"Your sacred identity is literally the symptom of an infectious brain parasite" would be a hell of a pill for the left to swallow, but it certainly looks like a fascinating avenue of research.
All Eukaryotes naturally carry billions of foreign microbio-organisms from even before your birth to your death. They are impossible to avoid, since you absorb millions of microbs just from breathing clear air and drinking clean water. Not all microbs are harmful or parasitic (including ones that are gained by and influence sexual behavior) most are neutral. Not all are like T. Gondii
All Eukaryotes (including Humans) are essentially Superorganisms that have basically co-evolved with the microbs inside of them.
So astounding, wow, kinda makes celibacy seem ok. So many peoples sexual proclivities seem absurd at times, this explains a lot. Such a strange world we live in. Our entire civilization would be radically altered if these parasites could be removed from the human biome. Maybe they could be replaced with genetically modified versions creating positive health outcomes.
"Our entire civilization would be radically altered if these parasites could be removed from the human biome. Maybe they could be replaced with genetically modified versions creating positive health outcomes."
That is a far out idea, but I guess, anything is possible.
The studies linked by Peter Frost never said that these parasites create the desire/urge for non-vaginal sex or the existence of bizarre paraphilias (the latter of which is actually more common in 1st World High-IQ countries).
Paraphilias are more openly practiced in the West, but it doesn't follow that they are less common elsewhere. In fact, some of them (fellatio, pedophilia) are more common in certain non-Western countries.
First, The Czech studies only point out that the parasite increases desire for paraphilic sex (but later leads to less actual engagement in it overtime compared to non-infected people), it never said that it was the origin of paraphilias since non-infected people also engage in these behaviors (and the studies make no claim as to why that is so).
Second, not all paraphilias are the same, nor are they all viewed the same by every culture (and if all non-vaginal sex is “paraphilic” then it's basically a universal across the entire Animal Kingdom). Many paraphilias vary by ethnicity and race in the popularity like the Foot Fetish or BDSM. Also, even studies on the popularity of pornography around the world point out that the Cuckold fetish (where a man actively encourages other men to sleep with their wife or girlfriend) has basically little to no audience outside of the West and mainly with White men in particular.
3rd, we don't need parasites to explain the existence of non-reproductive heterosexual behaviour in Humans nor other Animals. The notion that Sex is ONLY for procreation (a view that is absent in most cultures and religions) has largely been discredited by Neuroscience and Behavioral Genetics. Parasites/Germ theory only makes sense when applied to Homosexuality and Asexuality, both orientations that have zero possible evolutionary benefits.
1. I'm not claiming that paraphilias are always or even mainly due to behavior-altering parasites. Why do you keep saying I'm making that claim?
2. The cuckold fetish was non-existent in the West before the West African slave trade. I suspect that this fetish is due to a sexually transmitted pathogen that existed in West Africa at that time. Today, it may be extinct in its region of origin or circulating at a low level of frequency. The local people have probably had enough time to evolve counter-measures to prevent the pathogen from tampering with their brains. This is much less the case with people in the West.
3. Exclusive male homosexuality incurs a high fitness cost, so there must be a fitness benefit for someone or something. I'm not talking about facultative homosexuality, such as in a men's prison. That's easy to explain.
Speaking of prison sex, I've once read a study that says that over 70% of men in prison who have sex with other inmates were already having gay sex before they ever went to prison. If I can find it again I can post it.
I wouldn’t recommend taking this too much into account for explaining absurd sexual proclivities. There is so much going on in every human’s behaviors and drives that are both physical and psychological, structural and chemical. Every stimuli we perceive, everything we ingest, our genetics and our overall health contributes to such behaviors. We’ve likely all experienced this when taking the most benign medications or when ingesting common foods that have the most subtle effect on our brain chemistry, sometimes leaving us feeling almost completely asexual or sometimes “nymphomaniacal”. We now understand that microorganisms do have a substantial impact on our behaviors, but I wouldn’t bet on it being anywhere close to the defining factor.
I do appreciate Aporia for their somewhat niche articles, but it often seems that they come up with a conclusion before any research is done and then work backwards to support it with surprisingly selective and circumstantial studies. It’s unfortunate as it undermines ideas and theories that would otherwise be worth pursuing. But the more I read them the more I see that their agenda comes before any sort of serious thought, and it’s understandable why they have been ousted and ostracized by the institutions they once worked with.
All Eukaryotes naturally carry billions of foreign microbio-organisms from even before your birth to your death. They are impossible to avoid, since you absorb millions of microbs just from breathing clear air and drinking clean water. Not all microbs are harmful or parasitic (including ones that are gained by and influence sexual behavior) most are neutral. Not all are like T. Gondii
All Eukaryotes (including Humans) are essentially Superorganisms that have basically co-evolved with the microbs inside of them.
See also: "This article proposes that one of the essential purposes of sexual intercourse, and probably the most important one, is to transmit not our genes, but the genes of microbiome bacteria. This hypothesis makes it possible to explain not only the frequency of sexual intercourse but also of no fertilizing sexual behaviors, even risky ones."
Good to hear from you Philippe! Yes, sex can also transmit friendly parasites.
