Male Homosexuality: An Adaptation


MALE HOMOSEXUALITY: AN ADAPTATION                       Megan Funck

Homosexuality is currently a hot topic, due to the recent calls for marriage equality, although it most certainly is not a new or unique phenomenon. Most (if not all) cultures around the world have traditions and evidence of engaging in forms of homosexuality. Despite its prominence in human (and non-human primate) cultures , homosexuality does not overtly and directly contribute to reproductive success, and thus is a puzzle in conjunction with current evolutionary theory. However, it is reasonable to hypothesize that because homosexuality is such a widespread trait, that it served, and does serve, some adaptive purpose(s). The following paper will explore possible models of homosexuality as an adaptive strategy, while discussing the effects it contributes in cultural and individual realms. The evolutionary hypotheses of homosexuality which will be discussed are alliance formation and bisexuality, homosexuality as a side-effect of advantageous feminine traits, parental manipulation, and kin selection. .

This paper will not delve into any of the specific mechanisms for how homosexuality comes to be expressed in the individual. It should be mentioned, however, that current evidence suggests that homosexuality is correlated with many different traits: some genetic, some developmental, and some experiential (Kirkaptrick 2000:390). Birth order, genetics, intrauterine environment, culture, and other factors can come into play in determining one’s sexual orientation. While these are important, they are separate from the evolutionary issue of the existence of homosexuality. Researcher Edward Miller asserts that even “if an “environmental” explanation [for homosexuality] comes to be accepted, there will still be the evolutionary question of how humans evolved so as to have a genotype in which environmental factors could cause certain individuals to have a phenotype so poorly adapted to continuing the genotype as homosexuals are”(Miller 2012: 3).When hypothesizing that homosexuality is an adaptation, it is being assumed that it is inherited in one way or another, but this does not necessarily mean that the only way it can be passed on is through genetics- culture too can be an effective way of passing on traits (Kirkpatrick 389).


Anthropologist R.C. Kirkpatrick argues that same-sex alliance formations are greatly beneficial to individual and cultural success, which is how homosexual behavior evolved.  Humans and non-human primates rarely have sex for procreation, and there are non-procreative benefits to sex. When  we have sex, feel-good hormones are released (oxytocin and prolactin) which facilitate bonding behaviors. Homosexual and heterosexual sex are both used as a form of exchange (Kirkpatrick 398).  Our primate cousins have been observed to engage in homosexual behavior for maintenance of social relationships, and it is rational to assume that since we share a common ancestor, same-sex alliances were an important  part of our pre-human evolutionary past, which would  result in a psychological disposition for same-sex affiliation (Kirkpatrick 397).  Kirkapatrick cites examples of societies in which homosexual bonds were beneficial, such as in Native American tribes, where those individuals in homosexual pairings had more reliable food intake (Kirkpatrick 393).

Kirkapatrick argues there is significant data which indicates that most individuals who have engaged in homosexual behavior are actually bisexual in definition, especially those in traditional societies where homosexual behavior is encouraged along with heterosexual marriage (Kirkapatrick 394). Bisexuality would clearly have more direct reproductive benefits than homosexuality, and can therefore be seen as more adaptive than strict homosexuality. Bisexuality would allow one to form strong same-sex alliances, while also simultaneously allowing one to produce offspring. In some societies, such as 17th century Japan, classical Athens, some societies in Melanesia, and among the Hawaiian ali’i,  it was expected that men be attracted to other men (Kirkapatrick 397).

In the Gebusi tribe of New Guinea, young men often engaged in homosexual relationships before they had any type of sexual experience with a female. Once married,  many men still participated in same-sex relations, and it was not taboo or discouraged by their wives (only when the men had sex with another woman was it considered an affair). This system was very adaptive- especially in this particular tribe where others were frequently murdered  on suspicion of practicing witchcraft- the probability of being accused and murdered would likely be less for those who had a higher number of strong bonds and alliances (Knauft:2010:72).

