i've actually thought about this quite a lot before. personally, i feel that good and evil are not entirly seperate entities, of which hold sway over the happens of the mundane (or even the other way around), but rather manifest appellations which are defined by are social moralities (of which religion and law are taken into account, but that's a whole different discussion). if you think about it, what is truly evil? is murder? animals kill without so much of a thought ot regret. avarice? (from the saying that 'avarice is the root of all evil') no one in the history of the world has even publicly stated, I AM EVIL. All have swarn to the greater good. Hitler, Napolean, who only conquered to quench his own horendous appitite and the French still revere his as a hero, Stalin, etc are all examples, to much varying degrees. while many believe that this isnt the case, and that humans are inbued with an inherent quality to be either good or evil, eg. look at early Chinese philosophers such as Confucius and Mencius, who thought humans are born 'good', and Xun-zi, who thought humans would indellibly look out for themselves first (hence being evil).
one thing i keep going back to that i havent quite put my finger on, is Xun-zi's idea that humans look out for themselves first. i dont know if this is the case, or if its even evil. Adam Smith, in 18th or maybe 19th century england argued that self-interest is what makes markets work, and hence good (tho many socialists and communists would say that this is capitalism, hence evil)). also, countless happenstances throughout history have shown against this where one has sacrificed self-interest for the greater good of many. i'm sure i dont need to list any.
i still feel that when it comes to human nature, its a mixed bag. that we are the ones who decide the nature of good and evil, and that we are the ones who determine our own fate.
-just a few thoughts, and sorry if this was long, unorganized, and essayish... most people dont want to talk about philosophy with me because i dont stop ;)