The profound benefits of altruism in modern society are self-evident. However, the potential hurtful aspects of altruism have gone largely unrecognized in scientific inquiry. This is despite the fact that virtually all forms of altruism are associated with tradeoffs-some of enormous importance and sensitivity-and notwithstanding that examples of pathologies of altruism abound. Presented here are the mechanistic bases and potential ramifications of pathological altruism, that is, altruism in which attempts to promote the welfare of others instead result in unanticipated harm. A basic conceptual approach toward the quantification of altruism bias is presented. Guardian systems and their over arching importance in the evolution of cooperation are also discussed. Concepts of pathological altruism, altruism bias, and guardian systems may help open many new, potentially useful lines of inquiry and provide a framework to begin moving toward a more mature, scientifically informed understanding of altruism and cooperative behavior.Reality must take precedence over public relations, for nature cannot be fooled.-Richard Feynman