Familial patterning and prevalence of male androphilia among Istmo Zapotec men and muxes
Familial patterning and prevalence of male androphilia among Istmo Zapotec men and muxes
Francisco R. GoÂ mez 0 1
Scott W. Semenyna 0 1
Lucas Court 0 1
Paul L. Vasey 0 1
0 Department of Psychology, University of Lethbridge , Lethbridge, Alberta , Canada
1 Editor: Elisabetta Palagi, Universita degli Studi di Pisa , ITALY
Male androphilia (i.e., male sexual attraction to other adult males) is known to cluster within families. Some studies demonstrate that male androphilia clusters in both the paternal and maternal familial lines, whereas other studies demonstrated that it clusters only in the latter. Most of these studies were conducted in Euro-American populations where fertility is low and the sexual orientation of male relatives can sometimes be difficult to ascertain. These two factors can potentially confound the results of such studies. To address these limitations, we examined the familial patterning of male androphilia among the Istmo Zapotec of Oaxaca, Mexico±±a high fertility, non-Euro-American population where androphilic males are known locally as muxes, a third gender category. The Istmo Zapotec recognize two types of muxes±±muxe gunaa and muxe nguiiu±±who typify the transgender and cisgender forms of male androphilia, respectively. We compared the familial patterning of male androphilia between muxe gunaa and muxe nguiiu, as well as between gynephilic men and muxes (both cisgender and transgender forms combined). Istmo Zapotec muxe gunaa and muxe nguiiu exhibit similar familial patterning of male androphilia. Overall, muxes were characterized by significantly more muxe relatives than gynephilic men. This familial patterning was equivalent in both the paternal and maternal lines of muxes. The population prevalence rate of male androphilia was estimated to fall between 3.37±6.02% in the Istmo Zapotec. This is the first study that has compared cisgender and transgender androphilic males from the same high fertility population and demonstrated that the two do not differ with respect to the familial patterning of male androphilia.
Funding: Various stages of this research were
supported by grants awarded by the University of
Lethbridge Research Development Fund (www.
uleth.ca; grant number 13261), the University of
Lethbridge Office of Research Service (grant
number 41730), and the Social Sciences and
Humanities Research Council of Canada (www.
sshrc.ca; grant number 41140) to PLV. The
funders had no role in the study design, data,
Male androphilia refers to male sexual attraction and arousal to other adult males. The manner
in which male androphilia is publically expressed varies cross-culturally, but generally takes
one of two primary forms: cisgender and transgender [1±3]. Cisgender male androphiles behave
in a relatively masculine manner, whereas transgender male androphiles typically behave in a
relatively feminine manner. Both cisgender and transgender male androphiles can occur in
the same culture, but typically one or the other tends to predominate . Previous research
collection, and analysis, decision to publish, or
preparation of the manuscript.
has noted that the cisgender form of male androphilia is typically expressed in Euro-American
cultures, whereas the transgender form tends to prevail in non-Euro-American cultures [
Despite significant differences in gender role enactment and identity, cross-cultural
research suggests that both the transgender and cisgender forms of male androphilia share
numerous biopsychological correlates [
]. For example, compared to males who are gynephilic
(i.e., sexually attracted to adult females), both cisgender and transgender androphilic males
occur at a similar population rates, are later born among their siblings, have more older
brothers, come from larger families, have more androphilic male relatives, exhibit little or no
reproductive output, recall elevated gender atypicality and separation anxiety in childhood, and
exhibit a preference for female-typical occupations [
]. These converging lines of evidence
suggest that cisgender and transgender androphilic males are different expressions of the same
underlying trait, and that both share common biological foundations [
Regardless of how male androphilia is publically expressed, this trait represents an
evolutionary puzzle when expressed to the exclusion of gynephilia because it hinders direct
]. Compounding this puzzle is the fact that both twin [8±11] and molecular
genetic studies [12±14] indicate that male androphilia is influenced by genetic factors, and is
thus, at least partially heritable. A more precise understanding of the nature of this heritability
can be obtained by conducting family studies, which shed light on the way male androphilia
clusters in families (i.e., whether they are grouped on the maternal line, paternal line, or both).
