Human beings have always been an unfinished species, a story in the middle, a succession of families, tribes, and societies in transition to new awarenesses. Although we have always prided ourselves on our willingness to adapt to all habitats, and on our skill at prospering and making ourselves comfortable wherever we are -- in a meadow, in a desert, on the tundra, or out on the ocean -- we don't just adapt to places, or modify them in order to ease our burdens. We're the only species that over and over again has deliberately transformed our surroundings in order to stretch our capacity for understanding and provoke new accomplishments. And our growing and enhanced understanding is our most valuable, and our most vulnerable, inheritance.