Why be good?

[Simon Moon]

So, given that evolution is a presupposition in most atheists belief system, then I am interested in hearing an explanation for the obvious incoherence resulting from holding simultaneously that:

1. any species that evolves does so on the basis of natural selection and survival of the fittest, and
   
2. man has evolved in a different manner such that being "good" is now more beneficial to the group/species than the dominance of the weak by the strong.
   

Thanks.

Evolution is not a presupposition to atheism. My atheism is not dependent on evolution being true. My atheism is dependent on the case for the existence of a god, as presented by theists, not meeting its burden of proof. 

Almost 80% of Christians in Europe accept evolution as being true. Because, after all, it is.

Atheism dates back thousands of years before evolutionary theory.

Humans have not evolved in a different manner. Every social species values members of its own group over others. Cooperation, kin selection , reciprocity is seen in every single social species. That is why they are classifies as a social species. 

Bonobo chimps, our closest genetic cousins, have the following behaviors: share food with other members of their group even when in short supply, protect weaker members even at risk to their own safety, adopt orphaned babies and treat them like their own, punish violent members of the group, show sadness when a member of the group dies. And much more similar behaviors. 

Doesn't the above bonobo behavior sound an awful lot like morality to you?