Problem of good and evil for an atheist

[everythingafter]

Whether you like it or not. There ARE things which are absolutely evil and things which are absolutely good.
I know most atheists atempt to discredit this idea (There is a huge problem if there is such thing).

So what is one example of something absolutely evil?
Killing a baby, an innocent baby for any reason is evil. (please dont derail this thread with attacking the Bible)

If you think killing a baby is ever justified, I think it is safe to say, that you are sick and perveted.

Some cultures did practice killing babies, however, we would call them 'immoral'.

Since we are the only creature on this planet, who has the ability to do evil and good and not just to respond to external stimuli. This notion of good and evil had to come from somewhere.
Evolutionarily speaking why should I care if a child was killed in Africa?
There is no natural explanation for the concept of good and evil. So where did it come from?
I personally think it came from a cosmological battle between good and evil, although I cant conclude and prove that it, it explains things much better than anything else.

I think all we need to do to be able to show that objective morality can exist without a god (or other unknown) to insert it is to find examples of other species that experience things like empathy and altruism. This would be a sort of morality hard-wired in by natural selection, as it's more advantageous for some animals to work together and operate inside a certain social and moral framework for the betterment of the whole. Scientists have even recorded moral actions between different species.

Here are two links to that end: Animals can tell right from wrong and The moral status of animals. This would, if true, jettison the notion that we are the only moral creatures on earth.

One could argue that certain actions are not in a person's best interests no matter what culture or time period in which they live, but these "certain actions" can change relative to the time and place. Of course, I don't know that I can think of a culture which would openly allow stealing belongs, for instance (Save some anarchic state with no established law and no government whatsoever. Even then, within certain groups, certain actions would get you in trouble, stealing among them). There were cultures shrouded in slavery, human sacrifice and the like, but stealing seems to be one case that brings is frowned upon no matter what time period we might consider. I digress. The point is that cultures in all times and places seem to recognize the need for certain rules and guidelines by which societies can function. The recognition of a need for social guidelines and examples elsewhere in the animal kingdom seem to be the keys if we are to argue for any kind of objective morality without an external force inserting it. Of course, either way, like all questions of this nature, inserting a god to explain something explains nothing at all.