India, June 7 -- Dopamine, contrary to what many believe, is not about pleasure. It's an ancient molecule, whose processing machinery is conserved across mammals, birds, fish, insects; it's even in the roundworm, whose nervous system contains just 302 neurons. Five hundred million years of evolutionary persistence suggests that dopamine does something more fundamental. What is that? It motivates us. That word's Latin root, motivus, means moving or impelling; and dopamine, in a strict (and philosophical) sense, is about movement. Which is why people with very little of it - those suffering from Parkinson's, for instance - tend to be stiff and unable to move easily. More to the point, dopamine helps us decide what to move towards. Meaning, it...