Add to Favorites

The Quiet Guest

Robert Sapolsky, Toxoplasma gondii, and the question of free will
Meera Lee

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



ram 14
4 years ago

Article is very interesting,thanks for your sharing.I will visit this site.

Natural polymer suppliers

mas ion
3 years ago

These news are really great and I am so glad finding it in your site. As I see this blog is full of such valuable information like this publication so I will definitely bookmark it. Thanks again for informing us.
Greetings from Sbobet | Ibcbet | Agen Bola
Agen Ibcbet | Agen Bola Terpercaya | agen poker | dewa poker

Robert Willis
3 years ago

mere info her


Thanks for everything guys

David Sandall
3 years ago

Meera Lee, you are doing a great job.... thanks for everything



peter parker
3 years ago

I do not believe in free will anymore. Why the government is approving laws that can cut our free will. I have been thinking about it all day long. We should be able to do whatever we liked to do if that action does not cause any problems for others.

Q Spray

Julian Gärtner
3 years ago

Sapolsky  is truly amazing, thank you for sharing that article.. makes me really think.. webpagina

lili ana
3 years ago

I downloaded MXF Converter  free trial version last week, and I converted many MXF videos for playing on QuickTime. This software is good at converting any HD MXF, MTS, TOD, MP4 to MOV videos. With this perfect MXF converter for mac software, you can convert MXF to H.264 MOV for QuickTime, convert MXF to AIC MOV for editing in iMovie, convert MXF files to ProRes MOV for FCP X importing.

wahyu hidayat
3 years ago

A good website ... Thank you for the information, hopefully more successful ... Wootekh | Wootekh Indonesia | Greenworld Indonesia | MLM terbaru | Bisnis Online Greenworld Indonesia | MLM terbaru | Bisnis Online

Prakash Sharma
3 years ago

Here are some really good happy valentines day greetings for wife and husband by saint or also Valentine's day wishes for wife