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Genes affecting generosity may be found

Oct. 31, 2007
Special to World Science  

If you like easy games, you’d love this one. The rules: one play­er re­ceives some money. That play­er may then choose to give any part of it, or none, to a sec­ond play­er. The end.

It seems ab­surdly sim­ple—does­n’t the sec­ond play­er even do any­thing?—but that’s ex­actly the point. Sci­en­tists stu­dy­ing al­tru­ism, or gen­eros­ity, de­signed it to pro­vide a straight­for­ward meas­ure of a per­son’s al­tru­ism, un­tainted by con­sid­era­t­ions such as how the oth­er play­er might re­act.

Kind Heart by the Bel­gian paint­er Gus­tave Le­on­hard De­Jonghe (1829-1893), de­pict­ing a girl giv­ing mon­ey to the home­less.


In a new stu­dy, re­search­ers staged the game 203 times on­line be­tween dif­fer­ent play­ers un­aware of each oth­er’s ident­i­ties. The in­ves­ti­ga­tors an­a­lyzed the re­sults, as well as the par­ti­ci­pants’ genes. In this way they iden­ti­fied cer­tain vari­ants of a gene called AVPR1a as pos­sibly re­lat­ed to al­tru­ism.

Sci­en­tists are just be­gin­ning to find genes that may un­der­lie this en­ig­mat­ic qual­ity, which has long puz­zled bi­ol­o­gists be­cause of ques­tions over how it evolved.

The ex­pe­ri­ment pro­vided “the first ev­i­dence, to my knowl­edge, for a rela­t­ion­ship be­tween DNA vari­abil­ity and real (cost­ly) hu­man al­tru­ism,” wrote Ar­i­el Kna­fo of He­brew Un­ivers­ity in Je­ru­sa­lem, a mem­ber of the re­search team, in an e­mail. The study ap­pears in the early on­line edi­tion of the re­search jour­nal Genes, Brain and Be­hav­ior.

A study two years ago al­so linked vari­ants of anoth­er gene with al­tru­ism, though that re­search meas­ured al­tru­ism based on ques­tion­naires the par­ti­ci­pants them­selves filled out. Only the newer stu­dy—whose par­ti­ci­pants re­ceived the equiv­a­lent of $12 to keep or give as they chose—meas­ured gen­eros­ity through con­crete demon­stra­t­ions of it, Kna­fo said.

“Games rec­re­ate so­cial in­ter­ac­tions in the lab­o­r­a­to­ry us­ing real mon­ey pay­offs and thus en­gage peo­ple in ‘put your mon­ey where your mouth is’ de­ci­sions,” wrote Kna­fo and co-authors in the stu­dy. They found varia­t­ions in gen­eros­ity of up­wards of 44 per­cent in as­socia­t­ion with vari­ants in the AVPR1a gene.

The gene codes for the pro­duc­tion of a mol­e­cule, called a re­cep­tor, that lets a hor­mone known as vas­o­pres­sin act on brain cells. Vas­o­pres­sin in turn has been im­pli­cat­ed in so­cial bond­ing. The re­search­ers found great­er al­tru­ism in play­ers in which a key sec­tion of the AVPR1a gene, called its pro­mot­er, was long­er. A pro­mot­er is the re­gion of a gene that al­lows cel­lu­lar ma­chin­ery to ac­tu­ally read the gene and car­ry out its in­struc­tions. A long­er pro­mot­er can re­sult in great­er ac­ti­vity of the gene.

The study two years ago, con­ducted by a group that in­clud­ed some of the same re­search­ers in the new stu­dy, iden­ti­fied vari­ants in a gene en­cod­ing the so-called dopamine D4 re­cep­tor as af­fecting al­tru­ism. The gene plays a si­m­i­lar role for the brain chem­i­cal, or neu­ro­trans­mit­ter, dopamine as AVPR1a plays for vas­o­pres­sin. Be­cause dopamine is linked to the sense of re­ward or ex­cite­ment, re­search­ers hy­poth­e­sized that the gene might con­trib­ute to re­warding feel­ings as­sociated with help­ing oth­ers. That study ap­peared in the April 2005 is­sue of the jour­nal Mo­lec­u­lar Psy­chi­a­try.

The find­ings could help bi­ol­o­gists sort out al­tru­ism’s ev­o­lu­tion­ary histo­ry, ac­cord­ing to the sci­ent­ists. One re­mark­a­ble fact, they not­ed, is that a ver­sion of AVPR1a also exists in ro­dents called voles, where it al­so pro­motes so­cial bond­ing—sug­gest­ing al­tru­ism is root­ed in very an­cient genes. But these might have tak­en on pow­er­ful new roles dur­ing hu­man ev­o­lu­tion: ev­i­dence sug­gests many genes’ pro­mot­er re­gions be­came long­er in the line­age lead­ing to hu­mans com­pared to chimps and oth­er pri­ma­tes. 

