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Evolving research on the evolution of male androphilia.

Androphilia refers to sexual attraction and arousal to adult males, whereas gynephilia refers to sexual attraction and arousal to adult females. The manner in which male androphilia is expressed varies cross-culturally. Sex-gender congruent male androphiles occupy the gender role typical of their sex, behave in a relatively masculine manner, and identify as "men." In contrast, transgendered male androphiles often behave in a highly effeminate manner and identify as neither "men," nor "women." Instead, they typically identify as members of a third gender. Despite exhibiting different gender role presentations and gender identities, both forms of male androphilia share numerous biodemographic and developmental correlates, indicating that they have a common etiological basis. Male androphilia represents an evolutionary paradox because it appears to have a genetic component, yet it compromises reproduction. At the same time archaeological and cross-cultural evidence suggest that it has persisted for millennia. The ancestral form of male androphilia was likely the transgendered form. To date, only one population of transgendered male androphiles has been considered when testing hypotheses pertaining to the evolution of male androphilia: the fa'afafine of Samoa. Research indicates that the mothers, paternal grandmothers and maternal grandmothers of fa'afafine produce more offspring than those of male gynephiles, which is consistent with the Sexually Antagonistic Gene Hypothesis. However, definitive support for this hypothesis, in the form of elevated offspring production by the aunts of fa'afafine is lacking at present. Research also indicates that fa'afafine exhibit elevated avuncular tendencies and behaviour compared to women and gynephilic men, which is consistent with the Kin Selection Hypothesis. Also consistent with the Kin Selection Hypothesis is research indicating that the fa'afafine's avuncular cognition exhibits elements of adaptive design.

KEYWORDS: male androphilia, evolution, sexually antagonistic genes, kin selection, Samoa

BEYOND GAY: MALE SEXUAL ORIENTATION IN CROSS-CULTURAL PERPECTIVE

Gay men represent an increasingly visible aspect of Western culture. Consequently, regardless of their sexual orientation, it might come as a surprise to most individuals living in the West that "gay men" do not necessarily exist in other cultures. Indeed, it is not at all uncommon for individuals living in non-Western cultures to claim that "gay men" or "homosexuals" are unknown in their societies. Many of the individuals who are most vehement in making such assertions are biological males who routinely have sex with other biological males and make no secret of it.

What are we to make of such claims? Research has demonstrated that the identity categories of "gay" and "homosexual" are culturally and historically situated and, as such, do not necessarily translate to other places and times (Murray, 2000). Such categories, if they are known at all, might mean something to people in other cultures, but whatever that might be, they are not categories of personhood that those individuals draw upon when constructing personal narratives about who they are. As such, the way in which many non-Western, same-sex attracted males think about themselves and pattern their lives (sexual or otherwise) differs radically in many respects from Western gay men. Thus, when individuals from non-Western cultures say that there are no "gays" or "homosexuals" in their societies, they are not necessarily lying. Based on their understanding of what it means to be "gay" or "homosexual," no one in their societies identifies or behaves as such, and neither do they identify others members of their cultures in that way.

Given this, any attempt to undertake comparative cross-cultural research on sexual orientation must focus on the deep structure of sexual orientation that transcends differences related to how male same-sex sexual attraction is socially constructed within culturally specific contexts. The deep structure of male same-sex sexuality can be thought of as a set of traits that characterize same-sex attracted males regardless of the cultural context in which they are found. To this end, a focus on cross-culturally universal sexual feelings facilitates comparisons in a manner that culturally specific identity categories do not. As such, we employ the terms androphilia and gynephilia in our discussion of sexual orientation across cultures. Androphilia refers to sexual attraction and arousal to adult males, whereas gynephilia refers to sexual attraction and arousal to adult females. Although same-sex attracted "gay men" in Western societies differ in many dramatic ways from same-sex attracted males in a range of non-Western societies, in terms of the deep structure of sexual orientation, both can be accurately described as androphilic biological males.

HOW MALE ANDROPHILIA IS PUBLICALLY EXPRESSED VARIES CROSS-CULTURALLY

As should be evident from the discussion above, the manner in which male androphilia is publically expressed varies across cultures (Murray, 2000). This expression typically takes one of two forms, which are related to gender role enactment and gender identity. These two forms are sex-gender congruent and transgendered male androphilia. Sex-gender congruent male androphiles occupy the gender role typical of their sex, behave in a relatively masculine manner, and identify as "men." The term "sex-gender congruent" androphilia highlights the critical roles of gender role enactment and gender identity in distinguishing the two forms of male androphilia under consideration here.

Transgendered androphilic males typically behave in an effeminate manner and often identify as neither "men" nor "women," but rather, as a member of some "third" gender category. In some cultures, transgendered male androphilia is linked to particular institutionalized labour practices, which often involve specialized religious activities. This type of transgendered male androphilia has been referred to as role structured (Herdt, 1997). For example, on the Indian subcontinent, transgendered male androphiles known as hijra bestow blessings from Hindu gods and goddesses for luck and fertility at weddings and at the birth of male babies (Nanda, 1998).