" ... it is worth considering the possibility that the host’s behavior may be manipulated not just by parasites but also by mutualists and commensals, notably the gut microbiota. Clearly, gut microbes have the biochemical potential for manipulation and a privileged relationship with the host."
These friendly parasites may alter our food preferences, so that we don't eat food that is harmful to them.
Really interesting. I have a strong suspicion that in decades to come, Peter Frost's and Greg Cochran's educated speculations about pretty much everything will be proven right.
I wonder if I was alone in thinking, 'Oh Christ, was that unwise, unprotected dalliance four decades ago the reason I can no longer remember why I went into the kitchen or what I wanted from the bathroom cabinet? After all, the mite would have had 40 years in which to make itself at home in my limbic system. Yet even if true, it can't be of the variety that makes me fancy men or fantasise about my female partner in the arms of other men. That, at least, is something to be thankful for'.
We are the products of terrible events and terrible things. Our brains may even be products, to some extent, of our need to outfox behavior-manipulating parasites:
"How much of our neural complexity is a necessary defense against manipulative invaders? How much of the enormous redundancy is to provide system level functionality if part of the system is attacked? How much of the complex process of wiring a brain during development is to prevent pathogen re-wiring?”
Read A., Braithwaite V. (2012). Afterword. pp. 195-197, in: Host Manipulation by Parasites, edited by D. P. Hughes, J.Brodeur, and F.Thomas. Oxford (United Kingdom): Oxford University Press.
A lot of other studies on Toxoplasma gondii suggest that its supposed effects on Human behavior are largely overblown and are a confusion of cause and effect:
This reads like a diverting parody of reductionism, masquerading as a reductionist thesis. Even so, the impulse to force behaviour that is fundamentally mysterious and acausal into the mould of cause and effect is revealing. It feels like a miniature parable of the West’s intellectual exhaustion: brilliance applied in the service of a playful yet sterile dead end.
Reductionism isn't all bad. Yeah, I know: "The whole isn't the sum of its parts." But you still have to understand the parts before you can begin to understand the whole.
I think the toxoplasma Gondi stuff is completely overblown. As for homosexuality: in males it is usually preceded by feminine behavior which emerges as soon as the boy can express himself. Boys who love football don’t come down sick and start loving barbie one day. Every housewife would’ve come up with the gay germ theory a long time ago if that were the case. If it’s a gay germ, it’s not an active infection, it’s brain alteration during pregnancy or infancy – before clearing the system entirely. Nobody ever got paralysed from being in FDRs presence.
I don't understand the reference to FDR's illness. He had Guillain–Barré syndrome (GBS), which is an autoimmune disorder that attacks nerve cells. It can be caused by an infection, but most immune systems don't over-react as FDR's did.
Feminine behavior in male homosexuality may be a consequence of whatever it is that alters male sexual orientation.
It's difficult to tell whether an infection has been cleared completely from the body. Many pathogens become dormant and show no indication of their presence.
The comment about FDR was simply addressing the ‘contagious’ claims about homosexuality, which you see in more stupid areas of the Internet. E.g. people claiming the gay germ can be cleared via ivermectin. If Greg is correct, its very unlikely it has anything to do with an active infection, and everything to do with irreversible brain damage or insult.
Greg believes that the "gay germ" is transmitted through intimate contact, i.e., exchange of bodily fluids.
He was open to your argument (i.e., the germ is cleared from the body after it causes irreversible damage). But he also stressed the possibility of it going dormant and then reactivating later in life:
"This argument does not specify the details by which selection on pathogens maintains the disease over time. The characteristics of chronic disease, for example, could result from within host evolution that generates increased virulence over time, as with the causation of AIDS; or, chronic manifestations could result from compromises to host defenses, the aging process, reactivation of infections from a latent state, and/or coinfection with other pathogens. The important point is that damaging diseases can be maintained indefinitely over time when infectious agents are the cause." https://web.archive.org/web/20000815224048id_/http://www.isteve.com:80/Infectious_Causation_of_Disease.pdf
Greg does not believe the gay germ is transmitted by intimate contact (anymore, if ever). He has said in his blog comment section numerous times over the years that it would need to be something like RSV or Epstein Barr — that everybody gets but is only causing a problem in a small minority. I regularly message with him on Twitter as well, so you’re wrong.
Again, gay men are usually feminine in early childhood. There is no ‘intimate contact’ needed to explain neural feminization in a 3 year old. This is silly.
He did believe in that route of transmission when he published his paper in 2000. He has not published anything on the subject since then.
This is what he wrote:
"One possible route would be sexual, whereby homosexual behavior could facilitate spread because of the larger numbers of partners homosexual males may have on average, relative to heterosexual males."
Cochran, Gregory M., Paul W. Ewald, and Kyle D. Cochran. (2000). Infectious causation of disease: an evolutionary perspective." Perspectives in biology and medicine, 43.3, 406-448. https://doi.org/10.1353/pbm.2000.0016
In all fairness, he adds: "Alternatively, transmission could be partly or entirely by one or more nonsexual routes."
