Hormonal regulation of women’s prosocial, but not sexual, responses to kinship cues Short Title Hormonal regulation of responses to kinship cues Authors

Women’s affiliative behavior towards kin and responses to facial cues of kinship (self-resemblance) both change as a function of their hormonal status. Such hormone-mediated changes might serve to (1) avoid inbreeding during peak fertility and/or (2) increase kin affiliation during pregnancy. The first hypothesis predicts that responses to kinship cues will be most negative during hormonal states characteristic of high fertility (i.e., when estradiol-toprogesterone ratio is high). The second hypothesis predicts that responses to kinship cues will be most positive during hormonal states characteristic of pregnancy (i.e., when progesterone is high). We used a longitudinal design (N = 176) to investigate possible relationships between women’s responses to self-resembling faces and their measured salivary hormone levels. Women’s preferences for self-resembling male faces were not related to estradiol-toprogesterone ratio. However, preferences for self-resembling female faces were positively related to progesterone (and negatively to estradiol). These findings do not support the inbreeding-avoidance hypothesis, but do support the proposal that women's hormonal status influences attitudes to kin because of benefits associated with increased kin affiliation during pregnancy. Significance statement Biological theories predict that kinship cues have opposite effects on sexual and prosocial responses. Two hypotheses exist to explain how these differential responses could be modulated by hormonal status in women: (1) sexual responses decrease when fertility is high, and (2) prosocial responses increase during pregnancy. We used a longitudinal design to test these hypotheses by investigating the effects of hormonal profiles linked to fertility and pregnancy on women's responses to kinship cues. Our analyses show no evidence that responses to kinship cues track changes in women's fertility, instead suggesting that women show stronger preferences for female kin when raised progesterone prepares the body for pregnancy. not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/192054 doi: bioRxiv preprint first posted online Sep. 27, 2017;