Homosexuality as a Conundrum: Persistence of a Trait over Time and the Evolutionary Dance

Darwin’s Theory of Evolution has apparently thrown a metaphoric “curve ball” of homosexuality at humanity, and towards scientists in particular. Why would such a seemingly maladaptive trait, one that causes an individual to lose its reproductive fitness, persist throughout existence, especially in humans? To explain their quandary briefly, if a person cannot reproduce and pass on their genes, the trait should reduce in frequency over time, causing the organisms with that trait to perish. That is what Darwin’s theory would conclude, or would it? There are no shortages of layperson explanations about the existence of homosexuality. And if one examines the scientific arena, discussions are ubiquitous and some major hypotheses have been suggested by evolutionary scientists.

Regardless of whether or not science had produced answers to explain the mystery of homosexuality, this trait has persisted in animals and humans since time immemorial. Within the framework of evolutionary theory, the trait of homosexuality might conceivably be passed to successive generations by those who are reproducing and contributing to the gene pool. To better understand this, it is necessary to broaden our idea of sexuality to include many different expressions of sexuality, which do not fall into the traditional definition of exclusive homosexuality. In addition, science has focused on individual reproductive success, overlooking the significance of reproductive success at the population level.

Furthermore, scientific inquiry must look beyond modern-day humans and animals. It is necessary to examine “primitive,” pre-industrialized cultures and ancient human cultures to understand homosexuality within an evolutionary context. The persistence of homosexuality at a stable rate over time shows that it must have a beneficial effect and intrinsic value in the human population. Moreover, it likely contributes to the survival of our species. One hypothesis, the kin selection hypothesis, attempts to explain how the lack of reproductive fitness in homosexual individuals can be counterbalanced by looking at overall reproductive fitness. An organism’s inclusive fitness, or ability to successfully pass on genes, is reliant on direct fitness and indirect fitness. Direct fitness depends upon an individual procreating to pass alleles to its offspring, which in turn, successfully reproduce. Indirect fitness relies on an individual’s ability to pass traits through the reproduction of related organisms, which possess alleles in common with the non-reproducing individual. The kin selection hypothesis suggests that individuals, in this case homosexuals (with an emphasis on males), are able to facilitate the movement of alleles into future generations secondarily by helping to assist in the reproductive success of close family members. According to this hypothesis, indirect fitness possibly compensates for lack of direct fitness in homosexuals, allowing the persistence of this trait in the population (VanderLann and Vasey 2014:1009-1010).

A study by Vasey et al. (2007:164) sought to evaluate kin selection’s central assumption by comparing altruistic behavior of androphilic and gynephilic males in Independent Samoa. Androphilic “men,” known as fa’afafine, vary from highly effeminate to slightly masculine and are attracted to masculine “straight” men. Gynephilic men are typically heterosexual, are often attracted to these feminine men, and even will have sex with other “straight” men if women are not present (Vasey and VanderLann 2010:822). The research concluded that androphilic men revealed notably greater avuncular tendencies (nurturing tendency toward relatives) than their gynephilic counterparts. This provides some support for the kin selection hypothesis for androphilic men and indicates the potential that such men act as helpers, assisting with care of siblings, nieces and nephews. And such aid to family might enhance indirect fitness through their relatives’ reproductive successes. While this study highlights the likelihood that the stronger uncle-like tendencies of the androphilic men are “the adaptive products of special evolutionary design,” scientists cautioned that they lacked sufficient data to support that conclusion (Vasey et al. 2007:165).  They suggested one alternative that the heightened uncle-like behaviors of the fa’afafine could possibly indicate a basic inclination of all men to invest in relatives regardless of sexual preference. Additionally, Vasey et al. considered the idea that some men might display uncle-like tendencies, because they do not have to raise their own children and live in a socially and geographically connected environment with their kin. Researchers suggested the need for further study to compare androphilic men with gynephilic men without children and to see if loss in reproductive fitness is offset by inclusive fitness gained by assisting such family members (Vasey et al. 2007:166).

