Bipedalism in Humans and Other Primates

What is Bipedalism?

Bipedalism is a process of terrestrial locomotion in which an organism uses its two rear limbs or legs to travel. A biped is an animal or machine which normally moves on two legs (from Latin bis 'double' and pes 'foot'). Walking, running, and jumping are examples of bipedal movement. 

Examples of Bipedal Animals May Include: Humans, many lizards, birds, cockroaches, Kangaroos, some rodents and numerous birds hop bipedally, and crows and jerboas use a skipping gait. 

Bipedal locomotion is found in human species which are bipeds and that walk on two legs as their primary mode of locomotion. Habitual bipedalism has developed several times within mammals, with macropods, springhare, kangaroo mice and rats, pangolins, jumping mice, and hominin apes (australopithecines and humans) and also other extinct groups developing the trait separately. Most archosaurs (which comprises crocodiles and dinosaurs) evolved bipedalism during the Triassic period; within dinosaurs, most early forms and numerous later groups became habitual or exclusive bipeds; and birds are members of theropods, a clade of specifically bipedal dinosaurs.

A greater number of human species walk bipedally on occasion or for short periods of time. When moving, some lizard species travel bipedally, typically to avoid danger. In order to access food or explore their surroundings, many primate and bear species adopt a bipedal gait, however there are some exceptions where they walk solely on their hind limbs. Several arboreal species of primate, including gibbons and indriids, spend all of their time on the ground walking on two legs. When fighting or copulating, several animals rear up on their hind legs. Few animals don't move bipedally and remain on their hind legs to stand guard, reach food, threaten a rival or predator, or stand in courtship.

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Advantages:

Limited and exclusive bipedalism can provide a species with a number of benefits. Bipedalism lifts the head, allowing for a wider field of vision and better detection of distant threats or resources, as well as accessibility to deeper water for wading animals and the ability to enter higher food sources through the mouths. Non-locomotor limbs become free for many other purposes when upright, such as manipulation (in primates and rodents), flight (in birds), fighting (in bears, great apes, digging (in giant pangolins), and the large monitor lizard), or camouflage (in certain species of octopus) or combat (in great apes, bears, and the big monitor lizard).

The maximum bipedal speed tends to be slower than that of the maximum quadrupedal speed with a flexible backbone – the ostrich and red kangaroo can both achieve speeds of 70 km/h (43mph), although the cheetah can travel at speeds of more than 100 km/h (62 mph). As per the endurance running theory, despite being slower at first, bipedalism has enabled humans to outrun certain other animals across vast distances. Bipedality has been proposed as a way for kangaroo rats to enhance locomotor performance, which could help them avoid predators.

Facultative and Obligate Bipedalism:

A few arboreal species of primate, including gibbons and indriids, spend all of their time on the ground walking on two legs. When fighting or copulating, several animals rear up on their hind legs. Few animals don't move bipedally and remain on their hind legs to stand guard, reach food, challenge a rival or predator, or stand in courtship. There have also been records of humans walking on all fours holding their feet but not their knees on the ground, however these instances are the product of extremely unusual hereditary neurological disorders like Uner Tan syndrome, rather than natural behaviour.

Even if one disregards exceptions due to injury or disease, there are several ambiguous examples, such as the fact that "average" humans will crawl on their hands and knees. As a result, the words "facultative" and "obligate" are avoided in this article, and the emphasis is on the variety of locomotion types used by different animal classes. Normal humans can be classified as "obligatory" bipeds because the alternatives are inconvenient and are commonly used only when walking is difficult.

Movement:

Bipedalism is synonymous with a variety of different types of movement.

• Standing: On both legs, remain still. This is an ongoing process in most bipeds, requiring frequent balance adjustments.

• Walking: One foot in front of one at all times, including at most one foot on the floor.

• Running: For times when both feet are off the ground, one foot in front of one.

• Hopping/Jumping: Moving by jumping with both feet moving together in such a sequence of leaps.

Bipedal Animals:

Just a few living classes of terrestrial vertebrates are bipedal, while the vast majority of existing terrestrial vertebrates are quadrupeds. Gibbons, Humans, and large birds each raise one foot at a time while walking. Most macropods, lemurs, smaller birds, and bipedal rodents, from the other end, travel by jumping on both legs at the same time. Tree kangaroos can walk or jump, most often jumping on both feet simultaneously while on the ground and switching feet when travelling arboreally.

