An Updated Theoretical Framework for Human Sexual Selection: from Ecology, Genetics, and Life History to Extended Phenotypes

Sexual selection typically centers on bodily and psychological traits. Non-bodily traits ranging from housing and vehicles through art to social media can, however, influence sexual selection even in absence of the phenotype proper. The theoretical framework of human sexual selection is updated in this article by unifying four theoretical approaches and conceptualizing non-bodily traits as extended phenotypic traits.

Methods

Existing research is synthesized with extended phenotype theory, life history theory, and behavioral ecology. To test population-level hypotheses arising from the review, ecological and demographic data on 122 countries are analyzed with multiple linear regression modelling.

Results

A four-factor model of intelligence, adolescent fertility, population density, and atmospheric cold demands predicts 64% of global variation in economic complexity in 1995 and 72% of the variation in 2016.

Conclusions

The evolutionary pathways of extended phenotypes frequently undergo a categorical broadening from providing functional benefits to carrying signalling value. Extended phenotypes require investments in skills and bioenergetic resources, but they can improve survival in high latitudes, facilitate the extraction of resources from the environment, and substantially influence sexual selection outcomes. Bioenergetic investments in extended phenotypes create individual- and population-level tradeoffs with competing life history processes, exemplified here as a global tradeoff between adolescent fertility and economic complexity. The merits of the present model include a more systematic classification of sexual traits, a clearer articulation of their evolutionary-developmental hierarchy, and an analysis of ecological, genetic, and psychological mechanisms that modulate the flow of energy into extended phenotypes and cultural innovations.

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Notes

Inherited wealth may be an exception. In a limited number of cases, the causal succession from a phenotype to behavior to extended phenotypes can potentially skip the intermediate step behavior.

A possible exception may be fat tissue metabolized via excessive energy intake or muscle tissue growth stimulated by adaptations to physical work or exercise (Camera et al. 2016; Wells 2006).

Equatorial distance is a proxy of climate: it correlates significantly (r = .90) with daily minimum temperature (IJzerman et al. 2017) and cold demands (r = .88, as described below).

See Roth and Pravosudov (2009), Vincze (2016), and especially Fristoe et al. (2017), for similar results in bird species, as well as a discussion on direction of causality, which suggests that, in birds, it was brain expansion that led to the colonization of variable habitats rather than colonization of variable habitats leading to brain expansion.

Brussels was chosen as a proxy for Europe’s central point for the present purposes since it is located between Europe’s geographical centre (Suchowola, Poland) and financial centre (London, UK) and constitutes the administrative centre of the European Union.

Spearman’s rank correlation coefficient was used because of non-normal distribution of data for the variable coldest month.

References

Acknowledgements

This work was supported by the Otto A. Malm foundation, The University of Auckland Doctoral Scholarship, and the Emil Aaltonen Young Researcher Grant. The author is grateful for Brian Boyd’s and Quentin Atkinson’s meticulous criticism, Markus J. Rantala’s guidance, and for Oliver Sheehan, Ania Grant, and Patrick Neilands for their valuable comments on earlier drafts. The author wishes to thank the University of Auckland Language, Culture and Cognition group for several thoughtful discussions on the topic. The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Author information

Authors and Affiliations

  1. English, Drama and Writing Studies, University of Auckland, Auckland, 1010, New Zealand Severi Luoto
  2. School of Psychology, University of Auckland, Auckland, 1010, New Zealand Severi Luoto
  1. Severi Luoto