In 2008, Vasey and VanderLann conducted a study to determine if increased avuncular tendencies were a consequence of lacking biological children, permitting more time for investment in close kind. They compared the avuncular tendencies of androphilic men with gynephilic men without children to see if the lack of direct parental obligations played a role in such propensities (Vasey and VanderLann 2010:822-823). Nevertheless, the nurturing inclinations of the fa’afafine were substantially elevated when compared to their childless gynephilic counterparts. In fact, gynephilic men, whether childless or not, did not show any remarkable distinction with regard to this evaluation. Subsequently, the researchers analyzed to see if gynephilic men with a certain amount of children correlated negatively with scores for avuncular tendency, and no such correlation was identified. Thus, parental duties or the lack thereof did not appear to explain the increased avuncular disposition among androphilic men (Vasey and VanderLann 2010:827). These authors still felt research was lacking to show that the “fa’afafine’s androphilia is characterized by special design features that are indicative of adaptations” (Vasey and VanderLann 2010:827).  One of the conclusions of this study was that the fa’afafine’s heightened nurturing behavior between close kin may be a fundamental factor in the ability of male androphilic genes to survive (Vasey and VanderLann 2010:827).

While the findings in the studies of Independent Samoa provide some support for the kin selection hypothesis, studies in the UK and US did not. In a UK study conducted by Rahman and Hull, questionnaires measuring general affinity, feelings of generosity, and benevolent propensities demonstrated that there were no noteworthy distinctions between heterosexuals and homosexuals (Rahman and Hull 2005:464). When comparing groups of homosexual men to heterosexual men, there was no great distinction with regard toward their altruistic attitude toward their nieces and nephews. Neither group favored certain categories of siblings when allocating resources. This is relevant, because the main tenet of  the kin selection hypothesis purports that homosexuals should disproportionately invest in their closest relatives, like siblings or their children, to benefit from indirect fitness  (Rahman and Hull 2005:465). Another study done in the US reached a similar conclusion, noting that gay men were no more generous to their relatives (Bobrow and Bailey 2001:366).

There are flaws in how the UK and US studies were performed. They were conducted in modern, post-industrialized countries rather than non-Western cultures, which might resemble ancestral or primitive cultures more closely. Unlike Independent Samoa, these countries have more geographically disconnected families, are not as accepting of sexual variance (homophobic), and homosexuals are often ostracized from their families. If homosexuals are more isolated from their families, and thus unable to assist their relatives in familial obligations and potential familial reproductive success, it may be difficult to use this hypothesis explain the steady persistence of this trait in modern societies. In any event, most of human existence is composed of pre-industrial societies. Therefore, these studies do not represent the various societies that have existed over the course of human evolution.

The kin selection hypothesis has severe limitations for a variety of reasons. On a logical level, kin selection itself makes sense. Organisms tend to give preferential treatment to those that are related to them, and it makes sense that overall fitness would be increased as our genes are passed through successful fertility in our relations. It is a rational conclusion that close participation of homosexual family members, like that of Samoa, might assist in maintaining a trait like homosexuality in the gene pool in some cultures. However, this hypothesis rests on the premise that to offset the cost of not directly producing offspring, homosexuals would have to assist their siblings in order to produce twice the amount of nieces or nephews to compensate for each child they would have produced through reproduction (Vasey and VanderLann 2010:827-828). It is hard to show the direct relationship between the nurturing tendencies of homosexuals and the exact mathematical increase in the reproductive success of their relatives. It is also fair to say that scientists using this hypothesis have not addressed female sexuality, modern-day homosexuality, and the wide variation in expression of gender and/or sexuality. More generally, when I was researching, I noticed that the scientific literature was heavily skewed toward male homosexuality. Only Belcombe, Bagmihl, and Neill made references to female sexuality or lesbian behavior. I had to wonder if this bias that favored studying male homosexuality might be affecting scientific research negatively. If a person is working within a heterosexual paradigm and it does not recognize the importance of the female, does this bias affect the way data is collected and analyzed with regard to homosexuality as a trait? It is a serious and valid question that needs to be publicly discussed before undertaking any more research regarding homosexuality.

