Has homosexuality evolved as a response to overpopulation?
While some naïve bloggers make that claim out of poorly advised pondering, claiming such things, they are ill-advised, biologically.
“Given what we know about natural selection as an eminently versatile response to environmental endangerment, and what we know about the genome’s metabolic adaptability, it follows that humans over generations would develop a mechanism within them to check and balance procreative extravagance.”
This statement is incredibly false and is logically unsound according to the basic principles of biological evolution and natural selection. As Richard Dawkins clarifies in his video confronting such claims, emphasizing the fast that “nature does not do population control; that’s not how it works”. Natural selection works at the level of the individual gene and always will be positively selected via survival of the fittest, the “fittest” being the individual who produces the most offspring. Therefore a “homosexual gene” (if one does exist) will not be selected for due to two main factors: 1) it does not confer fitness and 2) it cannot be passed on and therefore be positively selected. The arguments I present in the following paragraphs provide possible exceptions to these two limitations to the “evolution” of homosexuality.
I believe claims such as that made in the second sentence derive from the observation of apparent suddenly exponentially increasing numbers of homosexuals, which is probably more of a social phenomenon, of more “closeted” homosexuals feeling comfortable with their identity such that the apparent number of homosexuals recently increased. And while there may seem to be some historical merit to the “evolution of homosexuality as a population control measure” due to the high prevalence of homosexuality in the flourishing and large city-states of Rome and Greece in comparison with other rural countries of the time, there isn’t nearly enough scientific evidence to confirm even the logical soundness of such a theory; there is probably a much more complex political and biological basis of the phenomenon of more apparent homosexuality concurrent with high population. Besides the social muddling of the proposed theory, one must consider the fact that homosexuality has existed since millions of years ago and occurs in a “a dizzying array of animals”; it is certainly not a novel phenomenon.
In dispute of homosexuality not being evolutionarily selected due to the non-reproduction of homosexuals: “In the US, around 37% of lesbian, gay, bisexual and transsexual people have a child, about 60% of which are biological.” Historically, even more homosexual people had children, “for much of modern history gay people haven’t been living openly gay lives. Compelled by society to enter marriages and have children, their reproduction rates may have been higher than they are now.” This is especially true in non-Western cultures and in traditional societies, “non-exclusive homosexuality [is] common.” Another theory, Kin Selection, claims that this caveat to evolutionary selection can be bypassed through providing care to relatives. Through this familial fitness, a homosexual may pass on a significant portion of “their” genes by helping to raise and increase the numbers of nieces and nephews through increasing the reproductive fitness of their brothers and sisters. This phenomenon has been observed in humans, particularly in the Samoan culture, where a study found the time commitment differential to be true. Bonobos have been studied to investigate the function of homosexuality as a group cohesion reinforcement.
An especially compelling and scientifically sound theory explaining the hereditary mechanisms of homosexuality is that homosexuality is inherited through epigenetics rather than encoded in the actual DNA of the gene. This theory is the only way to reconcile the two facts that, “Research has found that if an identical twin is gay, there is about a 20% chance that the sibling will have the same sexual orientation. While that’s a greater likelihood than random, it’s lower than you might expect for two people with the same genetic code.” And “Since the early 1990s, researchers have shown that homosexuality is more common in brothers and relatives on the same maternal line, and a genetic factor is taken to be the cause.” Since homosexuality is most likely genetic (based on our current understanding) yet is not concurrent in twins at any significant rate, epigenetics must play a role, through more transient and personalized marks on DNA that affect its expression through alteration of histone tails, which can wind or unwind the make DNA accessible for transcription onto functional genes. The one significant flaw in this theory is that in general, epigenetics are mostly inherited “on” the DNA but still within the chromosome such that there difference in twins would not be significant UNLESS they were fraternal.
Other theories regarding the heredity of homosexuality seem to bypass Mendelian inheritance altogether and almost propose constant de novo actualization of homosexuality through specialized maternal conditions. One theory proposes that with subsequent male pregnancies, the mother creates increasing antibodies to the male Y chromosome of the fetus and somehow inflicts effects upon it in such a way to propagate homosexuality. Evidence for this study includes statistics that, “with every older brother the chance of homosexuality increases by about a third,” and low birth weights and high miscarriage rates have been found in women who birth/go on to birth a homosexual male child. Another theory proposes lesbianism to be derived from increased fetal exposure to testosterone, perhaps via epigenetic disposition to uptake more testosterone. Neither of these theories have nearly enough empirical evidence to have any credit, though.
In dispute of homosexuality not being evolutionarily selected due to its failure to confer fitness, various examples of increased reproductive benefit due to homosexuality have been observed in nature. One important thing to remember is that the normative nature of homosexuality in nature is such that it is non-exclusive, such that the animals are actually bisexual and therefore do confer their genes to offspring. Actual fitness increases due to homosexuality have been observed due to homosexual individuals rising up social hierarchies, such that they have access to the most fit males. In some gull species, homosexual behavior occurs in the shortage of males, such that one hen helps another raise her offspring which she bore due to heterosexual relations. No specific such advantages have been discovered that may have been present in Neanderthals and more ancient humanoids such as to maintain homosexuality from monkey and ape populations, as much research has yet to have been explored on the subject of homosexuality.
While there are certainly many proposed mechanisms of homosexuality being inherited and thus selected for by natural selection and thus “evolving” in response to stimuli, though that stimuli definitely is not to prevent overpopulation, as that is not how evolution works. In addition, though it has not been “proven” that homosexuality is heritable, It is obviously absurd to search for “the gay gene” to prove that it is. This is just as naïve as looking for a happiness gene… There is indubitably a complex interplay of many genes in the heredity of sexual orientation.