Here is the fifth step we should take to reach a sustainable society (click here for step one, step two, step three, and step four). Five: Rapidly expand our empathy. We're a small-group animal, trying to live in large groups. Although we no longer can associate exclusively with a clan "family" of, say, 125 relatives, most of us have a group of "pseudokin"—friends and close associates of about the same number. In both cases, we develop a sort of "we" versus "them" culture, with the "themness" increasing with physical and cultural distance. People are gradually gaining more empathy toward those others distant from us in skin color, gender, religion, class, culture or physical space, but our ability to inflict harm on them has also increased. Cultural evolution is not rapidly enough reducing this discounting by distance (caring less about situations the further away they are). The same can be said about discounting by time—not caring enough about the world we will leave to our children and our descendants in the more distant future. Can affluent people in the West learn to care enough about a starving child in Darfur to take real action to save her? If society takes step five, the answer will be "yes," and we'll be on the kind of road that could lead to a level of global cooperation that might allow a billion, perhaps three billion small-group animals to live together sustainably in relative peace. What do you think? Leave us a comment. Check back next week for the sixth step we should take toward a sustainable society. ———- Paul R. Ehrlich is Bing Professor of Population Studies and Professor of Biological Sciences at Stanford University. He is the author of hundreds of scientific papers, and numerous books including The Population Bomb and Betrayal of Science and Reason (Island Press, 1997). His latest book is The Dominant Animal: Human Evolution and the Environment, which he co-authored with his wife Anne.