The studies in Samoa, which give the most support to this hypothesis, are not broadly applicable and are dependent on transgendered behavior, which is not realistically paralleled in modern society. Unlike post-industrialized societies, these transgendered people, the fa’afafine, are sexually attracted and have sex with men that identify as “straight.” The androphilic males in Independent Samoa do not pair up with each other like modern gay couples (Vasey and VanderLann 2010:822). In addition, there are comparatively less pre-industrial societies to study, and therefore, the sampling populations are not substantial enough to be accurate or applicable.

Next, I want to explore homosexuality by looking at the evolution of pleasure as an adaptation. Pleasure is an innate mechanism, or proximate cause, which leads animals to perform certain behaviors that are often adaptive, or enhance survival. Unlike ultimate evolutionary causes, which attempt to explain traits through genetics, natural selection, and reproductive success, this analysis looks at an underlying quality in animals, pleasure-seeking, and its effect on preferences (Balcombe 2009:211). According the Jonathan Balcombe, a researcher of animal behavior, pleasure is a product of evolution. He explains that the evolution of pleasure was reliant on two other developments: the development of movement along with an intricate nervous system for enhanced perception of stimuli in the environment. As movement and complex sensory systems emerged, it became necessary for organisms to develop heightened perception in order to detect unpleasant and rewarding stimuli in the environment. Just as pain developed as an adaptive mechanism to avoid unpleasant circumstances, pleasure is an advantageous adaptation, which provides compensation to an organism for engaging in activities that enhance survival. Pleasure drives organisms to perform positive acts, like seeking out food, copulating, and maintaining body temperature (Balcombe 2009:211). Homosexuality and any sexual expression could be viewed as behaviors resulting from pleasure-seeking, activities which provide gratification and accomplish other survival goals simultaneously. As aptly stated by Balcombe, “We do know that pleasure is a powerful reinforcer of sex drive in humans” (Belcombe 2009:215). He further adds that in the search for sexual satisfaction of desire and accompanying benefits, great sexual diversity is the consequence (Belcombe 2009:215).

To explore this hypothesis, it is helpful to examine the range of non-reproductive activities, in addition to homosexuality, that are ubiquitous in the animal world. Much of sexual activity has nothing to contribute to directly reproductive fitness, yet it still accounts for a significant amount of sexual behaviors (Balcombe 2009:215). Having sex during pregnancy, while menstruating, and outside of breeding season or ovulation provide three noteworthy examples. Group sex, in which few or no individuals pass on their genetics is inefficient. This activity has been documented in spinner dolphins, swallows, and herons, to name a few. Diverse non-copulatory mountings are abundant as well including: mounting without apparent sexual arousal, mounting without consummation, female/male mountings, or mounting in positions that do not allow for fertilization. Masturbation, oral sex, stimulation of another organism’s genitals, anal manipulation, and interspecies pairings (all activities plentiful in the animal world) are behaviors that offer no added reproductive consequences (Balcombe 2009:215-216).  Chimpanzees and baboons have been seen mating with each other in the wild (Bagemihl 1999:328), which must be considered a futile effort (Balcombe 2006:115). Particularly interesting is homosexual behavior among birds. Parrots and gulls often form same-sex pairings, perform courtship rituals, and nest together. To illustrate, female New Zealand gulls often go through the motions of copulation, apparently using a male for sperm only. The females proceed to make a nest, share in incubating eggs, and raise offspring together (Balcombe 2006:110). Other than interspecies sexuality, these behaviors are common in macaques, waterbuck, mountain sheep, and many animals, in addition to humans. (Balcombe 2009: 215-216). Finally, attempting to reach orgasm, either individually or with others, hardly seems necessary for survival, yet it occurs. All of these non-reproductive behaviors discussed are applicable to humans.

The information presented above illustrates that homosexuality is only one of the many non-reproductive behaviors. In my opinion, too much emphasis is being placed on individual losses of fitness. It appears that overall group reproductive success may be enough to pass and sustain successful genes in the population. Pleasures drive organisms to engage in varied behaviors, giving rise to sexual preferences, but also ensuring that enough individuals reproduce to accomplish the long-range goal of survival in evolutionary terms. In this sense, pleasure might also be a large part of an ultimate explanation for the development of sexual preferences, including homosexuality.

