Now, our hominoid ancestors were faced with two options tot he decreasing abundance and increased scattering of food: (1) they could maintain quadrupedalism and evolve a fission-fusion grouping system, or (2) they could evolve bipedalism.

Quadrupedalism, while fast, tires out the individual very easily, therefore limiting the amount of land crossed per day. An excellent example is the cheetah, which can put on tremendous bursts of speed, but sadly lasting for less than a minute. Therefore, in order to maintain survival, it would have been imperative for the chimpanzee ancestors to evolve small group sizes, thereby cutting down on the number of mouths to feed.

Bipedalism, on the other hand, is an extremely slow means of locomotion, since the individual is forced to support the body weight on just two limbs. In fact, no savanna primate in his right mind would evolve bipedalism due to the severe limitations on speed. That is why partially-bipedal species are more numerous in forested regions than in open terrain. There is a catch: bipeds do have increased stamina, enabling them to traverse more land per day than quadrupeds. Therefore, they are capable of maintaining larger group sizes, the benefits of which we shall see later.

A study by Dan Gebo published in the American Journal of Physical Anthropology proposed four phases before the advent of bipedalism: (1) arborealism [tree-climbing], (2) brachiation [swinging], (3) back to arborealism, and (4) terrestrial quadrupedalism. (Gebo, 1996). Other paleoanthropologists, such as Steve Savage, claim that it is brachiation to bipedalism (Savage). There is much controversy over this subject, so in the interests of convenience, the author shall write this paper from the perspective of quadrupedalism to bipedalism.

   

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