Estudo de caso para alunos de microeconomia - jogo do ultimato (II) - está tudo nos genes?

A mesma edição de The Economist mencionada na postagem anterior relata os resultados de um outro experimento, realizado por pesquisadores da Stockholm School of Economics e também baseado no "jogo do ultimato", destinado a testar se o senso humano de justiça tem raízes genéticas ou culturais:
"The human sense of fairness is not rooted in culture. Rather, it is genetic—as it would have to be in order to evolve. Paradoxically, discovering this relies on the fact that not everyone possesses it to the same degree. Researchers have shown this by playing the ultimatum game with twins. They used the classic trick of neutralising the effect of upbringing and exposing that of genetics by comparing identical twins (who share all their genes) with fraternal twins (who share half). Each twin of a pair played the ultimatum game, both as proposer and as responder. A striking correlation between the average division that each member of a pair proposed and also between what they were willing to accept was found, in the case of identical twins. In other words, their senses of what was fair were similar. No such correlations were seen in the behaviour of fraternal twins".