There really is no such thing as good or evil. Societal morality is subjective and has changed over time. Speaking more practically for your question, (and assuming evil = causing pain and good = helping people) I do not think humanity has a firm disposition to "mostly do good" or "mostly do bad. " There is plenty of hardship, Violence, And hurting people; but at the same time plenty of love, Generosity, And beauty. There's a ton of variance and granularity on behavior, And not all of humanity even agrees on good and bad behaviors. So yeah, Humans don't really have a natural good or evil disposition.
Every man, Woman, And child is fallen and in need of a savior. It is only through Jesus we can become good. Our impulses are brash, Rude, And unnecessary. But it reveals a lot about anyone person who thirsts for righteousness and casts aside their old self in pursuit of love, Fairness, And equality.
The way we originally learned to express the idea of good and bad was through our emotions. For example, Murder does not make any one happy. Most people naturally have empathy and guilt, So when that person kills someone else, The feel these negative emotions, And dubbed killing as bad. And luckily most people can agree with the idea that killing is bad, And that's how we formed most laws. But of course there are some gaps in the way evolution formed our brains. Often times we don't help people because of the laws. We help people because it makes us feel good. And that's why big companies can destroy things. They likely feel some guilt, But they get greedy, And because the brain naturally looks for shortcuts, They do not consider the consequences.