Human sensitivity to fairness may have evolved along with empathy and other traits that allow individuals to cooperate, Jensen said. Groups of cooperative individuals would have competitive advantages over groups whose members didn't cooperate, he said. To get along, people need to have some degree of concern for others.
Jensen added, though, that the origins of fairness "are very speculative and debatable."
Ohio State University psychologist Sarah Boysen, who studies animal behavior, warned against over-interpreting the results. Chimps have a strong sense of justice, she said; it is just not the same as humans'.
"Deviations from their code of conduct are dealt with swiftly and succinctly, and then everybody moves on," said Boysen, who was not involved with the study. "They're more adaptive than we are -- just look at the Middle East."
In the second study, published Tuesday in the Proceedings of the National Academy of Sciences, researchers from Sweden and the United States showed that identical twins were more likely to use the same strategy in the ultimatum game, suggesting that our sense of fairness is partly shaped by genetics.
Researchers proposed 11 ways to divide $15 and asked 71 pairs of fraternal twins and 258 pairs of identical twins to record which offers they would accept or reject. Offers ranged from the entire amount to nothing.
Because identical twins share all the same genes but fraternal twins do not, the study is thought to detect genetic influences in how participants played the game while controlling for some environmental factors, such as upbringing.
Researchers looked at each set of twins to see how closely their rejection decisions matched. They found there was no correlation among fraternal twins but a 42% likelihood that identical twins would make the same choices.
The results mean that many personal economic choices, such as whether to save money or spend it, may be substantially heritable, said Wallace, who conducted the research with colleagues from Sweden's Karolinska Institutet and MIT.
However, environmental factors were still important, and relationships not shared by the twins, such as friends and jobs, had a greater influence on decisions than genetics in the study, Wallace said.
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denise.gellene@latimes.com
