Original Article
Facial resemblance between women's partners and brothers

https://doi.org/10.1016/j.evolhumbehav.2017.04.006Get rights and content

Abstract

Research on optimal outbreeding describes the greater reproductive success experienced on average by couples who are neither too closely related, nor too genetically dissimilar. How is optimal outbreeding achieved? Faces that subtly resemble family members could present useful cues to a potential reproductive partner with an optimal level of genetic dissimilarity. Here, we present the first empirical data that heterosexual women select partners who resemble their brothers. Raters ranked the facial similarity between a woman's male partner, and that woman's brother compared to foils. In a multilevel ordinal logistic regression that modeled variability in both the stimuli and the raters, there was clear evidence for perceptual similarity in facial photographs of a woman's partner and her brother. That is, although siblings themselves are sexually aversive, sibling resemblance is not. The affective responses of disgust and attraction may be calibrated to distinguish close kin from individuals with some genetic dissimilarity during partner choice.

Introduction

In selecting a partner, the most reproductively successful individuals are those that avoid partners who are too closely or too distantly related, thereby avoiding both inbreeding and outbreeding (see e.g. Edmands, 2007). Inbreeding is biologically detrimental due to the accumulation of harmful recessive genes, a reduction in useful genetic heterozygosity, the possibility of increased competitiveness between similar offspring, and a reduction in offspring variability (Bateson, 1983). Excessive outbreeding, on the other hand, may separate genes that work well together, disrupt the inheritance of traits that have been adapted to work well in the local environment, and increase the costs of altruism (Bateson, 1983, Rushton, 1989). Empirical data that support the value of intermediate relatedness (‘optimal outbreeding’) have been presented for many species, including humans. For example, a study of all known couples born in Iceland during a 165-year period found that the optimal level of relatedness in that population in terms of number of grandchildren was around the level of third or fourth cousin (Helgason, Pálsson, Guðbjartsson, Kristjánsson, & Stefánsson, 2008).

How do people avoid both inbreeding and excessive outbreeding? The avoidance of inbreeding appears to be operationalised by the Westermarck effect, whereby people are not sexually attracted to those with whom they socialise during childhood (reviewed in Rantala & Marcinkowska, 2011). An aversion to siblings as sexual partners seems to develop through maternal perinatal association and co-residence duration (De Smet et al., 2014, Lieberman, 2009, Lieberman et al., 2007). To avoid excessive outbreeding however, slight physical resemblance might provide an appropriate cue. Features found in parental faces might be one of the most useful cues to genetic similarity, particularly in the environment in which humans evolved, without frequent exposure to views of themselves in reflective surfaces. Data support this: several studies have found that people choose partners and prefer faces that resemble their parents (Bereczkei et al., 2002, Bereczkei et al., 2004, Dixson et al., 2013, Heffernan and Fraley, 2013, Jedlicka, 1980, Jedlicka, 1984, Little et al., 2003, Marcinkowska and Rantala, 2012, Perrett et al., 2002, Rantala et al., 2010, Saxton, 2016, Seki et al., 2012, Wilson and Barrett, 1987, Zei et al., 1981; see also Fraley and Marks, 2010, Rantala and Marcinkowska, 2011; but see Nojo, Ihara, Furusawa, Akamatsu, & Ishida, 2011).

However, parental appearance is an incomplete source of information. Maternal appearance provides just one point of reference. Reliance on paternal faces is potentially problematic: serial relationships in both traditional (Hill & Hurtado, 1996) and modern societies (Cherlin, 1981) mean that the father might no longer be present. In addition, the putative father is not the biological father in cases that may average around 2% of births worldwide (see Bressan & Kramer, 2015). Sibling facial features therefore could be a useful point of reference, especially given the extensive presence of siblings during an individual's childhood in historically high-fertility populations. Additionally, younger brothers are more readily detected as kin than older brothers (Lieberman et al., 2007), and thus might be the better referent for kin resemblance. Accordingly, our study used a multilevel ordinal logistic regression analysis to investigate resemblance between a woman's partner and her brother, alongside the possible moderating effects of absolute and relative age, in two separate samples.

Section snippets

Material and methods

All of the research described herein was granted ethical approval by the Northumbria University Psychology Department Ethics Committee.

Results

Rating data were modeled using multilevel ordinal logistic regression implemented in the ordinal package (Christensen, 2015) within R (http://www.R-project.org/). Using an ordinal model permitted us to model the cumulative probability of the brother and partner being ranked as 1) most similar to each other; 2) most or second most similar; and 3) most, second most or third most similar. The advantage of a multilevel model is that variability in both faces and raters can be incorporated into the

Discussion

We present clear evidence that women select partners who resemble their brothers. This is true irrespective of whether the sample is based around a student or a celebrity population. People experience strong aversion and disgust towards incest (Antfolk, Karlsson, Bäckström, & Santtila, 2012). However, identity is not the same as resemblance; the proper domain of kinship detecting mechanisms (Lieberman et al., 2007) might entail the creation of aversion to siblings themselves, and not to those

Data availability

The data associated with this research are available in the Supplementary Online Material 3.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

References (54)

  • T.K. Saxton

    Experiences during specific developmental stages influence face preferences

    Evolution and Human Behavior

    (2016)
  • T.K. Saxton et al.

    Adolescents' preferences for sexual dimorphism are influenced by relative exposure to male and female faces

    Personality and Individual Differences

    (2009)
  • J. Vukovic et al.

    Concurrent parent–child relationship quality is associated with an imprinting-like effect in children's facial preferences

    Evolution and Human Behavior

    (2015)
  • A. Alvergne et al.

    Human ability to recognize kin visually within primates

    International Journal of Primatology

    (2009)
  • T. Baguley

    Serious stats: A guide to advanced statistics for the behavioral sciences

    (2012)
  • P. Bateson

    Chapter 11: optimal outbreeding

  • T. Bereczkei et al.

    Sexual imprinting in human mate choice

    Proceedings of the Royal Society of London, Series B: Biological Sciences

    (2004)
  • P. Bressan et al.

    Human kin detection

    Wiley Interdisciplinary Reviews: Cognitive Science

    (2015)
  • A.J. Cherlin

    Marriage, divorce, remarriage: Social trends in the United States

    (1981)
  • R.H.B. Christensen

    Ordinal - Regression models for ordinal data. R package version 2015

    (2015)
  • F. Cooke et al.

    Assortative mating in lesser snow geese (Anser caerulescens)

    Behavior Genetics

    (1976)
  • F. Cooke et al.

    Mate selection and colour preferences in lesser snow geese

    Behaviour

    (1975)
  • H.R. Davidson

    A large family with patent ductus arteriosus and unusual face

    Journal of Medical Genetics

    (1993)
  • L.M. DeBruine

    Trustworthy but not lust-worthy: Context-specific effects of facial resemblance

    Proceedings of the Biological Sciences

    (2005)
  • B.J. Dixson et al.

    Do women's preferences for men's facial hair change with reproductive status?

    Behavioral Ecology

    (2013)
  • S. Edmands

    Between a rock and a hard place: Evaluating the relative risks of inbreeding and outbreeding for conservation and management

    Molecular Ecology

    (2007)
  • R.C. Fraley et al.

    Westermarck, Freud, and the incest taboo: Does familial resemblance activate sexual attraction?

    Personality and Social Psychology Bulletin

    (2010)
  • Cited by (2)

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