Wheth­er such find­ings will help il­lu­mi­nate the murkier ques­tion of why great­er al­tru­ism seems to have evolved in hu­mans—as scientists have found—is harder to say. 

Ev­o­lu­tion­ary the­o­ry ex­plains the pop­u­la­t­ion­wide spread of cer­tain genes as re­sulting from the ad­van­tage those genes pro­vide. Such a sche­ma seems to have lit­tle place for genes that prompt us to hand over ad­van­tages to oth­ers. None­the­less, sim­ula­t­ions and ex­pe­ri­ments sug­gest that for var­i­ous rea­sons, some forms of al­tru­ism can evolve. As “an in­her­ent hu­man trait dis­tin­guish­ing us from all oth­er ver­te­brate species,” as Kna­fo and col­leagues wrote, it re­mains one of the most keen­ly stu­died issues in bio­lo­gy.


* * *

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References:

A. Knafo, S. Israel, A. Darvasi, R. Bachner-Melman, F. Uzefovsky, L. Cohen, E. Feldman, E. Lerer, E. Laiba, Y. Raz, L. Nemanov, I. Gritsenko, C. Dina, G. Agam, B. Dean, G. Bornstein, R.P. Ebstein, 2007. 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. Genes Brain Behav. Aug 13 [Epub ahead of print]

R. Bachner-Melman, I. Gritsenko, L. Nemanov, A.H. Zohar, C. Dina, R.P. Ebstein, 2005. Dopaminergic polymorphisms associated with self-report measures of human altruism: a fresh phenotype for the dopamine D4 receptor. Mol. Psychiatry 10, 333-5.

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If you like easy games, you’d love this one. The rules: one player receives some money. That player may then choose to give any part of it, or none, to a second player. The end. It seems absurdly simple—doesn’t the second player even do anything?—but that’s exactly the point. Scientists studying altruism, or generosity, designed it to provide a straightforward measure of a person’s altruism, untainted by considerations such as how the other player might react. In a new study, researchers staged the game 203 times online between different players unaware of each other’s identities. The investigators analyzed the results, as well as the participants’ genes. In this way they identified certain variants of a gene called AVPR1a as possibly related to altruism. Scientists are just beginning to find genes that may underlie this enigmatic quality, which has long puzzled biologists because of questions over how it evolved. The experiment provided “the first evidence, to my knowledge, for a relationship between DNA variability and real (costly) human altruism,” wrote Ariel Knafo of Hebrew University in Jerusalem, a member of the research team, in an email. The study appears in the early online edition of the research journal Genes, Brain and Behavior. A study two years ago also linked variants of another gene with altruism, though that research measured altruism based on questionnaires the participants themselves filled out. Only the newer study—whose participants received the equivalent of $12 to keep or give as they chose—measured generosity through concrete demonstrations of it, Knafo said. “Games recreate social interactions in the laboratory using real money payoffs and thus engage people in ‘put your money where your mouth is’ decisions,” wrote Knafo and co-authors in the study. They found variations in generosity of upwards of 44 percent in association with variants in the AVPR1a gene. The gene codes for the production of a molecule, called a receptor, that allows a chemical known as vasopressin to affect brain cells. Vasopressin in turn has been implicated in social bonding. The researchers found greater altruism in players in which a key section of the AVPR1a gene, called its promoter, was longer. A promoter is the region of a gene that allows cellular machinery to actually read the gene and carry out its instructions. A longer promoter can result in greater activity of the gene. The study two years ago, conducted by a group that included some of the same researchers in the new study, identified variants in a gene encoding the so-called dopamine D4 receptor as affecting altruism. The gene plays a similar role for the brain chemical, or neurotransmitter, dopamine as AVPR1a plays for vasopressin. Because dopamine is linked to the sense of reward or excitement, researchers hypothesized that the gene might contribute to rewarding feelings associated with helping others. That study appeared in the April 2005 issue of the journal Molecular Psychiatry. The findings could help biologists sort out altruism’s evolutionary history, according to the researchers. One remarkable fact, they noted, is that AVPR1a has also been found in rodents called voles, and also promotes social bonding in them—suggesting altruism is rooted in very ancient genes. But these might have taken on powerful new roles during human evolution: evidence suggests many genes’ promoter regions became longer in the lineage leading to humans compared to chimps and other primates. Whether such findings will help illuminate the murkier question of why greater altruism seems to have evolved evolved in humans, is harder to say. Evolutionary theory explains the populationwide spread of certain genes as resulting from the advantage those genes provide. Such a schema seems to have little place for genes that prompt us to hand over advantages to others. Nonetheless, simulations and experiments suggest that for various reasons, some forms of altruism can evolve. As “an inherent human trait distinguishing us from all other vertebrate species,” as Knafo and colleagues wrote, it’s sure to remain an active area of research.