Presumably, a 3 year-old would be infected by a carrier, most likely the mother. A carrier would harbor the pathogen without being otherwise affected. Yes, women can be infected by gay men, particularly in times and place where most gays use a heterosexual relationship as a cover.
It's not unusual for academics to change their mind. But they have a moral obligation to state this change of opinion in the literature. Can you provide a link to a paper or a blog post where Greg dissociates himself from what he wrote in 2000?
Greg has published multiple blog posts on the gay germ in the last 10 years, and has had multiple (public) Twitter discussions about it. I don’t have time to fish out tweets and blog comments but it won’t be hard to find.
"Studies by Flegr and Kuba (2016) and Flegr (2017) have shown that latent toxoplasmosis significantly influences
sexual preferences and behaviours. Infected individuals, particularly men, report stronger tendencies toward
masochism, rape fantasies, bondage, same-sex experiences, and anal sex. Women with latent toxoplasmosis also
report higher attraction to violent sexual practices and same-sex experiences. However, despite their heightened inclinations, infected individuals tend to engage in these
behaviours less frequently than uninfected individuals.
This discrepancy suggests that while Toxoplasma may increase sexual arousal and fantasies, the physical and psychological effects of chronic infection may inhibit
actual participation (Flegr et al. 2014b, Escudero et al.
2021).
"Beyond hormonal changes, neurobiological mechanisms may also contribute to altered sexual behaviour.
Studies have shown that Toxoplasma infection can lead to the demethylation of arginine vasopressin promoters within the amygdala, a process that may influence behaviour (Dass and Vyas 2014). Additionally, increased dopamine levels (Flegr et al. 2003, Prandovszky et al. 2011) have
been linked to heightened sexual motivation (Hull et al. 2004), while reduced serotonin levelsmay contribute to decreased sexual satisfaction and engagement (Henriquez
et al. 2009). These neurochemical shifts, combined with the broader health deterioration commonly observed in infected individuals (Flegr et al. 2024), could in part explain
both an increased inclination toward certain sexual behaviours and a concurrent reduction in their actual execution."
This is what I was getting at in my previous comments. The existence of Toxoplasma and sex-influencing parasites doesn't explain the existence of promiscuity, non-vaginal, non-reproductive and paraphilic sex in people who aren't infected. And this research from the Czech studies say that while infected people desire these things more, they seem to do it less often in the long run than non-infected people.
"The existence of Toxoplasma and sex-influencing parasites doesn't explain the existence of promiscuity, non-vaginal, non-reproductive and paraphilic sex in people who aren't infected."
No one ever said it did. Of course, one could argue for a broader cultural effect, i.e., infected men look and act more masculine and thus become role models for non-infected men.
"the Czech studies say that while infected people desire these things more, they seem to do it less often in the long run than non-infected people."
I'm not sure I follow you here. The above statement is true only in the sense that infected men tend to die sooner.
"No one ever said it did. Of course, one could argue for a broader cultural effect, i.e., infected men look and act more masculine and thus become role models for non-infected men."
Tons of biological research on male sexuality have shown that "culture" has very little to do with male sexual behavior and that male sexuality in general isn't at all fluid nor highly environmentally influenced at all.
"I'm not sure I follow you here. The above statement is true only in the sense that infected men tend to die sooner."
The point was that infected people do those things less frequently compared to non-infected people according to the Czech study, regardless of lifespan
"The point was that infected people do those things less frequently compared to non-infected people according to the Czech study, regardless of lifespan"
All right, let's go over the passages you quoted. We seem to disagree on the meaning of your term "those things." If by "those things" you mean sexual promiscuity, you're wrong:
"Toxoplasma infection has also been associated with increased sexual promiscuity in men, as observed in a study by Alvarado-Esquivel et al. (2021). The study found that men with latent toxoplasmosis reported a higher number of sexual partners, suggesting a link between infection and riskier sexual behaviours. Notably, this association was not observed in women."
If by "those things" you mean extreme sexual desires and sexual fantasies, you're also wrong:
"Infected individuals, particularly men, report stronger tendencies toward masochism, rape fantasies, bondage, same-sex experiences, and anal sex. Women with latent toxoplasmosis also report higher attraction to violent sexual practices and same-sex experiences."
You're right when you talk about actual participation in extreme sexual experiences:
"However, despite their heightened inclinations, infected individuals tend to engage in these behaviours less frequently than uninfected individuals. This discrepancy suggests that while Toxoplasma may increase sexual arousal and fantasies, the physical and psychological effects of chronic infection may inhibit actual participation."
None of this argues against the theory that T. gondii is manipulating sexual behavior to increase its propagation to new hosts. The relevant behavioral manipulation is an increase in sexual promiscuity, particularly oral sex (which seems to be a more effective route of transmission).
Flegr doesn't mention oral sex in the above passages. But he does in this one:
"Their article also presents empirical data showing that men and women engaging in oral sex (fellatio) with male partners exhibit increased rates of toxoplasmosis compared to control groups. Additional indirect findings lend further plausibility to this potential transmission route. For instance, in adolescents aged 10 to 14 years – an age group where oral sexual activity may precede penetrative intercourse – the prevalence of toxoplasmosis is significantly higher in females than in males."
