It’s timely because the parasite has most recently been discussed in the press due to a new study that found a correlation between infection rates and national IQ levels. However, it’s previously been linked (again, correlated) with a whole host of human characteristics.
This is from some insightful coverage from Not Exactly Rocket Science:
Indeed, as I alluded to earlier, this new paper is the latest in a long line of hypothesis-generating publications from Fincher and Thornhill linking parasites and infections to pretty much any sweeping aspect of human life you can think of. Through similar studies based on correlations at the national level, Thornhill and Fincher have suggested that infections are linked to individualism and collectivism, religious diversity, linguistic diversity, armed conflicts and civil war, and democracy and liberal values. Like any attempt to explain very complex patterns of human behaviour through a single cause, this ought to raise an eyebrow. I‚Äôm raising two.
The case for the parasite being linked to football success in the Slate article sounds about as reasonable as everything else it’s been linked to as all the arguments are based on a correlation and some conjectures about how one could cause the other.
However, we could probably find dozens of things that might correlate with toxoplasma gondii on the national level (levels of traffic accidents? Eurovision song contest performance? spiciness of the food?).
It could be that such infections genuinely cause changes in aspects of thought or behaviour, but we won’t find this out from these sorts of studies because the links could be entirely incidental as our World Cup example likely demonstrates.
Full disclosure: I’m an occasional writer for Slate.