Benefits of bipedalism
What’s so useful about walking on two feet? A lot, actually. A twolegged primate can stand up and reach food (as chimps do) that a fourlegged primate would ﬁnd challenging. A two-legged primate can move more efficiently between patches, since two-legged walking uses less energy than four-legged walking, and a bipedal ape can stand up to survey for danger (as meerkats do), which comes in handy in a savanna ﬁlled with carnivores. In addition, by standing upright, a two-legged primate exposes less of its body’s surface area directly to the hot African sun and thus requires about two-thirds the water of a similarly sized four-legged primate.
Robert L. Kelly, The Fifth Beginning, p. 25