In Euro-American cultures, various family studies have consistently demonstrated that
cisgender androphilic (gay) males have more androphilic male brothers than gynephilic males,
thus bolstering the conclusion that male androphilia is familial [
]. However, these studies
have provided a mixture of results with respect to whether male androphilia is inherited
through the maternal line, paternal line, or both. Some studies demonstrate that gay men have
a preponderance of gay male relatives, but only in the maternal line [16±18]. These studies
suggest that X-linkage factors might play an essential role in the expression of male androphilia
because males can only share X-linked genes with maternal kin. At the same time, other
studies demonstrate that gay men exhibit a preponderance of gay male relatives in both the
maternal and the paternal lines [
]. This pattern of familial clustering is consistent with the
conclusion that genes for male androphilia can be inherited from both parents through
The discrepancies between the family studies described above may be partially explained by
the low fertility rates typical in most Euro-American cultures [
]. Families in Euro-American
societies tend to cease reproduction after obtaining a certain number of children, or after
having one child of each sex. The existence of these so called ªstopping rulesº may obscure the
familial patterning of low-frequency traits such as male androphilia [
], as has been shown to
be the case for other well-established biodemographic correlates of male sexual orientation
such as the fraternal birth order effect [21±23].
Additionally, because cisgender androphilic males in the West identify as men, and there
are numerous cultural reasons for not disclosing one's sexual orientation (e.g., [
]) it is
possible that Euro-American participants may report inaccurate or incomplete information
regarding the sexual orientation of both themselves and their male relatives. This potential
confound is circumvented in cultures in which androphilic males are recognized as occupying
a third gender category that is distinct from men and women, as is the case in some
non-EuroAmerican cultures. Identification by males as third gender in these non-Euro-American
cultures is therefore a reliable indicator of male androphilia. As such, family studies conducted in
high fertility non-Euro-American populations, where androphilic males are recognized as a
third gender, are valuable complements to studies carried out with gay men in lower fertility
2 / 17
Research conducted in SamoaÐa Polynesian, high fertility populationÐhas consistently
demonstrated that the families of transgender androphilic males (known locally as a third
genderÐfa’afafine) have a higher proportion of androphilic male relatives (i.e. brothers, uncles,
and cousins) when compared to the families of gynephilic males [
5, 26, 27
]. These studies
showed that fa’afafine have a preponderance of fa’afafine relatives in both their maternal and
paternal lines, suggesting that autosomal-linkage factors are important for the inheritance of
male androphilia. However, the rate of male androphilia among relatives with whom
participants were more likely to share X-linked genes (i.e., maternal uncles and cousins via maternal
aunts) was higher for fa’afafine than gynephilic males [
], furnishing some support, as well, for
the role of X-linkage factors in the maintenance of male androphilia. Thus, evidence derived
from family studies in Samoa indicates that male androphilia is familial, and is influenced by
both autosomal and X-linkage factors.
Data from these family studies have also been used to estimate the population prevalence
rate of male androphilia in Samoa. VanderLaan and colleagues [
] reported a population
prevalence rate between 1.43±4.65%. In a larger follow-up study, Semenyna and colleagues [
reported similar, but more circumscribed results (0.61±3.51%). These rates are comparable to
those obtained for gay men in Euro-American cultures (~1±5%) (e.g., [
Research conducted in Samoa provides the first empirical evidence that transgender male
androphilia clusters within families. However, further evidence from additional
non-EuroAmerican, high fertility populations would help to elucidate the patterns of inheritance that
typify transgender and cisgender male androphiles, especially if that evidence was derived
from a culture that is unrelated to Samoa. In addition, such data could be used to generate
prevalence rates of male androphilia in additional non-Euro-American populations, thereby
addressing calls for such research [
]. With this in mind, we examined the familial patterning
of male androphilia among the Istmo Zapotec of Oaxaca, Mexico.
The Zapotec are an indigenous Mesoamerican culture found primarily in the southern
Mexican state of Oaxaca [
]. Zapotec civilization predates Spanish conquest by millennia,
and despite foreign influences, Zapotec culture still remains an integral part of Oaxacan
]. Federal statistics show that of the ~400,000 individuals in Mexico who speak
Zapotec, 87% of them resided in Oaxaca [
]. Furthermore, fertility rates in Oaxaca are
estimated to be higher than neighboring Mexican states [
], as well as a variety of Euro-American
countries (e.g., Canada, Italy, US, and UK) [
The Istmo ZapotecÐa subgroup of Zapotec living in the Istmo region of
OaxacaÐrecognize three genders: men, women, and muxes. The term muxe likely originates from a Zapotec
adaptation of the Spanish word mujer, which means ªwomanº [
]. Muxes are androphilic
males who commonly take the receptive role during anal intercourse. Qualitative studies
indicate that muxes exhibit gender atypical behavior from an early age [34±36]. These observations
are supported by recent quantitative research demonstrating that muxes recall elevated
indicators of childhood separation anxiety [
], a trait most often displayed by females [
Istmo Zapotec recognize two types of muxes: muxe gunaa and muxe nguiiu (i.e., Zapotec for
muxe ªwomanº and muxe ªman,º respectively). Muxe gunaa are transgender androphilic
males who present publically in a relatively feminine manner, similar to the Samoan fa’afafine.