Both sex-gender congruent and transgendered male androphilia may occur within a given culture, but typically one or the other tends to predominate (Whitam, 1983). For example, the sex-gender congruent form tends to be much more common in many Western cultures. In contrast, the transgendered form appears to be more common in many non-Western cultures (Murray, 2000). In places where these two forms co-exist, albeit with one predominating, the two often consider each other to be members of the same community (Whitam, 1983).

SOME CORRELATES OF MALE ANDROPHILIA REOCCUR CONSISTENTLY ACROSS DIVERSE CULTURES

Quantitative research indicates that the sex-gender congruent and transgendered forms of male androphilia share numerous developmental and biodemographic correlates that appear to be cross-culturally invariant. In terms of biodemographic correlates, when compared to gynephilic males, both sex-gender congruent and transgendered male androphiles tend to be later born among their siblings (e.g., Blanchard, 2004; VanderLaan & Vasey, 2011; Vasey & VanderLaan, 2007), have greater numbers of older biological brothers ("fraternal birth order effect (1)," e.g., Bogaert & Skorska, 2011; VanderLaan & Vasey, 2011; Vasey & VanderLaan, 2007), exhibit larger family sizes (e.g., Blanchard & Lippa, 2007; Camperio-Ciani, Corna & Capiluppi, 2004; Iemmola & Camperio Ciani, 2009; King et al. 2005; Schwartz, Kim, Kolundzija, Rieger & Sanders, 2010; VanderLaan, Forrester, Petterson & Vasey, 2012; VanderLaan & Vasey, 2011; Vasey & VanderLaan, 2007), cluster within families (e.g., Schwartz et al., 2010; VanderLaan, Forrester, Petterson & Vasey, 2013; VanderLaan, Vokey & Vasey, 2013), occur at similar prevalence rates across cultures (e.g., Smith, Rissel, Richters, Grulich & de Visser, 2003; VanderLaan, Forrester, et al" 2013; Whitam, 1983), and exhibit little or no reproductive output (e.g., King et al., 2005; Schwartz et al., 2010; Vasey, Parker & VanderLaan, 2014). In addition, the odds ratios associated with the fraternal birth order effect in various populations of sex-gender congruent and transgendered male androphiles are remarkably consistent, suggesting that the manner in which older brothers influence the development of male androphilia is constant across culturally diverse populations (e.g., Cantor, Blanchard, Paterson & Bogaert, 2002; VanderLaan & Vasey, 2011).

Prospective and retrospective cross-cultural research on early psychosocial development among transgendered and sex-gender congruent male androphiles has shown that the childhood behaviour of such males is characterized by greater levels of female-typical behaviour (e.g., nurturing play with dolls) and lower levels of male-typical behaviour (e.g., rough-and-tumble play; Bailey & Zucker, 1995; Bartlett & Vasey, 2006; Cardoso 2005, 2009; Whitam, 1983). In addition, both types of male androphiles express elevated cross-sex beliefs and wishes in childhood (e.g., "I wish I was a girl") (Bailey & Zucker, 1995; Vasey & Bartlett, 2007; Whitam, 1983). Furthermore, both sex-gender congruent and transgendered male androphiles also experience elevated traits of childhood separation anxiety (i.e., anxiety related to separation from major attachment figures such as parents; VanderLaan, Gothreau, Bartlett & Vasey, 2011; Vasey, VanderLaan, Gothreau & Bartlett, 2011; Zucker, Bradley & Lowry Sullivan, 1996), which tend to be more common among girls compared to boys (e.g., Shear, Jin, Ruscio, Walters, Kessler, 2006; VanderLaan, et al., 2011).

Even though sex-gender congruent androphilic males are relatively feminine as boys compared to their gynephilic counterparts (Bailey & Zucker, 1995), they behaviourally defeminize to varying degrees as they develop. It has been suggested that this behavioural defeminization probably occurs in response to culturally-specific gender role expectations, which hold that male-bodied individuals should behave in a masculine manner (Bailey, 2003; Rieger & Savin-Williams, 2012). In contrast, in cultures where transgendered male androphilia is the norm, feminine boys develop into feminine adult males. Consequently, adult sex-gender congruent male androphiles are relatively masculine when compared to transgendered adult male androphiles. Conversely, they are, on average, relatively feminine when compared to adult male gynephiles (Bailey, 2003; Lippa, 2005). Thus, regardless of how it is manifested, male androphilia is associated with gender atypicality in childhood and adulthood. However, the strength of this association varies with the manner in which male androphilia is publically expressed.

Taken together, these numerous, cross-culturally uniform biodemographic and developmental correlates of male androphilia indicate that sex-gender congruent and transgendered male androphilia are cultural variants of what is essentially the same phenomenon with a common biological basis. In this regard, the cross-culturally invariant biodemographic and developmental correlates described above can be thought of as part of the deep structure of male androphilia.

