Final answer:
There are three major hypotheses regarding the origin of bipedalism: the savanna hypothesis, which suggests bipedalism evolved as an adaptation to the savanna habitat; the thermoregulation hypothesis, which posits it evolved to help with temperature maintenance; and the hypothesis that bipedalism provided free hands for carrying items, a significant advantage for early hominins.
Step-by-step explanation:
There are several hypotheses regarding the origin of bipedalism in hominins, each proposing different evolutionary advantages that this trait might have conferred. The savanna hypothesis suggests that bipedalism evolved as an adaptation to a savanna habitat, which provided the benefit of elevation to see over tall grasses and possibly to reduce exposure to the harsh sun. Secondly, the thermoregulation hypothesis indicates that walking on two legs exposed less of the body's surface to the sun while increasing wind flow, thus helping in maintaining the body's temperature. Lastly, the provision of a free hand to carry tools, food, or offspring is another compelling hypothesis, as it would grant early hominins greater flexibility and survival opportunities. It is challenging to confirm any of these hypotheses as bipedalism's exact origin is not directly testable and relies heavily on the fossil record, like the fossil evidence found by Mary Leakey including the Laetoli footprints, which indicate a modern striding gait of Australopithecus afarensis roughly 3.5 million years ago.