Latifi, A., Flegr, J., & Kaňková, Š. (2025). Re-assessing host manipulation in Toxoplasma: the underexplored role of sexual transmission-evidence, mechanisms, implications. Folia Parasitologica. https://doi.org/10.14411/fp.2025.015
Looks like Dr Flegr recycled the same paragraphs from one study to the next. Most academics are guilty of this self-plagiarism. I've done it. One day you'll do it.
You're absolutely right! I am confusing cause and effect —and consciously at that. In a positive feedback loop, the effect becomes the cause. If a pathogen enters a human body because of a certain behavior, selection will favor the survival and reproduction of those pathogens that can increase the same sort of behavior. The effect thus becomes a cause.
The Cuckold fetish seems to only exist among Western Men, largely White. It's unlikely to have been a product of contact with West Africans where the fetish is non-existent.
It may or may not be non-existent in West Africa. It is almost taboo to discuss this sort of subject with the local people. In African culture, a man must become a father and, eventually, be revered as an ancestor by his numerous descendants. One of my colleagues did his dissertation on male infertility in Benin, and he found it very difficult to interview infertile men. They were very self-conscious and unhappy about their condition.
The human body is in a continual arms race with parasites. We evolve a counter-measure to infection, and the parasite evolves a counter-counter-measure. Since West Africans have had more time to evolve counter-measures, they are probably less affected behaviorally than Europeans or North Americans, for whom such a parasite would be relatively novel.
That's a myth, the real rates of paternal fraud are far lower than that.
The Cuckold fetish is when a man actively encourages other men to have sex with their wife or girlfriend while they watch. There's no evidence of it's popularity outside of White Western men (and surprisingly, some research says that it's more common among Right Wing Whites than Leftist Whites)
The Czech study didn't say that Toxoplasma Gondii directly causes an increase inclination to non-vaginal sex, they just assumed it might based on circumstantial evidence such as the decline in sperm count and reduced fertility.
There's also no Neurological evidence according to these studies that Toxoplasma Gondii causes an actual increase in libido/sex drive in infected people, that too is an assumption based on circumstantial evidence like an increase in body size for males and a reduce in inhibitions in women, etc which could lead someone indirectly into having an increase in sexual partners.
However, homosexual orientation being caused by such parasites is more or less confirmed true
There have been several studies by the same group of Czech researchers. The latest one is probably the best statement of their views on the subject:
"The findings reviewed in this article suggest that Toxoplasma gondii may exert a broader influence on host sexual behaviour and physiology than previously assumed. While its best-known behavioural effects have traditionally been interpreted in the context of predation facilitation, growing evidence indicates that some of these changes – particularly those related to sexual attraction, behaviour, and reproductive physiology – may also serve to enhance the parasite’s sexual transmission.
Although alimentary and vertical transmission remain the primary pathways in humans, the detection of viable parasites in semen, behavioural alterations that may alter sexual activity or enhance certain physical traits related to sexuality and attractiveness (such as height and dominance), and epidemiological associations with certain sexual practices support the hypothesis that sexual transmission could represent an additional, evolutionarily significant route.
In humans – but not necessarily in other species – sexual transmission likely accounts for only a minority of cases. Nevertheless, it may have disproportionate clinical consequences. If infection occurs during unprotected sexual intercourse at the moment of conception, the parasite may bypass maternal immunity and directly infect the embryo, increasing the risk of congenital toxoplasmosis – the most serious and life-threatening form of the disease."
Abstract
"This review explores the hypothesis that some behavioural effects of toxoplasmosis - especially those related to attraction, sexual activity, and mate choice - may have evolved to facilitate sexual transmission of the parasite. We summarise findings from animal models and human studies that show modified sexual preferences, altered sexual activity, enhanced attractiveness in infected individuals, and elevated prevalence of T. gondii in groups exhibiting high sexual activity or non-traditional sexual behaviour patterns."
"Your sacred identity is literally the symptom of an infectious brain parasite" would be a hell of a pill for the left to swallow, but it certainly looks like a fascinating avenue of research.
Pathogens of one sort or another have made us what we are. Our DNA is 8% of viral origin, and our brains have likely been shaped by mechanisms to prevent parasites from manipulating our neural circuitry. See: https://marcodg.net/wp-content/uploads/2019/06/delgiudice_2019_invisible-designers_qrb.pdf
Aporia should force del giudice to write for it.
All Eukaryotes naturally carry billions of foreign microbio-organisms from even before your birth to your death. They are impossible to avoid, since you absorb millions of microbs just from breathing clear air and drinking clean water. Not all microbs are harmful or parasitic (including ones that are gained by and influence sexual behavior) most are neutral. Not all are like T. Gondii
All Eukaryotes (including Humans) are essentially Superorganisms that have basically co-evolved with the microbs inside of them.
Those little guys are creepy as all hell.
Something similar is the fungus that turns ants into suicidal robots.
https://en.wikipedia.org/wiki/Ophiocordyceps_unilateralis
Yes, I wanted to write more about what happens in other species. And it's not just that one fungus.
https://en.wikipedia.org/wiki/Behavior-altering_parasite
Peter thanks for an intriguing article, but at the same time alarming.