THE EXISTENCE OF MALE ANDROPHILIA IS AN EVOLUTIONARY PARADOX

Research indicates that male androphilia is influenced by genetic factors (e.g., Alanko, Santtila, Harlaar, Witting, Vaijonen, Jern et al., 2010; Hamer, Hu, Magnuson, Hu & Pattatucci, 1993; Langstrom, Rahman, Carlstrom, & Lichtenstein, 2010). Nevertheless, androphilic males reproduce at significantly lower rates than gynephilic males and often, they do not reproduce at all (e.g., King et al., 2005; Schwartz et al., 2010). This finding is not merely reflective of the situation among contemporary Western gay men. A lack of reproduction among androphilic males from non-Western populations has also been well documented (Vasey et al., 2014).

Since male androphilia appears to have a genetic component, but male androphiles reproduce little, if at all, one would have expected genes for male androphilia to have become extinct given the relative reproductive costs associated with this trait and the reproductive benefits associated with male gynephilia. Any species-typical trait that has a genetic component, but that lowers direct reproduction and persists over evolutionary time requires explanation when viewed within the context of natural selection, a process that favours the evolution of reproductively viable traits. For this reason, the existence of male androphilia represents one of the outstanding paradoxes of evolutionary biology.

If it could be definitively demonstrated that male androphilia was a historically recent phenomenon that did not extend back into the evolutionary past, then one might reasonably dismiss the characterization of male androphilia as an evolutionary paradox. However, archaeological and crosscultural evidence suggest that this conclusion lacks credibility. Sexual orientations such as gynephilia or androphilia are not part of the archaeological record, nor could they ever be, because sexual orientations cannot be preserved in the form of archaeological artifacts. However, depictions of sexual behaviours involving same-sex individuals do exist as part of the archaeological record, albeit rarely (e.g., Gebhard, 1970; Nash, 2001) and, on the basis of these depictions, it seems reasonable to suggest, at a very minimum, that some prehistoric peoples understood that such activity was within the realm of possibility. A somewhat stronger supposition is that such depictions are, in fact, evidence that same-sex sexual behaviour existed in prehistoric times.

Certain constellations of funerary remains may also be indicative of male androphilia in the ancestral past. For example, graves containing male skeletal remains and female-typical artifacts are indicative of transgendered males in the distant past (e.g., Hollimon, 1997). Given what we know about the exclusive androphilic orientation of most transgendered males from comparable populations (e.g., Harrington 1942), archaeological indicators of such individuals are once again suggestive of the presence of male androphilia in human antiquity.

All told, the archaeological evidence for male androphilia in the prehistoric past is suggestive, but limited. Perhaps more compelling is research that suggests that male androphilia occurs in the majority of cultures for which data are available (e.g., Murray, 2000) and its population prevalence rate appears to be similar (-1.5-5%) across a variety of different cultures (e.g., Smith et al., 2003; VanderLaan, Forrester, et al., 2013; Whitam, 1983). Thus, male androphilia appears to be a predictably and reliably reoccurring phenomenon in most human cultures. The cross-culturally widespread and consistent nature with which male androphilia is expressed suggests that it is not an evolutionarily recent aspect of the human sexual condition.

WHAT WAS THE ANCESTRAL FORM OF MALE ANDROPHILIA IN HUMANS?

Given that the manner in which male androphilia is publically expressed varies cross-culturally, the question arises as to which form, sex-gender congruent or transgendered, was the ancestral form? Identifying the ancestral form of male androphilia is critical if we seek to test hypotheses pertaining to the evolution of this trait in an accurate manner. More derived forms of this trait might reflect historically recent, cultural influences which may obscure the outcome of evolutionary process. If it were possible to establish that one form of male androphilia was associated, more often than not, with sociocultural conditions thought to characterize ancestral humans, then this would bolster the conclusion that that particular form of male androphilia was ancestral. Implementation of this approach requires establishing at least some of the sociocultural features that characterized ancestral humans.

With this concern in mind, VanderLaan, Ren, and Vasey (2013) attempted to identify the ancestral form of male androphilia. They did so by examining whether societies in which transgendered male androphilia predominates exhibit more of the sociocultural features that are believed to have characterized the human ancestral past relative to a comparison group of societies in which transgendered male androphilia did not predominate. Numerous researchers have presented evidence indicating that the ancestral human sociocultural environment was likely characterized by hunter-gatherers living in small groups with relatively egalitarian sociopolitical structures and shamanistic religious belief systems (e.g., Hill, Walker, Bozicevic, Eder, Headland, Hewlett et al., 2011; McBrearty & Brooks, 2000; Sanderson & Roberts, 2008; Woodburn, 1982). If these conditions are more often associated with societies in which transgendered male androphilia predominates, then this would bolster the argument that male androphilia was primarily expressed in the transgendered form under ancestral conditions.

