Bipedalism is a more efficient way of covering large areas. It elevates the head improving the ability to spot potential food and frees the hands for carrying. While bipedalism predates manufacture of tools it is not unreasonable that prre-tool making hominids would make use of rocks to break open bones and extract the marrow. Finally, Shipman proposes that the earliest hominids retained the ability to climb trees to feed, sleep and escape from some predators. Wheeler focuses on heat stress as a major problem for primates exploiting savannah resources.
Bipedalism exposes less body surface to direct solar radiation.
Erect posture exposes more body surface to air movement and thus promotes evaporative cooling. The net result is to increase forging time on the savannah. Most view the models described above focus on the development of bipedalism as a consequence of the transfer of habitate from arboreal to terrestrial and the exploitation of resources on the African savannah. Yet, each focuses on a specific niche on the savannah that hominids exploited. There is no single theory but there are a number of competing hypotheses.