Muxe nguiiu are cisgender androphilic males who present publically in a relatively masculine
manner, similar to Euro-American gay men. Within the Istmo region of Oaxaca, both the
transgender form of male androphilia (muxe gunaa) and the cisgender form (muxe nguiiu)
occur at appreciable rates. Despite differences in gender expression, both types of muxes are
relatively feminine when compared to their gynephilic male counterparts, as is generally the
case for androphilic males worldwide (e.g., [40±44]). Interestingly, a widespread belief among
3 / 17
the Istmo Zapotec is that muxes ªrun in families,º and their status as muxe is determined at
birth by biological factors [
Our study tested this folk belief by examining whether male androphilia is familial among
the Istmo Zapotec. Given that substantial numbers of both transgender and cisgender muxes
exist among the Istmo Zapotec, a unique within-culture comparison can be made on the
proportion of androphilic male relatives in the families of both cisgender (muxe nguiiu) and
transgender (muxe gunaa) androphilic males. Thus, the first aim of the present study was to
compare the familial patterning and prevalence of androphilic male relatives between muxe
gunaa and muxe nguiiu. Next, the prevalence of muxe relatives (i.e., brothers, uncles, and
cousins) was compared between the families of Istmo Zapotec muxes (cisgender and transgender
combined) and gynephilic males. In addition, we conducted within-group comparisons to
determine whether there were any differences in the prevalence of androphilic male relatives
between paternal and maternal kin categories (i.e., uncles, male cousins via uncles, male
cousins via aunts, and all categories combined) for the probands of Istmo Zapotec men and muxes.
Finally, a population prevalence rate of male androphilia among the Istmo Zapotec was
calculated. Based on these aims, and on the literature mentioned above, our hypotheses and
predictions were as follows:
Hypothesis 1. Both transgender and cisgender androphilic males have similar familial
patterning of male androphilia.
Prediction 1. Istmo Zapotec muxe gunaa (transgender) and muxe nguiiu (cisgender) will not
differ significantly with respect to the proportion of muxe relatives within their families.
Hypothesis 2. Androphilic males have more androphilic male relatives than gynephilic males.
Prediction 2. Istmo Zapotec muxes (both cisgender and transgender combined) will have
significantly more muxe relatives than Istmo Zapotec gynephilic males.
Hypothesis 3. Androphilic males in non-Euro-American cultures have similar familial
patterning of male androphilia in both maternal and paternal lines.
Prediction 3. Istmo Zapotec muxes will not differ significantly with respect to the prevalence
of muxe relatives between the paternal and maternal kin categories (i.e., uncles, male
cousins via uncles, and male cousins via aunts, and all combined).
Hypothesis 4. The prevalence rate of male androphilia is similar across cultures (~1±5%).
Prediction 4. The prevalence rate of muxes among the Istmo Zapotec will be similar to the
prevalence rate of male androphilia found across cultures (~1±5%).
This research was approved by the University of Lethbridge Human Subjects Research Ethics
Committee (Protocol #2015±069). Canadian, USA and French foreigner nationals are
permitted to conduct research in Mexico for a period of 180 days if they have a valid passport [
All the authors held valid passports from these countries and our field trips did not exceed this
period of time. The authors also confirmed with the Mexican Embassy in Ottawa, Canada, and
the Mexican Consulate in Calgary, Canada, that a research permit from Mexican authorities
was not required to conduct this study. While in JuchitaÂn, we met with some of the leaders of
the muxe community to explain our research and these leaders offered their support.
Furthermore, we visited the local police station and the police were made aware of our research
4 / 17
activities. As such, this research was conducted in compliance with local research regulations
Consistent with previous family studies conducted in Samoa [
], all participants were
recruited using a network sampling procedure which consisted of contacting randomly chosen
initial participants, who gave referrals for additional participants, who in turn provided further
referrals, and so on. Data were collected in the city of JuchitaÂn de Zaragoza, as well as 14 other
towns and villages within the JuchitaÂn and Tehuantepec districts in the Istmo region of
Oaxaca, Mexico. Three separate field trips took place between November-December, 2015,
February-March 2016, and November-December 2016. Participants were required to provide
informed written consent prior to participating in the study.