The alliance formation hypothesis has some holes, as it does not directly deal with the issue of there existing men who identify themselves as solely homosexual and who never engage in heterosexual sex, but asserts that nearly all men who engage in homosexual behavior are bisexual. However, it could be that humans are not either one of three sexual orientations (homosexual, heterosexual, or bisexual), but that all humans are innately bisexual, with the potential to be attracted to either sex. Freud argued that “neither homosexuality nor heterosexuality is learned; it is bisexuality that is forgotten” ( Kirkapatrick 397). In relation to this, it could be considered that somewhere along our human evolutionary path, it is likely that some men who had a  homosexual orientation were in cultural circumstances where they were convinced (or coerced) to marry and produce offspring (and possibly engage in same-sex relationships in addition, or suppress their homosexual instincts).  In this scenario, the potential negative reproductive effects of their homosexuality were not realized, but the positive effects potentially were (such as forming same-sex alliances and/or the benefits of possessing adaptive feminine traits), therefore homosexuality became adaptive under those circumstances.  There are many modern examples of men who identify themselves as homosexual who have married and had children. For example, it was a common suggestion several decades ago in the Mormon religion for men who were “struggling” with homosexuality to try to “cure” it by marrying. Many of these men married and had children, and ended up suppressing their homosexual desires. It seems that non-attraction to females does not mean that a homosexual man can not still perform sex with a woman and pass on his genes . However, in cultures such as these, there are increased suicide rates and depression among homosexual male adolescents and men, due to extreme social pressures, stress, and possibly from the belief instilled in them that their homosexuality is a “sin”.  Today, it is possible that some individuals who are engaging in solely homosexual relationships may be doing so now because it is becoming more culturally acceptable- whereas if they were living in a different culture/time/place, they would conform to social pressures and end up marrying a woman despite their sexual orientation.


Some researchers hypothesize that feminizing traits are advantageous in heterosexuals who carry them (Zietsch: 2008: 425), and that homosexuality is  a less-common side-effect of the possession of these traits (Dewar:2003:228). In males, there a number of alleles which affect levels of femininity. If only some of these alleles are possessed, then reproductive success is enhanced. If many of the alleles are inherited, then even the feminizing trait of male attraction is produced (Zietsch 425).

Researcher Colin Dewar hypothesizes that with the arrival of agriculture 10,000 years ago, humans, especially men, were under new and different selective pressures. Prior to the advent of agriculture, humans typically lived in smaller hunter-gatherer groups, and  men would have had an advantage if they were more aggressive, daring, and competitive (typical masculine traits) (Dewar 228). Engaging in physical combat with other males may have been a frequent occurrence. In the new world of agricultural production, humans began living in larger populations and were in close social contact with one another. Whereas previously, success may have depended on more typically masculine traits, these traits were now maladaptive. In turn, more feminine traits (such as better language skills, patience, and the ability to carefully plan) were now adaptive.

Having these feminine traits in this environment would assist one in “getting ahead” and gaining a higher social status, rather than aggression or competitiveness. As civilization further developed, financial wealth and social status became the markers of success. Women are naturally drawn and attracted to (and in turn, mate with)  males who are successful. There is evidence that women are also directly attracted to men with feminine traits such as tenderness, kindness, and feminized faces (although this fluctuates with the menstrual cycle) (Zietsch 425). Therefore, if these beneficial feminizing traits were expressed in a heterosexual man, who then become successful due to these traits, and in turn produced a lot of offspring, these traits were adaptive.  Dewar asserts that even for men who carry these feminizing traits, it would not automatically mean they will be homosexual, but that many environmental factors (including intrauterine or after birth) come into play in ultimately determining sexual orientation (Dewar 230).There is some evidence which could support this hypothesis, including the fact that the brains of homosexual men function differently than those of heterosexual men- they function more similarly to those of heterosexual females in many specific ways. For instance, research showed that homosexual men and heterosexual females had more connections from the right amygdala, while homosexual females and heterosexual males had more connections from the left amygdala. (Gooren: 2006:597).  Homosexual men have also been shown to have superior language skills compared to heterosexual men- similar to the language skills possessed by heterosexual females (Dewar 229).


The parental manipulation is one evolutionary hypothesis for homosexual behavior which has little support, but some anecdotal evidence  The premise of parental manipulation is that parents can manipulate their selected offspring by encouraging them to take non-heterosexual roles in life, which would bring benefit to the parents by increased social status, which would enhance their success. An extreme example of this would be when parents castrate their sons to qualify them to be eunuchs in the Byzantine Court (Kirkpatrick 393). Another example is parents who would make their sons be sexual servants to influential leaders (in 15th century Florence). This again raises the question of how much culture can influence an individual’s sexual desires. It is apparent in the case of some homosexual men, culture influences sexual orientation very little. They are homosexual despite the ideals of their culture, which ostracizes, condemns, and judges those who are homosexual.


