Toxoplasma Gondii

A parasite with the ability to change behaviour

- Robert Sapolsky

Toxoplasma gondii

In the endless sort of struggle that neurobiologists have in terms of free will and determinism and all of that, my feeling has always been that there's not a whole lot of free will out there, and if there is, it's in the least interesting places and getting more sparse all the time.

But there's a whole new realm of neuroscience which I've been thinking about, and starting to do research on, that throws in another element of things going on below the surface affecting our behavior. And it's got to do with this utterly bizarre world of parasites manipulating our behavior. It turns out that this is not all that surprising. There are all sorts of parasites out there that get into some organism, and what they need to do is parasitize the organism and increase the likelihood that they, the parasite, will be fruitful and multiply—and in some cases, they can manipulate the behavior of the host.

Some of these are pretty astounding. There's a barnacle that rides on the back of a crab and is able to inject oestrogenic hormones into the crab if the crab is male, and at that point the male's behavior becomes feminized. The male crab digs a hole in the sand for his eggs, except he has no eggs, but the barnacle sure does and has just succeeded in getting this guy to build a nest for him. There are other examples where wasps parasitize caterpillars and get them to defend the wasp's nests for them—extraordinary examples.