The gay germ hypothesis

Incidence of chlamydia, a major cause of infertility. The high polygyny rate among the “female farming” peoples of sub-Saharan Africa may have favored the evolution of STDs. Is this where we should look for the precursor of the hypothetical “gay germ”? (source)

 

Heritability for male homosexuality is low to moderate (30 to 45%). There is thus some kind of genetic predisposition, but it’s weak and may simply be a low degree of pre-natal androgenization. All things being equal, such individuals would still develop a heterosexual orientation.

But all things aren’t equal. Something out there is tipping these individuals over the threshold that separates heterosexual from homosexual orientation. What is it? I suspect there are several causes, including the rising level of estrogens and estrogen-like substances in the environment over the past century (see previous post).

The cause may also be a pathogen that alters its host’s sexual orientation in order to enhance its chances of spreading to other hosts. This is the “gay germ” theory proposed by Greg Cochran (Cochran et al., 2000). It’s interesting, and there are certainly precedents for this kind of psychological manipulation … from zombie ants to rats losing their fear of cats.

But so far there’s no smoking gun. No candidate pathogens have been identified, although some STDs seem to have adapted to non-heterosexual modes of transmission, e.g., the bacterium responsible for bacterial vaginosis, particularly Gardnerella vaginalis, and some strains of vaginal yeast (see previous post).

Another objection is that natural selection should reduce host susceptibility. As Ron Unz (2013) has recently argued:

Cochran and others ridicule the gene model as absurd, arguing that strong selective pressure would have rapidly eliminated any such genes from the population, and this is not unreasonable. But similar criticism could applied to their own model, since genetic susceptibility to the germ would obviously be subject to equally powerful selective disadvantage.

A lot of pathogens seem undeterred by this argument. People die all the time from infections of one sort or another. One reason is that pathogens have shorter generation times and thus can evolve faster than their hosts can. An evolutionary equilibrium will eventually fall into place, but it will be heavily weighted in the pathogen’s favor. There are also limits to what a host can do. If the host’s defense system becomes too sensitive, it will attack not only possible pathogens but also host tissues.

Still, the most catastrophic epidemics tend to burn themselves out, largely because they destroy the pool of individuals they can most easily spread amongst. The Plague of Justinian of the 6th and 7th centuries may have wiped out half of Europe’s population. Then it disappeared. The Black Death of the 14th century killed between one and two thirds of all Europeans. It too disappeared, the last possible outbreaks being in the 18th century. This is not the case, however, with STDs, even in places where the consequences are dramatic, such as Africa’s “infertility belt”:

Africa shares the largest burden of infertility in the world. Estimates indicate that an average of 10.1% of couples experience infertility in Africa, with a high percentage of 32% in some countries and ethnic groups within Africa. An infertility belt” spreading through West Africa, through Central Africa to East Africa has been described. In some countries in this belt, up to one-third of women may be childless at the end of their reproductive lives. (Okonofu & Obi, 2009)

A pathogen would not sterilize one third of the population, generation after generation, unless it had something to gain, as Ron Unz notes. In sub-Saharan Africa, infertility can lead to abandonment of the wife, thus making her a better vehicle for pathogen transmission:

The high prevalence of untreated STD, resulting in increased infertility acts paradoxically to increase rather than decrease the fertility in Africa. Infertility is devastating for an African woman, resulting in divorce and diminished social status that often leads to prostitution. The fear of infertility results in refusal of contraception and early childbearing to demonstrate fertility. (O’Reilly, 1986)

Other separated women owe their status to infertility, which is a frequent reason for being driven from marriage and for being unable to marry […] Nadel […] identified such women as a major source of prostitutes: “Adultery and unchastity count less in her than other women. [The] paramount stigma [is] barrenness itself.” (Caldwell et al.,1989)

The existence of Africa’s infertility belt is generally attributed to a high prevalence of STDs, particularly gonorrhea and chlamydia (Collet et al., 1988), which in turn is related to a high polygyny rate (20 to 40% of all sexual unions throughout most of sub-Saharan Africa), which in turn is related to the low cost of maintaining a second or third wife, which in turn is related to year-round hoe farming and the ability of women to support themselves and their children with little male assistance.

We know that the AIDS virus evolved in sub-Saharan Africa, and it may be that syphilis evolved out of yaws, likewise endemic to sub-Saharan Africa. It may be that this region favors the evolution of STDs; if so, we might best look for the precursor of the “gay germ” there as well, assuming of course that it does exist.

 

References

Caldwell, J.C., P. Caldwell, and P. Quiggin. (1989). The social context of AIDS in sub-Saharan Africa, Population and Development Review, 15, 185-234.

https://www.soc.umn.edu/~meierann/Teaching/Population/Readings/Feb%209%20Caldwell.pdf

Collet, M., J. Reniers, E. Frost, R. Gass, F. Yvert, A. Leclerc, C. Roth-Meyer, B. Ivanoff, and A. Meheus. (1988). Infertility in Central Africa: Infection is the cause, International Journal of Gynecology & Obstetrics, 26, 423–428 http://dx.doi.org/10.1016/0020-7292(88)90340-2

Cochran, G.M., Ewald, P.W., and Cochran, K.D. (2000). Infectious causation of disease: an evolutionary perspective, Perspectives in Biology and Medicine, 43, 406-448.

Okonofu, F.E. and H. Obi. (2009). Specialized Versus Conventional Treatment of infertility in Africa: Time for a Pragmatic Approach, African Journal of Reproductive Health, 13, 9-11.

http://www.ajrh.info/vol13_no1/13_1_editorial_english.php

O’Reilly, K.R. (1986). Sexual behaviour, perceptions of infertility and family planning in sub-Saharan Africa, African Journal of Sexually Transmitted Diseases, 2, 47-49.

