Man's true nature is one that cannot be labeled with "good" or "evil". Both are placeholders for a concept. It's a dangerous over-simplification to believe that some people are innately "good" while others are innately "evil" or "bad". Human nature is infinitely more complex than this.

There is a degree of truth behind the idea that we all want what's best for ourselves, and that we'll go great lengths to get it. However, this doesn't automatically translate to savagery. We have evolved behaviors that increase our chances of survival and reproduction. When in a stable and safe environment with enough food in our bellies, having a biology of morality sustains our place in the community of humans who help ensure our biological imperatives. In highly stressful, resource poor environments, we'll step on whoever is in front of us if it helps us survive. But, what's best for us may not be best for others, which is when the idea of good and evil gets tossed around.

The conflicts in the world are not based on good and evil, they are simply two groups with opposing opinions. "Good" and "evil" are terms created to praise or condemn another. Our concepts of each are always established by the authority in power. Stanley Milgram developed an ingenious research procedure to demonstrate the extent to which situational forces could overwhelm individual will to resist. His unexpected finding of extremely high rates of compliance to the demands of an authority figure to continue shocking an innocent victim to the maximum possible level revealed that ordinary American citizens could so easily be led to engage in electrocuting a nice stranger, as the Nazis had been led to murder Jews. It is perfectly possible for an alternate version of our race where killing and enslaving millions can be called good and noble, if Hitler had won the war. 

When two animals are fighting, is one good and the other evil? No, they are simply two opposing ideas, and at the end of the day, neither good nor evil exists in human nature. They are manmade concepts created to condemn or praise people, opposites that allow you to know the existence of the other extreme. It is how we measure the acts of men. There are no conflicting forces locked in a cosmic struggle for your soul. It is a choice we make, not a force controlling us.