Brooks, R. C. | Search bioRxiv

bioRxiv2020

Sex and Power: sexual dimorphism in trait variability and its eco-evolutionary and statistical implications

Biomedical and clinical sciences are experiencing a renewed interest in the fact that males and females differ in many anatomic, physiological, and behavioral traits. Sex differences in trait variability, however, are yet to receive similar recognition. In medical science, mammalian females are assumed to have higher trait variability due to estrous cycles (the estrus-mediated variability hypothesis); historically in biomedical research, females have been excluded for this reason. Contrastingly, evolutionary theory and associated data support the greater male variability hypothesis. Here, we test these competing hypotheses in 218 traits measured in >26,900 mice, using meta-analysis methods. Neither hypothesis could universally explain patterns in trait variability. Sex-bias in variability was trait-dependent. While greater male variability was found in morphological traits, females were much more variable in immunological traits. Sex-specific variability has eco-evolutionary ramifications including sex-dependent responses to climate change, as well as statistical implications including power analysis considering sex difference in variance.

evolutionary biology↗

bioRxiv2019

Gendered Fitness Interests: A Method Partitioning the Effects of Family Composition on Socio-Political Attitudes and Behaviors

Whereas most people are biologically either male or female, their genetic interests are almost never aligned with just their own sex. Drawing on the evolutionary theory of inclusive fitness gained through relatives, we partition the effects of kin on fitness into those that derive from female versus male relatives. We argue that the balance of these female- and male-derived effects, which we call Gendered Fitness Interests (GFI), might influence human behavior, especially the adoption of socio-political attitudes that have a gendered dimension. Our proposal builds on observations that individual socio-political views covary with the sex of their children or the numbers of relatives of each sex. Further, it is consistent with the relatively small average differences between womens and mens socio-political positions. We outline a method for partitioning GFI, and use simulation models to explore some of its properties. We then show that (1) the GFI component of womens and mens socio-political attitudes will converge, on average, with age. (2) The contributions of both descendent and non-descendent kin lead to considerable variation in GFI. (3) When men have longer average reproductive lifespans than women, GFI can show small male-biases. (4) Paternity uncertainty reduces the variation in GFI between individuals, and (5) Large family sizes are associated with more variation among individuals in GFI. Our proposal provides a framework for the study of the effects of kin on traits and attitudes with a gendered dimension. In this respect, it may prove generally useful in resolving the complex origins of gendered behavior.

evolutionary biology↗