Walking on Two Feet

Biological Evolution and Early Human Evidence ANTH 2301 Walking on Two Feet All animals that are thought to have a direct ancestry to humans are referred to as hominins, and this includes the genera Ardipithecus, Paranthropus, Australopithecus, and Homo. All extant and contemporary great apes, including humans, gorillas, chimpanzees, orangutans, and their progenitors, are referred to as hominids. Over time, these phrases have come to mean different things; nonetheless, the definitions given below are the most recent. Bipedal locomotion is a shared anatomical behavioural complex among all hominins, notwithstanding their diverse differences. By examining several facets of a creature's morphology, scientists might make assumptions about how it moved. Animals that move by swinging from branch to branch, known as brachiators, often have long arms, whereas animals that move by using the force of their lower limbs to push themselves have legs that are comparatively longer. The length of the arms and legs is the same in arboreal primates. One leg is referred to as the stance leg and the other as the step leg when walking on two legs. The step leg is off the ground and moving forward as the stance leg remains on the ground. Only around 25% of the time when walking normally are both feet on the ground. The percentage of time spent with both feet on the ground reduces as locomotion speed rises. Consequently, bipedal creatures maintain their body balance on only one leg (the stance leg) during the majority of their locomotion. Since the earliest human ancestors, bipedal creatures have undergone several structural adaptations to ensure that they do not topple over while balanced on their stance leg. The tilting of the femur (upper leg bone) inward at a valgus angle, which places the knees and feet beneath the centre of the pelvis, is one of the most significant anatomical alterations that enable effective bipedalism. Additionally, the spinal curvature that allow the hips to support the weight of the upper body have evolved in bipedal hominins. Weight transmission during the step phase of bipedal locomotion is further aided by the development of the foot's arch and the big toe's realignment to run parallel to the other toes. The study of English paleoanthropologist Mary Leakey provides the most significant evidence of early hominid bipedalism. About 3.5 million years ago, Mary Leakey found a 75-foot path of tracks left by three bipedal people who had traversed a thick layer of wet volcanic ash. These footprints were discovered at the Laetoli site in East Africa. Australopithecus afarensis is most likely the maker of these footprints given the date and the location. An examination of the Laetoli footprints reveals a contemporary striding pattern. Bipedalism in hominid evolution necessitated intricate anatomical reorganisation. The advantages of these modifications must have been substantial for natural selection to generate such a massive quantity of variation. Numerous theories have been proposed to explain these changes, ranging from improving energy efficiency or thermoregulation (the capacity to regulate body temperature) by exposing more surface area to freeing hands for carrying tools, food, or children. Since none of the theories can be verified, it is extremely difficult to comprehend why the progenitors of humans underwent such a drastic change in behaviour. The following sections discuss some of the most significant findings on early hominin fossils, where anthropologists find some of the first evidence of bipedalism's adaptation in the human tale.