Using information derived from the Standard Cross-Cultural Sample (SCCS), VanderLaan, Ren, and Vasey (2013) compared 46 societies in which male androphilia was expressed in the transgendered form to 146 comparison societies in which it was not. Relative to the comparison societies, transgendered societies were characterized by a significantly greater presence of ancestral sociocultural conditions. Given the association between transgendered male androphilia and ancestral human sociocultural conditions, it seems parsimonious to conclude that the transgendered form of male androphilia is ancestral to the sex-gender congruent form.

The existence of two forms of transgendered male androphilia (i.e., institutionalized role structured and non-role structured) raises the question as to which one preceded the other in evolutionary time. It seems likely that role structure transgendered male androphilia is derived from a more ancestral form of transgendered male androphilia that does not involve role specialization. Once transgendered male androphilia originated in humans, it could then be culturally elaborated to serve any number of distinct social roles. This represents the most parsimonious evolutionary sequence in the evolution of transgendered male androphilia because, phylogenetically, less specialized forms of traits tend to precede more specialized ones (Dean, Vale, Laland, Flynn & Kendal, 2014).

THE FA'AFAFINE OF SAMOA

To date, tests of evolutionary hypotheses pertaining to male androphilia have been conducted on a single population of transgendered androphilic males--the fa'afafine of Samoa. Our research group has conducted this work. Previous discussions pertaining to the evolution of male androphilia have centred almost exclusively on sex-gender congruent male androphiles. Consequently, the remainder of this review concentrates on our Samoan fa'afafine research given its unique focus on transgendered male androphiles.

In the Samoan language, fa'afafine means: "in the manner of a woman." Like Samoan men, fa'afafine are biological males. However, fa'afafine do not identify as men, nor do the members of their society recognize them as such. Consequently, they have been described as a type of "third" gender. In addition, fa'afafine differ from Samoan men in that their gender role enactment tends to be highly effeminate. From a Western perspective, many fa'afafine would be considered transgendered. The majority are not transsexual, however, because they do not experience dysphoria with respect to their genitals (Vasey & Bartlett 2007). Although it is not unusual for fa'afafine to occupy certain occupations (e.g., florist) more than others (e.g., mechanic), unlike the hijra of India, fa'afafine have no institutionalized role in Samoa.

Individuals are recognized in childhood as fa'afafine based on their tendencies to engage in female-typical activities (e.g., playing with girls) and their aversion toward male-typical activities (e.g., rough-and-tumble play). This process of recognition does not mean that Samoans make male children into fa'afafine. Rather, in Samoan culture, boyhood femininity is interpreted to mean that such individuals simply are fa'afafine and it is understood that they will not grow up to be "men." Some families react negatively to the presence of a fa'afafine child with corporal punishment, but the majority have a more laisser-faire attitude, and some even facilitate the child's feminine behaviour--sewing "her" dresses, for example (Bartlett & Vasey, 2006; Vasey & Bartlett, 2007).

In adulthood, most fa'afafine are exclusively androphilic and, consequently, they do not have children of their own (Vasey et al., 2014). All fa'afafine recognize the term "gay" although the precise meaning of this term varies depending on the individual asked. That being said, none of the fa'afafine use the term "gay" to describe themselves. "Gays" as one fa'afafine told the first author "sleep with each other, but fa'afafine don't do that." Indeed, fa'afafine express disgust at the thought of engaging in sexual activity with another fa'afafine and stress that they do not do so. Instead, they point out, in contrast to "gays," they have sex with "straight men."

In a Samoan cultural context, regardless of sexual orientation, "straight man" means a male who is masculine and who self-identifies as a "man." Some "straight men" in Samoa are gynephilic and only have sex with women. However, other men who are gynephilic will have sex with fa'afafine when they are unable to access their preferred sexual partners (i.e., adult females). The majority of men who sleep with fa'afafine likely fall into this group. This may seem perplexing from a Western cultural perspective, however, it is important to note that in cultures where transgendered male androphilia predominates, many male gynephiles may experience relatively little sexual aversion to the idea of engaging in certain types of same-sex sexual interactions because, to a certain extent, transgendered male androphiles resemble their preferred sex partners (i.e., adult females). The remaining minority of men who have sex with fa'afafine appear to be a combination of individuals who are either bisexual, androphilic, or gynandromorphophilic (i.e., peak sexual attraction and arousal to individuals with penises and breasts). In short, the Samoan category of "straight man" is a very heterogeneous one with respect to sexual orientation.

In Samoa, fa'afafine enjoy a high level of social acceptance that, while not absolute, stands in stark contrast to the situation experienced by Western transgendered male androphiles (e.g., Namaste, 2000). Indeed, fa'afafine are highly visible and active members of Samoa society. They occupy all manner of positions from stay-at-home caregivers to Assistant Chief Executive Officers in the government. The Prime Minister of Samoa, the Honorabe Tuilaepa Sailele Malielegaoi, is Patron of the National Fa'afafine Association and has spoken publically on many occasions about the value of fa'afafine for Samoan society.

