I Am Fascinated By Human Behavior

I'd say we're born with it. Like other animals, it is in our best interest to cooperate and help each other. To not have that instinct is very detrimental to our survival. You can just see it in children. They start off so innocent and non-judgmental.

i think we're taught it because some people are sociopaths so obviously there are people who lack it.

And lack of compassion, is it learned? Or faulty wiring?

True, I think it is not something that can be pigeonholed. Each individual, each circumstance could have a different answer. But it is definitely interesting to ponder.

Some definitely just have faulty wiring (I think that's due to an ill-developed frontal lobe?). But I think it is more-often learned from those who are already "bad apples." In addition, some turn to bad acts because they actually think they're right or they must do it to survive. These would be people who steal because they're poor, kill a murderer who killed someone they loved and didn't want to let the law handle it, etc.

@daisthedestroyer: By saying some start bad, you're also admitting that everyone else starts off good. So I think my original thought (that evil must be taught more than good) still stands.

i never said we start off evil. we're neutral until we're taught to be good. evil-neutral-good

Studies on infants have shown that even in the youngest age, humans lean to compassion. This was evidenced by a puppet show portraying good/bad characters.
The lack of of it thereof, works backwards , and may be seen as deficient. It has advantages though, this inability for empathy.