Innovation Blog

HAIR! Why Do Humans Lack It?  How Lice Reveal the Secrets

By Shlomo Maital

   

 A Head  Louse – Real One!

The 1968 Broadway musical Hair! is about long-haired hippies.  Perhaps a more appropriate title would be Skin!  Humans are almost the only mammals without a thick covering of fur or hair.  It turns out that this conveys a huge evolutionary advantage.  But how? And when did humans lose their furry hair (we know a branch of homo sapiens evolved from chimpanzees some 6 million years ago).  And since human hair does not exist in million-year-old human fossils, how can we ever know the answer?  Writing in Scientific American *  Mark Pagel notes:

“We humans are conspicuous among the 5,000 or so mammal species in that we are effectively naked. Just consider what your pet dog or cat (or, for that matter, a polar bear) would look like, and how it might feel, if its furry coat were shorn.  Scientists have suggested three main explanations for why humans lack fur. All revolve around the idea that it may have been advantageous for our evolving lineage to have become less and less hairy during the six million years since we shared a common ancestor with our closest living relative, the chimpanzee.”

    The main advantage of no hair?  Skin. Humans can sweat, and their sweat glands produce a liter of sweat an hour. This helps cool the brain, which generates 20 watts of energy and heat! (Try putting a 20 watt light bulb in a closed box, and see what happens!).  The human body’s skin and pores make possible a larger brain because it can be cooled. (Three degrees of extra body heat destroys the brain). 

     An innovative researcher at the University of Florida has used the DNA of lice to discover when humans lost their hairy covering.  He discovered that by studying the DNA of human lice that live in hair, humans lost their body fur about 3 million years ago!  Somehow, lice moved from gorillas to humans, then evolved and adapted to human hair.  He has also discovered, by analyzing the DNA of clothes lice (human lice that live only in clothing), that humans first put on clothes about 170,000 years ago.  This enabled humans to move out of Africa and migrate to Asia.  This also means that ancestral humans, descended from apes, went naked for over 2 million years.  

  Who is the brilliant researcher who figured out how to study human evolution through studying the DNA of lice?  His name is   David Reed, associate curator of mammals at the Florida Museum of Natural History on the University of Florida campus.    His study  appears in the January print edition of Molecular Biology and Evolution.    

 * http://www.scientificamerican.com/article.cfm?id=latest-theory-human-body-hair