In the following sections, we describe some of our Samoan research that furnishes supporting evidence for two hypotheses that attempt to account for the evolution of male androphilia, namely, the Sexually Antagonistic Gene Hypothesis and the Kin Selection Hypothesis.

TESTS OF THE SEXUALLY ANTAGONISTIC GENE HYPOTHESIS IN SAMOAN FA'AFAFINE

The Sexually Antagonistic Gene Hypothesis for male androphilia posits that genes associated with the development of androphilia result in decreased reproductive output in male carriers, but the same genes result in increased reproductive output in female carriers. For this reason, this hypothesis is routinely referred to as the Female Fecundity Hypothesis for male androphilia. Given that kin share a disproportionate number of genes in common, the female kin of male androphiles should experience, on average, greater increased reproductive output than females with no androphilic male relatives. In theory, the fitness benefits that accrue to the female relatives of male androphiles offset the fitness costs associated with male androphilia. Consequently, sexually antagonistic selection occurs for the genes in question owing to their fitness-enhancing properties in female carriers. A by-product of this sexually antagonistic selection is that male androphilia persists in populations over evolutionary time, despite its fitness-reducing consequences. Given all this, the basic prediction that flows from the Sexual Antagonistic Gene Hypothesis is that the female relatives of androphilic males should tend to produce more offspring than those of gynephilic males.

Three studies have been conducted in Samoa by our research group that furnish data pertaining to the Sexually Antagonistic Gene Hypothesis. Vasey and VanderLaan (2007) demonstrated that the mothers of fa'afafine produce more offspring than those of gynephilic men. This finding was replicated by VanderLaan and Vasey (2011), who also showed that elevated offspring production among the mothers of fa'afafine was not an artifact of the fraternal birth order effect. This later finding was important because if a true fecundity effect exists, one would expect to observe elevated reproductive output for additional offspring categories apart from older brothers (i.e., older sisters, younger sisters, and/or younger brothers). More recently, VanderLaan et al. (2012) extended these findings by demonstrating that fa'afafine's maternal and paternal grandmothers exhibit elevated offspring production, compared to those of gynephilic men. However, elevated reproductive output by the maternal and paternal aunts of fa'afafine was not observed.

Our findings from Samoa provide some tentative support for the Sexually Antagonistic Gene Hypothesis, but there is reason to be cautious about rushing to conclude that this hypothesis has been proven. Elevated reproductive output by androphilic males' maternal aunts, paternal aunts, or both, would provide the clearest support for the Sexually Antagonistic Gene Hypothesis because androphilic and gynephilic male probands do not share genes with their aunts' male reproductive partners, whereas, this is not the case for mothers and grandmothers. Studies conducted in one Italian lab have repeatedly shown that the maternal aunts of male androphiles are more fecund then those of male gynephiles (Camperio-Ciani et al., 2004; Iemmola & Camperio Ciani, 2009); however, multiple studies by independent researchers failed to obtain similar results (Blanchard & Lippa, 2007; King et al., 2005; Schwartz et al, 2010; VanderLaan et al., 2012).

Given the current state of the literature, we conclude that the Sexually Antagonistic Gene Hypothesis remains a viable hypothesis, but the role of sexually antagonistic selection in the evolution of male androphila is equivocal at present. Future research in Samoa is needed to ascertain whether group differences remain non-existent for maternal and paternal aunts when using a larger sample and it will also need to be established whether group differences for maternal and paternal grandmothers can be replicated.

Apart from the fact that our Samoan-based research was conducted in a population in which transgendered male androphilia predominates, we believe that a major strength of this research is that it examined female reproductive output in a population with a high fertility rate (Central Intelligence Agency, 2012). Consequently, anomalous reproductive patterns should be less likely to occur in the Samoan population, compared to lower-fertility Western populations where similar research has been conducted. If the Samoan population is relatively free of susceptibility to anomalous reproductive patterns compared to Western populations, then the study by VanderLaan et al. (2012) indicates that male androphilia is associated with elevated reproductive output in both the maternal and paternal lines. This is not the case for some of the research that has been presented from certain Western populations (e.g., Camperio Ciani et al., 2004; Iemmola & Camperio Ciani, 2009; Camperio Ciani & Pellizzari, 2012; Rahman, Collins, Morrison, Orrells, Cadinouche, Greenfield et al., 2008). On the basis of our Samoan research, it seems reasonable to argue that sexually antagonistic genetic factors may be present on the autosomal chromosomes because androphilic males share genetic factors on these chromosomes with both paternal and maternal relatives. Indeed, autosomal linkage of sexually antagonistic genetic factors favouring the evolution of male androphilia is plausible given previously reported mathematical models of sexually antagonistic selection for the evolution of male androphilia (Gavrilets & Rice, 2006).

