The extraordinary thing about exchange is that it breeds: the more of it you do, the more of it you can do. And it calls forth innovation. Which only raises another question: why did economic progress not accelerate towards an industrial revolution there and then? Why was progress so agonisingly slow for so many millennia? The answer, I suspect, lies in the fissile nature of human culture. Human beings have a deep capacity for isolationism, for fragmenting into groups that diverge from each other.
