What is going on here? Does Toxo really make people better at soccer?
The relationship is neither linear nor foolproof. Italy managed to win the World Cup in 2006, despite its relatively average infection rate of 33 percent. Certain African countries plagued with public health problems have astronomical Toxo rates. Yet the heavily infected players of Ghana, Gabon (71 percent), and the Ivory Coast (60 percent) have not yet managed to win a single cup. On the other end, England (6 percent), the U.S. (12 percent), and Japan (6 percent) are pretty OK at soccer yet have some of the lowest rates in the world.
So what can we make of the statistics? It looks like having some Toxoplasma gondii in the collective brains of your home country makes your team a little bitbetter at soccer, so long as you're already among the top teams in the sport. Thus a difference in infection might separate a team like Germany (43 percent, three * World Cups) from perpetually lackluster England (6 percent, one World Cup). And a bit of reflection reveals that the U.S. (12 percent) didn't stand a chance against Ghana (92 percent), neither in this tournament nor the last one.
Now, what does the Toxo parasite do that could possibly relate to soccer performance? Not much is known about its impact on the human brain, but there are clues. We know that infection increases testosterone in male brains, making them more likely to get into car accidents, more attractive to females, and more prone to being jealous, dogmatic, and dismissive of authority. Evidence even suggests that motorcyclists are more likely to have Toxo. Something like a James Dean effect. Generally, males with Toxo are more aggressive and less inhibited. Keep in mind that FIFA, in line with most sporting organizations in the world, bans testosterone supplements of any kind. But they do not ban Toxo, and if Toxo increases testosterone levels, we may be dealing with a form of inadvertent, cultural doping.
Certainly, there are caveats. First, it might be foolish to assume that the players on a national team will have the same rate of infection as their countrymen (especially if infection confers some kind of competitive advantage). On the other hand, having more Toxo-infected people around you at a young age might help your development as a player. Second, some studies have shown that those infected with Toxo have slower reaction times on certain tests than matched controls. It's not clear how or why that effect would be helpful to a soccer player—or indeed that it would be something other than a detriment. Finally, it's possible—likely, even—that the correlation between Toxo infection and World Cup success is a coincidence, or that it reflects some other common trait among successful soccer nations. Maybe it helps to have raw meat in your diet, and Toxo is just a side effect?
In any case, let's pause a moment before we start serving goat sushi at youth soccer camps. Prudence would say we wait until we know exactly how Toxo does what it does. Let's use what information we have in just the sensible and cautious way you might expect from a nation without Toxoplasma gondii or, coincidentally, a World Cup.
Correction, July 2, 2010:The original article assigned four World Cup trophies to Germany instead of three. (Return to the corrected sentence.)