People have the capacity for both evil and good. IMO, most people lean toward good. If this were not the case, I don't think we'd have lasted this long as a species.
I agree that humans have both good and evil present within themselves. I think we choose what we do with both of them. Some lean towards goo, some evil. Some can even use evil tendencies for good, or use good tendencies for evil. It's all choice.
I believe that humans are like any other animals and have a core drive towards self-preservation above all else. I think that humans are more evil than other animals...or at least have potential to be.