At the beginning of his book Breaking the Spell, Daniel Dennett wrote:
You watch an ant in a meadow, laboriously climbing up a blade of grass, higher and higher until it falls, then climbs again, and again, like Sisyphus rolling his rock, always striving to reach the top. Why is the ant doing this? What benefit is it seeking for itself in this strenuous and unlikely activity? Wrong question, as it turns out. No biological benefit accrues to the ant. It is not trying to get a better view of the territory or seeking food or showing off to a potential mate, for instance. Its brain has been commandeered by a tiny parasite, a lancet fluke that needs to get itself into the stomach of a sheep or cow in order to complete its reproductive cycle. This brain worm is driving the ant into position to benefit its progeny, not the ants. This is not an isolated phenomenon. Similarly manipulative parasites infect fish, and mice among other species. These hitch hikers cause their hosts to behave in unlikely-even suicidal-ways, all for the benefit of the guest, not the host.
Professor Dennett used this example to make the case that ideas can do, and do do, the same thing as the lancet fluke: commandeer the brain of a host organism as a vector for self-propagation. (It’s an idea we’ve taken up in these pages too, for example here.)
But leaving aside memetic infection, it’s becoming clearer that this sort of behavioral hijacking by biological parasites is more common than you might imagine. We cited another example of ant-commandeering, for instance, in this post from last March.
Now an article in The Atlantic makes the case that the cat-borne organism Toxoplasma gondii, which is commonly found to be carried by humans, may have similar, and quite far-reaching, effects on the people it infects.
Learn more here.