The kin selection hypothesis was first constructed by Trivers and Spith, who hypothesized that although homosexual men did not reproduce directly, they reproduce indirectly, by channeling resources and energy to relatives (Bobrow 362). Other researchers (Ruse and Weinrich) who supported this theory assert that males who are homosexual are those who had poor mating prospects from early in life, and that homosexual men were lower in weight and did not carry as much muscle mass and bone density as heterosexual men (Bobrow 362). Researchers Bobrow and Bailey conducted surveys that included men who identified as homosexual, and men who identified themselves as heterosexual. The survey asked questions such as “Have you contributed financially to a relative? How much?”, “How often do you talk on the phone with your mom?”, and many more similar questions. The results found that homosexual men were not more generous to their relatives than heterosexual men, and that they were more emotionally distant from their families (Bobrow 366).

Although there isn’t yet sufficient evidence in support of the kin selection hypothesis, it should not be completely dismissed as a possible model. It is important to consider that the tests conducted to gather data for this hypothesis were done in modern America, where there has been a strong bias against homosexuality, mostly due to religious persuasions (Adamczyk:2009:339). This is most certainly not representative of all human history and may be a completely different environment from the one in which this trait first became adaptive. If a person who is homosexual belongs to a family who ostracizes and is non-accepting of him or her due to their sexual orientation, it is not likely this individual will want to contribute extra energy (money or time) to benefit them.  In other cultures, past or present, where homosexuality is not seen as something “wrong” or “unnatural”, it seems much more likely that a person with homosexual orientation would contribute to their relatives.

In conclusion, there is not yet a definitive answer to the question of why homosexuality is a trait which is so widespread. It is possible that it is being approached from the wrong angle- as it is “a fallacy to assume that all components of a behavioral act are under equal selection pressure, and [to treat] behavioral acts as discrete adaptive units when in fact they usually have both adaptive and nonadaptive and neutral components (Dickemann:2000: 399). The current adaptive hypotheses require more research. The hypothesis that homosexuality is a side effect of other genetic components which were adaptive includes the most direct evidence and provides the strongest argument, due to the fact that homosexual men have similar traits as heterosexual females, such as similar brain function and language skills. Kirkpatrick’s alliance formation hypothesis can provide much insight on the adaptation of bisexuality, which is much more widespread than homosexuality. There is strong evidence that same-sex alliances were very important in our evolution as a species, and bisexuality behavior could be used as a viable vehicle to strengthen same-sex bonds while still allowing for direct reproductive success. However, the alliance theory does not address the existence of individuals who are solely homosexual (and who have differing brain function of heterosexual men to illustrate it). The parental manipulation model seems weak and needs more evidence. It is difficult to imagine that parental influence could affect sexual evolution so drastically. The kin selection hypothesis, which asserts that homosexuals would have channeled more resources to their relatives, may have been true in the past, but there is no evidence today that this is or was the case. All of these adaptive hypotheses of human homosexual behavior are valuable in providing potential models of the evolution of homosexuality, but can not be made into more solid theories until there is more concrete evidence.







          • REFERENCES

Adamczyk, Amy. 2009. Social Science Research Volume 38. “Shaping Attitudes about homosexuality: The role of religion and cultural context”. Pp338-351


Bobrow, David. Bailey, Michael. 2001. Evolution and Human Behavior volume 22. “Is male homosexuality maintained via kin selection?” pp 361-368


Dewar, Colin. 2003. Medical Hypotheses “An Association Between Male Homosexuality and Reproductive Success”. Pp225-232


Dickemann, Jeffrey. 2001. Current Anthropology volume 50. Review of “The Evolution of Human Homosexual Behavior”. pp385-410


Gooren, L.2006. Hormones and Behavior volume 50. “The Biology of Human Psychosexual Differentiation”. Pp589-601


Kirkpatrick, R.C. 2000. Current Anthropology volume 41. “The Evolution of Human Homosexual Behavior”. Pp385-410


Knauft, Bruce. The Gebusi: Lives Transformed in a Rainforest World. 2010. McGraw Hill Publishing.


Miller, Edward. 2000. Archives of Sexual Behavior.Volume 29. “Homosexuality, Birth Order, and Evolution: Toward an Equilibrium Reproductive Economics of Homosexulity”.

Zietsch, Brendan. 2008. Evolution and Human Behavior volume 29. “Genetic Factors Predisposing to Homosexuality May Increase Mating Success in Heterosexuals”.pp 424-433