Anisogamy and the Darwin-Bateman paradigm

The Darwin-Bateman paradigm advanced as the central concept to explain the evolutionary origin of sex differences. However, debates regarding its theoretical underpinnings persist, particularly with respect to the role of anisogamy in sexual selection. The theoretical work presented by Lehtonen and Parker (2024) suggests that the initial split in gamete production rate drives sex differences in sexual selection but that any further variation in the degree of anisogamy is not expected to alter the strength of sexual selection in males and females. Here, I discuss the historical background of a recently emerged controversy and present empirical data that corroborate the theoretical predictions. Lehtonen and Parker’s contribution refines our understanding of the Darwin-Bateman paradigm by providing a broad theory for large-scale patterns of sex differences that can be observed in nature. Further understanding of how demographic and environmental factors influence sexual selection is essential to predict the vast diversity of sex differences across the tree of life, beyond the primordial impact of anisogamy.

Methods
This dataset combines information obtained from two pervious studies:

Mokos, J., Scheuring, I., Liker, A., Freckleton, R.P. & Székely, T. (2021) Degree of anisogamy is unrelated to the intensity of sexual selection. Scientific Reports, 11, 19424.

Janicke, T., Häderer, I.K., Lajeunesse, M.J. & Anthes, N. (2016) Darwinian sex roles confirmed across the animal kingdom. Science Advances, 2, e1500983.

Only the Bateman gradient data can be published here. Data on gametic investment bias (GIB) and gametic size bias (GSB) can be requested from the author of this article or from the authors of Mokos et al. (2021).