Evil is the absence of good... Really?

A source in 1528 stated - 'For the one rotton apple lytell and lytell putrifieth an wholeheap'

Sometime in the 1940's this phrase became 'One rotten apple can spoil the barrel'.

It's an interesting phrase with depth never quite understood by logic - rationally speaking the majority of anything always takes the lead. If nine people voted yes at an ellection and one voted no, the candidate with the majority vote would win, and it would be a landslide victory with a 90% majority.

However if nine apples are in good condition, and one is spoiled... the spoiled one will slowly rot the others.

A reasonable question is why don't the good apples influence the bad one? There are nine of them and there is only one of it...

Well, the rotton apple has something the good ones do not - it used to be good. You see, apples don't grow rotton - they are good until something happens to them - whether that is an environmental factor, an insect or human it needn't matter, the point is, something caused them to change from being 'good' to 'rotten' apples.

So is it possible that the same theory applies to good and evil? St Augustine famously quotes 'For what is that which we call evil but the absence of good?' but is it the absence of good that causes evil or is good a stage that leads to evil?

Assuming evil occurs when good becomes influenced by fear - a perfectly good person can become evil due to envy, jealousy competition etc (fear of replacement)... this is natural, and it complies with laws of individualistic survival - becoming evil and scheming can and has in many cases been an excellent way to get rid of a potential threat. But is being good (when evil is, theoretically speaking a stronger instinct) a natural act?

Is it as natural to become good after being evil as it is to become evil after having been good?