Crosby didn't think we were better off. The Columbian Exchange has included man, and he has changed the old and new world, sometimes inadvertently, sometimes intentionally, often brutally. It is possible that he and the plants and animals he brings with him have caused the extinction of more species of life forms in the last 400 years than the usual processes of evolution might kill off in a million. The Columbian Exchange has left us with not a richer, but a more impoverished genetic pool, and we, all of life on the planet, are the less for Columbus, and the impoverishment will increase. But let's give you the last word today. Do you agree with Crosby? Are longer, healthier lives for more humans worth the sacrifice of an impoverished biosphere?