Posted on April 7, 2008

‘Ruthlessness Gene’ Discovered

Michael Hopkin, Nature News (London), April 4, 2008

Could a gene be partly responsible for the behaviour of some of the world’s most infamous dictators?

Selfish dictators may owe their behaviour partly to their genes, according to a study that claims to have found a genetic link to ruthlessness. The study might help to explain the money-grabbing tendencies of those with a Machiavellian streak—from national dictators down to ‘little Hitlers’ found in workplaces the world over.

Researchers at the Hebrew University in Jerusalem found a link between a gene called AVPR1a and ruthless behaviour in an economic exercise called the ‘Dictator Game’. The exercise allows players to behave selflessly, or like money-grabbing dictators such as former Zaire President Mobutu, who plundered the mineral wealth of his country to become one of the world’s richest men while its citizens suffered in poverty.

The researchers don’t know the mechanism by which the gene influences behaviour. It may mean that for some, the old adage that “it is better to give than to receive” simply isn’t true, says team leader Richard Ebstein. The reward centres in those brains may derive less pleasure from altruistic acts, he suggests, perhaps causing them to behave more selfishly.

Prosocial hormone

Ebstein and his colleagues decided to look at AVPR1a because it is known to produce receptors in the brain that detect vasopressin, a hormone involved in altruism and ‘prosocial’ behaviour. Studies of prairie voles have previously shown that this hormone is important for binding together these rodents’ tight-knit social groups.

Ebstein’s team wondered whether differences in how this receptor is expressed in the human brain may make different people more or less likely to behave generously.

To find out, they tested DNA samples from more than 200 student volunteers, before asking the students to play the dictator game (volunteers were not told the name of the game, lest it influence their behaviour). Students were divided into two groups: ‘dictators’ and ‘receivers’ (called ‘A’ and ‘B’ to the participants). Each dictator was told that they would receive 50 shekels (worth about US$14), but were free to share as much or as little of this with a receiver, whom they would never have to meet. The receiver’s fortunes thus depended entirely on the dictator’s generosity.

About 18% of all dictators kept all of the money, Ebstein and his colleagues report in the journal Genes, Brain and Behavior 1. About one-third split the money down the middle, and a generous 6% gave the whole lot away.

Long and short

There was no connection between the participants’ gender and their behaviour, the team reports. But there was a link to the length of the AVPR1a gene: people were more likely to behave selfishly the shorter their version of this gene.

It isn’t clear how the length of AVPR1a affects vasopressin receptors: it is thought that rather than controlling the number of receptors, it may control where in the brain the receptors are distributed. Ebstein suggests the vasopressin receptors in the brains of people with short AVPR1a may be distributed in such a way to make them less likely to feel rewarded by the act of giving.

Though the mechanism is unclear, Ebstein says, he is fairly sure that selfish, greedy dictatorship has a genetic component. It would be easier to confirm this if history’s infamous dictators conveniently had living identical twins, he says, so we could see if they were just as ruthless as each other.

Keen players

Researchers should nevertheless be careful about using the relatively blunt tool of the Dictator Game to draw conclusions about human generosity, says Nicholas Bardsley at the University of Southampton, UK, who studies such games.

His research suggests that players who routinely give money away as Dictators are also perfectly happy to steal money off other players in games that involve taking rather than giving. This suggests that the apparently more altruistic players in Ebstein’s game may in fact be motivated by a desire simply to engage fully with the game, perhaps just because they feel that that is what’s expected of them.

If that is true, then apparently ruthless dictators may be motivated not by out-and-out greed but by a simple lack of social skills, which leaves them unable to sense what’s expected of them.

That certainly fits with the image of a naïve yet arrogant dictator with no sense of the inappropriateness of his actions and attitudes. Such figures have cropped up with surprising regularity throughout history, all the way from the emperors of Rome, through to Napoleon Bonaparte, Benito Mussolini, Saddam Hussein or Robert Mugabe, now tenaciously clinging to power in the face of uncertain electoral results.


1. Knafo, A. et al. Genes Brain Behav. 7, 266-275 (2008)

[Editor’s Note: “Individual Differences in Allocation of Funds in the Dictator Game Associated With Length of the Arginine Vasopressin 1a Receptor RS3 Promoter Region and Correlation Between RS3 Length and Hippocampal mRNA,” by A. Knafo, et al can be read on-line as an HTML document here. or as a PDF file here.]

