From Camille Parmesan, biologist, quoted 04-23-06 in the Austin American-Statesman:

People don't realize that humans evolved right smack dab in the middle of nature--that we're really not adapted to urban life. We have these millions of years of evolution that have trained our psyche to need green grass and trees and interactions. We need nature, psychologically. When you go out into nature, the first thing that happens is it slows you down...The level of people on Prevacid and Prozac in urban areas is a testament, I think, to the fact that we're fooling ourselves into thinking we can live in a high-stress, high-paced environment and be OK. We can't.