Sexual selection favors traits that increase mating and, thus, reproductive success. Some scholars have suggested that intrasexual selection driven by contest competition has shaped human male aggression. If this is the case, one testable hypothesis is that beliefs and behavior related to male aggression should be more prevalent in societies where the intensity and strength of sexual selection is higher. Measured by factors such as (a) the presence and scope of polygyny; (b) the number of same-sex competitors relative to potential mates, and (c) the amount of effort males are available to allocate to mating. Using Bayesian item response models with imputation and data from 78 societies in the Standard Cross-Cultural Sample, we found robust support for this hypothesis when using variables related to male aggression. We ruled out some potential alternative explanations by controlling for geographic region and confounding variables such as political complexity and warfare.
Intersexual selection or mate attraction has been well studied in both evolutionary psychology and human behavioral ecology. Intrasexual selection or competition between members of the same sex for mates has been investigated much less. Of the current studies, there is still a divide in the literature as to whether intrasexual selection could have shaped human male aggression. For this reason, we tested the idea with data from a wide range of societies, the first systematic cross-cultural study to do so. Our results suggest that factors affecting the intensity of competition for mates led to the evolution of beliefs and behavior related to male aggression in small-scale human societies. This provides support for the hypothesis that intrasexual selection has been a driving force in shaping human male aggression.
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We thank Carol Ember for providing data on male mortality from war. We thank Michael Jennions and anonymous reviewers for useful feedback on an earlier version of the manuscript. We also thank Caleb Carter for assistance with computation.
Conflict of interest
The authors declare that they have no conflict of interest.
This research does not require ethics board approval as it makes use of data from the Standard Cross Cultural Sample, an open source collection of cross-cultural data from 186 cultures.
The data in this study comes from a historical and fully web-accessible database; individuals cannot be identified and as such informed consent is not applicable.
Communicated by M. Raymond
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Carter, T., Kushnick, G. Male aggressiveness as intrasexual contest competition in a cross-cultural sample. Behav Ecol Sociobiol 72, 83 (2018). https://doi.org/10.1007/s00265-018-2497-3
- Sexual selection
- Sex ratio
- Subsistence-mating tradeoff
- Human behavioral ecology