It is still a great mystery as to why do humans have so little hair despite the fact that hair could keep our bodies warm and could have provided many more benefits. In fact, human beings are the only hair less primates under the sun. Despite this odd, we have managed to survive and conquer the world. There are few theories which have tried to find out the answer of this complex question.
One explanation is that little hair helps us cool down fast. The theory says that we lost our fur through the evolution in order to control our body temperature. Apes, our ancestors used to spend most of their time in forests and hence fur was fine with them but walking on tropical places like Savannah would have overheated and killed them.
Another recent theory says that we lost ‘fur’ in order to protect ourselves from being infested by parasites, worms and harmful bacteria. Creatures like ticks, lice, bugs, etc find fur a safe place to inhabit and multiply which in turn can lead to several kinds of infections, all of which can cause medical problems and can sometimes prove fatal.
Another hypothesis is that once hairlessness evolved, it probably became subject to sexual selection – a feature in one sex that was liked by another sex. Smooth and clear skin became a sign of good health and beauty and that is why we find women with less hair and always keen to defuzz their bodies.
Despite the threat of head lice, humans probably retained the hair on their scalp because it helped them stay cool under the sun and during winters helped them stay warm. Pubic hair and under arms hair may have been retained because of the role of pheromones in enhancing sexual attraction.