Why do we pick similar mates, or do we?

Abstract

Humans often mate with those resembling themselves, a phenomenon described as positive assortative mating (PAM). The causes of this attract broad interest, but there is little agreement on the topic. This may be because empirical studies and reviews sometimes focus on just a few explanations, often based on disciplinary conventions. This review presents an interdisciplinary conceptual framework on the causes of PAM in humans, drawing on human and non-human biology, the social sciences, and the humanities. Viewing causality holistically, we first discuss the proximate causes (i.e. the ‘how’) of PAM, considering three mechanisms: stratification, convergence and mate choice. We also outline methods to control for confounders when studying mate choice. We then discuss ultimate explanations (i.e. ‘the why’) for PAM, including adaptive and non-adaptive processes. We conclude by suggesting a focus on interdisciplinarity in future research.

A variance partitioning perspective of assortative mating: Proximate mechanisms and evolutionary implications

“…Assortative mating can evolve towards higher values when the tendency to mate assortatively is heritable and when assorted pairs have a higher fitness than pairs that do not mate assortatively ('adaptive hypothesis' cf. Versluys et al, 2021, for example, Ariyomo, & Watt, 2013Both et al, 2005;Sinn et al, 2006). These benefits can be direct (e.g.…”

“…Assortative mating within a population can also arise as a by‐product of mechanisms that have evolved for other purposes (‘non‐adaptive hypothesis’ cf. Verluys et al, 2021), such as conspecific mating (e.g. through imprinting or mechanical compatibility (see Kopp et al, 2018)), mate choice for indices of quality, dispersal (see Versluys et al, 2021), habitat choice (see Edelaar et al, 2008), phenology (e.g.…”

“…Verluys et al, 2021), such as conspecific mating (e.g. through imprinting or mechanical compatibility (see Kopp et al, 2018)), mate choice for indices of quality, dispersal (see Versluys et al, 2021), habitat choice (see Edelaar et al, 2008), phenology (e.g. Moiron et al, 2020), or plasticity.…”

“…via similar habitat choice), temporal (e.g. via similar phenological traits) or cultural segregation of phenotypes (Versluys et al, 2021), for example, because partners with similar phenotypes choose the same habitat, or occur at the same place in the same point of time, or have similar sociocultural profiles. Through this mechanism, individuals have access to a biased pool of potential partners, which results in positive assortment in spatiotemporally and culturally variable populations (e.g.…”

“…via similar habitat choice), temporal (e.g. via similar phenological traits) or cultural segregation of phenotypes (Versluys et al, 2021), for example, because partners with similar phenotypes choose the same habitat, or occur at the same place in the same point of time, or have similar sociocultural profiles.…”