Durk Pearson & Sandy Shaw’s®
Life Extension NewsTM
Volume 16 No. 1 • January 2013


Preference for “Fairness” is Heritable:
Possible Role of Dopamine D4 Receptor Gene

We have written about “fairness” before in this newsletter. It joins other personality traits that have been identified as being at least in part inherited. “Fairness” is famously studied in experimental games like the ultimatum game where one person, the proposer, holds a sum of money (provided by the experimenters) and divides it into an amount he proposes to keep and another part of which he proposes to be given to another person; that second person may accept the split as offered or may reject it. If the deal is accepted, each person gets the amount agreed upon, but if the deal is rejected, they each get nothing. The tremendous amount of scientific interest that has developed around this game has to do with the fact that, even though being offered 20% (say) of a sum of money is a lot better than nothing, offers below 30% are usually rejected as “unfair.” There has been considerable research looking into what environmental factors and personality traits are associated with what percentage split is rejected as “unfair.” A recent paper1 has focused upon a gene that may be linked to a specific preference for “fairness.”

Fairness (equality/inequality) is something that is of considerable importance to many people, important enough that to punish somebody who makes an “unfair” offer in the ultimatum game, they are willing to forego a sum of money they are offered in the ultimatum game. In real life, the perception of fairness (or equality/inequality) is a major source of political dissension. Note the focus by many politicians on whether certain people pay their “fair” share of taxes or the remarkable statement by President Obama that he wants to increase taxes on the wealthiest Americans for “fairness,” even if it brings in less tax revenue for the government! There is a lot of subjective emotional baggage contained in the concept of “fairness.” As revealed by games such as the ultimatum game, many different factors can distinguish those who have a high tolerance for “unfair” offers as compared to those who don’t.

The recent paper mentioned above where researchers were looking for possible links between genes and tolerance for “unfair” offers identified the dopamine D4 receptor (DRD4) gene as a gene with a significant association with fairness preference. The gene comes in different variations (alleles). A highly polymorphic region in exon 3 is a 48 bp (base pair) repeat. In Caucasian populations, the most common repeat allele is the 4-repeat allele, followed by the 7-repeat allele and the 2-repeat allele. In Far Eastern groups, the 7-repeat allele is said to be extremely rare1 and is “displaced” by the 2-repeat allele as the second most common allele. The authors present evidence that the 2-repeat allele may have similar functionality as the 7-repeat allele, with association studies showing similar occurrence in attention-deficit hyperactivity disorder (ADHD).

“The DRD4 48 bp VNTR is known for contributing to individual differences in traits including novelty seeking, financial risk taking, self-report altruism, ADHD, mood, and substance abuse.”

The researchers also found that the season of birth (SoB) affected the expression of the gene. For example, non-winter born children carrying the DRD4 48 bp VNTR 7-repeat allele showed higher scores for venturesomeness. The authors interpret the interaction of season of birth and the effects on personality traits of the DRD4 48 bp VNTR polymorphism as reflecting an environmental risk factor in which individuals carrying “risk alleles” and born at certain times have a vulnerability to developing maladaptive behaviors. Season of birth would pose additional envirnomental challenges on the developing fetus that might predispose to the emergence of these behaviors. The authors note that “SoB has been associated with a wide range of behavioral traits, including suicide, schizoid-like features in non-clinical groups, impulsivity and sensation seeking, novelty seeking, self-mutilating behavior, schizophrenia, and eating attitude.”1

The different alleles of subjects playing the ultimatum game showed variations in “fairness preference.” For example, “the non-winter born male and winter-born female subjects with the 4/4 genotype tend to have a higher minimum acceptable offer than subjects with 2/2 & 2/4 genotype.”1 These subjects were more likely to reject an offer as unfair.

In another study involving 15 small societies that the authors cite, mean offers in the ultimatum game ranged from 26% to 58% with rejection rate for low offers of 20% or less ranging from zero to 100%. Hence, there is a tremendous effect of culture on the perception of “fairness,” though there was apparently no genetic analysis done in that study to distinguish the different societies and their tolerance to “unfair” offers.

References

  1. Zhong et al. Dopamine D4 receptor gene associated with fairness in ultimatum game. PLoS One 5(11):e13765 (3 Nov. 2010).

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