anthropologist and paleo-biologist nina jablonski thinks the ability to lose body heat through sweating helped make possible the dramatic enlargement of the brain. the brain is the most temperature-sensitive human organ. the loss of fur was also a factor in other adaptations. some of these changes are thought to be the result of sexual selection. by selecting more hairless mates, humans accelerated changes which were first done by natural selection. sexual selection may also account for the remaining human hair in the pubic area and armpits, which are sites for pheromones, while hair on the head continued to provide protection from the sun. humans had hairlessness, upright posture, and high brain capacity by 260,000 to 350,000 years ago.