The only hairs that humans have completely lost are the vibrissae, or sensory whiskers. The rest of our bodies are actually covered with very short, very fine hair called vellus. The difference between humans and apes lies in the relative proportions and distribution of vellus hair compared with our longer, darker hair (known as terminal hair). There have been many different attempts to explain the relative hairlessness of humans, but so far none have achieved general consensus. It has been suggested that our hair was lost during a semi-aquatic period of our prehistory, that it was lost to allow improved cooling from sweating on the hot African savannah and even that we didn’t lose our hair until Neanderthal man started wearing clothes about 200 million years ago. This is all speculative however as hair doesn’t fossilise well so we don’t even know for sure if hairlessness is unique to humans.