TESTS OF THE KIN SELECTION HYPOTHESIS IN SAMOAN FA'AFAFINE

The Kin Selection Hypothesis holds that genes for male androphilia could be maintained in a population if enhancing one's indirect fitness offset the cost of not reproducing directly (Wilson, 1975). Indirect fitness is a measure of an individual's impact on the fitness of kin (who share some identical genes by virtue of descent), weighted by the degree of relatedness (Hamilton, 1963). Theoretically speaking, androphilic males can increase their indirect fitness by directing altruistic behaviour toward kin, which, in principle, would allow kin to increase their reproductive success. In particular, androphilic males should allocate altruistic behaviour toward close kin because they share more genes in common with such individuals.

Research conducted on transgendered male androphiles in Samoa has repeatedly furnished support for the Kin Selection Hypothesis. Multiple studies have shown that the avuncular (uncle-like) tendencies of fa'afafine are significantly elevated compared to those of Samoan gynephilic men (VanderLaan & Vasey, 2012; Vasey et al., 2007; Vasey & VanderLaan, 2010a). In addition, fa'afafine exhibited significantly elevated avuncular tendencies compared to the materteral (aunt-like) tendencies of Samoan women (Vasey & VanderLaan, 2009).

Elevated avuncular tendencies among fa'afafine have also been documented when comparing them to groups of childless women and gynephilic men (Vasey & VanderLaan, 2009, 2010a). These latter comparisons indicated that the fa'afafine's elevated avuncular tendencies cannot be characterized as a simple by-product that is due to a lack of parental care responsibilities and, thus, greater availability of resources for avuncular investment. If this were true, then the avuncular tendencies of fa'afafine should have been similar to those of childless men and women, but this was not the case. Moreover, these same findings indicate that the elevated avuncular tendencies of fa'afafine could not be characterized as a simple by-product that is due to the male members of this "third" gender group adopting feminine gender roles, which included expectations for elevated childcare. If this were true, then the materteral tendencies of Samoan mothers and childless women should have been similar to the avuncular tendencies of fa'afafine, but again this was not the case.

We have also demonstrated that fa'afafine's avuncular tendencies are significantly higher than their altruistic interest in non-kin children (Vasey & VanderLaan, 2010b). As such, fa'afafine's elevated avuncular tendencies are not a by-product of general altruistic interest in all children. This same research also demonstrates that fa'afafine's self-reports of elevated avuncular tendencies cannot be explained away as a desire by members of this group to appear more socially virtuous compared to women or gynephilic men. If this were so, then one would expect fa'afafine to also report that they had elevated altruistic interest in non-kin children, but this was not the case. In fact, the three groups did not differ from each other in this regard.

Additional research indicates that fa'afafine exhibit similar levels of sexual/romantic relationships involvement compared to Samoan women and gynephilic men (VanderLaan & Vasey, 2012). As such, the fa'afafine's relatively elevated avuncular tendencies cannot be characterized as a simple by-product of their failure to form, and invest in, intimate sexual/romantic relationships, which, in turn, leaves them with more time and resources. Finally, research demonstrates that Samoans in general, and fa'afafine themselves, do not believe that fa'afafine are primarily responsible for the care of nieces and nephews. Consequently, the elevated avuncular tendencies exhibited by fa'afafine cannot be explained in terms of such (trans)gender role expectations (VanderLaan, Petterson, Mallard & Vasey, 2014).

It should be clear from the research described above that much of our work has focused on falsifying the Kin Selection Hypothesis for male androphilia by examining alternative explanations that might account for the fa'afafine's elevated avuncularity. It should be equally clear that none of the alternative explanations we have tested, to date, have been supported. Taken together, this body of work is consistent with the conclusion that elevated avuncularity by androphilic males is an adaptation that evolved via kin selection. That being said, establishing that a given trait is an adaptation involves repeatedly satisfying adaptive design criteria empirically while simultaneously ruling out alternatives (Buss, Haselton, Shackelford, Bleske, & Wakefield, 1998). Adaptive design implies complexity, economy, efficiency, reliability, precision, and functionality (Williams, 1966).

We have conducted several studies indicating that, compared to Samoan women and gynephilic men, the avuncular cognition of fa'afafine is more adaptively designed. First, the avuncular tendencies of the fa'afafine are more dissociated from (i.e., co-vary less with) their altruistic interest in non-kin children, compared to Samoan women and gynephilic men (Vasey & VanderLaan, 2010b). Such a dissociation would allow fa'afafine to channel resources toward nieces/nephews in a more optimal manner (i.e., economical, efficient, reliable, and precise), while minimizing resources directed toward non-kin children. Second, whereas Samoan men and women show a tendency to decrease their willingness to invest in nieces and nephews when they have sexual/romantic relationship partners, the cognition of fa'afafine appears to protect against this tendency by maintaining a high level of willingness to invest in nieces and nephews regardless of their relationship status (VanderLaan & Vasey, 2012). Third, due to the mechanics of human reproduction, individuals can always be certain that their sisters' offspring are their genetic relatives. Yet, due to the possibility of cuckoldry, individuals are necessarily less certain in the case of brothers' offspring. The elevated avuncular tendencies of fa'afafine are contingent on the presence of sisters, not brothers, which suggests the avuncular cognition of fa'afafine is sensitive to the relative fitness benefits of investing in sisters' versus brothers' offspring (VanderLaan & Vasey, 2013). Fourth, compared to gynephilic men and androphilic women, fa'afafine are generally better at allocating investment toward categories of kin that are more likely to maximize their fitness (i.e., sisters' younger daughters) and they do so in a manner that reflects greater sensitivity to non-frivolous versus frivolous investment contexts (VanderLaan & Vasey, 2014).

