The female rivalry hypothesis for concealed ovulation in humans: An agent-based model

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Description: After half a century of debate and few empirical tests, there is still no consensus as to why ovulation in human females is considered concealed. The existing literature focuses largely on the potential benefits that females might have gained by concealing ovulation from males. Here, we investigate whether females might have benefitted by concealing ovulation because they avoided aggression that could potentially be inflicted upon them by other females. This hypothesis emerges from a growing body of empirical evidence suggesting that women are active, purposeful agents who engage in effective intrasexual aggression in the course of mating competition, and also that females may preferentially and selectively aggress against ovulating mating rivals. To test the predominant “male investment hypothesis” and also our “female rivalry hypothesis” for concealed ovulation, we created an agent-based model of mating behavior and paternal investment in the human ancestral environment, using theory and empirical data on human mating and reproduction in small-scale societies. We did not find strong support for the male investment hypothesis. In contrast, we did find support for the female rivalry hypothesis: When females could aggress specifically towards ovulating female rivals (not just attractive females), females who concealed ovulation had higher paternal investment and reproductive success than females who revealed ovulation. Exploring the boundary conditions, we find that the advantage of concealing ovulation holds only when (a) aggression is costly to the target and relatively low-cost to the individual, (b) aggression imposes long-lasting costs on targets (i.e., rivals heal from aggression slowly), and (c) the proportion of promiscuous males (i.e., males leaving mates rather than investing in offspring) is moderate to low. These results suggest that concealed ovulation may have been an evolutionarily-viable strategy for ancestral human females, at least in part because concealing ovulation could help females avoid costly intrasexual aggression. More generally, this work suggests that explicitly considering female-female interactions may lead to new insights into female mating behavior and reproductive physiology.


.Rmd files contain code for analysis and visualisation. .html files are knitted RMarkdown documents outlining the analyses. Data (both raw and clean) are in .csv files. Agent-based model code (for Netlogo v4 and v6) are contained in .nlogo files. Any issues, please email:


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