Look closely at the very moment of creation in Michelangelo's The Creation of Adam on the ceiling of the Sistine Chapel, and you'll notice that Adam's rather limp wrist bears a striking resemblance to the human hand in the image below:
The photograph is from a 1994 article written by Daniel J. Povinelli and D. Richard Davis and published in the Journal of Comparative Psychology. What it's vividly illustrating is the difference between the relaxed postures of the human hand versus that of our closet living relative, the chimpanzee. In particular, the authors are calling your attention to how the resting state of the index finger in the human hand, but not the chimpanzee hand, is differentially extended from the other fingers. (Go on, try it yourself, no one's watching.)
According to the authors, this subtle anatomical difference, which occurred sometime after the two species last shared a common ancestor 5-7 million years ago, is at least partially responsible for the fact that pointing with one's index finger is so culturally ubiquitous.
The argument goes something like this. When young infants begin reaching for objects just out of their range, adults are most likely to respond to these reaching attempts and retrieve the item for the baby when the index finger is more prominently extended. Over time, this dynamic between the child and adult serves to further "pull out" the index finger so that it becomes a genuine pointing gesture.
Pointing is in fact more sophisticated than it looks, and there are several varieties. Typically, before 18-24 months of age, pointing is used to manipulate others' behaviours only -- if a baby drops its toy on the ground and points to it while looking at you, he's basically saying "well, what are you waiting for, give it to me!" This is called imperative pointing since it's more or less a demand. But once the child begins to conceptualise others as conversational partners who have minds that hold information, pointing becomes declarative. The 18-24 month old now uses pointing to say, "hey, look at that over there!" because he or she recognizes that you're not aware of whatever it is (the neighbour's cat in the bushes, the exorbitantly large man eating a snow cone at the park, the hot air balloon floating above the car dealership, whatever) and wants to share this interesting information with you.
Indexical pointing is no small cognitive feat; this thing we do with our hands every day belies a very substantial evolutionary achievement in human psychology. The next time you're out for a walk with your dog, for example, see what happens when you point with your index finger to something across the street. Chances are, he won't get it. There could be a hottie poodle over there wearing a sausage bikini and lounging on a fire hydrant, but he'll just stare at your finger thinking, "Yeah, and???"
(Yes, I'm aware of these findings reporting that dogs can comprehend communicative intentions in their masters' indexical points. But I'm still a skeptic, and not the only one. Who would've thought pointing would be so contentious a topic in the research world? In any event, it sounds like a good homework assignment to do with your own dog, and then report back to us about what happens.)
See also:
Kita, S. (2003). Pointing: Where language, culture, and cognition meet. Mahwah, NJ: Lawrence Erlbaum.