The article gave me a mix of fascination and the urge to have a shower.
So astounding, wow, kinda makes celibacy seem ok. So many peoples sexual proclivities seem absurd at times, this explains a lot. Such a strange world we live in. Our entire civilization would be radically altered if these parasites could be removed from the human biome. Maybe they could be replaced with genetically modified versions creating positive health outcomes.
"Our entire civilization would be radically altered if these parasites could be removed from the human biome. Maybe they could be replaced with genetically modified versions creating positive health outcomes."
That is a far out idea, but I guess, anything is possible.
The studies linked by Peter Frost never said that these parasites create the desire/urge for non-vaginal sex or the existence of bizarre paraphilias (the latter of which is actually more common in 1st World High-IQ countries).
The Czech studies make that claim.
Paraphilias are more openly practiced in the West, but it doesn't follow that they are less common elsewhere. In fact, some of them (fellatio, pedophilia) are more common in certain non-Western countries.
First, The Czech studies only point out that the parasite increases desire for paraphilic sex (but later leads to less actual engagement in it overtime compared to non-infected people), it never said that it was the origin of paraphilias since non-infected people also engage in these behaviors (and the studies make no claim as to why that is so).
Second, not all paraphilias are the same, nor are they all viewed the same by every culture (and if all non-vaginal sex is “paraphilic” then it's basically a universal across the entire Animal Kingdom). Many paraphilias vary by ethnicity and race in the popularity like the Foot Fetish or BDSM. Also, even studies on the popularity of pornography around the world point out that the Cuckold fetish (where a man actively encourages other men to sleep with their wife or girlfriend) has basically little to no audience outside of the West and mainly with White men in particular.
3rd, we don't need parasites to explain the existence of non-reproductive heterosexual behaviour in Humans nor other Animals. The notion that Sex is ONLY for procreation (a view that is absent in most cultures and religions) has largely been discredited by Neuroscience and Behavioral Genetics. Parasites/Germ theory only makes sense when applied to Homosexuality and Asexuality, both orientations that have zero possible evolutionary benefits.
We seem to be talking past each other.
1. I'm not claiming that paraphilias are always or even mainly due to behavior-altering parasites. Why do you keep saying I'm making that claim?
2. The cuckold fetish was non-existent in the West before the West African slave trade. I suspect that this fetish is due to a sexually transmitted pathogen that existed in West Africa at that time. Today, it may be extinct in its region of origin or circulating at a low level of frequency. The local people have probably had enough time to evolve counter-measures to prevent the pathogen from tampering with their brains. This is much less the case with people in the West.
3. Exclusive male homosexuality incurs a high fitness cost, so there must be a fitness benefit for someone or something. I'm not talking about facultative homosexuality, such as in a men's prison. That's easy to explain.
Speaking of prison sex, I've once read a study that says that over 70% of men in prison who have sex with other inmates were already having gay sex before they ever went to prison. If I can find it again I can post it.
I wouldn’t recommend taking this too much into account for explaining absurd sexual proclivities. There is so much going on in every human’s behaviors and drives that are both physical and psychological, structural and chemical. Every stimuli we perceive, everything we ingest, our genetics and our overall health contributes to such behaviors. We’ve likely all experienced this when taking the most benign medications or when ingesting common foods that have the most subtle effect on our brain chemistry, sometimes leaving us feeling almost completely asexual or sometimes “nymphomaniacal”. We now understand that microorganisms do have a substantial impact on our behaviors, but I wouldn’t bet on it being anywhere close to the defining factor.
I do appreciate Aporia for their somewhat niche articles, but it often seems that they come up with a conclusion before any research is done and then work backwards to support it with surprisingly selective and circumstantial studies. It’s unfortunate as it undermines ideas and theories that would otherwise be worth pursuing. But the more I read them the more I see that their agenda comes before any sort of serious thought, and it’s understandable why they have been ousted and ostracized by the institutions they once worked with.
Isn't celibacy also maladaptive? There's no evolutionary benefit to having no interest in sex
All Eukaryotes naturally carry billions of foreign microbio-organisms from even before your birth to your death. They are impossible to avoid, since you absorb millions of microbs just from breathing clear air and drinking clean water. Not all microbs are harmful or parasitic (including ones that are gained by and influence sexual behavior) most are neutral. Not all are like T. Gondii
All Eukaryotes (including Humans) are essentially Superorganisms that have basically co-evolved with the microbs inside of them.
Maybe a larger biome is the way to go then, should we be increasing our total biodiversity by incorporating more organisms to hang out with us?
The non-parasitic ones, yes
See also: "This article proposes that one of the essential purposes of sexual intercourse, and probably the most important one, is to transmit not our genes, but the genes of microbiome bacteria. This hypothesis makes it possible to explain not only the frequency of sexual intercourse but also of no fertilizing sexual behaviors, even risky ones."
Gouillou, P. (2020, 2022). What Is Sex For? To Transmit the Genes of the Microbiome... PsyArXiv, k7u8w. https://doi.org/10.31234/osf.io/k7u8w
Good to hear from you Philippe! Yes, sex can also transmit friendly parasites.
