Asking which single motive explains cooperation is the wrong question.

Evidence

In a modern state, people are motivated by some version or degree of each of the sorts of motivations that have been distinguished, and their actions are often overdetermined, quite often by all four. The right question to ask, at this level of generality, is not which of these simple models could be made to do all the work, but rather what combinations of such motivations make sense. — Diego Gambetta, Trust - Making and Breaking Cooperative…, 230