Abstract
How sexual selection maintains variation in attractive traits remains a complex problem in evolutionary biology (Kokko et al. 2006). Humans provide an additional challenge to testing sexual selection theories on morphology as many features of the human face and body can be altered, accentuated or extended culturally. Luoto (2018) tackles this additional layer of complexity by integrating theories spanning phenotypic plasticity, life history, behavioral ecology and sexual selection to discuss human extended phenotypes. A cross-national study using data on intelligence, population density, climate and economic complexity from 122 countries revealed that countries with more variable climates and greater population densities had greater economic complexity, while countries with higher parasite stress had lower economic complexity. A strong negative relationship was also reported between earlier age at first reproduction and economic complexity, which Luoto suggests represents life history trade-offs between energetic investment in extended phenotypes and reproduction. Luoto then outlines a research program for testing how sexual selection has shaped human extended phenotypes with a focus on their role in men’s mating success. While this contribution represents an important advance in human behavioral ecology, some of the shortcomings of the past literature on sexual selection and human morphology are echoed. Here I outline some of these issues so that researchers may avoid their pitfalls when testing how sexual selection has shaped extended phenotypes.