Evolution is going to give you a good sense of how the world is. Figuring out how the world should be -that is, morality- is a different matter, to be informed by (but probably not based on) what you know of evolution. That's a little like trying to make a cake using your knowledge of physics.

If you want to Sequences' answer to this question, I'd go with this post: http://lesswrong.com/lw/sm/the_meaning_of_right/ . There's also a wealth of other writing on the subject from any number of authors - don't feel compelled to limit yourself to any single author in your efforts to tackle this (or any) question. And consider the possibility that this may be a hard problem to which you may lack a perfect answer at the moment, and content yourself with incinerating terrible non-answers. You do not need to have the full answer to point out that someone else is wrong.