What Makes us Human?

August 26, 2010 - 09:53
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Recently PBS produced and broadcast a two part series called “Becoming Human” that described several key traits that developed as humans evolved from apes.  Of these, the one that surprised me most was that humans are unique in having white sclera (the region around the pupil and iris of the eye).  In other primate species the sclera is dark.  According to geneticists, this trait must have conferred a strong survival advantage to early humans. 

What could possibly explain this?  One clue is that another of the key traits that developed in early humans was the ability to work together as a group, to collaborate.  For example, if three people are walking through the woods and one person sees something moving in the bushes, the others can use the contrast of the vigilant person’s white sclera to track their eye movements and help the group determine if a danger is lurking. 

However, white sclera simultaneously disadvantaged early humans with the trait in that it revealed some of their inner thoughts thereby placing them at a competitive disadvantage.  For example, if three people are walking through the woods and one person sees a tiger lurking ahead, the others can track their eye movements and see the danger more quickly, allowing them to make a simultaneous dash.  As the old joke goes, “you don’t have to run faster than the tiger, you just have to run faster than the other guy.”

The spread of white sclera as a trait in humans indicates that collaboration with others was more important for survival than competing with them.  Conversely, in all other primate species the sclera is dark indicating that amongst non-human primates competing with others is more important for survival than collaborating with them.  The primacy of collaboration over competition is therefore part of what makes us both successful and human.

 
I would like to acknowledge and thank Michael O’Shaughnessy for reviewing this post and providing helpful comments and edits.

 

Author: Nick Franano, Founder