Quiz

Bipedalism is a form of terrestrial locomotion where a tetrapod moves by means of its two rear (or lower) limbs or legs.

Several groups of modern species are habitual bipeds whose normal method of locomotion is two-legged.

Bipedalism raises the head; this allows a greater field of vision with improved detection of distant dangers or resources, access to deeper water for wading animals and allows the animals to reach higher food sources with their mouths.

The maximum bipedal speed appears slower than the maximum speed of quadrupedal movement with a flexible backbone.

Humans are the only primates who are normally biped, due to an extra curve in the spine which stabilizes the upright position, as well as shorter arms relative to the legs than is the case for the nonhuman great apes.

Bipedalism evolved well before the large human brain or the development of stone tools.

Non-human primates often use bipedal locomotion when carrying food.

Limited bipedalism in mammals includes giant pangolins, the extinct giant ground sloths, numerous species of jumping rodents and macropods.

Bipedal movement is less common among mammals, most of which are quadrupedal.

Bipedalism is unknown among the amphibians.

Bipedalism is rarely found outside terrestrial animals, though at least two types of octopus walk bipedally on the sea floor using two of their arms.Evolution of Bipedalism in Hominins

• Humans' upper bodies appear to have evolved from living in a more forested setting, which made arboreal travel advantageous.
• Multiple factors, such as freeing the hands for carrying and using tools, changes in climate and environment, and reducing sun exposure, may have led to the evolution of bipedalism.
• The savanna-based theory suggests that early hominids were forced to adapt to bipedal locomotion on the open savanna after they left the trees.
• The postural feeding hypothesis suggests that early hominids were bipedal only when eating, and that bipedalism evolved more as a terrestrial feeding posture than as a walking posture.
• The traveling efficiency hypothesis suggests that bipedalism offered greater efficiency for long-distance travel between clusters of trees than quadrupedalism.
• The provisioning model suggests that the evolution of bipedalism was linked to monogamy and male provisioning of food for offspring.
• Recent studies of Ardipithecus ramidus suggest that bipedalism evolved very early in homininae and was reduced in chimpanzees and gorillas when they became more specialized.
• The warning display (aposematic) model suggests that bipedalism was one of the central elements of the general defense strategy of early hominids, based on warning display and intimidation of potential predators and competitors.
• Other ideas propose specific changes in behavior as the key driver for the evolution of hominid bipedalism, such as bipedal threat displays, the need for more vigilance against predators, or male phallic display.
• Lucy, the famous Australopithecus afarensis, had curved fingers that would still give her the ability to grasp tree branches, but she walked bipedally.
• "Little Foot," a nearly-complete specimen of Australopithecus africanus, had a divergent big toe as well as the ankle strength to walk upright and could grasp things using his feet like an ape, perhaps tree branches.
• Fossilization is a rare occurrence, and the fact that no hominine fossils were found in forests does not ultimately lead to the conclusion that no hominines ever died there.
• It is possible that bipedalism evolved in the trees, and was later applied to the savanna as a vestigial trait.Theories of the origin of bipedalism
• The thermoregulatory model suggests that bipedalism reduces heat gain and helps heat dissipation, making the organism more comfortable in hotter conditions.
• Carrying models suggest that the carrying of meat or infants was the key factor in the origin of bipedalism.
• Wading models suggest that bipedalism may have been influenced by waterside environments and the exploitation of aquatic food sources.
• Prehistoric fossil records show that early hominins first developed bipedalism before an increase in brain size, leading to the obstetrical dilemma, where a narrow pelvis for bipedalism is countered by larger heads passing through the constricted birth canal. Physiology
• Bipedal movement requires many mechanical and neurological adaptations, including adjustments of balance, shoulder stability, and strong leg muscles.
• Walking is characterized by an "inverted pendulum" movement, where the center of gravity vaults over a stiff leg with each step.
• Running is characterized by a spring-mass movement, where energy is stored and released from a spring-like limb during foot contact.
• Respiration through bipedality means better breath control, which can be associated with brain growth and the development of verbal communication.
• Bipedal robots have become more feasible due to recent cheap and compact computing power, and principles gleaned from the study of human and animal locomotion are often used to minimize power consumption.