Participants were asked to report their gender as either men or muxe. If they identified as
muxes, they were then asked to identify as either muxe gunaa or muxe nguiiu. A total of 171
gynephilic men and 169 muxes (110 muxe gunaa and 59 muxe nguiiu) were interviewed for
this study. Participants could answer the questionnaires alone, but it was not unusual for them
to also receive assistance from relatives if they were nearby. None of the participants were
brothers or first cousins. Participants' sexual orientations were assessed using a 7-point Kinsey
], which asked about sexual feelings over the previous year. Participants' response
options ranged from Sexual feelings only toward females (i.e., exclusively gynephilic; Kinsey
rating = 0) to Sexual feelings only toward males (i.e., exclusively androphilic; Kinsey rating = 6).
All men identified as exclusively (Kinsey rating = 0, n = 165 men) or predominantly gynephilic
(Kinsey rating = 1, n = 6 men). All muxes identified as predominantly (Kinsey rating = 5, n = 7
muxe nguiiu) or exclusively androphilic (Kinsey rating = 6, n = 52 muxe nguiiu; n = 110 muxe
Participants were asked to report information regarding their age (in years). A one-way
analysis of variance (ANOVA) showed that the average age of gynephilic men (M = 30.33,
SD = 9.18), muxe gunaa (M = 30.58, SD = 9.15), and muxe nguiiu (M = 31.37, SD = 10.08), did
not differed significantly (F[
] = .275, p = .760). Participants were also asked to report
their average weekly income with a scale that ranged from 1 (0±250 Mexican Pesos) to 9 (more
than 2000 Mexican Pesos). A one-way ANOVA revealed that the average level of income for
gynephilic men (M = 5.00, SD = 2.47), muxe gunaa (M = 4.72, SD = 2.24), and muxe nguiiu
(M = 5.24, SD = 2.58), did not differed significantly (F[
] = .951, p = .387). As such, none
of the biographic variables were used as covariates when conducting inferential statistics.
Participants were interviewed using questionnaires, which were available in Spanish after
being translated and back-translated by two fluent Spanish-English speakers. Two of the
authors (FRG, LC) and Spanish-speaking research assistants were available to answer
participants' questions. When participants were not fully fluent in Spanish, a Zapotec-speaking
research assistant was also present for interviews. Questions were read out loud by research
assistants in Spanish or Zapotec as necessary.
Participants reported the total number of biological brothers they had, as well as all
biological male relatives (i.e., uncles, male cousins via aunts, and male cousins via uncles) for both the
paternal and maternal sides of their families. An additional category was created combining
maternal uncles and male cousins via aunts in order to test for potential X-linkage factors of
5 / 17
male androphilia. These kin categories are the only males with whom probands might share
common X-linked genes. Brothers were not included in this category because they share both
X-linked genes and the same Y chromosome as probands, thus confounding comparisons
between the paternal and maternal lines. The participants identified how many of those
relatives were muxes. This information was used to calculate the proportion of muxes relatives
within each kin category for each participant. These proportions were then averaged for each
kin category within each group so as to have a mean proportion of muxe relative to conduct
Some of the participants had relatives who moved outside of the Istmo to different states
within Mexico or to different countries that are known to have lower fertility rates (e.g.,
Mexico City, United States). Since our primary aim in this study was to analyze the prevalence
of male androphilia within the Istmo region of Oaxaca, only male relatives whose parents had
spent their entire reproductive history within the Istmo were included in the analysis.
Mann-Whitney U tests where employed when comparing the average proportion of muxe
relatives between Istmo Zapotec muxe gunaa and muxe nguiiu in the paternal line, maternal line,
and both lines combined (Table 1). Within group comparisons were conducted comparing the
paternal and maternal relatives of muxe gunaa and muxe nguiiu using Wilcoxon signed-rank
tests (Table 2). Finally, additional within group comparisons were conducted using Friedman
tests in order to compare the prevalence of maternal and paternal muxe relatives across
different kin categories (i.e., uncles, male cousins via uncles, and male cousins via aunts) for both
muxe gunaa and muxe nguiiu (Table 3). Post hoc analyses for the Friedman tests were
conducted using Wilcoxon signed-rank tests (Table 3). The same between-group and
withingroup statistical analyses were used when comparing Istmo Zapotec muxes (both cisgender
and transgender combined) to gynephilic men (Tables 4±6). Given the numerous statistical
comparisons carried out, a more conservative critical alpha of 0.01 was used in order to control
the type I error rate. Due to the skewed nature of the data, all Cohen's d effect sizes should be
interpreted with caution. For Tables 2, 3, 5 and 6, the r effect sizes were calculated using the z
scores from the Wilcoxon signed-rank test. Effect size interpretations are as follows: r = .1
small, .3 medium, .5 large; d = .2 small, .5 medium, and .8 large [
Comparison between muxe gunaa and muxe nguiiu
Consistent with Prediction 1, the two types of muxes did not significantly differ with respect to
the proportion of muxe relatives overall (i.e., maternal and paternal lines combined) (Table 1).
