Lynne A. Isbell


On her book The Fruit, the Tree, and the Serpent: Why We See So Well

Cover Interview of August 06, 2009

A close-up

I’m intrigued about the implications of the Snake Detection theory for human behavior, and, in the epilogue, I write most directly about humans.

Have you ever wondered about our ability to point for the purpose of sharing attention?  My guess is probably not.  But this truly is a special ability.  A boy pointing up in the sky and saying, “Look!  It’s a bird!  It’s a plane!  It’s Superman!” directs others to an object for the purpose of sharing attention.  “Declarative pointing,” as this is called, is apparently unique to our species.

But why us and not any other species?  What in our ancestors’ environment prompted the evolution of declarative pointing only in us?

Pointing draws our eyes closer to the target.  If we want someone else to see a venomous snake barely visible in the grass, for instance, we might point to it to make it easier to find—and avoid.  It turns out that we are more accurate at pointing down than up and quicker at responding when someone else points down rather than up.  We also automatically look in the direction of the pointing finger—unless we purposely refuse to do so.  In an environment with cryptic snakes and without the luxury of snake gaiters, these responses would seem quite helpful for reducing the frequency of deadly snakebites.

From the time our ancestors began to walk upright, the threat from snakes has come largely from the ground.  But accompanying this new posture were eyes that were farther away from the ground and perhaps less effective at detecting well-camouflaged snakes.  Those who happened to detect such snakes and point to share attention to them would have helped save others’ lives; those who responded most quickly and automatically would have been helped even more.

I link declarative pointing with social relationships.  Think about this: we don’t point when we’re alone.  Interestingly, declarative pointing is also closely linked with language, another skill done in a social context.  For instance, the extent of infants’ involvement in declarative pointing (both their own and their mothers’) predicts the extent of vocabulary development when they become toddlers.  People with autism don’t point declaratively nor do they have well developed language skills.

Gestures in general are often argued to have been a precursor to language.  Is it possible that declarative pointing as a specific gesture helped facilitate the evolution of language?  If so, then snakes could have led the way.