Oh I love the bamboo bicycle idea, David. So many great ideas, if only more of us were motivated toward ecological thinking. Isn't there is kind of mud-brick construction that doesn't use concrete? Perhaps a key is not trying to build permanent structures, just expect to be tearing them down and rebuilding every few years. I guess that doesn't scale, no way we'll build mega cities that way. But maybe mega cities and population sizes they house aren't desireable in the first place.