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The Ascent of Man (continued) Also, by 5 million years ago, there was a marked transition to C3 plants adapted to warm, dry climates. (Cerling et al., 1993). Interestingly, this period coincides with the ape-hominid divergence period, calculated by biochemists Vincent Sarich and Allen Wilson to be 5 to 7 million years ago.5 (Sarich & Wilson).  Quadrupedalism, while speedy, exhausts the individual very easily, therefore limiting the distance traversed per day. 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. There is one catch: bipeds do have increased stamina, enabling them to cover more land per day than quadrupeds. But why did bipedalism prove more successful than quadrupedalism? Isbell and Young built their argument upon the previous work of Peter Rodman and Henry McHenry in 1980, who reasoned that bipedalism was more efficient in locomoting between food located in sparse forest patches. Isbell and Young advanced this theory one step further through implicating behavioral ecology. Large sized groups gain an advantage over smaller sized groups because they are usually able to outcompete their adversaries through scramble competition. There is also a greater probability of there being more adaptively fit individuals than in small groups. The increased intra-group (mainly) contest competition makes large groups more versatile in inter-group competition. The negative effect of large group size is that, through intra-group scramble competition, it is less capable of supporting its members with the available resources.  
Copyright ©2001-2003, Allegra H., all rights reserved. Please contact me via e-mail if you wish to reproduce this material.
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