Bipedalism

Adaptations require a reproductive advantage to become fixed in a population. Bipedality has many negative factors including increased risk of injury, decreased speed and agility, and the inability to cooperatively carry infants. Considering these drawbacks of bipedality, there had to be an extreme selective pressure to adapt bipedality. Ape populations declined as the Miocene progressed, except for hominids. This was a result of the Miocene apes becoming increasingly K-selected. Unlike hominids, Miocene apes were unable to compensate for the extended interbirth interval and were outcompeted by OWM. Hominids decreased their interbirth intervals through increased male parental investment. A wholesale change in social structure among early

They were forest floor omnivores, which means that bipedality did not arise on the savanna (Lovejoy et. al, 2009). Bipedalism became a fixed adaptation because it was reproductively advantageous as it allowed for more effective provisioning. Effective provisioning was important in early hominids because females would exchange copulations for foods that were high in fat and protein. Extended and continuous upright walking had to be practiced for bipedality to be under strong selection. The necessity to carry food back for females would be to enough to force this kind of locomotion to become constant (Lovejoy, 1981). Males with reduced canines had an advantage because it signaled to females that they would not waste energy in dominance displays and could, therefore, spend more time provisioning for them (Lovejoy et al. 2009). The advantage of bipedality was that males could carry food back to the females. The extra food would give the females more energy, which would decrease interbirth intervals. To keep receiving provisions from males, females would exchange copulations. Male-male competition would decrease as males spent more time provisioning and eventually the males would start to provision cooperatively for extra protection in their expanding territories. These changes in the social structure would have been reproductively advantageous because they would have combatted the extended interbirth interval