Fine-scale variation in lip and cheek colour according to the timing of ovulation in women

Abstract

Various animal species have evolved a sexual communication system with females displaying and males discriminating information about the timing of ovulation through sexual signals. More research is now investigating the potential ovulatory signalling function of female red skin colour in human and non-human primates. However, to date, it is still challenging to draft satisfying hypotheses about the evolution and function of the female red skin colour, due to methodological discrepancies between human and non-human primate studies. The present study used a within-individual design and objective methods to analyse the relationship between fine-scale variation in cheek and lip colour (luminance and redness) and the estimated day of ovulation in 15 cycling women. I found weak evidence that intra-cycle variation in lip luminance only may be less modulated by inter-individual variation, with lips getting slightly darker around ovulation. However, day to day variation in lip luminance is likely imperceptible, meaning that lip luminance may not act as an ovulatory signal in humans. This study adds to the growing research and discussion on the role and evolution of the female red skin colour of human and non-human primates in the context of sexual signalling and mate attraction. In human and non-human primates, red skin and red ornaments are attractive for both sexes and often associated with mating and fertility. While female red skin colour can be informative about the reproductive status and thus influences mating strategies in some primate species, it is not clear if humans share with non-human primates a colourful trait of ovulation. This study shows a weak relationship between lip luminance only and the timing of ovulation. This study adds to the growing research and discussion on the role and evolution of the female red skin colour of human and non-human primates in the context of sexual signalling and mate attraction.