A sense for justice

Hans-Werner Bierhoff (in a recent ZEIT interview) believes that our ability to recognise a punishment as fair/just or not fair/just depends on social norms. The ultimate driving force to sense justice, however, seems to be an inborn trait. I even believe in a QTL – a quantitative trait that can clearly defined and even mapped some time to distinct genetic variants.
Monkeys reject unequal pay (scienceblog:doi:10.1038/nature01963:) in the famous Brosnan study – why should humans do?
More details may be found at tit-for-tat.