A noted anthropologist explains how our sense of ethics has changed over the course of human evolution.

Darwin's inner voice -- Living the virtuous life -- Of altruism and free riders -- Knowing our immediate predecessors -- Resurrecting some venerable ancestors -- A natural Garden of Eden -- The positive side of social selection -- Learning morals across the generations -- Work of the moral majority -- Pleistocene ups, downs, and crashes -- Testing the selection-by-reputation hypothesis -- The evolution of morals -- Epilogue: humanity's moral future.