> why do we have this desire to leave something around for future generations?
Evolution gave us that. Some people think that evolution is all about creating some wonderful new critter... when all it really is is a means of preserving and propogating DNA. The purpose to all life on the planet is to pass on one's DNA. Consequently, having an interest in leaving a better world for your kids is an evolutionary advantage for perpetuating your DNA.
This bothers some people. Shrug. Some people were bothered by not being the center of the universe.
"The purpose to all life on the planet is to pass on one's DNA."
All this time I've been looking up to Jesus and Mother Teresa and Pope John Paul II, but I guess they didn't do a very good job of fulfilling the "purpose" of their lives on the planet.