Within populations of social animals, altruism, or acts of behavior that are disadvantageous to one individual while benefiting other group members has evolved. This notion seems to be contradictory to evolutionary thought, due to the fact that an organism's fitness and success is defined by its ability to pass genes on to the next generation. According to E. Fehr, in the article, "The Nature of Human Altruism", the evolution of altruism can be accounted for when kin selection and inclusive fitness are taken into account; meaning reproductive success is not just dependent on the number of offspring an individual produces, but also the number of offspring that related individuals produce. Outside of familial relationships altruism is also seen, but in a different manner typically defined by the prisoner's dilemma, theorized by John Nash. The prisoner's dilemma serves to define cooperation and defecting with and against individuals driven by incentive, or in Nash's proposed case, years in jail. In evolutionary terms, the best strategy to use for the prisoner's dilemma is tit-for-tat. In the tit-for-tat strategy, an individual should cooperate as long others are cooperating, and not defect until another individual defects against them. At their core, complex social interactions are driven by the need to distinguish sincere cooperation and defection.

Brune details that theory of mind has been traced back to primates, but it is not observed to the extent that it is in the modern human. The emergence of this unique trait is perhaps where the divergence of the modern human begins, along with our acquisition of language. Humans use metaphors and imply much of what we say. Phrases such as, "You know what I mean?" are not uncommon and are direct results of the sophistication of the human theory of mind. Failure to understand another's intentions and emotions can yield inappropriate social responses and are often associated with human mental conditions such as autism, schizophrenia, bipolar disorder, some forms of dementia, and psychopathy. This is especially true for autism spectrum disorders, where social disconnect is evident, but non-social intelligence can be preserved or even in some cases augmented, such as in the case of a savant. The need for social intelligence surrounding theory of mind is a possible answer to the question as to why morality has evolved as a part of human behavior.

মানষের সামাজিক বুদ্ধিমত্তা (Human social intelligence)
বিরক্তি
শাস্তি সমস্যা (The punishment problems)
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