Original Paper

Archives of Sexual Behavior

, Volume 40, Issue 3, pp 495-503

First online:

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

  • Doug P. VanderLaanAffiliated withDepartment of Psychology, University of Lethbridge Email author 
  • , Paul L. VaseyAffiliated withDepartment of Psychology, University of Lethbridge

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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.


Birth order Maternal immune hypothesis Fecundity Sexual orientation Samoa Fa’afafine