In the UK and Japan, both men and women prefer somewhat feminised opposite-sex faces, especially when choosing a long-term partner. Such faces are perceived as more honest, caring, and sensitive; traits that may be associated with successful male parental investment. By contrast, women prefer less feminised faces for short-term relationships and when they are near ovulation. As genetic quality may be associated with facial masculinity, women may trade-off cues between genetic quality and paternal investment in potential partners. No analogous trade-off has been suggested to influence men’s preferences, as both attributions of prosociality and potential cues to biological quality are associated with facial femininity in female faces.
Ecological and cultural factors may influence the balance of trade-offs leading to populational differences in preferences. We predicted that Jamaican women would prefer more masculine faces than British women do because parasite load is higher in Jamaica, medical care less common (historically and currently), and male parental investment less pronounced. Male preferences, however, were predicted to vary less cross-culturally, as no trade-off has been identified in female facial characteristics. We constructed masculinised and feminised digital male and female face stimuli of three populations (Jamaican, Japanese, and British) and presented them to men and women in Jamaica and in Britain. The results demonstrated that Jamaican women preferred more masculine male faces than their British counterparts did. Jamaican men tended to prefer more masculine female faces than did British men did, but this effect was complicated by an interaction suggesting that more feminised faces were preferred within culture.
And from the discussion section:
Cultures will evolve differently in different ecological environments, and preferences for cues to good genes or paternal investment may become selected for at a cultural level following increases in reproductive success that they offer in varying environments, current or historical. In addition, differences in parasite load and/or male parental investment have existed for ample time to generate some genetic differences between populations.
(Populational differences in attractiveness judgements of male and female faces: Comparing British and Jamaican samples. 2004. Evolution and Human Behavior, Volume 25, Issue 6, Pages 355-370 I. Penton-Voak, A. Jacobson, R. Trivers.)