27 May 2009

The altruism gene

A gene has been found that affects the propensity for good deeds
Alexander Markov, "Elements"Many aspects of social behavior in animals and humans are regulated by the neuropeptides oxytocin and vasopressin.

Israeli geneticists have found that some variations in the nucleotide sequence of the OXTR gene encoding the oxytocin receptor are directly related to the tendency of people to do good deeds to the detriment of personal gain. The discovery was another step in understanding the hereditary foundations of altruistic behavior.

The influence of oxytocin and vasopressin on the social behavior of animals and people "Elements" have been told repeatedly. In particular, it has been shown that in humans, pernasal administration of oxytocin increases trustfulness and generosity (see: Genes control behavior, and behavior – genes, "Elements", 12.11.2008). On the other hand, the twin analysis showed that these character traits are partly hereditary (see: Credulity and gratitude – hereditary signs, "Elements", 07.03.2008). This suggested that certain variants (alleles) of genes associated with the synthesis of oxytocin or with its perception by brain neurons may influence people's tendency to trust others and share valuable resources with them (for example, money). However, until now, specific variations of "oxytocin" genes with such an effect have not been detected.

This gap was filled by Israeli geneticists. In an article published in the journal PLoS ONE, they reported that they were able to find a link between some allelic variants of the OXTR gene and the tendency of people to show disinterested altruism. The OXTR gene encodes the oxytocin receptor, a protein produced by some brain cells and responsible for their susceptibility to oxytocin.

Earlier, the same authors did similar work with the gene of the vasopressin receptor AVPR1a. It turned out that there is a direct connection between some variations in the nucleotide sequence of the regulatory regions of this gene and the willingness of people to share money with a stranger. We mentioned this study in the article "Genes control behavior, and behavior is controlled by genes."

However, it would be naive to assume that AVPR1a is the only gene influencing these traits. Specialists studying the genetics of behavior know well that this almost never happens. Complex behavioral traits usually depend on multiple genes. At the same time, we must not forget about the important role of the environment, education, and training: no one denies their influence, but in many cases it is not absolute, and genetics also contributes to the development of the human personality (see: Z. A. Zorina, I. I. Poletaeva, Zh. I. Reznikova. Fundamentals of ethology and genetics of behavior).

The study involved two groups of subjects: the first consisted of 203 students of both sexes, the second – of 98 adult women.

To determine the propensity for altruism, two standard tests were used, which are sometimes incorrectly called "games". The first test is called "dictator" (see Dictator game). Two people participate in this test, but only one of them performs active actions (makes decisions), and the second is absolutely passive. In this case, there was actually no second participant at all, but the subjects did not know about it. Each participant was told that he was "playing" with another person unknown to him, and the experimenters guaranteed complete anonymity. That is, the subjects were not afraid of the partner's revenge and did not count on his gratitude. The subject received a small amount of money (50 shekels) and had to distribute it between himself and an invisible partner at his discretion. He could safely keep all the money for himself – and this would be the only right decision from the point of view of game theory.

However, it is well known that many human actions cannot be adequately explained using game theory, that is, from the standpoint of personal gain (Henrich et al., 2005. "Economic man" in cross-cultural perspective: behavioral experiments in 15 small-scale societies). As practice shows, most people in this situation still share with a partner. The "game" ends here. The money was real, how much money the subject kept for himself, so much he took with him. The amount donated to a non-existent partner remained with the experimenters.

In the second test (SVO test; see: Social Value Orientations), the subject was asked to make a series of economic decisions on the division of money. In each case, it was necessary to choose one of three options for the section. The options could be, for example, as follows: 1) take 500 conventional monetary units for yourself, do not give anything to the partner; 2) 500 for yourself and 500 for the partner; 3) 550 for yourself, 300 for the partner. In this case, the choice of the first option indicates an "irrational" (from the point of view of game theory) desire to mess with a partner, the third – about the usual "healthy egoism", the choice of the second option is an act of altruism (and the incentive to choose the second option may also be the desire for equality, see: Altruism in children is associated with the desire for equality, "Elements, 04.09.2008). Based on the totality of the decisions taken, it is possible to assess the degree of "prosociality" of the subject, that is, his tendency to take care of the interests of the partner, including to the detriment of his personal interests. In this test, the money was also real: after testing, the units were transferred to cash, and the subject received his share in full.

The test results were then compared with the results of genetic analysis.

In the non-coding (presumably regulatory) regions of the OXTR gene, there are several so-called single nucleotide polymorphisms, or "snips" (single nucleotide polimorphisms, SNP). Most of the OXTR gene is the same in all people (this is true for all other genes), but for some nucleotides, different versions of the gene may differ. It is these nucleotides, which may be different in different people, that are called "snips".

In all subjects of the first group, the allelic state of 15 snips in non-coding regions of the OXTR gene was determined. In 8 cases out of 15, a relationship was found between which nucleotide stands in a given position in the OXTR gene and the tendency to altruism, which was revealed in two tests. Some snips affect altruism only in men, others – only in women, and others – in both sexes. The most significant correlation with altruism was found in three snips, one of which (its symbol – rs1042778) is located in the promoter region of the gene, the other two are in the intron (non–coding insert).

Then the study was repeated on the second group of subjects. This time, only three snips were tested, the importance of which was established in the previous experience, and only one of the two tests was used – the Dictator game. Adult women in this game behaved in general much more altruistic than students. The most significant correlation with altruism was found in snip rs1042778. People who have the nucleotide G in this polymorphic position are more willing to share money with strangers than those who have the nucleotide T. So, women from the second group with the genotypes GG and GT gave an average of 25 shekels to their partner in the Dictator game, and carriers of the TT genotype – only 18.5.

The frequency of the allele T, which correlates with greed, among the participants of the experiment was 29%; the frequency of the "generous" allele G, respectively, 71%.

Thus, the study showed that the propensity for altruistic actions depends on the genes of not only vasopressin, but also oxytocin receptors. Since the identified snips are not in the coding, but in the regulatory regions of genes, it can be concluded that kindness does not depend on the structure of the receptors themselves, but on how the activity of genes encoding these receptors is regulated in certain brain cells. This activity ultimately determines how many receptors will be on the membrane of neurons, and this, in turn, determines the degree of sensitivity of neurons to oxytocin and vasopressin.

So if now pharmacologists want to create the notorious "pills for greed" that exist only in jokes so far, then they already have as many as two good "therapeutic targets" (this is what specific biochemical processes or genes are called, acting on which one or another defect can be corrected or the disease cured). The development of new medicines usually begins with the search for such "targets".

Source: Salomon Israel et al. The Oxytocin Receptor (OXTR) Contributes to Prosocial Fund Allocations in the Dictator Game and the Social Value Orientations Task // PLoS ONE. 2009. V. 4(5): e5535.

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