Does Narcissism Determine the Type of Faces We Find Attractive?

General background. Computer simulations suggest that sex among genetically complex organisms requires mate-choice strategies to reduce excessive genetic variance produced by out-crossing (Alvarez, 2004), while also avoiding "inbreeding depression" that might lead to an increased frequency of maladaptive recessive traits (Bovet et al., 2012). In addition, individuals would also be expected to select mates with compatible behavioural and sociocultural traits, signalled in some cases by physical appearance (e.g., sexually dimorphic male features have been linked to aggression and dominance). Consequently, mating should follow an assortative (i.e., non-random) pattern in which individuals attempt select for both sociocultural and genetic compatibility, the latter of which is usually characterised by "optimal outbreeding" involving the selection of mates that are subtly but not excessively similar to oneself. Research demonstrates a general trend toward positive assortative mating in many species, including humans and other primates.
Face shape assortment. Face shape provides a useful axis of assortment for identifying compatible partners. Genetically, facial morphology is relatively stable across the adult lifespan compared to many other physical traits, suggesting that it is a fairly reliable signal of underlying genetic characteristics, and, in humans, cross-cultural studies have linked facial morphology to specific areas of the genome. Behaviourally, human face shape is associated with a wide range of traits, including dominance, empathy, generosity, and sexual fidelity, suggesting that it also signals information about social compatibility. Current research provides evidence of positive assortment (i.e., selecting similar traits) for face shape in humans. For example, Laeng et al. (2013) showed that people find their current partner's faces more attractive when morphed with 22% of their own features. In several studies, the faces of couples were judged more similar to one another by observers than the faces of random pairs (Alvarez et al. 2004; Zajonc et al. 1987; Wong et al. 2018).
Research opportunity. There are several gaps in the literature on facial assortative mating that will be address in this project. First, studies demonstrating positive assortment for face shape have tended to focus on "global similarity" between faces, rather than the specific aspects of facial morphology (i.e., the size, shape, and configuration of specific features) that might signal compatibility. Second, most studies have used 2D facial images, which are unable to capture the morphological 3D detail of faces as they are viewed in the real world. Third, research has focussed almost exclusively on heterosexual assortative mating, despite homosexual mating occurring at a high frequency across present and historical human societies and among many other species. This is potentially guided to a large extent by non-reproductive mate-choice criteria, such as signals of social or coalitionary compatibility. Fourth, assortative mating studies have tended to focus on phenotypic assortment rather than the population genetic consequence of this process, especially with respect to trait-associated variants (Li et al., 2017). Fifth, there has been little attempt to explore assortative mating for facial morphology in other primate species, despite the importance of faces for social interactions being well-established (Ferrari et al. 2009).