Because most of human history occurred prior the modern industrial age, an examination of ancient society assists in providing a deeper understanding of human evolution. Modern society includes the last two hundred to three hundred years, and on an evolutionary scale, this is like “a blink of the eye.” Homosexual behavior has clearly occurred in many ancient societies and appears to have been more accepted in those contexts. I am going to use ancient Mesopotamian culture to illustrate a cultural view that differs greatly from our modern vantage point. According to James Neill, who extensively researched homosexuality in human and animal societies for twelve years, it is reasonable to conclude that homosexual behavior was very common among Neolithic peoples and their Paleolithic ancestors. He explains that the prevalence of homosexual behavior in primates and in the aboriginal peoples of the world supports this assertion that homosexuality has ancestral roots. (Neill 2009:82). Neill demonstrates the ubiquity of homosexuality by citing examples from art, law, politics, and religious texts (Neill 2009:83).

Archeological evidence from Mesopotamian civilizations from 3000 B.C. reveals clay sculptures that depict people having sex, including numerous depictions of anal sex between men. Codified law contributes more confirmation of ancient attitudes toward same-sex behavior. The Code of Hammurabi from 1700 B.C. contains proscriptions governing sexuality. While it mentions prostitution and marital indiscretion, homosexuality is not addressed. Neill contends that the absence of homosexuality from this code implies cultural acceptance of it. Assyrian law from about 1500 B.C. includes two codes that relate to homosexuality. The mere existence of such laws indicates that same-sex relations were commonplace in ancient Mesopotamia. In fact, King Hammurabi not only had male sexual partners, but his wife discussed that in written correspondence (Neill 2009:83).

Religious texts offer further evidence of homosexuality’s presence. An almanac of Babylonian prayers consists of prayers relating to a man seeking the love of another man. Other religious texts refer to sex between male partners and reference female same-sex relations. Neill concludes that the inclusion of same-sex sexuality in such texts show its significance not only in daily life but also suggest it was viewed as permissible option outside of heterosexual unions. To underscore his position, I will include a quote Neill used in his writing taken from a Babylonian religious text: “If a man has intercourse with the hindquarters of his equal (male), that man will be foremost among his brothers and colleagues”(Neill 2009:84). Obviously, homosexuality was not viewed negatively here, rather male homosexual sex is associated with societal benefits (Neill 2009:83). Neill’s work gives impetus to the argument that homosexuality is an ancient behavior, which existed for our ancestors without the modern-day emphasis on its negative aspects, one of those being lack of reproduction. It is true that there is no way to directly study these types of societies any longer, outside of archaeological examination of their remnants, but a detailed historical examination shows us that our sexuality has been much more diverse and accepting of homosexual behavior over the course of human existence. The historical presence of homosexuality might not give a scientific explanation, but its presence in Mesopotamian cultures and many others signify that it made a significant contribution to human development and societal success.

Given the historical evidence coupled with the varied sexual behaviors of animals, particularly primates, it is evident that homosexuality is a constant trait. The underlying scientific controversy lies in trying to determine what caused the trait and its persistence. Both of the above-mentioned hypotheses shed some light on this phenomenon. The kin selection hypothesis has its flaws, but it has something to offer in terms of increased indirect fitness. In general terms, organisms share similar genes. Thus, when those related to us have offspring, they pass down traits in common whether each of us individually reproduces or not. I feel this applies to all humans and organisms, regardless of whether individuals assist kin or are homosexual. Having said that, in contrasting modern culture with ancient cultures, it is a reasonable deduction that the infant mortality rate was higher for societies in ancient history. With that in mind, homosexual, transgendered, or non-reproducing individuals likely helped by providing assistance to their relatives to ensure a higher success rate in the pregnancies that occurred within the group as a whole. Belcombe’s hypothesis, one that proposes that pleasure is an evolutionary adaptation, is my favorite of the two that I have presented. Its basic, logical assertion is that pleasure-seeking is an innate, universal force residing in all organisms (including humans), which has led to the development many preferences, including sexual inclinations like homosexuality. The quest for pleasure brings gratification to humans while simultaneously accomplishing the tasks of survival. It seems key to the survival of our species.

