IBC 2011;3:13 • DOI: 10.4051 / ibc.2011.3.4.0013 www.ibc7.org 1 Interdisciplinary Bio Central SYNOPSIS Evidence of Sexual Selection for Evening Orientation in Human Males: A Cross Cultural Study in Italy and Sri Lanka K.G. Chandrika Gunawardane 1, *, Deborah M. Custance 1 and Davide Piffer 2 1 Department of Psychology, Goldsmiths College, London, UK 2 Department of Anthropology, University of Durham, Durham, UK Previous research has established the existence of individual differences with regards to in- dividuals’ optimum time of well-functioning; speci ically 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 signi icant 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 lirtatious behaviors in the later part of the day. Shoulder-to-hip and handgrip strength, as measures of testosterone lev- els, were not signi icantly associated with eveningness. The results are discussed in terms of sexual selection and its interplay with human cultural variation. Key Words: morning and evening types; western and non-western regions; sexually evolved trait; human mating; circadian typology; sexual selection Subject areas: General Author contribution: K.G.C.G. developed the research study by formulating the hypothesis, underlying theories and constructed the sexual behavior questionnaire, wrote the draft paper, did statistical analyses and collected the dataset; D.M.C. supervised the study and reviewed the draft paper; D.P. reviewed the inal manuscript providing important feedback. *Correspondence and requests for materials should be addressed to K.G.C.G. (chandrikag@ hotmail.co.uk). Editor: Keun Woo Lee, Gyeongsang National University, Korea Received September 14, 2011 Revised September 28, 2011 Accepted October 07, 2011 Published October 11, 2011 Citation: Chandrika Gunawardane, K.G., et al. Evidence of Sexual Selection for Evening Orientation in Human Males: A Cross Cultural Study in Italy and Sri Lanka. IBC 2011, 3:13, 1-8. doi: 10.4051/ibc.2011.3.4.0013 Competing interest: All authors declare no inancial or personal conlict that could inappropriately bias their experiments or writing. © Chandrika Gunawardane, K.G. et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by- nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access FULL REPORT IBC 2011;3:13, 1-8 • DOI: 10.4051 / ibc.2011.3.4.0013 Interdisciplinary Bio Central