I've been thinking about the idea of culpability.

What is it for, exactly? Why did societies that use the concept win out over those who stuck with the default response of not assigning any particular emotional significance to a given intangible abstraction?

If I'm understanding correctly, a given person can be said to be responsible for a given event if and only if a different decision on the part of that person (at some point prior to the event) would be a necessary condition for the event to have not occurred. So, in a code of laws, statements along the lines of "When X happens, find the person responsible and punish them" act as an incentive to avoid becoming 'the person responsible,' that is, to put some effort into recognizing when a situation where your actions might lead to negative externalities, and to make the decision that won't result in someone, somewhere down the line, getting angry enough to hunt you down and burn you alive.

A person cannot be said to be culpable if they had no choice in the matter, or if they had no way of knowing the full consequences of whatever choice they did have. Recklessness is punished less severely than premeditation, and being provably, irresistably coerced into something is hardly punished at all. The causal chain must be traced back to the most recent point where it was sensitive to a conscious decision in a mind capable of considering the law, because that's the only point where distant deterrence or encouragement could have an effect.

"Ignorance is no excuse" because if it were, any halfway-competent criminal could cultivate scrupulous unawareness and be untouchable, but people think it should be an excuse because the law needs to be predictable to work. Same reason punishing someone for doing what was legal at the time doesn't make sense, except as a power-play.

So, let's say you're a tribal hominid, having just figured out all the above in one of those incommunicable, unrepeatable flashes of brilliance. How do you go about implementing it? With limited resources, you can't implement it widely enough to benefit everyone in the known world, even if you wanted to. You can't lay down a written code of laws because standardized writing hasn't even been invented yet, and you can't trust the whole tribe to carry on an oral tradition because you can barely trust half of them not to stab you in the back when you catch something unusually juicy. You can, however, trust your immediate family and/or the spear-carriers you go hunting with to cooperate with you and suffer short-term disadvantages, even when you're not looking, so long as there's a big, plausible payoff within a month (for hunters) or a few years (for family).

You offer them this: "We tell the tribe about this idea of 'responsibility,' and then, whenever someone steals from one of us, we all get together and hurt the one responsible until they've lost more than they gained by stealing. When the rest of the tribe can see that stealing from any of us is pointless, we can just leave our stuff sitting out instead of having to worry about hiding it, and then we'll have more time for hunting and grooming."

It works out well enough that soon everybody's doing the revenge thing. Causality and culpability are enough of a puzzle that specialization is necessary to do it right; the problem is, a judgement rendered by someone you don't trust is worse than useless, and the only people it's remotely safe to trust with life-changing decisions are kin.

You ever notice how corrupt police act sorta like abusive parents?