Darwin’s theory of evolution has more depth than many give it credit for, and it recognized the obvious diversification of species, especially that which formed in response to particular environmental pressures. His theory did not revolve around the individual, but rather groups of individuals developing in ecological niches. Both competition and cooperation took place during evolution. When Darwin’s theory is oversimplified to only embrace the individual’s ability to reproduce, pass on genes, and engage in a competition for survival, it undermines the importance of life experiences and individual diversity. While competition plays a role in evolution, cooperation has been vital to human existence. There does not appear to be a Darwinian paradox at all, but rather it seems that the population has variations, one of those being homosexuality. I am genuinely surprised that many scientists view this supposed lack of some individuals to reproduce to their full potential as clashing with the theory of evolution. Darwin’s writing about social insects illuminates how valuable non-reproducing individuals can be to a community, and he sees no conflict between their sterility and natural selection:

I will here take only the case of working or sterile ants. How the workers have been rendered sterile is a difficulty; but some insects and other animals in a state of nature do occasionally become sterile, and if such insects had been social, and it had been profitable to the community that a number should have been born capable of work, but incapable of procreation, I can see no especial difficulty in this having been effected through natural selection (Darwin 1979:140).

It is not that unusual for certain individuals not to reproduce or to encounter challenges with reproduction. In reality, mate choice often causes individuals to lose reproductive success, when infertility presents itself. Couples may not be able to have children due to fertility issues. Many humans choose to remain single and outright decide not to have children. Certain people live a life of abstinence, for example, monks or nuns in religious orders. Outside of religion, individuals may be asexual for personal, or perhaps biological, reasons. Belcombe’s studies showed that there is also an abundance of non-reproductive sexual activities, which do not lead to offspring and could be argued to cause a reduction in fitness. In the scheme of life, homosexuals represent only a portion of those not reproducing, and some people that identify as homosexual do procreate. Why are we not questioning the other non-reproducing humans, but continue to question the reason for the existence of homosexuality? It is possible to view those that forego having children as benefiting overall success by mitigating over-population and allowing more resources to be available for the entire society. Non reproducing individuals assist the broader society, taking on roles that reproducers may not be able to accomplish efficiently. The benefits that might arise from same-sex pairings could be hard to detect and quantify, especially, but not limited to looking at the gene pool.

There are aspects of sexuality that must be examined in order to explain one possible reason for the persistence of homosexuality in our genetics. Sexuality, as a trait, is difficult to measure scientifically, and it is possible that human sexuality can be viewed more accurately as occurring on a scale or continuum. Alfred Kinsey expressed his thoughts on this topic in the following quote:

Males do not represent two discrete populations, heterosexual and homosexual. The world is not to be divided into sheep and goats. It is a fundamental of taxonomy that nature rarely deals with discrete categories . . . The living world is a continuum in each and every one of its aspects (Kinsey, et al.1948:639).

Sexuality is defined in a rigid, dichotomous manner. For example, some people consider themselves heterosexual, but they have engaged in homosexual behavior during their life. The heterosexual men in Samoa discussed above are a case in point. Likewise, others identify as homosexual, but have engaged in heterosexual behavior throughout their lives. Ascertaining sexual preferences is challenging, partly because people tend to hide parts of their sexuality. There is societal pressure to pick one side of the spectrum and display it “properly” in today’s world. To compound this, some are not aware of their sexual status and the idea that it can change throughout time. If a state of bisexuality is more common in the population than thought, it might explain how this trait is passed from parents to succeeding generations. Sexual preference could present in a part of the human genome, and homosexuality might be one phenotypic expression, occurring at a lower frequency. If this trait is coded for in most or all humans, maybe it is only potentiated in society under certain environmental conditions. Furthermore, a gene might have existed ancestrally, which served a specific function that was vital to survival. While it might have manifested itself one way in more ancient environments, that same gene might express itself as homosexuality in more modern times.