Unz, R. (2013). “Gay gene” vs. “gay germ”, April 16, The American Conservative,

http://www.theamericanconservative.com/gay-gene-vs-gay-germ/

 

Pathogen-stress theory

A Paris suburb, on the eve of the French Revolution. The shift to democracy and individualism began under conditions of high pathogen prevalence and long before modern sanitation (source)

Is stress from parasites a major cause of psychological differences among humans? Yes, if we are to believe a popular theory in evolutionary psychology. According to this theory, when people develop in a parasite-infested environment, they behave in a way that reduces their likelihood of infection. They become less curious, less exploratory, and less open to strangers. The result is a cultural system that is less conducive to learning, openness, and tolerance—in short, what we like to call progressive values.

As Thornhill et al. (2010) argue:

[…] the predictions of the parasite-stress model are consistent with the marked increase in the liberalization of social values that began to occur in the West in the 1960s and 1970s (e.g., civil rights, women’s rights, gay and lesbian rights, anti-authoritarianism, etc.). In the West, but not outside of it, infectious-disease prevalence was reduced dramatically a generation or two earlier as a result of widespread availability of antibiotics, child vaccination programs, food- and water-safety practices, increased sanitation and vector control.

This theory is used to explain not only cultural differences over time, but also cultural differences over space, i.e., between different human populations:

The parasite-stress model of human sociality provides an evolutionarily informed explanation of why specific human populations inhabiting different parts of the planet (northern Europe versus southern Europe, for instance) are often described by different traits, different values, and different cultural norms.

[…] parasite prevalence also is expected to predict other forms of political liberalism. For example, democratization is accompanied by the liberation of women from the tradition of masculine social control, which manifests in an increase in women’s civil rights and political representation (Inglehart, 2003; Wejnert, 2005; Welzel, 2007). It follows from the parasite-stress model that this form of liberalism should be more pronounced within populations that have a relatively low prevalence of parasites. It is. Across many countries of the world, parasite prevalence correlates negatively with national indicators of gender equality (Thornhill et al., 2010)

Several objections come to mind. Liberalism goes back long before the 1960s. Think of the American and French revolutions. Think of the abolitionists, the chartists, and the suffragettes. These were genuine mass movements that caught the imagination of ordinary people, and not just the elites. Yet they occurred at a time when young men and women routinely died from pathogens under conditions like those of the developing world today. And those conditions persisted well into the 20th century. It really wasn’t until the interwar years that doctors began to cure more people than they killed.

The parasite-stress model has been re-examined by Hackman and Hruschka (2013) with respect to the United States. They confirm that pathogen prevalence correlates with collectivism, strength of family ties, homicide, child maltreatment, and religious commitment. These correlations, however, hold true only for sexually transmitted diseases. Non-STD infections show no correlation with the above behaviors. Moreover, the STD correlation may simply be a side effect of lifestyle choices. As the authors note: “A life history model can explain these ambiguous results by treating STDs as an outcome of faster life history strategies rather than a driver of behavioral adaptations.” Indeed, the data are best explained by two variables: early childbirth and race, i.e., non-Hispanic white American, Hispanic American, or black American:

Our two-component measure [early childbirth and race] showed that across race categories, teenage birth rates are predictive of three-generation households and proportion of the population living alone. We conclude that these findings are inconsistent with the PST [pathogen-stress theory], but fit well with an alternative model based on life history allocations. (Hackman and Hruschka, 2013)

Parasite-stress theory reverses cause and effect. Pathogens are less prevalent in those human populations that have integrated principles of modern hygiene into their lives. Those same populations have also adopted other aspects of behavioral modernity—pacifism, individualism, reduced importance of kinship, etc. More broadly speaking, the construction of freer, more open societies cannot happen without certain psychological predispositions: first, higher anger thresholds and less willingness to use violence as a means to settle personal disputes; second, a time orientation that allocates more resources to the future and fewer to the present. Evidently, if you’re more oriented to the future, you’ll avoid choices that may lead to illness and early death.

This point may seem obvious, yet it’s surprising how unobvious it seems to some people, especially those, like evolutionary psychologists, who should know better. How come? Keep in mind that elite approval is necessary for advancement in society, particularly for academics who work amidst offspring of the elite and who help legitimize the dominant social agenda. To gain acceptance for their own pet ideas, academics unconsciously, or consciously, sign on to the elite's agenda.

As Thornhill et al. (2010) note: “[…] public health initiatives are most likely to have additional consequences for societies (e.g., promotion of civil liberties and egalitarian value systems).” Here, the academic is no longer pretending to be a disinterested observer. The role is more like that of a cheerleader … or worse.

References

Barkow, J.H., Cosmides, L., & Tooby, J. (eds.) (1992). The Adapted Mind. Evolutionary Psychology and the Generation of Culture, New York, Oxford: Oxford University Press.

Hackman, J. and D. Hruschka. (2013). Fast life histories, not pathogens, account for state-level variation in homicide, child maltreatment, and family ties in the U.S., Evolution and Human Behavior, 34, 118-124.

Thornhill, R., C.L. Fincher, D.R. Murray, and M. Schaller. (2010).  Zoonotic and Non-Zoonotic Diseases in Relation to Human Personality and Societal Values: Support for the Parasite-Stress Model, Evolutionary Psychology, 8, 151-169.

http://www.epjournal.net/wp-content/uploads/EP08151169.pdf