Hormones play evolutionarily ancient roles in social behaviour; yet the degree to which hormone systems influence human socio-emotional behaviour remains unclear. It is hypothesized that (i) hormone-associated genes linked to psychiatric conditions contribute to variation in social traits among non-clinical populations, and (ii) changes in endogenous hormone levels coordinate adaptive social behaviour with stimuli in the environment. Consistent with the first hypothesis, a vasopressin receptor polymorphism linked to autism was significantly associated with autistic-like traits in healthy individuals. Consistent with the second hypothesis, an empathy-inducing stimulus was found to mediate a trade-off in hormone levels, with oxytocin increasing and testosterone decreasing. Furthermore, a common polymorphism in the general transcription factor II-I gene, which is linked to Williams syndrome, was associated with oxytocin response to the empathy-inducing stimulus and social anxiety among healthy individuals. Together, these findings highlight the diverse ways through which hormone systems contribute to variation in human sociality
