Every year, the online salon Edge.org invites leading scientists, philosophers, artists, entrepreneurs, and intellectuals to answer a brief, open-ended question—usually no longer than 7 or 8 words. The answers it receives are often profound and surprising. In 2013, the Edge Foundation asked: “What should we be worried about?” The Chinese eugenics program, responded one contributor. The failure of genomics to solve mental illness, said another. The lack of neural data privacy. The implications of synthetic biology.
What’s neuroscientist and behavioral biologist Robert Sapolsky worried about? How hard it is for us to believe we have no free will.
Sapolsky, like many thinkers we’ve featured here, doesn’t wonder whether human beings are capable of making wholly free and independent choices. We are highly complex biological machines, he says, and every move we make—from ordering goat curry at dinner, scratching an itch, or choosing whom to marry—is the result of an intricate cascade of genetic, cellular, historical, cultural, and personal factors.
But it’s really, really hard to feel that way. And when we forget, argues Sapolsky, we tend to praise and damn people for behaviors they haven’t in any real sense chosen.
You wouldn’t expect a microscopic parasite to have much to do with such an existential issue. Yet the protozoa Toxoplasma gondii is one of the most fascinating examples Sapolsky gives to poke a hole in our concept of self-determination. His lab has been studying the effects of Toxoplasma on rat behavior for years. The parasite reproduces sexually in cats and uses rats as carriers. According to Sapolsky’s research, the cysts formed by the parasite in a rat’s brain are more concentrated in the amygdala, a structure associated with emotional states—including both anxiety and attraction. The Sapolsky lab has also published findings showing that a Toxoplasma infection changes brain activity in pathways associated with the normal defensive response, dampening anxiety; at the same time, it stimulates activity in pathways associated with sexual arousal, heightening attraction. As a result, infected rats lose their instinctive fear of cats, and even become drawn to the smell of their urine.
In humans, the same protozoa causes a disease known as toxoplasmosis, which can lead to retinal damage, brain damage, and death. You've probably heard that toxoplasmosis can be passed from cats to humans (and from mother to fetus, the reason pregnant women aren't supposed to clean litterboxes).
What does all this have to do with free will?
Current estimates hold that up to 2 or 3 billion people worldwide may be silent carriers of the parasite, which resides in brain and muscle cells permanently after the first infection. And as Sapolsky writes, “If someone is infected with the protozoan parasite Toxoplasma gondii, they are likely to become subtly more impulsive.” For example, a Czech study found people whose behavior put them at increased risk of being in a traffic accident (pedestrians who prematurely entered a crosswalk, or drivers who caused a crash) were more likely to be infected with Toxoplasma than a random sampling of the Czech population.
This quiet guest, then—like the DNA we inherit, our childhood experiences, the written and unwritten rules we learn, our accumulated memories and our physical bodies—seems to add its subtle influence to the choices we only feel are freely made. All our supposedly free decisions are at least influenced by—and perhaps even totally determined by—numerous factors over which we have no control. Try to remember that. It’ll keep Robert Sapolsky a little less worried.
See Robert Sapolsky talk live at Being Human 2013