Women’s attractiveness judgments of self-resembling faces change across the menstrual cycle Lisa M. DeBruine a, * , Benedict C. Jones b , David I. Perrett a a University of St Andrews, School of Psychology, St Andrews, Scotland, KY16 9AJ, UK b University of Aberdeen, School of Psychology, Aberdeen, Scotland, AB24 2UB, UK Received 6 October 2004; revised 22 November 2004; accepted 22 November 2004 Available online 25 January 2005 Abstract Two lines of reasoning predict that women’s preferences for people exhibiting cues to kinship will be lower in the follicular phase than in the luteal phase of the menstrual cycle. Women may avoid kinship cues during the follicular phase when they are most fertile due to the costs of inbreeding. Alternatively, women may seek kinship cues during the luteal phase as a byproduct of the benefits of associating with kin during pregnancy, which is also characterized by high progesterone. We find that preferences for facial resemblance, a putative kinship cue, follow this predicted pattern and are positively correlated with estimated progesterone levels based on cycle day. Neither estimated estrogen levels nor conception risk predicted preferences for self-resemblance, and the cyclic shift was stronger for preferences for female faces than male faces. These findings lead to the possibility that this cyclic change in preference for self-resemblance may be a byproduct of a hormonal mechanism for increasing affiliative behavior toward kin during pregnancy rather than a mechanism for preventing inbreeding during fertile periods. D 2004 Elsevier Inc. All rights reserved. Keywords: Menstrual cycle; Kin recognition; Face preferences; Progesterone; Estrogen; Conception risk Introduction Women’s preferences for masculine male faces (Johnston et al., 2001; Penton-Voak et al., 1999), faces with cues associated with apparent health (Jones, in press), the body odor of symmetric men (Gangestad and Thornhill, 1998), the body odor of men with immunocompetent genotypes (Thornhill et al., 2003), and masculine behavioral displays (Gangestad et al., 2004) have all been shown to change across the menstrual cycle. While traits such as masculinity and symmetry that are thought to be associated with indirect benefits (i.e., those that reflect good genetic quality) are preferred in the follicular phase when women are most fertile, traits such as current health and diverse genes for immune system strength that are thought to be associated with direct benefits (i.e., non-heritable benefits) are preferred in the luteal phase and also during pregnancy (Jones, in press). Cues of kinship can signal both increased direct benefits in the form of altruism from family members and decreased indirect benefits in the form of inbreeding depression. Major histocompatibility complex (MHC) similarity is one poten- tial cue of kinship. Manning et al. (1992) reported that pregnant female mice prefer to nest with others who share their MHC odor signature. Women who use oral contra- ceptives, which increase progesterone to levels similar to pregnancy and the luteal phase, have been shown to prefer MHC similarity more than women with natural cycles (Wedekind et al., 1995). Results regarding MHC prefer- ences suggest that other cues of kinship, such as facial resemblance, may also be preferred when women’s hormo- nal profile is similar to that of pregnancy. In addition, the costs of inbreeding are highest when women are most fertile, which could cause preferences for cues of kinship to be lowest in the follicular phase. The genetic costs of 0018-506X/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2004.11.006 * Corresponding author. E-mail addresses: lisa@debruine.info (L.M. DeBruine)8 ben.jones@abdn.ac.uk (B.C. Jones), dp@st-andrews.ac.uk (D.I. Perrett). URLs: www.debruine.info, www.abdn.ac.uk/~psy411, www.perceptionlab.com. Hormones and Behavior 47 (2005) 379 – 383 www.elsevier.com/locate/yhbeh