" ... it is worth considering the possibility that the host’s behavior may be manipulated not just by parasites but also by mutualists and commensals, notably the gut microbiota. Clearly, gut microbes have the biochemical potential for manipulation and a privileged relationship with the host."
These friendly parasites may alter our food preferences, so that we don't eat food that is harmful to them.
See: https://marcodg.net/wp-content/uploads/2019/06/delgiudice_2019_invisible-designers_qrb.pdf
Really interesting. I have a strong suspicion that in decades to come, Peter Frost's and Greg Cochran's educated speculations about pretty much everything will be proven right.
I wonder if I was alone in thinking, 'Oh Christ, was that unwise, unprotected dalliance four decades ago the reason I can no longer remember why I went into the kitchen or what I wanted from the bathroom cabinet? After all, the mite would have had 40 years in which to make itself at home in my limbic system. Yet even if true, it can't be of the variety that makes me fancy men or fantasise about my female partner in the arms of other men. That, at least, is something to be thankful for'.
We are the products of terrible events and terrible things. Our brains may even be products, to some extent, of our need to outfox behavior-manipulating parasites:
"How much of our neural complexity is a necessary defense against manipulative invaders? How much of the enormous redundancy is to provide system level functionality if part of the system is attacked? How much of the complex process of wiring a brain during development is to prevent pathogen re-wiring?”
Read A., Braithwaite V. (2012). Afterword. pp. 195-197, in: Host Manipulation by Parasites, edited by D. P. Hughes, J.Brodeur, and F.Thomas. Oxford (United Kingdom): Oxford University Press.
Why have I never heard of this before? Or, even worse, have I and the organisms just make us all forget?
It's not just tiny parasites. Many of our fellow humans actively seek to make us forget certain things and "remember" others in their place.
https://www.aporiamagazine.com/p/how-modern-culture-distorts-reality
Particularly the Persistent Predatory Personalities that arguably rule over and terrorize us neurotypicals.
A lot of other studies on Toxoplasma gondii suggest that its supposed effects on Human behavior are largely overblown and are a confusion of cause and effect:
https://pubmed.ncbi.nlm.nih.gov/22325983/
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0148435
This reads like a diverting parody of reductionism, masquerading as a reductionist thesis. Even so, the impulse to force behaviour that is fundamentally mysterious and acausal into the mould of cause and effect is revealing. It feels like a miniature parable of the West’s intellectual exhaustion: brilliance applied in the service of a playful yet sterile dead end.
Reductionism isn't all bad. Yeah, I know: "The whole isn't the sum of its parts." But you still have to understand the parts before you can begin to understand the whole.
Good piece, Peter. Though causal research seems quite limited.
I thought the prime suspect for MS was EBV.
https://www.nature.com/articles/s41582-023-00775-5
I think the toxoplasma Gondi stuff is completely overblown. As for homosexuality: in males it is usually preceded by feminine behavior which emerges as soon as the boy can express himself. Boys who love football don’t come down sick and start loving barbie one day. Every housewife would’ve come up with the gay germ theory a long time ago if that were the case. If it’s a gay germ, it’s not an active infection, it’s brain alteration during pregnancy or infancy – before clearing the system entirely. Nobody ever got paralysed from being in FDRs presence.
I don't understand the reference to FDR's illness. He had Guillain–Barré syndrome (GBS), which is an autoimmune disorder that attacks nerve cells. It can be caused by an infection, but most immune systems don't over-react as FDR's did.
Feminine behavior in male homosexuality may be a consequence of whatever it is that alters male sexual orientation.
It's difficult to tell whether an infection has been cleared completely from the body. Many pathogens become dormant and show no indication of their presence.
The comment about FDR was simply addressing the ‘contagious’ claims about homosexuality, which you see in more stupid areas of the Internet. E.g. people claiming the gay germ can be cleared via ivermectin. If Greg is correct, its very unlikely it has anything to do with an active infection, and everything to do with irreversible brain damage or insult.
Greg believes that the "gay germ" is transmitted through intimate contact, i.e., exchange of bodily fluids.
He was open to your argument (i.e., the germ is cleared from the body after it causes irreversible damage). But he also stressed the possibility of it going dormant and then reactivating later in life:
"This argument does not specify the details by which selection on pathogens maintains the disease over time. The characteristics of chronic disease, for example, could result from within host evolution that generates increased virulence over time, as with the causation of AIDS; or, chronic manifestations could result from compromises to host defenses, the aging process, reactivation of infections from a latent state, and/or coinfection with other pathogens. The important point is that damaging diseases can be maintained indefinitely over time when infectious agents are the cause." https://web.archive.org/web/20000815224048id_/http://www.isteve.com:80/Infectious_Causation_of_Disease.pdf
Greg does not believe the gay germ is transmitted by intimate contact (anymore, if ever). He has said in his blog comment section numerous times over the years that it would need to be something like RSV or Epstein Barr — that everybody gets but is only causing a problem in a small minority. I regularly message with him on Twitter as well, so you’re wrong.
