Volunteers who had inherited two copies of the “long” variant of 5-HTTLPR – a gene that controls transport of the mood-affecting neurotransmitter serotonin – showed clear avoidance of negative images, such as fierce animals, and a clear preference for positive ones, such as puppies. People with this variant combination are dubbed “LL” carriers…

Earlier studies had revealed a tendency for negativity and anxiety among individuals with at least one short variant of the gene, but the study is the first to reveal an optimistic streak in LL individuals.