The hormone oxytocin – which promotes pair bonding, maternal care, and reproductive behavior in mammals – also regulates emotions. To have effects, oxytocin must bind to its receptor.
Numerous studies have reported that persons with the nucleotide G (guanine) in a certain noncoding position of the oxytocin receptor gene tend to be more trustful, optimistic, and empathetic than persons with an A (adenine), although the underlying mechanism is poorly understood.