Sunday, April 06, 2008

'Ruthlessness Gene' Discovered

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'.

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.

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. 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.
I am curious how much difference there was between those with the shorter version of AVPR1a and those with the longer. I found the journal article, but you can only read the abstract for free, so all I found out was:
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).
I really don't know what a likelihood ratio, P, or a df mean (if any smart readers out there can explain what this means, please leave a comment).

If your genes can make you more or less altruistic based on how the brain handles vasopressin, I wonder if you will see 'altruism steroids' in the future. There is a nasal spray for oxytocin which is said to increase trust, and oxytocin and vasopressin are very similar. Will we see a nasal spray for vasopressin in the future, with prescriptions for those that are genetically deficient in altruism?

via Nature

Update: This gene is also linked to a propensity for men to skip out on women, or to have marital problems if they do tie the knot.


Paradigm said...

I don't much about statistics but p is the probability that the result is just a coincidence. So 0.001 (a tenth of a percent) is a very low chance of that.

I wonder if they took into account that the value of even 14 dollars depend on the participants financial situation.

Fat Knowledge said...

Thanks Paradigm, that is good to know.

I still wonder how much difference there was in the average amount of dollars given between the two genetic types. And, what the probability that a randomly selected "ruthlessness gene" person would give more than a random "altruistic gene" person. I guess I am looking for a mean and a standard deviation on the values.

Audacious Epigone said...

I thought a likelihood ratio was the factor for which a person with a 'symptom' was more likely than a person without it to suffer from the measured outcome. But that would mean those with the shorter versions are 15x more likely to be stingy, which seems incredibly high so I'm probably wrong.

The p-value is the chance that a result is based on randomness, not any relationship between the variables. If the p-value is less than .05, it's generally considered to be statistically significant.

DF = degrees of freedom. In this case it just means that the analysis was done on "short" vs "long" versions, not by actual length. So the 310 person and the 324 person are 'identical' in their alphabet soup gene.

Fat Knowledge said...


Thanks for the info, that is really helpful.

If you are right on likelihood ratio, I would take that to mean that if you randomly selected a short version person and a long version person and had them both play the game, the odds that the short version person would be more generous in the game would be 1/(1+14.75) = 6.3%.

Darwin said...

Genesis Biolabs is offering a mail-in test for the "ruthlessness" gene.

"We are a product not just of our genetics, but of our experiences and our choices. However, one can conceal or misrepresent ones choices and motives, but genetics do not lie. There are numerous situations where knowing if someone has the ruthless or altruistic version of AVPR1a might be useful. Before getting married, or making a business partnership, this genetic test might be appropriate. All of our politicians should probably submit to this test. "

An objective test of whether someone really has only his own interests at heart seems very valuable to me.

Fat Knowledge said...


Interesting, thanks for the link.

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