Amphibians: There are no recognized amphibians that are obligate bipedal, either living or extinct.

Extant Reptiles: Numerous lizard species, such as the world's fastest lizard, the spiny-tailed iguana (genus Ctenosaura), turns bipedal throughout high-speed sprint locomotion.

Early Reptiles and Lizards: Eudibamus, a bolosaurid that lived 290 million years ago, has been the first known biped. Its bipedalism is suggested by its long hind legs, narrow forelegs, and differentiated joints. Later in the Permian, the species went extinct.

Archosaurs (Includes Crocodiles, Birds, and Dinosaurs):

Birds: While on the ground, both birds are bipeds, a trait they inherited from their dinosaur ancestors. Hoatzin chicks, on the other hand, include claws on their wings that they use to ascend.

Other Archosaurs: In archosaurs, the group that comprises both crocodiles and dinosaurs, bipedalism occurred more than once. Both dinosaurs are believed to have evolved from a completely bipedal gait like Eoraptor. Some dinosaur lineages, including the iguanodons, have re-evolved bipedal walking. 

Few extinct species of the crocodilian line, a sister group to the dinosaurs, evolved bipedal types as well; Effigia okeeffeae, a crocodile relative from the Triassic, is assumed to be bipedal. Initially, bipedal pterosaurs were believed to exist, but latest trackways have almost all revealed quadrupedal locomotion.

Mammals:

Humans, extinct giant ground sloths, various species of jumping rodents, giant pangolins, and macropods are among the extant mammals that have evolved bipedalism as their primary mode of locomotion. Humans are mentioned in the following section since their bipedalism has been thoroughly studied. Macropods are thought to have adopted bipedal hopping only once during their evolution, about 45 million years ago.

The majority of mammals are quadrupedal, so bipedal walking is uncommon. While all primates have had some bipedal ability, several species prefer to move around on land using quadrupedal locomotion. Apart from primates, macropods (wallabies, kangaroos, and their relatives), jumping mice, kangaroo rats and mice, and springhare all walk on two legs. Apart from apes, only few animals walk bipedally with an alternating gait rather than jumping. The ground pangolin and, in certain cases, the tree kangaroo are cases.

Primates:

Many bipedal animals walk through their backs near to horizontal, balancing their bodies with a long tail. The primate type of bipedalism is unique in that the back is nearly vertical (almost vertical in humans) and the tail can be completely absent. Numerous primates may stand without assistance on their hind legs. Bipedalism is seen in chimps, gibbons, gorillas, bonobos, and baboons. Sifakas walk like every indrids on the field, with bipedal sideways jumping motions of the hind legs and forelimbs held up for balance. While geladas are typically quadrupedal, they will occasionally use a squatting, shuffling bipedal mode of locomotion to travel amongst feeding patches.

Limited bipedalism:

In Mammals: Bipedalism in several other mammals is selective and non-locomotor. Rats, raccoons, and beavers, for example, can squat on their hindlegs to handle certain items but return to four limbs while running. For using the forelegs as arms, bears may fight in a bipedal stance. In some cases, including when feeding or fighting, a variety of mammals will adopt a bipedal stance. Meerkats and ground squirrels may stand on their hind legs to survey their surroundings, but they will not move bipedally. If conditioned or if quadrupedalism is not possible due to a birth defect or accident, dogs (such as Faith) may stand or walk on two legs.

The gerenuk antelope, like the extinct giant ground sloth and chalicotheres, eats from trees while standing on its hind legs. When attacked, the spotted skunk may move on its front legs, rearing up and showing the attacker so that its anal glands, which can spray an explosive oil, are facing the attacker.

In Non-mammals: Amphibians do not have the ability to walk on two legs. Bipedalism is uncommon amongst non-archosaur reptiles, but it is seen in the "reared-up" running of lizards like agamids and monitor lizards. Most reptile species may also embrace bipedalism for the duration of a war. Basilisk lizards of one genus may move bipedally throughout the surface of water for long distances. Cockroaches are expected to travel bipedally at high speeds amongst arthropods. Outside of terrestrial animals, bipedalism is uncommon, but at least two species of octopus walk bipedally on the seafloor with two of their arms, enabling the second arms to be used to disguise the octopus as a or a floating coconut or mat of algae.