Additionally, muxe gunaa and muxe nguiiu did not differ significantly with respect to the
prevalence of muxe relatives in either their combined paternal or combined maternal lines. Within
All effect size estimates are listed in order of comparing uncles to male cousins via uncles; uncles to male cousins via aunts; male cousins via uncles to male cousins via
a Post-hoc Wilcoxon's test between overall male cousins via uncles versus overall male cousins via aunts was significant (p = .008). However, the preceding omnibus test
7 / 17
the maternal line, muxe gunaa were found to have significantly more muxe cousins via aunts
compared to muxe nguiiu. The prevalence of muxe relatives in the category
ªX-chromosomelinked male kinº (i.e., maternal uncles and male cousins via maternal aunts combined) did not
differ significantly between groups. Lastly, no significant difference was observed when
comparing the proportion of muxe brothers between muxe gunaa and muxe nguiiu probands.
For both types of muxes, no significant differences were observed within groups for the
prevalence of androphilic male relatives in paternal and maternal kin categories (i.e., uncles,
male cousins via uncles, and male cousins via aunts) (Table 2). When comparing the
prevalence of muxe relatives among uncles, cousins via uncles, and cousins via aunts (Table 3), no
significant differences were found for muxe gunaa. Similarly, muxe nguiiu showed no
significant differences in the proportion of muxe relatives in any of these kin categories.
8 / 17
All follow-up pairwise comparisons were conducted using Wilcoxon's test with no tests reaching significance (all p .055). All effect size estimates are listed in order of
comparing uncles to male cousins via uncles; uncles to male cousins via aunts; male cousins via uncles to male cousins via aunts.
Comparison between muxes and gynephilic males
Given that proportions of muxe relatives among the families of muxe gunaa and muxe nguiiu
were largely equivalent, the two muxe types were combined in order to compare them to
gynephilic males. Consistent with Prediction 2, muxe probands had significantly more muxe
relatives overall (i.e., maternal and paternal lines combined) than gynephilic male probands
(Table 4). Muxe probands also had a significantly higher proportion of androphilic male
paternal relatives compared to gynephilic males, whereas maternal relatives did not differ
significantly between the groups. Within muxes' paternal line, no individual kin category was found
to be driving the preponderances of paternal muxe relatives compared to those of gynephilic
males. When considering the category ªX-chromosome-linked male kinº (i.e., maternal uncles
and male cousins via maternal aunts combined), no significant differences in the prevalence of
muxe relatives were found between groups. Lastly, muxes reported having significantly more
muxe brothers than gynephilic males.
Consistent with Prediction 3, no significant differences were observed for the prevalence of
androphilic male relatives in paternal and maternal kin categories (i.e., uncles, male cousins
via uncles, and male cousins via aunts) within the families of muxes (Table 5). The same was
also true for families of gynephilic males. Finally, when comparing the prevalence of muxe
relatives among uncles, male cousins via uncles, and male cousins via aunts (Table 6), both muxes
and gynephilic men showed no significant differences.
Population prevalence estimate of male androphilia among the Istmo
The data collected in the current study were used to calculate a population prevalence estimate
of muxes (i.e., male androphilia) among the Istmo Zapotec. Consistent with previous studies
], the population prevalence estimate was comprised of the overall proportion of muxe
relatives (i.e., paternal and maternal lines combined, including brothers) in relation to all male
relatives (listed in Table 4). Specifically, the upper bound of the population prevalence estimate
was calculated using the proportion of muxe relatives among muxe probands, while the lower
bound was calculated using the proportion of muxe relatives among gynephilic male probands.
Given the binomial nature of these estimates (i.e., relatives either are muxes, or are not), the SD
9 / 17
was calculated as pnpq, where n is the total number of male relatives (i.e., 3716 for muxes and
3183 for gynephilic men), p is the proportion of male relatives who are muxes (i.e., 197/3716
for muxes and 129/3183 for gynephilic men), and q is the proportion of male relatives who are
not muxes (i.e., 1 ±p). The standard deviations (SDs) of these estimates were used to calculate
95% confidence intervals on the upper bound (i.e., the prevalence of muxe relatives among
muxe probands) and the lower bound (i.e., the prevalence of muxe relatives among gynephilic
male probands) respectively.
