Bipedalism: Some proponents of AAH claim that bipedalism offers numerous advantages in water, including permitting deeper wading, improved balance and reduced strain on the back, hips and knees as well as improved blood circulation.[16][27][28] But bipedalism also gives many advantages on land, particularly lower energy expenditure and the ability of long-distance running—which humans do better than most terrestrial mammals. Proponents of the AAH suggest that bipedalism is disadvantageous when comparing humans to medium-sized, terrestrial quadrupeds, but the fossil record shows that the evolution of humans from ape ancestors did not include a period of quadrupedal locomotion. Instead, human evolution features mainly brachiation, suspension and climbing as the primary method of transportation, with a gradual increase in bipedal locomotion over time.
In addition, the elongated lower limbs of humans, which is explained by AAH proponents as improving swimming speeds, appears only after the evolution of the genus Homo [4] and biomechanical analysis indicates humans are far too poor swimmers to have derived from an ape ancestor that swam,[29] and pre-human apes would face similar problems.[30] There is no single accepted explanation for human bipedalism but freedom of the hands for tool use, carrying of infants, feeding adaptations, improved energy expenditure or some combination of these are suggested, with considerable diversity in pre-human skeletal adaptations that would assist in bipedalism.[31]