Time for another evolutionary tune-up?...

     What is the big human brain for?  About five hundred thousand years ago, the cranial capacity of our hominid ancestors' skulls doubled in size from 600 cubic centimeters to its present 1,200 cubic centimeters.  The fashionable explanation for all this extra brain is to enable us to make tools and weapons;  you have to be really smart to deal instrumentally with the physical world.  The British theoretical psychologist Nick Humphrey has presented an alternative:  the big brain is a social problem solver, not a physical problem solver.   As I converse with my students, how do I solve the problem of saying something that Marge will think is funny, that won't offend Tom, and that will persuade Derek that he is wrong without rubbing his nose in it?  These are extremely complicated problems - problems that computers, which can design weapons and tools in a trice, cannot solve.  But humans can and do solve social problems, every hour of the day.  The massive prefrontal cortex that we have is continually using its billions of connections to simulate social possibilities and then to choose the optimal course of action.  So the big brain is a relationship simulation machine, and has been selected by evolution for exactly the function of designing and carrying out harmonious but effective human relationships.

-Martin E. P. Seligman,  Flourish:  A Visionary New Understanding of Happiness and Well-being