Elevated avuncular tendencies must translate into real-world avuncular behaviour if they are to have any impact on the fitness of nieces and nephews and the uncles themselves. Vasey and VanderLaan (2010c) used money given to, and received from, oldest and youngest siblings' sons and daughters as a behavioural assay of expressed kin-directed altruism. In line with the predictions of the Kin Selection Hypothesis, compared to women and gynephilic men, fa'afafine gave significantly more money to their youngest siblings' daughters. No other group differences were observed for money given to, or received from, nieces and/or nephews. Moreover, there were no correlations between the number of children parented and monetary exchanges with the niece and nephew categories examined, suggesting, once again, that childlessness cannot account for why fa'afafine give more money to their youngest siblings' daughters.

KIN-DIRECTED ALTRUISM BY ANDROPHILIC MALES IN THE HUMAN ANCESTRAL ENVIRONMENT

Analyses by VanderLaan, Ren, and Vasey (2013) demonstrated that societies in which transgendered male androphilia predominates were more likely to show social characteristics that facilitate investment in kin. Relative to comparison societies, transgendered societies were more likely to exhibit bilateral (2) and double descent (3) systems than patrilineal, matrilineal, and ambilineal (4) descent systems. In addition, correlational analysis showed that as the presence of ancestral sociocultural conditions increased, so too did the presence of bilateral (and double) descent systems. Ethnologists have argued that bilateral decent systems and bilocal patterns of residence following marriage are maximally inclusive of kin because they do not bias individuals to interact with only one subset of relatives (e.g., Kramer & Greaves, 2011). Consequently, it is reasonable to deduce that these patterns of descent and post-marital residence would have allowed for more altruistic interactions with a full range of genetically related kin. Taken together, these analyses are consistent with the conclusion that bilateral descent characterized ancestral humans, and that such patterns were features of ancestral societies in which male androphilia was expressed in the transgendered form.

VanderLaan, Ren, and Vasey (2013) also examined the acceptance of same-sex sexuality in 27 transgendered societies for which information could be obtained. The significant majority of these societies expressed no negative reactions to same-sex sexual behaviour. Overall then, the same-sex sexual orientation of transgendered males in transgendered societies appears to be socially tolerated. Such tolerance, particularly on the part of the kin of transgendered androphilic males, might be considered essential for kin selection to be deemed as a plausible contributing factor toward the persistence of male androphilia over evolutionary time. Unless transgendered androphilic males are accepted by their families, their opportunity to invest in kin is likely limited.

In sum, it is likely that transgendered male androphilia is the ancestral form of this trait and that key aspects of the ancestral environment of transgendered androphilic males would have facilitate elevated kin-directed altruism. In addition, data from contemporary transgendered male androphiles (fa'afafine) indicates that they exhibit elevated avuncularity. Given all this, it seems reasonable to suggest that kin selection played some role in the evolution of male androphilia. As such, the elevated kin-directed altruism documented in Samoan fa'afafine is more likely to have been characteristic of ancestral androphilic males, compared to the lack thereof documented in sex-gender congruent androphilic men from industrialized cultures (e.g., Abild, VanderLaan & Vasey, 2014; Bobrow & Bailey, 2001; Rahman & Hull, 2005; Forrester, VanderLaan, Parker & Vasey, 2011; Vasey & VanderLaan, 2012).

CONCLUDING REMARKS

Until very recently, it would not have been possible to write a commentary such as this one, which examines the evolution of male androphilia from an evidence-based, quantitative perspective. There simply was not enough information available to justify such a publication. In recent years, however, progress has finally been made toward gaining an empirically based understanding of how male androphilia persists over evolutionary time. Although male androphilia varies dramatically with respect to the manner in which it is publicly expressed, there are multiple lines of developmental and biodemographic evidence indicating that different cultural forms of male androphilia (i.e., transgendered, sex-gender congruent) share the same etiological basis. Quantitative research indicates that the transgendered form of male androphilia was likely ancestral to the sex-gender congruent form.

To date, theories pertaining to the evolution of male androphilia have been tested in one population of transgendered male androphiles: the fa'afafine of Samoa. In keeping with the predictions of the Sexually Antagonistic Gene Hypothesis, it has been shown that the mothers, maternal grandmothers, and paternal grandmothers of fa'afafine have more offspring than those of gynephilic males. However, definitive support for this hypothesis, in the form of elevated offspring production among the aunts of fa'afafine is lacking at present. In keeping with the predictions of the Kin Selection Hypothesis, it has been repeatedly shown that fa'afafine exhibit elevated avuncular tendencies compared to women and gynephilic men. Several studies also indicate that the avuncular cognition of fa'afafine exhibits hallmarks of adaptive design.

