Interdisciplinary Bio Central SYNOPSIS Evidence of Sexual Selection for Evening Orientation in Human Males: A Cross Cultural Study in Italy and Sri Lanka

Previous research has established the existence of individual differences with regards to in-dividuals ’ optimum time of well-functioning; specifically in terms of being either morning or evening oriented. An association has also emerged between being more evening, as op-posed to morning, oriented and having a greater number of sexual partners. The aim of the present study was to investigate whether “eveningness ” in males is an evolved sexually dimorphic trait consistent across different cultures. A sample of 179 male Sri Lankan men residing in two different cultural and economic settings, Italy and Sri Lanka, were adminis-tered the Morningness-Eveningness Questionnaire (MEQ) followed by assessing their sexual behavior history. The results robustly portrayed a highly significant main effect of MEQ types highlighting the twofold sexual success enjoyed by the evening individuals in both regional locations. Morning oriented individuals, showed a stronger preference for going out and partying than evening-types, suggesting that the higher mating success of eve-ning types is not due to their different lifestyles allowing more opportunities to encounter females. However, evening types exhibited a preference for flirtatious behaviors in the later part of the day. Shoulder-to-hip and handgrip strength, as measures of testosterone lev