Thursday, August 24, 2006

They're in your braaaaaains.

So I've finally gotten my lazy arse (mantle?) in gear and signed on as a writer of this blog. Er...hi.

The reason I did this was not, unfortunately, because of any amazingly insightful commentary I had to provide; instead, it's more of a link dump, because something in Seed Magazine was just too awesome to pass up. It's likely a lot of my posts will be of this nature.

This article discusses some new findings that suggest an internal parasite, Toxoplasma gondii, has some effects on human (as well as rodent) behaviour, causing neuroticism and uncertainty avoidance. Now Toxoplasma is an exceedingly common parasite, afflicting significant -- but varying -- percentages of the population in different countries. The CDC has this to say about Toxoplasma gondii:
A single-celled parasite called Toxoplasma gondii causes a disease known as toxoplasmosis. While the parasite is found throughout the world, more than 60 million people in the United States may be infected with the Toxoplasma parasite. Of those who are infected, very few have symptoms because a healthy person's immune system usually keeps the parasite from causing illness.
So we have a transmissible agent of infection that afflicts large proportions of the human population and has measurable effects on behaviour. You know what that sounds like to me?


Yeah, so that's what this article in Seed is saying too. Earlier research has indicated that humans, Toxoplasma infection correlates highly with certain personality traits: Infected men tended to have lower levels of intelligence, superego strength and novelty-seeking, while infected women exhibited higher levels of intelligence, superego strength and warmth. Infected people of both sexes tend to be susceptible to feelings of guilt. [Seed]

This researcher from USGS, name of Kevin Lafferty, argues in his paper that infected women, intelligence, superego strength (rule-conscious, dutiful, conscientious, conforming, moralistic, staid and rule-bound) and affectothymia (warm, outgoing, attentive to others, kindly, easy-going, participating and likes people) are higher, while infected men have lower intelligence, superego strength and novelty-seeking (low novelty-seeking indicates rigid, loyal, stoic, slow-tempered and frugal personalities); both infected men and women have higher levels of guilt-proneness (they tend to be more apprehensive, self-doubting, worried, guilt prone, insecure, worrying and self-blaming; Flegr & Hrdy 1994; Flegr et al. 1996, 2000, 2003).
Toxoplasma gondii appears to manipulate human personality as a result of adaptations that normally help complete its complex life cycle from intermediate hosts to the final host, a cat (Webster 2001)....Parasites are under selection to increase the chance that final hosts eat intermediate hosts (Lafferty 1999). As a result, many parasites alter the behaviour of intermediate hosts to increase predation risk (Moore 2002). For example, T. gondii appears to manipulate rodent behaviour in sophisticated ways that would increase transmission to domestic cats (Webster 2001). Rodents infected with T. gondii are more active (Hay et al. 1983, 1984), first to enter traps (Webster et al. 1994), and less fearful of cats and their associated smells (Berdoy et al. 2000). Mice infected with T. gondii have elevated levels of dopamine (Stibbs 1985), a neurotransmitter known to alter novelty-seeking (Benjamin et al. 1996; Ebstein et al. 1996) and neuroticism (Lee et al. 2005).... Currently, cats rarely eat humans, so there should be little selective advantage for T. gondii to specifically manipulate human behaviour. Still, T. gondii cysts infecting a human have nothing to lose, evolutionarily speaking, in trying manipulative strategies adaptive in other intermediate host species.
The seroprevalence (percentage of people with antibodies to latent infections) of T. gondii varies geographically nearly from 0 to 100% (Tenter et al. 2000), suggesting that T. gondii could lead to variation in aggregate personality among populations (Lafferty 2005). In other words, the average personality of a population might be shifted if a higher proportion of individuals are infected with T. gondii. [from Lafferty's paper]

The paper's here in full text, if you can get to it; if not, try this. (Lafferty, K., 'Can the common brain parasite, Toxoplasma gondii, influence human culture?', Proceedings of the Royal Society B: Biological Sciences, 2006.) His data, collected from 39 countries, seem to bear out the idea of cultural changes mediated by this parasite's manipulation of its hosts' brains. In fact -- and this is where it gets really interesting -- they bear out a strong correlation between
...a society's preference for strict laws, an expression of uncertainty avoidance, and its valuation of 'masculine' priorities such as competitiveness and financial success over 'feminine' values like relationship-building.
"Toxoplasma appears to explain 30% of the variation in neuroticism among countries, 15% of the uncertainty avoidance among Western nations and 30% of the sex role differences among Western nations," Lafferty said via e-mail.
Lafferty analyzed preexisting data on Toxoplasma prevalence and mean trait levels in 39 countries. He found a significant linear correlation between latent Toxoplasma prevalence and neuroticism with a few outliers, including the unusually neurotic nations of Hungary and China and the notably easygoing Turkey. [Seed]

So, obviously, the really interesting thing that's going on here is this: a parasite in the brain is responsible for 30% (!) of the differences in neuroticism, uncertainty avoidance, and attachment to sex roles -- this last, I suspect, being of particular interest to readers of this blog -- among all the nations Lafferty managed to survey. I'm not any kind of neuropsychologist, so I won't try to analyse his results in depth, but it's still worth some more investigation.

Traditional sex roles: don't listen to your parents, it's just their BRAIN PARASITES talking.