I don't want to defend a naturalistic perspective on morals, which is unfortunately popular nowadays and leads to a lot of immorality, but there are definitely

I don't want to defend a naturalistic perspective on morals, which is unfortunately popular nowadays and leads to a lot of immorality, but there are definitely bio-logical reasons for not killing others in your group. Humans are altruistic, group-based apes whose survival depends on collaboration. Originally, this might have been small groups only. Today society is based on the collaboration between (nearly all) nations, because modern technology and labour division would break down entirely within about six weeks without massive global trade and shipping. There are also some moral principles that follow directly from factual matters, provided some very basic first assumptions are made. Theories of just resource distribution and social justice are of that kind. The principles that get things going are very basic, e.g. reciprocity, generality of moral statements, and fairness in the sense of trade/bargaining/exchange fairness get you very far. It is a myth that religion provides values, as it can be shown very easily by historical comparison that it never has. The values defended by major religions such as Christianity and Islam have changed over the centuries again and again. Modern Christian values, for instance, mostly come from the enlightenment movement and were not endorsed at all earlier. (Christianity is just an example, AFAIK this is true for all religions.) Churches and 'holy men' have always had a vested interest in selling their values as a product of their religion, though, and they are very good at selling this false story to the public.