In Africa there was a tremendous drought that caused the trees over time to recede. Hence the African savannah. Arborial apes over time began to decend more and more to the grasslands to exploit the new nich. Tall grasslands and predation perhaps led to Bipedalism and the scavanging adaptatations freed up the hands , which in turn increased intelligence. Hair as another member suggested was not advantageous and the gene for hairyness through mutation and natural selection was not propagated. Fast forward....Homosapiens sapiens year 2004. This is theory but is supported by facts we evolved from arborial apes on the plains of Africa to eventually become the domiant creature on the Earth. Evolution experts feel free to nit pick and correct my laymans understanding of this.