Again, gay men are usually feminine in early childhood. There is no ‘intimate contact’ needed to explain neural feminization in a 3 year old. This is silly.
He did believe in that route of transmission when he published his paper in 2000. He has not published anything on the subject since then.
This is what he wrote:
"One possible route would be sexual, whereby homosexual behavior could facilitate spread because of the larger numbers of partners homosexual males may have on average, relative to heterosexual males."
Cochran, Gregory M., Paul W. Ewald, and Kyle D. Cochran. (2000). Infectious causation of disease: an evolutionary perspective." Perspectives in biology and medicine, 43.3, 406-448. https://doi.org/10.1353/pbm.2000.0016
In all fairness, he adds: "Alternatively, transmission could be partly or entirely by one or more nonsexual routes."
Presumably, a 3 year-old would be infected by a carrier, most likely the mother. A carrier would harbor the pathogen without being otherwise affected. Yes, women can be infected by gay men, particularly in times and place where most gays use a heterosexual relationship as a cover.
It's not unusual for academics to change their mind. But they have a moral obligation to state this change of opinion in the literature. Can you provide a link to a paper or a blog post where Greg dissociates himself from what he wrote in 2000?
Greg has published multiple blog posts on the gay germ in the last 10 years, and has had multiple (public) Twitter discussions about it. I don’t have time to fish out tweets and blog comments but it won’t be hard to find.
"Studies by Flegr and Kuba (2016) and Flegr (2017) have shown that latent toxoplasmosis significantly influences
sexual preferences and behaviours. Infected individuals, particularly men, report stronger tendencies toward
masochism, rape fantasies, bondage, same-sex experiences, and anal sex. Women with latent toxoplasmosis also
report higher attraction to violent sexual practices and same-sex experiences. However, despite their heightened inclinations, infected individuals tend to engage in these
behaviours less frequently than uninfected individuals.
This discrepancy suggests that while Toxoplasma may increase sexual arousal and fantasies, the physical and psychological effects of chronic infection may inhibit
actual participation (Flegr et al. 2014b, Escudero et al.
2021).
"Beyond hormonal changes, neurobiological mechanisms may also contribute to altered sexual behaviour.
Studies have shown that Toxoplasma infection can lead to the demethylation of arginine vasopressin promoters within the amygdala, a process that may influence behaviour (Dass and Vyas 2014). Additionally, increased dopamine levels (Flegr et al. 2003, Prandovszky et al. 2011) have
been linked to heightened sexual motivation (Hull et al. 2004), while reduced serotonin levelsmay contribute to decreased sexual satisfaction and engagement (Henriquez
et al. 2009). These neurochemical shifts, combined with the broader health deterioration commonly observed in infected individuals (Flegr et al. 2024), could in part explain
both an increased inclination toward certain sexual behaviours and a concurrent reduction in their actual execution."
This is what I was getting at in my previous comments. The existence of Toxoplasma and sex-influencing parasites doesn't explain the existence of promiscuity, non-vaginal, non-reproductive and paraphilic sex in people who aren't infected. And this research from the Czech studies say that while infected people desire these things more, they seem to do it less often in the long run than non-infected people.
"The existence of Toxoplasma and sex-influencing parasites doesn't explain the existence of promiscuity, non-vaginal, non-reproductive and paraphilic sex in people who aren't infected."
No one ever said it did. Of course, one could argue for a broader cultural effect, i.e., infected men look and act more masculine and thus become role models for non-infected men.
"the Czech studies say that while infected people desire these things more, they seem to do it less often in the long run than non-infected people."
I'm not sure I follow you here. The above statement is true only in the sense that infected men tend to die sooner.
"No one ever said it did. Of course, one could argue for a broader cultural effect, i.e., infected men look and act more masculine and thus become role models for non-infected men."
Tons of biological research on male sexuality have shown that "culture" has very little to do with male sexual behavior and that male sexuality in general isn't at all fluid nor highly environmentally influenced at all.
"I'm not sure I follow you here. The above statement is true only in the sense that infected men tend to die sooner."
The point was that infected people do those things less frequently compared to non-infected people according to the Czech study, regardless of lifespan
"The point was that infected people do those things less frequently compared to non-infected people according to the Czech study, regardless of lifespan"
All right, let's go over the passages you quoted. We seem to disagree on the meaning of your term "those things." If by "those things" you mean sexual promiscuity, you're wrong:
"Toxoplasma infection has also been associated with increased sexual promiscuity in men, as observed in a study by Alvarado-Esquivel et al. (2021). The study found that men with latent toxoplasmosis reported a higher number of sexual partners, suggesting a link between infection and riskier sexual behaviours. Notably, this association was not observed in women."
If by "those things" you mean extreme sexual desires and sexual fantasies, you're also wrong:
"Infected individuals, particularly men, report stronger tendencies toward masochism, rape fantasies, bondage, same-sex experiences, and anal sex. Women with latent toxoplasmosis also report higher attraction to violent sexual practices and same-sex experiences."
