If evolution is completely indifferent to morality (indeed, it doesn't care that it doesn't even care) then why has it gone on produce creatures (us at least) that do!
Because helping others is beneficial to your own survival. Humans with a sense of empathy are more likely to survive than humans without one. Having survived they go on to make more humans with a sense of empathy. 2 million yrs later almost everyone has a tendency to be empathetic.