Every man must decide whether he will walk in the light of creative altruism or the darkness of destructive selfi shness. This is the judgment. Life's most persistent and urgent question is, What are you doing for others?As a neurobiologist, I was somewhat surprised, but also thrilled, to receive an invitation to Oakland University's Evolution of Morality conference. I was surprised because I work with rats. Although I think very highly of rats, I also recognize reality. Morality is a stretch for members of the Rodentia order. It may even be a stretch for monkeys, but I will leave that question for Sarah Brosnan and other primatologists. On the other hand, my surprise was incomplete ("somewhat surprised") because for the past several years, my work has focused on pro-social behavior, also known in less stilted language as helping, among rats.Why study helping in rats? The answer is simple. Rats don't have religion or culture; adult rats don't teach rat pups to follow the Golden Rule . Therefore, a fi nding that rats help is evidence that helping may be an evolutionarily conserved behavior. Simply put, if rats help another in distress, then maybe at least part of what motivates us humans to help is similar to what motivates rats to help. Maybe the Golden Rule is not our motivation for helping. Maybe we help because of a biological inheritance that we share with rats and other mammals. In this chapter, I will make the argument that affective communication drives pro-social behavior in mammals, including rats and humans alike.I will not make the argument that pro-social behavior is the same as moral behavior. In fact, past this introductory section, I will not discuss morality. However, I will advance the idea that helping greases the wheels of social groups, facilitating social