Does a serotonin gene variant shape moral attitudes and choices?
People carrying two short copies of a serotonin transporter gene variant showed weaker implicit moral attitudes and were less willing to accept harming someone even when that harm was unavoidable.
Source
The Multifaceted Effects of Serotonin Transporter Polymorphism (5-HTTLPR) on Anxiety, Implicit Moral Attitudes, and Harmful Behaviors
Study at a glance
- Design
- Cross-sectional — Genotyped Han Chinese adults from cheek swabs and compared S/S, L/S and L/L groups on justice sensitivity, a moral IAT, moral dilemmas and state anxiety.
- N
- N=114 · 114 genotyped adults (L/L 13, L/S 39, S/S 62), drawn from a larger project that evaluated 567 adults.
- Population
- Right-handed Han Chinese adults from the general population in Taiwan, screened for major psychiatric illness.
- Outcome
- Implicit moral attitude (IAT D score), permissibility ratings for personal, impersonal and non-moral dilemmas, justice sensitivity, state anxiety.
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
The researchers genotyped 114 adults for the 5-HTTLPR serotonin transporter polymorphism and grouped them as having two long, one of each, or two short versions. Participants completed a justice sensitivity questionnaire, an anxiety inventory, an Implicit Association Test pairing animated moral and immoral actions with positive and negative words, and a set of moral dilemmas including impersonal, personal-avoidable and personal-unavoidable harm.
What they found
Genotype groups did not differ in justice sensitivity, but implicit moral attitude scores were lower for people with two short copies than for those with two long copies, falling by about 0.117 per extra short copy. Short-short carriers were also less willing to endorse harm in personal dilemmas where the victim's harm was inevitable, with willingness dropping about 9.27% per short copy; genotype did not matter for the other dilemma types. State anxiety related to harm permissibility in opposite directions depending on the dilemma type.
The limits
What it doesn't show
The long-long group was very small (13 people), which the authors flag as a reason for replication. Many outcomes were tested and several effects were marginal; the dilemma effect became non-significant in a multivariate test controlling for age and gender. Candidate-gene associations in small samples often fail to replicate, the sample is one ethnic group, and the design cannot show that the gene causes the moral differences rather than being linked through unmeasured factors.
Key terms
- 5-HTTLPR
- A length variation (short or long) in the promoter of the serotonin transporter gene that alters how much serotonin is taken back into neurons.
- Implicit Association Test (IAT)
- A reaction-time task measuring how easily people pair categories (here moral or immoral actions) with positive or negative words.
- D score
- The standardised IAT effect: the difference in reaction times between incongruent and congruent blocks divided by their pooled standard deviation.
- Personal versus impersonal dilemma
- Personal dilemmas involve harming someone through direct physical contact; impersonal ones cause harm indirectly, such as by flipping a switch.
- Differential susceptibility hypothesis
- The idea that some genetic variants make people more sensitive to their environment, for better or worse.
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Quiz yourself
How were participants grouped for analysis?
Common questions
What does 'inevitable harm' mean in these dilemmas?
The victim would be harmed or die anyway, so the question is whether it is acceptable to be the one who causes it to save others.
Does this show a 'morality gene'?
No. It shows a small, partly marginal association in one modest sample; genotype explained only a small share of variance, and such findings need replication in larger samples.
Was anxiety simply explaining the gene effect?
The authors report that genotype remained significant after controlling for state anxiety and implicit attitude scores in a combined model.
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