In its simplest form, people might carry a gene or set of genes for the trait of sexuality, which are expressed in a heterozygous fashion (expressed as basically heterosexual). If two such heterozygous persons have a child and a child results that identifies primarily gay, it is a fair assumption that he or she received the gene/genes that allowed for the expression of that trait. Because this trait is seen uniformly across cultures, I think it is likely to be present in some way in a large portion of the population. Keeping this in mind, homosexual behavior should not be viewed as an anomaly in today’s world.

Sexuality is not nearly as concrete as it has been presented during discussions about it. The view of sexuality as either “normal” heterosexuality or “abnormal” exclusive homosexuality has an effect on the way it is studied. Clearly, a variety of sexual behaviors exist in many organisms and cultures–both ancient, modern, and preindustrial types. As shown in my discussion, ancient societies and non-Western societies can offer insights that are not visible when scientists study modern-day societies. This paper has attempted to explain how genes might be passed on and maintained in the gene pool; however, part of the problem with our inability to understand this trait is in our simplistic outlook on how genes determine traits. Just as sexuality is complex, genes need not be as deterministic as they appear. As mentioned before, the manner in which a genetic code is expressed likely changes as organisms evolve and encounter new environments. In other words, one genetic code may lead to many different qualities under varying conditions. If science finds an answer to the question that is so pressing to science and society, it will likely be found by looking at a combination of factors: inclusive fitness, culture, pleasure-seeking, and the manipulation of genes in the presence of environmental factors. There are definitely more hypotheses than I have presented, and some answers might be revealed as more studies are conducted. Regardless of whether or not science finds answers, Darwin’s discussion of social insects that are sterile indicate that the existence of non-reproductive humans does not conflict with natural selection. The importance of cooperation, diversity, and group success and survival are understated by science and society. Homosexuality and all sexual behaviors must be observed and considered in that light.

I want to close by discussing the impact that culture can and does have on humans, in particular. The power of culture should not be underestimated with regard to this subject. Culture affects human choices, and we are raised in a world that values heterosexuality. There are powerful, cultural suggestions about what the “norm” is. People are highly susceptible to such suggestions and want to be accepted by society. This might affect humans as a whole, and consequently, inaccurately reflect the actual number of people that have homosexual inclinations. In more open, accepting environments, this trait might be expressed more and have more visibility if it were valued. Culture might influence choices in sexuality on both a conscious and unconscious level.

References Cited

Bagemihl, Bruce

1999 Biological Exuberance: Animal Homosexuality and Natural Diversity. New York: St. Martin’s Press.

Balcombe, Jonathan

1999 Biological Exuberance: Animal Homosexuality and Natural Diversity. New York: St. Martin’s Press.

Balcombe, Jonathan

2009 Animal Pleasure and its Moral Significance. Applied Animal Behaviour Science 118(3): 208-216.

Bobrow, David and J. Michael Bailey

2001 Is Male Homosexuality Maintained via Kin Selection? Evolution and Human Behavior 22:361-368.

Darwin, Charles

1979 The Illustrated Origin of Species. New York: Hill and Wang.

Kinsey, Alfred C., Wardell B. Pomeroy, and Clyde E. Martin.

1948 Sexual Behavior in the Human Male. Philadelphia:W.B. Saunders.

Neill, James

2009 The Origins and Role of Same-Sex Relations in Human Societies. Jefferson NC: McFarland.

Rahman, Qazi and Matthew S. Hull

2005 An Empirical Test of the Kin Selection Hypothesis for Male Homosexuality. Archives of Sexual Behavior 34(4):461-467.

VanderLaan , Doug P. and Paul L. Vasey

2014 Evidence of Cognitive Biases for Maximizing Indirect Fitness in Samoan Fa’afafine. Archives of Sexual Behavior 43(5):1009-1022.

Vasey, Paul L., David S. Pocock and Doug P. VanderLaan

2007 Kin Selection and Male Androphilia in Samoan Fa’afafine. Evolution and Human Behavior 28:159-167.

Vasey, Paul L. and Doug P. VanderLaan

2010 Avuncular Tendencies and the Evolution of Male Androphilia in Samoan Fa’afafine. Archives of Sexual Behavior 39(4):821-830.



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