Look at me while having sex! Eye-to-eye contact affects homosexual behaviour in bonobo females

In humans, eye-to-eye contact (EEC) or mutual gazing is a reflexive predisposition occurring in intimate contexts. We investigated the role of EEC during bonobo socio-sexual contacts. Females engage in homosexual ventro-ventral, genito-genital rubbing (VVGGR) during which they embrace each other while rubbing part of their vulvae and, sometimes, clitoris. VVGGR facilitates conflict resolution, anxiety reduction and social bonding. We found that EEC was negatively affected by female bonding: the more the eye contact, the weaker the social relationship. This suggests that EEC promotes an intimate contact between the more unfamiliar subjects. Moreover, VVGGRs were successfully prolonged in presence of at least one event of EEC compared to VVGGRs during which none of the partners looked towards the other or only one looked at the other's face. EEC has been probably favoured by natural selection to enhance the cohesion between bonobo females, who can gain social power through socio-sexual contacts.