You're right when you talk about actual participation in extreme sexual experiences:
"However, despite their heightened inclinations, infected individuals tend to engage in these behaviours less frequently than uninfected individuals. This discrepancy suggests that while Toxoplasma may increase sexual arousal and fantasies, the physical and psychological effects of chronic infection may inhibit actual participation."
None of this argues against the theory that T. gondii is manipulating sexual behavior to increase its propagation to new hosts. The relevant behavioral manipulation is an increase in sexual promiscuity, particularly oral sex (which seems to be a more effective route of transmission).
Flegr doesn't mention oral sex in the above passages. But he does in this one:
"Their article also presents empirical data showing that men and women engaging in oral sex (fellatio) with male partners exhibit increased rates of toxoplasmosis compared to control groups. Additional indirect findings lend further plausibility to this potential transmission route. For instance, in adolescents aged 10 to 14 years – an age group where oral sexual activity may precede penetrative intercourse – the prevalence of toxoplasmosis is significantly higher in females than in males."
Latifi, A., Flegr, J., & Kaňková, Š. (2025). Re-assessing host manipulation in Toxoplasma: the underexplored role of sexual transmission-evidence, mechanisms, implications. Folia Parasitologica. https://doi.org/10.14411/fp.2025.015
You quoted a different study than the one I did, and again, demonstrate a confusion of cause and effect
https://web.natur.cuni.cz/flegr/pdf/revToxoSex.pdf
Looks like Dr Flegr recycled the same paragraphs from one study to the next. Most academics are guilty of this self-plagiarism. I've done it. One day you'll do it.
You're absolutely right! I am confusing cause and effect —and consciously at that. In a positive feedback loop, the effect becomes the cause. If a pathogen enters a human body because of a certain behavior, selection will favor the survival and reproduction of those pathogens that can increase the same sort of behavior. The effect thus becomes a cause.
The Cuckold fetish seems to only exist among Western Men, largely White. It's unlikely to have been a product of contact with West Africans where the fetish is non-existent.
It may or may not be non-existent in West Africa. It is almost taboo to discuss this sort of subject with the local people. In African culture, a man must become a father and, eventually, be revered as an ancestor by his numerous descendants. One of my colleagues did his dissertation on male infertility in Benin, and he found it very difficult to interview infertile men. They were very self-conscious and unhappy about their condition.
The human body is in a continual arms race with parasites. We evolve a counter-measure to infection, and the parasite evolves a counter-counter-measure. Since West Africans have had more time to evolve counter-measures, they are probably less affected behaviorally than Europeans or North Americans, for whom such a parasite would be relatively novel.
That's a myth, the real rates of paternal fraud are far lower than that.
The Cuckold fetish is when a man actively encourages other men to have sex with their wife or girlfriend while they watch. There's no evidence of it's popularity outside of White Western men (and surprisingly, some research says that it's more common among Right Wing Whites than Leftist Whites)
The Czech study didn't say that Toxoplasma Gondii directly causes an increase inclination to non-vaginal sex, they just assumed it might based on circumstantial evidence such as the decline in sperm count and reduced fertility.
There's also no Neurological evidence according to these studies that Toxoplasma Gondii causes an actual increase in libido/sex drive in infected people, that too is an assumption based on circumstantial evidence like an increase in body size for males and a reduce in inhibitions in women, etc which could lead someone indirectly into having an increase in sexual partners.
However, homosexual orientation being caused by such parasites is more or less confirmed true
There have been several studies by the same group of Czech researchers. The latest one is probably the best statement of their views on the subject:
"The findings reviewed in this article suggest that Toxoplasma gondii may exert a broader influence on host sexual behaviour and physiology than previously assumed. While its best-known behavioural effects have traditionally been interpreted in the context of predation facilitation, growing evidence indicates that some of these changes – particularly those related to sexual attraction, behaviour, and reproductive physiology – may also serve to enhance the parasite’s sexual transmission.
Although alimentary and vertical transmission remain the primary pathways in humans, the detection of viable parasites in semen, behavioural alterations that may alter sexual activity or enhance certain physical traits related to sexuality and attractiveness (such as height and dominance), and epidemiological associations with certain sexual practices support the hypothesis that sexual transmission could represent an additional, evolutionarily significant route.
In humans – but not necessarily in other species – sexual transmission likely accounts for only a minority of cases. Nevertheless, it may have disproportionate clinical consequences. If infection occurs during unprotected sexual intercourse at the moment of conception, the parasite may bypass maternal immunity and directly infect the embryo, increasing the risk of congenital toxoplasmosis – the most serious and life-threatening form of the disease."
Abstract
"This review explores the hypothesis that some behavioural effects of toxoplasmosis - especially those related to attraction, sexual activity, and mate choice - may have evolved to facilitate sexual transmission of the parasite. We summarise findings from animal models and human studies that show modified sexual preferences, altered sexual activity, enhanced attractiveness in infected individuals, and elevated prevalence of T. gondii in groups exhibiting high sexual activity or non-traditional sexual behaviour patterns."
https://web.natur.cuni.cz/flegr/pdf/revToxoSex.pdf
My GP recently pointed out I have antibodies to Toxiplasmosis. So, interesting that it might be sexually transmitted (I'm male).