Conception Risk and the Ultimatum Game: When Fertility is High, Women Demand More

Article history: Received 10 February 2016 Received in revised form 8 April 2016 Accepted 11 April 2016 Available online xxxx Evidence suggests that women become more intrasexually competitive in the fertile window of the menstrual cycle. Studies using the ultimatum game have extended this to economic decisions, finding that women in the fertile window are less generous towards and more likely to punish other women. In the present study, we used continuous estimates of conception risk to test replication of these findings in a sample of women who played the ultimatum game with same-sex partners. We found that women at higher conception risk made higher demands of their partners, indicating less inclination to cooperate and perhaps greater willingness to engage in costly punishment. Possible functions of cycle-phase shifts in intrasexual competition are discussed, and directions for future research on the psychology of cooperation are suggested. © 2016 Elsevier Ltd. All rights reserved.