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Male Sexual Orientation in Independent Samoa: Evidence for Fraternal Birth Order and Maternal Fecundity Effects

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Abstract

In Western cultures, male androphiles tend to have greater numbers of older brothers than male gynephiles (i.e., the fraternal birth order effect). In the non-Western nation of Independent Samoa, androphilic males (known locally as fa’afafine) have been shown to have greater numbers of older brothers, older sisters, and younger brothers (Vasey & VanderLaan, 2007). It is unclear, however, whether the observed older brother effect, in the context of the additional sibling category effects, represented a genuine fraternal birth order effect or was simply associated with elevated maternal fecundity. To differentiate between these two possibilities, this study employed a larger, independent replication sample of fa’afafine and gynephilic males from Independent Samoa. Fa’afafine had greater numbers of older brothers and sisters. The replication sample and the sample from Vasey and VanderLaan were then combined, facilitating a comparison that showed the older brother effect was significantly greater in magnitude than the older sister effect. These results suggest that fraternal birth order and maternal fecundity effects both exist in Samoa. The existence of these effects cross-culturally is discussed in the context of biological theories for the development of male androphilia.

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Notes

  1. Within the context of the alternative explanation provided by Vasey and VanderLaan (2007), the Samoan population sex ratio corresponds to the equation: \( 1.0 9 = r_{\text{f}} s_{\text{f}} x + s_{\text{g}} ( 1- x), \) where 1.09 is the Samoan population sex ratio; r f is the reproductive rate of women who reproduce like the mothers of fa’afafine (i.e., greater number of children) relative to women who reproduce like the mothers of gynephilic males; s f is the offspring sex ratio of women who reproduce like the mothers of fa’afafine (i.e., expected offspring sex ratio); s g is the offspring sex ratio of women who reproduce like the mothers of gynephilic males (i.e., lower than expected offspring sex ratio); x is the proportion of reproductive women in the Samoan population who reproduce like the mothers of fa’afafine. As an illustration, estimating the equation’s parameters from descriptive statistics derived from the combined sample in the current study yields r f = 1.3, s f = 1.09, and s g = 0.89. Solving the equation to find the value of x shows that x = 0.38, which corresponds to an estimate of 38% of Samoan reproductive women who reproduce like the mothers of fa’afafine.

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Acknowledgments

The authors wish to thank Scott Allen, Resitara Apa, Ray Blanchard, Nancy Bartlett, Anthony Bogaert, Peniamina Tolovaa Fagai, Vester Fido Collins, Liulauulu Faaleolea Ah Fook, Vaasatia Poloma Komiti, Anita Latai, Martin Lalumière, Tyrone Laurenson, Gaualofa Matalavea, Nella Tavita-Levy, Sergio Pellis, David Pocock, Palanitina Toelupe, Trisha Tuiloma, Avalogo Togi A. Tunupopo, John Vokey, the Kuka family of Savai’i, the National University of Samoa, the Samoan AIDS Foundation, the National University of Samoa, the Government of Samoa, the Editor, and one anonymous referee. We are grateful to all of the individuals who agreed to participate in our study. We extend special thanks to Alatina Ioelu without whose help this study would not have been possible. Various stages of this research were supported by the University of Lethbridge, by a NSERC Canada Graduate Scholarship-D3 and a Sigma Xi, Grant in Aid of Research, to DPV as well as by a NSERC of Canada Discovery Grant to PLV.

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  1. Department of Psychology, University of Lethbridge, Lethbridge, AB, T1K 3M4, Canada

    Doug P. VanderLaan & Paul L. Vasey

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  1. Doug P. VanderLaan
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Correspondence to Doug P. VanderLaan.

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VanderLaan, D.P., Vasey, P.L. Male Sexual Orientation in Independent Samoa: Evidence for Fraternal Birth Order and Maternal Fecundity Effects. Arch Sex Behav 40, 495–503 (2011). https://doi.org/10.1007/s10508-009-9576-5

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