For the muxe probands, a frequency of 197 muxe relatives out of 3716 total male relatives
(5.30%) yielded a SD of 13.66, which represents 0.37% of the total number of muxe probands'
male relatives. For the gynephilic male probands, a frequency of 129 muxe relatives out of 3183
total male relatives (4.05%) yielded a SD of 11.13, which represents 0.35% of all gynephilic
male probands' relatives. The 95% confidence intervals (CIs) for the prevalence of muxe
relatives were calculated as p 1:96 SnD. Similar to the SD formula, p is the proportion of male
relatives who are muxes and n is the total number of male relatives. Therefore, the 95% CI for the
prevalence rate of muxe relatives was 4.58±6.02% (0.0458, 0.0602) for muxe probands, and
3.37±4.74% (0.0337, 0.0474) for gynephilic male probands. Given previous research suggesting
that androphilic males have more androphilic male relatives than gynephilic males [
5, 26, 27
and that the CI for the muxe probands was higher than the CI of gynephilic male probands, we
used the upper bound of the CI of the muxe probands (6.02%) and the lower bound of the CI
of the gynephilic male probands (3.37%), as the upper and lower bound for the population
prevalence rate of male androphilia, respectively. As such, we estimate that the true rate of
androphilia among the Istmo Zapotec must falls between 3.37±6.02%, thus providing some
support for Prediction 4.
In order to determine whether male androphilia clusters within families among the Istmo
Zapotec, the current study compared the proportion of muxe relatives in the paternal and
maternal lines of gynephilic males and muxes. Comparisons between transgender (muxe
gunaa) and cisgender (muxe nguiiu) muxes revealed that both reported analogous family
patterning of male androphilia. This held true when comparing the paternal and maternal lines
separately, and when combined. There was, however, one significant difference observed
between the two types of muxes. Muxe gunaa reported having more androphilic male cousins
via maternal aunts than did muxe nguiiu (Table 1). Given that a substantial body of research
demonstrates that transgender and cisgender male androphiles share numerous
biodemographic correlates [
], there is no a priori reason to predict why this pattern would emerge
within this specific kin category alone. This difference, while statistically significant, is
probably an artifact of the small sample size for muxe nguiiu in this kin category (n = 40). As such it
is likely to be the result of type I error. These subtle differences did not overshadow the larger
pattern, which showed that muxe gunaa and muxe nguiiu did not differ with respect to the
clustering of male androphilia within their families.
After establishing that the two types of muxes had comparable proportions of androphilic
male relatives, groups were combined in order to compare them to gynephilic males.
Consistent with previous family studies conducted in both Euro-American and non-Euro-American
cultures, the results presented here provide evidence that Istmo Zapotec muxes have more
muxe relatives than gynephilic males. Muxes reported having more muxe relatives in the
paternal line than did gynephilic males (Table 4). However, when comparing within groups, there
were no significant differences with respect to the prevalence of muxe relatives in the paternal
and maternal lines for both muxe and gynephilic male probands (Table 5). Taken together, the
10 / 17
results suggest that male androphilia clusters in the families of Istmo Zapotec muxes, and this
clustering is equivalent in both the maternal and paternal lines.
It has been suggested that male androphilia is not a trait governed by simple Mendelian
inheritance (i.e., single gene accounting for the expression of a trait), but requires instead a
multifactorial genetic explanation involving both X-linkage as well as autosomal-linkage
13, 14, 49
]. The current study provides findings that are consistent with this conclusion
among the Istmo Zapotec. We did not find strong evidence implicating X-linked genetic
factors as exclusively underpinning male androphilia because muxe probands did not exhibit a
significant preponderance of muxe relatives in their maternal lines overall (Table 5), nor
among the specific kin with whom they are capable of sharing X-linked genes (i.e., maternal
uncles and cousins via maternal aunts) (Table 4). The fact that our data did not support an
exclusively X-linked genetic explanation for male androphilia does not mean that genes on the
X-chromosome do not play a role in the maintenance of male androphilia within this culture.
Instead, it is likely that Istmo Zapotec muxes and androphilic males elsewhere inherit both
autosomal and sex-linked genes that act in synchrony (i.e., polygenic inheritance) to influence
the development and expression of sexual orientation. In supporting this argument, both
Xlinked (i.e., Xq28) and autosomal (i.e., the centromeric region of the chromosome 8) genetic
regions appear to be involved in the development of male androphilia [12±14].
