What purpose does one have to do anything to assist another human if it does not directly benefit one? Our lives are short (sometimes), why should we even consider doing things which do not directly help ourselves? Why do we feel better about ourselves when we help others? Survival of the fittest says we should abandon everyone else to ensure our own survival and procreation. Why do we and animals alike have the need to ensure the survival of our species instead of ensuring the survival of ourselves or our immediate kin.

You seem to be raising a couple of puzzles here. One is how it has come about that human beings are sometimes motivated to help strangers, given that we might have expected evolution to produce beings concerned to promote the survival only of themselves and their kin. One immediate answer to this question is that, despite what some fanatical sociobiologists say, you can't explain everything about human behaviour as it is now merely by reference to our evolutionary history -- even if you allow in cultural as well as biological evolution. Evolution made it possible for impartial benevolence to develop, but it didn't necessitate it. Its emergence -- where it has emerged -- is to be understood primarily in terms of history rather than biology. The second puzzle is why we *should* help others even when doing so doesn't benefit us. Many people have believed egoism -- the view that the only reason we have to do anything is grounded in the promotion of our own well-being. Philosophy has so far failed to...

If science (i.e. evolutionary psychology) can explain why I have the morality I do, does that mean morality is subjective? If what I believe about morality is just a product of my evolution and my upbringing, can I still expect other people to live up to my principles even though they may have had a different upbringing? What about myself? Can I still hold myself to my own standards or am I being deceived by my evolution into thinking it would be wrong to do so?

It might be helpful to follow a strand of British empiricism and to think about 'morality' as a social phenomenon, involving various 'sanctions' such as blame, guilt, shame, and so on. (So in that respect it is rather like law, though the sanctions there are somewhat different.) Your worry is that some moral principle you accept -- that it's wrong to cause serious suffering merely for fun, say -- has emerged only because of the evolutionary advantage conferred on groups which accept something like that principle. So it seems quite contingent which principles we come to believe -- as you imply, in different circumstances we might accept different principles. But, to pick up Alex's point, we have the capacity to stand back from our 'morality' and assess whether we have independent reason to accept its principles. In which case, if you believe there is a reason not to cause suffering for fun, you may think that this justifies the moral principle which forbids it (as it would also justify a law forbidding it).