* A. Knafo††Psychology Department, Hebrew University,

* S. Israel††Psychology Department, Hebrew University,

* A. Darvasi‡‡The Alexander Silberman Institute of Life Sciences, Faculty of Science, Hebrew University,

* R. Bachner-Melman††Psychology Department, Hebrew University,

* F. Uzefovsky††Psychology Department, Hebrew University,

* L. Cohen§§School of Education, Hebrew University,

* E. Feldman††Psychology Department, Hebrew University,

* E. Lerer¶¶Department of Neurobiology, Hebrew University,

* E. Laiba****Human Genetics, Hebrew University,

* Y. Raz††††Brain and Behavioral Sciences, Hebrew University,

* L. Nemanov‡‡‡‡S. Herzog Memorial Hospital, Jerusalem, Israel,

* I. Gritsenko‡‡‡‡S. Herzog Memorial Hospital, Jerusalem, Israel,

* C. Dina§§§§Genomics and Molecular Physiology of Metabolic Diseases, Centre National de la Recherche Scientifique, Lille, France,

* G. Agam¶¶,***¶¶Stanley Research Center and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev***Mental Health Center, Beer-Sheva, Israel,

* B. Dean††††††Rebecca L. Cooper Research Laboratories, Mental Health Research Institute of Victoria, Victoria, Australia,

* G. Bornstein††Psychology Department, Hebrew University and

* R. P. Ebstein*,†,‡‡†Psychology Department, Hebrew University‡‡S. Herzog Memorial Hospital, Jerusalem, Israel

†Psychology Department, Hebrew University, ‡The Alexander Silberman Institute of Life Sciences, Faculty of Science, Hebrew University, §School of Education, Hebrew University, ¶Department of Neurobiology, Hebrew University, **Human Genetics, Hebrew University, ††Brain and Behavioral Sciences, Hebrew University and ‡‡S. Herzog Memorial Hospital, Jerusalem, Israel, and §§Genomics and Molecular Physiology of Metabolic Diseases, Centre National de la Recherche Scientifique, Lille, France, ¶¶Stanley Research Center and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev and ***Mental Health Center, Beer-Sheva, Israel, and †††Rebecca L. Cooper Research Laboratories, Mental Health Research Institute of Victoria, Victoria, Australia

*R. P. Ebstein, Scheinfeld Center of Human Genetics for the Social Sciences, Department of Psychology, Hebrew University (S. Herzog Memorial Hospital), Jerusalem 91905, Israel. E-mail: [email protected]


Human altruism is a widespread phenomenon that puzzled evolutionary biologists since Darwin. Economic games illustrate human altruism by showing that behavior deviates from economic predictions of profit maximization. A game that most plainly shows this altruistic tendency is the Dictator Game. We hypothesized that human altruistic behavior is to some extent hardwired and that a likely candidate that may contribute to individual differences in altruistic behavior is the arginine vasopressin 1a (AVPR1a) receptor that in some mammals such as the vole has a profound impact on affiliative behaviors. In the current investigation, 203 male and female university students played an online version of the Dictator Game, for real money payoffs. All subjects and their parents were genotyped for AVPR1a RS1 and RS3 promoter-region repeat polymorphisms. Parents did not participate in online game playing. As variation in the length of a repetitive element in the vole AVPR1a promoter region is associated with differences in social behavior, we examined the relationship between RS1 and RS3 repeat length (base pairs) and allocation sums. Participants with short versions (308—325 bp) of the AVPR1a RS3 repeat allocated significantly (likelihood ratio = 14.75, P = 0.001, df = 2) fewer shekels to the ‘other’ than participants with long versions (327—343 bp). We also implemented a family-based association test, UNPHASED, to confirm and validate the correlation between the AVPR1a RS3 repeat and monetary allocations in the dictator game. Dictator game allocations were significantly associated with the RS3 repeat (global P value: likelihood ratio É’2 = 11.73, df = 4, P = 0.019). The association between the AVPR1a RS3 repeat and altruism was also confirmed using two self-report scales (the Bardi—Schwartz Universalism and Benevolence Value-expressive Behavior scales). RS3 long alleles were associated with higher scores on both measures. Finally, long AVPR1a RS3 repeats were associated with higher AVPR1a human post-mortem hippocampal messenger RNA levels than short RS3 repeats (one-way analysis of variance (ANOVA): F = 15.04, P = 0.001, df = 14) suggesting a functional molecular genetic basis for the observation that participants with the long RS3 repeats allocate more money than participants with the short repeats. This is the first investigation showing that a common human polymorphism, with antecedents in lower mammals, contributes to decision making in an economic game. The finding that the same gene contributing to social bonding in lower animals also appears to operate similarly in human behavior suggests a common evolutionary mechanism.