Offspring Production among the Extended Relatives of Samoan Men and Fa'afafine

Doug P Vanderlaan,Deanna L Forrester,Lanna J Petterson,Paul L Vasey,Virginia J Vitzthum

doi:10.1371/journal.pone.0036088

Abstract

Androphilia refers to sexual attraction to adult males, whereas gynephilia refers to sexual attraction to adult females. Male androphilia is an evolutionary paradox. Its development is at least partially influenced by genetic factors, yet male androphiles exhibit lower reproductive output, thus raising the question of how genetic factors underlying its development persist. The sexual antagonism hypothesis posits that the fitness costs associated with genetic factors underlying male androphilia are offset because these same factors lead to elevated reproduction on the part of the female relatives of androphilic males. Western samples drawn from low fertility populations have yielded inconsistent results when testing this hypothesis. Some studies documented elevated reproduction among the matrilineal female kin of androphilic males, whereas others found such effects in the paternal line. Samoa is a high-fertility population in which individuals reproduce closer to their maximum capacities. This study compared the reproductive output of the paternal and maternal line grandmothers, aunts, and uncles of 86 Samoan androphilic males, known locally as fa'afafine, and 86 Samoan gynephilic males. Reproductive output was elevated in the paternal and maternal line grandmothers, but not aunts or uncles, of fa'afafine. These findings are consistent with the sexual antagonism hypothesis and suggest that male androphilia is associated with elevated reproduction among extended relatives in both the maternal and paternal line. Discussion focuses on how this study, in conjunction with the broader literature, informs various models for the evolution of male androphilia via elevated reproduction on the part of female kin.

Highlights

The manner in which male same-sex sexual orientation is publicly expressed varies cross-culturally [1]
Some studies conducted in low fertility, Western populations reported elevated offspring production among the matrilineal female kin of androphilic males [18,19,20] while others reported elevated offspring production among female paternal relatives [11,12]
The present study compared the number of children born to the paternal and maternal line grandmothers, aunts, and uncles of androphilic versus gynephilic males in Samoa, a relatively high fertility population in which individuals are more likely to reproduce closer to their maximum capacities

Summary

Introduction

The manner in which male same-sex sexual orientation is publicly expressed varies cross-culturally [1]. Discrepancies between Western studies of the familial patterning of male androphilia may, result from examining samples from low fertility populations The susceptibility of these populations to producing anomalous familial patterning raises the possibility that some subset, or possibly all, of the aforementioned Western studies on male sexual orientation and family size are inaccurate (i.e., they do not provide clear indications of the reproductive output tendencies of androphilic males’ extended relatives). As such, when constructing a participant group of gynephilic Samoan men to compare to androphilic fa’afafine, it is appropriate to use sexual attraction as a basis for inclusion, not sexual behavior This measure provides a window on sexual orientation in the absence of real-world constraints. The current study compared the reproductive output of the maternal and paternal line male and female extended relatives (i.e., grandmothers, aunts, and uncles) of Samoan fa’afafine and gynephilic males. It did so to shed light on whether male androphilia in this relatively high fertility population is associated with elevated reproduction in the maternal line, paternal line, or both

Methods

Results

Discussion