People often mimic each other's facial expressions or postures without even knowing it, but new research shows that they also mimic the size of each other's pupils, which can lead to increased trust

The findings reveal that participants who mimicked the dilated pupils of a partner were more likely to trust that partner in an investment game, but only when the partner was part of the same ethnic group. According to the researchers, these findings suggest that group membership plays an important role in how we interpret pupil signals. In this study, participants were more likely to trust partners with dilated pupils when they belonged to the same group (in this case Western European descent) than when they didn't belong to the same group (for example Asian descent). "The results of the current study further confirm the important role for the human eye in what people love and fear," the researchers write. "More specifically, pupil mimicry is useful in social interactions in which extending trust and detecting untrustworthiness in others go hand in hand, and it benefits in-group interactions, survival, and prosperity."