Good question
where are it's roots
psychologist will have a wide explanation. I believe that values and principles are different in everybody . And the definition of good and bad is more than a perception

We define "Evil" so it exists because we say it does. If you look at the animal kingdom, just about any trait humans exhibit is also shared by one other animal. "Human nature" contains the evil, and it is a direct result from evolution.

According to the Bible, God created it.

Isaiah 45:7 I form the light, and create darkness: I make peace, and create evil: I the LORD do all these things.

Because evil people exist.

Evil itself is nto always culturally universal. Some aspects are, but much of evil is defined by superstition and religious influences, which have no factual basis.

What most humans fail to realize is that humans are animals, with animal instincts and survival strategies, just like any other animal. Most evil comes out of our survival instincts, although they may no longer be appropriate to modern cultures and societies. For the mos tpart rational thought can keep our more destructive instincts at bay, but old survival instincts are just stronger in some peopel than they are in others.

As an example, the quyest for power most likely arose out of instinct to lead and prove themselves as "worthy mates" and those attracted to the powerful are attracted because a pwerful mate would better insure the survival of offspring. While for the person in power it would mean a wide choice of mates and often many mating opportunities. The wuest for power often will make person commit all sorts of "evil" acts.

Thus, our animal instincts to insure survival often translate into evil deeds, but we all have these instincts to some extent. Evolution does not make moral judgements, but only leans towards the best strategies towards survival of a species.

So, evil exists as a residue of our evolutionary past. I do not believe that we, as a species, will be rid of "evil" anywhere in the foreseeable future because those instincts that spawn "evil" behavior has been hard wired into us, in order for us to survive as a species. You can't undo or overcome million sof years of evolution in just a few thousand years. At least, it is unlikely.

Evil does not exist in and of itself. It is the impact of decisions and actions that is sometimes evil. Any time that one chooses to act in a manner which harms people and/or the environment, he is acting in an evil manner.

Evil is a catalyst used to accelerate the efficiency of the meaning and purpose of life. It's not the only catalyst but it is one of the most effective ones.

It doesn’t. Evil is a value judgement based upon varying ethical systems. It has no ontological significance.

Because you touched yourself and made Jesus cry. (What? That's what I was told when I was a kid.)

If evil didnt exist, neither would religion