In addition to examining familial patterning of male androphilia, this study also produced a
population prevalence estimate of male androphilia among the Istmo Zapotec. The upper and
lower bounds for this estimate were the proportion of muxe relatives among the families of all
muxes combined and gynephilic males, respectively (Table 4). As such, the true prevalence of
male androphilia among the Istmo Zapotec is estimated to fall between 3.37±6.02%. This is
largely consistent with estimates derived from Euro-American cultures, where the population
prevalence of cisgender ªgay menº falls between ~1±5% [
]. The current estimate, while
valuable, does not tell us the actual differences in prevalence between cisgender and
transgender muxes in the Istmo, as participants were not asked to identify their muxe relatives as being
muxe nguiiu or muxe gunaa. Nonetheless, the population prevalence rate of muxes, which is
composed by a highly noticeable number of muxe gunaa, appears to be much higher than the
prevalence of Euro-American transsexual women (i.e., biological males who opt for sex
reassignment surgery), which is notably smaller (i.e.,< 0.001%) [50±52].
The Istmo Zapotec are somewhat unique in that both cisgender and transgender forms of
male androphilia occur at appreciable rates in the culture. It is unclear, however, how
androphilic males within the same culture come to adopt either a cisgender or transgender identity.
Semenyna and colleagues [
] argued that the differences in gender identity and gender-role
enactment between cisgender and transgender androphilic males are a result of the manner in
which male androphilia is culturally elaborated. There are several factors that could influence
whether an androphilic male in the Istmo Zapotec will adopt a cisgender instead of a
transgender identity. Primary among them are variations in female-typical behavior,
acceptance/tolerance of feminine gender expression in males by family members or peers, and exposure to
Euro-American culture. The Istmo Zapotec represent a suitable model in which to test
whether these or other factors are responsible for the gender role enactment of the different
muxe types, and what specific influences canalize the development of either a transgender or a
cisgender identity among androphilic males.
This study, coupled with other family and twin studies (see above), indicates that male
androphilia is familial, while molecular genetic studies indicate that it is partly influenced by
genetic factors. These insights, however, raises further questions as to how exactly genes
associated with male androphilia persist across generations given that androphilic males reproduce
at far lower rates than gynephilic males, if at all [
]. The two most prominent explanations
11 / 17
for this evolutionary conundrum are the Kin Selection Hypothesis (KSH), and the Sexual
Antagonistic Gene Hypothesis (SAGH) .
The KSH holds that genes for male androphilia persist over evolutionary time if androphilic
males behave altruistically (e.g., provide care or resources) toward their close kin with whom
they share numerous copies of their genes by virtue of common descent. This altruism may
then increase kin fitness, thus offsetting the costs of not reproducing directly . Research
conducted on cisgender androphilic males in industrialized cultures has provided little support
for the KSH [2, 54±58]. In contrast, research conducted on transgender androphilic males in
Samoa has repeatedly found support for the KSH by means of elevated kin directed altruism
among fa’afafine [59±64]. Because the transgender form of male androphilia appears to be
ancestral to the cisgender form [
], the former likely represents a better model when testing
evolutionary hypotheses pertaining to male androphilia than the later.
The SAGH±±a complementary rather than competing hypothesis±±states that genes
associated with male androphilia reduce reproduction when present in males, but increase
reproduction when present in the female relatives of androphilic males [
]. Some studies conducted
on cisgender androphilic male in Euro-American cultures have provided results consistent
with the SAGH (Italy: [
16, 66, 67
]; Caucasian participants in the UK: [
]), whereas others
have not (USA: [
]; non-Caucasian participants in the UK: ). It is possible that the
existence of reproductive stopping rules, which leads to lower fertility rates in Euro-American
cultures, limits the increase in female reproduction that is hypothesized by the SAGH. However,
studies of the SAGH in Samoa have shown that while the maternal grandmothers and mothers
of fa’afafine demonstrate elevated reproduction, maternal aunts do not, leaving support for the
SAGH equivocal at present [
In line with the KSH, GoÂmez and colleagues [
] demonstrated that muxes recall elevated
indicators of childhood separation anxiety, which appears to be a developmental precursor to
elevated kin-directed altruism [
]. Additionally, the results presented in this study are
consistent with the SAGH, in that families of muxes were comprised of a higher number of
total relatives compared to those of gynephilic males (Table 4). Nonetheless, a detailed
comparison of the expression of kin-directed altruism, as well as the offspring production among
the extended relatives of Istmo Zapotec gynephilic males and muxes, should be conducted in
order to adequately test both the KSH and the SAGH. Given the inconsistencies across studies
associated with the KSH and the SAGH, the Istmo Zapotec offers a compelling locale to
conduct further tests among a non-Euro-American, high fertility population where male
androphilia is commonly expressed in both the transgender and cisgender form.
