That proved bipedalism did not evolve on the savannah, but since hair does not fossilise, it is hard to establish when the hominids began to lose it. In 2006, Nina Jablonski, an anthropologist at Penn State University, wrote a book, Skin: A natural history, in which she proposed that after the bipeds finally moved to the savannah - and nobody doubts some eventually did - their profuse sweating created the need to shed body hair to allow the sweat to evaporate. She calculated such a hominid could have sweated up to 13.6 litres a day. But she did not explain why the equally sweaty patas monkey did not lose its hair in the same environment, nor how the hominids could have drunk so much in a hot, dry landscape.
