From a discussion on Slashdot, the original topic was something unrelated.
I'm just wondering why, genetically speaking, it should feel so good to hear about justice being served?
(The original question was longer, but that's the gist of it)
If co-operation is beneficial for groups, co-operation by an individual will benefit the group and thereby themselves, reinforcing that behaviour in the gene pool.
If a group is largely co-operative, defecting (in the terminology of the prisoner's dilemma) may benefit you greatly and be a detriment to the group as a whole. This would be selfishness, since only you benefit.
If a group is mostly co-operative but there are occasional defectors, it is to the benefit of the group to exile or beat the living crap out of the defector, since they are harming the group - and thereby reducing the reproductive success of defectors - so this should be reinforced.
In a pre-rational species, behaviour would be reinforced by associationg good feelings with successful behaviours. This can arise without any planning if individuals start with randomly genetically coded preferences or dislikes for behaviours and are (naturally) selected for if they like beneficial behaviours.
Finally, since people generally like co-operating (even without a clear benefit to them) we can assume that it has been beneficial in our recent evolution. It should also feel good to hear about justice being served, since that is a natural pairing with enjoying co-operation.
Also, in my experience people who say that humans are inherently selfish are just pushing an agenda, probably a religious one, which says that you should submit to their benevolent control because you don't know what's best for you.
Of course this is all an extremely simplified view. There should be an equilibrium between co-operation and defection which is based on how easy it is to successfully defect. This would imply that people should enjoy gaining by defection BUT only if they are not found out and punished by the co-operators, even though they are themselves co-operative in most situations.
Then we get into gossiping, so we know who has defected in the past... but spreading false rumour then becomes a successful defective behaviour as long as you're not found out.
And there are Us vs Them issues where groups can co-operate within themselves, but still defect relative to other groups without wrecking internal co-operativeness. This tends to have a genetic basis, since co-operating with your relations at the expense of strangers increases your genes' reproductive success, even if the total result is damaging to society in general.
That last point is, I think, the largest problem with our society at the moment. Praising the defective actions of people in your in-group while refusing to co-operate with an out-group without rational cause is rife, from school sports teams all they way up to international relations. It is something that happens most often when we go with 'gut feelings' instead of reasoning, and is the natural result of fear-mongering in the media and by government.
Boy, what a rant. I hope some of that was useful.
I'm interested to know if there was anything obviously wrong with that, allowing for the fact that it's entirely unreferenced and hastily written on a random web site.