Given these results, one potential way that male androphilia could be conceptualized within an evolutionary framework is as a by-product of an adaptation (sensu Buss et al. 1998) for increased female fecundity that results from sexually antagonistic selection. By-products of adaptations are characteristics that evolve in association with particular adaptations because they happen to be coupled with those adaptations (Buss et al. 1998). Although they may have some beneficial effect on fitness, they did not originally evolve to solve adaptive problems and, thus, at their point of origin they did not have an evolved fitness-enhancing function, nor were they products of natural selection. In such a situation, increased avuncularity among male androphiles could potentially facilitate reproduction by female kin and thereby have positive "effects" on the genetic factors for both increased fecundity in females and, by extension, its conjectured by-product, male androphilia. Williams (1966) invoked the term "effect" to designate the fortuitous operation of a useful characteristic not built by selection for its current role.

Humans have evolved, via kin selection, to preferentially allocate altruism toward close relatives (e.g., Daly, Salmon & Wilson, 1997). Consequently, kin nepotism should characterize all individuals, regardless of their sex, sexual orientation, or gender identity. However, markedly elevated avuncularity, such as that observed among fa'afafine, might result in distinct fitness advantages that could form a unique basis on which kin selection might act. If so, then the cognitive underpinnings mediating avuncularity in male androphiles may have subsequently undergone secondary adaptive modification. Such a conclusion is consistent with our findings that the avuncular cognition of fa'afafine exhibits special design features (VanderLaan & Vasey, 2012, 2013, 2014; Vasey & VanderLaan 2010b). It is likely that certain features of the ancestral sociocultural environment of transgendered males, including maximally inclusive descent systems (e.g. double or bilateral descent) and social tolerance of male-male sexuality, would have facilitated this process.

doi: 10.3138/cjhs.23.3-CO1

Acknowledgements: We thank Resitara Apa, Jean-Baptiste Leca, Nancy Bartlett, Gardenia Elisaia, Vaosa Epa, Vaasatia Poloma Komiti, Anita Latai, Sarah Faletoese Su'a, Vester Fido Collins, Liulauulu Faaleolea Ah Fook, Tyrone Laurenson, Gaualofa Matalavea, Avau Memea, Nella Tavita-Levy, Karen Olsen Bruhns, Palanitina Toelupe, Trisha Tuiloma, Avalogo Togi A. Tunupopo, Erin Zelinski, the Kuka family of Savai'i, the Samoan AIDS Foundation, the National University of Samoa, the Samoan Ministry of Health, and the Government of Samoa. We are grateful to all of the individuals who agreed to participate in our studies. We extend special thanks to Alatina Loelu without whom this research could not have been conducted. Our research on the evolution of male androphilia has taken place over the past decade and has been generously supported by the University of Lethbridge and a variety of funding agencies. PLV received funding from an Alberta Provincial Government S.T.E.P. Award, an Alberta Innovates Health Solutions (AIHS) Sustainability Fund Grant, a Canadian Institutes of Health Research (CIHR) Catalyst Grant in Methods and Measures for Gender, Sex and Health, three Natural Sciences and Engineering Research Council (NSERC) of Canada Grants, and a Social Sciences and Humanities Research Council of Canada (SSHRC) Insight Grant. DPV received funding from a NSERC of Canada Graduate Scholarship-D3, the Sigma Xi Scientific Research Society Grant-in-Aid-of-Research, a Ralph Steinhauer Award of Distinction, an American Psychological Foundation Henry David Travel Grant, and a Sexual Medicine Society of North America Post-Doctoral Fellowship Stipend.

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NOTES

(1) The fraternal birth order effect refers to the well-established finding that the number of older biological brothers increases the odds of androphilia in later born males (Blanchard, 2004; Bogaert & Skorska, 2011).

(2) In bilateral descent systems, ego's mother's and father's lineages are equally important for emotional, social, spiritual, and political support, as well as for transfer of property or wealth.

(3) In double descent systems, individuals receive some rights and obligations from the father's side of the family and others from the mother's side.

(4) Some sources treat ambilineal and bilateral descent systems as synonymous, but ambilineal descent systems are defined as existing when individuals have the option of choosing one of their lineages for membership.

Paul L. Vasey [1] and Doug P. VanderLaan [2]

[1] Department of Psychology, University of Lethbridge, Lethbridge, AB

[2] Gender Identity Service, Child, Youth and Family Services, Centre for Addiction and Mental Health, Toronto, ON

Correspondence concerning this article should be addressed to Paul Vasey, Ph.D., Department of Psychology, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta, T1K 3M4, Canada
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Title Annotation:COMMENTARY
Author:Vasey, Paul L.; VanderLaan, Doug P.
Publication:The Canadian Journal of Human Sexuality
Article Type:Viewpoint essay
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Date:Dec 1, 2014
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