A theory has been put forth that humans lack body hair in an attempt to reduce the number of parasites that affect us. There are many parasites such as ticks, fleas and lice that actually prefer to make their home in coats of deep fur. Humans lack body hair which makes us unique among primates and in a category shared only by a few semi-aquatic species of animals such as hippopotamuses, dolphins and whales.
The study was developed by a behavioral ecologist and an evolutionary biologist. It basically states that because ancient humans were able to use fire, wear fire and construct shelters they no longer needed the thick coats of fur that early humanoids may have had. The hair on humans still exists in many areas but it has become so fine that it no longer works for heat regulation and no longer can support colonies of annoying parasites.
There are differences in body hair between men and women and the authors of the study say this supports their theory as well. It was believed that hairlessness became a desirable trait in mates and this may have been one reason why women have less body hair than men. A desirable mate was one which was less susceptible to parasitic infestation and being hairless advertised that an individual did indeed possess this desirable trait. It also explained why head and facial hair continued to be so thick. Humans use facial and head hair (or a lack of it) as a way of determining physical attractiveness in a mate. By retaining head and facial hair, this method of determining sexual attractiveness would not have been lost.
In the past, scientists thought that we abandoned our fur coat as a way of surviving in hot environments such as the African savanna. Scientists have accepted this theory even though other primates who lived in the same environment did not lose their hair coats like humans did.
It was also believed that the change in our fur coat came when we left the trees and began to dwell on the ground. A third theory stated that we lost our hair coat when we became semi-aquatic approximately 8 million years ago. At that time, humanoids began to swim and to immerse themselves in water. It was not surprising that we would adopt the same kind of thin hair coat that other aquatic mammals had.
Humans were still plagued by parasites even after they became hairless. A number of parasites such as body lice continued to affect early humanoids. They tended to live in the clothing and bedding that humans used on a regular basis. It was much easier to change clothing or bedding than it would have been for humans to get rid of parasites living in a thick coat of hair or fur.
While this theory seems to explain many of the reasons why humans would have lost their body hair it has not totally been proven as fact. Scientists would need to compare the amounts of body hair that populations have against the number of parasites that plague that population. That way they may be able to tell whether humans lost their hair to keep parasites at bay.