There are several limitations in the current study that deserve comment. First, the identity
status of muxe relatives was not corroborated with the male relatives themselves. That being said,
none of the family studies that have been conducted to date have independently corroborated
the sexual orientation of the relatives of participants. We suspect that Istmo Zapotec
participants are probably less likely to misreport the sexual orientation of their male relatives
compared to Euro-American study participants, because the former live in a culture where
androphilic males constitute a distinct gender category, in which identification as muxe±±
whether nguiiu or gunaa±±is both obvious and an unambiguous indicator of male androphilia
], whereas the latter do not. Furthermore, during many of the interviews, participants
consulted with nearby members of their family in order to provide a precise report of their
family pedigree. To a large extent, this reflects the reality of conducting fieldwork in a
collectivistic cultural context where individuals are in close proximity to their family much of the time.
12 / 17
The advantage of this is that information provided by the probands can be corroborated,
corrected, or elaborated upon by those family members who are present. Moreover, the sexual
activity and orientation of individuals is the source of much monitoring and gossip and, as
such, is rarely kept secret to the extent that is possible in more individualist cultures. The
disadvantage is that group differences could conceivably exist between those who provide
information versus those who have input from family members. We did not perceive any
differences in this regard, but we have no data that speaks to this possibility. This issue could
be addressed in future studies.
Second, the aims of this study were to determine patterns of familial clustering and
prevalence of male androphilia among the Istmo Zapotec as opposed to patterns and prevalence of
the specific form of male androphilia (i.e., cisgender or transgender). Consequently,
participants were not asked if their muxe relatives identified as muxe gunaa or muxe nguiiu. As such,
we are only able to draw firm conclusions regarding the familial patterning of male androphilia
in general, but not the specific ways cisgender and transgender male androphilia cluster in
Because male androphilia occurs at a relatively low frequency in any population, this study
utilized a network sampling procedure. It is possible that this method produced a sampling
bias, resulting in an unrepresentative sample of Istmo Zapotec muxes, men, or both. Efforts
were made to avoid such bias by interviewing participants throughout the city of JuchitaÂn de
ZaragozaÐthe largest urban center in the Istmo region±±as well as 14 towns and villages
throughout the JuchitaÂn and Tehuantepec districts in the Istmo region of Oaxaca. Nonetheless,
future research conducted in the Istmo Zapotec could consider using random sampling
This study on the Istmo Zapotec muxes, coupled with the research conducted on the Samoan
5, 26, 27
] and Euro-American gay men [6, 15±18], suggests that having more
androphilic male relatives is a cross-culturally universal aspect of male androphilia. This is the first
study that has compared cisgender and transgender androphilic males in the same culture,
showing that both report analogous proportions of androphilic male relatives, and a familial
patterning of male androphilia that is overwhelmingly similar. The findings presented in this
study are in accordance with previous research, which suggest that both forms of male
androphilia share similar biological foundation. Future studies should directly assess different
biological traits (e.g., genetic, morphological, and neurological) in order to determine the extent
to which biological similarities between cisgender and transgender androphilic males exist.
S1 Appendix. Question about your father's and mother's side of the family (English Version).
S2 Appendix. Question about your father's and mother's side of the family (Spanish Version).
We thank Dan Weeks, Julio C. JimeÂnez RodrÂõguez, Felina Santiago, ReneÂ DÂõazleal Vega, Cesar
Miravette CorteÂs, and Francisco J. LoÂpez Bartolo.
13 / 17
Conceptualization: Francisco R. GoÂmez, Paul L. Vasey.
Formal analysis: Francisco R. GoÂmez, Scott W. Semenyna.
Funding acquisition: Paul L. Vasey.
Investigation: Francisco R. GoÂmez, Lucas Court, Paul L. Vasey.
Methodology: Paul L. Vasey.
Project administration: Paul L. Vasey.
Supervision: Paul L. Vasey.
Writing ± original draft: Francisco R. GoÂmez.
Writing ± review & editing: Scott W. Semenyna, Paul L. Vasey.
14 / 17
15 / 17
16 / 17
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