on them, in order to survey their surroundings. Finally Gerenuk antelope are known to stand on their hind legs in order to eat leaves from trees. The extinct giant Ground Sloth had hip joints whose form indicates that they also did this. Among the non- Archosaur Reptile s bipedalism is rare, and it is unknown among the Amphibian s, however it its found in the "reared-up" running of certain Lizard s. An interesting example is found in at least one genus of Basilisk Lizard that by this method can run across the surface of water. Bipedalism in the form of reared-up running can also be found in some Insect s such as the Cockroach . Otherwise bipedal movement is unknown in Arthropod s. Bipeds are almost exclusively Terrestrial animals. However, at least two types of Octopus are known to walk bipedally. This form of locomotion appears to allow them to remain somewhat camouflaged while moving quickly, taking a form like a coconut or seaweed and moving on the tips of two of its arms. Exceptional cases Many animals that do not use Bipedal Locomotion in nature can be trained to walk on hind legs. This includes dogs, elephants, horses and pretty much every Mammal or Reptile that has 4 legs. Some animals can also be trained to walk on front limbs, although this method lacks any practical benefits, save for Gymnastic versatility for spectacle. Humans too, can learn to walk using their arms for aid, or solely their arms ( Handstand ). This is unusual and requires mental and physical training, like many physical movements, otherwise it can result in injury due to lack of protection by atrophied or unbalanced muscles not developed for or genetically inclined for the movement. Some unusual individual primates have been known to be bipedal. There has been one recorded case of a macaque switching to bipedal walking completely after recovering from a serious illness, and at least one example of a captive chimp who only walked upright, Oliver . Advantages Bipedalism and associated traits can offer a species several advantages:
Evolution
Humans are generally thought to have evolved bipedalism either through living on plains (the Savanna Theory ), or wading like their semi-bipedal wading cousins the Bonobo chimps, the lowland gorillas, and Proboscis Monkey s (the Aquatic Ape Theory ) which would provide the advantage of keeping the head above water for breathing. PHYSIOLOGY OF BIPEDALISM Bipedal movement occurs in a number of ways, and requires many mechanical and neurological adaptations. These are described below. Biomechanics Engineers who study bipedal walking or running describe it as a repeatedly interrupted fall. The phenomenon of "tripping" is informative with regards to the "controlled falling" concept of walking and running. The common way to think of tripping is as pulling a leg out from under a walker or runner. In fact, however, merely stopping the movement of one leg of a walker, and merely slowing one leg of a runner, is sufficient to amount to tripping them. They were already "falling", and preventing the tripped leg from aborting that fall is sufficient to cause bipeds to collapse to the ground.
Energy-efficient means of standing bipedally involve constant adjustment of balance, and of course these must avoid Overcorrection .
Efficient walking is more complicated than standing. It entails tipping slightly off-balance forward and to the side, and correcting balance with the right timing. In humans, walking is composed of several separate processes:
Running is an inherently continuous process, in contrast to walking; a bipedal creature or device, when efficiently running, is in a constant state of falling forward. This is maintained as relatively smooth motion only by repeatedly "catching oneself" with the right timing, but in the case of running only delaying the nearly inevitable fall for the duration of another step.
Musculature Bipedalism requires strong leg muscules, particulary in the thighs. Contrast in Domesticated Poultry the meaty Drumstick and thigh, against the small and bony wing. Likewise in humans, the Quadriceps and Hamstring muscles of the thigh are both so crucial to bipedal activities, that each alone is much larger than even any well-developed biceps of the arms. Nervous system The famous knee jerk (or Patellar Reflex ) emphasizes the necessary bipedal control system: the only function served by the nerves involved being connected as they are is to ensure quick response to imminent disturbance of erect posture; it not only occurs without conscious mental activity, but also involves none of the nerves which lead from the leg to the brain. A less well-known aspect of bipedal Neuroanatomy can be demonstrated in human infants who have not yet developed toward the ability to stand up. They can nevertheless run with great dexterity, provided they are supported in a vertical position and offered the stimulus of a moving treadmill beneath their feet. Respiration A biped also has the ability to breathe whilst it runs. Humans usually take a breath every other stride when their Aerobic system is functioning. During a sprint, at which point the anaerobic system kicks in, breathing slows until the Anaerobic system can no longer sustain a sprint. BIPEDAL ROBOTS - a bipedal robot]] For nearly the whole of the 20th Century , bipedal Robot s were very difficult to construct. Robots which could move usually did so using wheels, treads, or multiple legs. Increasingly cheap and compact computing power, however, has made two-legged robots more feasible. In recent years, Honda and Sony have developed these machines. EXTERNAL LINKS
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