Whether you see life as a glass half-empty or half-full may depend on a single, hormone-delivery gene, scientists in Britain reported this week.

Some folks, in other words, are likely hardwired for happiness while others are genetically gluttons for gloom, they suggested in a study published in Britain’s Proceedings of the Royal Society B.

Earlier research had already established that the gene known as 5-HTTLPR plays a key role in determining how the neurotransmitter serotonin functions within the brain.

Serotonin, a hormone, transmits chemical messages between nerve cells, and has been closely linked to mood. Several anti-depressant drugs regulate serotonin levels.

Scientists had also identified three variants of the gene. Two so-called “short” alleles, or variants, were linked to a higher risk of depression and suicide attempts.

Unlike the third “long” allele, they were also thought to trigger an exaggerated neurochemical response to stressful situations.

A trio of researchers from the University of Essex in Britain led by Elaine Fox decided to find out if people with different variants were more or less drawn to or repelled by both distressing and pleasing situations.

Individually, 97 participants were shown a series of slides, each containing a pair of images drawn from a psychological tool called the International Affective Picture Set.

The images were divided into three categories: negative ones designed to inspire fear or stress such as a menacing spider or person on the verge of committing suicide, erotic or pleasant ones, and neutral ones. The two pictures on each slide were drawn from different groups.

The 16 participants who had the long variant of the 5-HTTLPR gene “showed a marked avoidance of negative material alongside a vigilance for positive material,” the researchers found.

They paid close attention to the pretty pictures, in other words, and screened out the frightening ones.

By contrast, the short allele groups showed opposite preferences, though not as strongly.

“The results indicated that a genetically driven tendency to look on the bright side of life is a core cognitive mechanism underlying resilience to general life stress,” the study concludes.

The absence of this “protective bias,” they said, was probably linked to a greater vulnerability to mood disorders and anxiety, as indicated in earlier studies.