Free Will and Microbes Among Us

A ladybug standing on a cocoon of a parasite that took away her free will when it parasitized her

Not Captains of Our Souls

The more we learn about the creatures who inhabit this planet with us, the more obvious it seems that, regardless of what William Ernst Henley believed, we are not the captain of our souls, nor can we master our fate. [1] Yes, to some degree we can choose how to respond to adversity, and this is really what his poem is about. Written when he lay ill with tuberculosis and feared he might lose a foot, which was especially worrisome because he’d already had one leg cut off when he was sixteen, Henley’s poem honors his courage and his “unconquerable soul.” His words have inspired many people to struggle against fierce odds and to keep going no matter how dire things look.

This is a wonderful thing. By taking messages like this seriously and by using tools gathered from counselors, teachers, and online self-help blogs, we can become ever more resilient. Change is a given in life. Sometimes we even manage to change ourselves according to plan.

Yet life can get in the way. Not only are we a product of our genes, our upbringing, and our culture, but we are also influenced by microscopic life.

Parasites Among Us

Take the parasite Diplostomum pseudospathaceum. John Green mentioned this organism in his novel about Aza Holmes, a sixteen-year-old obsessed with bacteria, parasites, and the fear that her life is determined by forces outside her control. [2] The Diplostomum pseudospathaceum begins its life in egg form, resting in the belly of a bird until pooped into a body of water. Once there, the creatures hatch and seek out their first host, a water snail, where they stay until large enough to move into a fish. There they wriggle around until they find their way into the animal’s eye.

At first, the parasites exert their influence on the fish to keep their host safe. You might not notice there was any influencing going on, for wouldn’t the fish would do its best to protect itself, anyway? Yet once the creatures grow to maturity, the fish’s behavior changes. It starts swimming near the surface of the water, moving in ways that will get it noticed by a bird who will snatch it up, allowing the Diplostomum to get inside an avian belly where it can lay its own eggs. [3]

By making itself an obvious target, the fish bows to the parasite’s will. It can’t help itself. One might then wonder, as Aza does, how we can know for sure we’re not “doing the bidding of some parasite.” [4]

Beyond Parasites

Parasites are not the only things that change the behavior of their hosts. We all know that rabies causes an infected animal to be more aggressive. Because the virus spreads through saliva, it wants the creature to bite something.

The Dinocampus coccinellae wasp lays its eggs inside the abdomen of another insect, such as a ladybug. Once it grow large enough, the larva crawls out of the insect and weaves a cocoon beneath its host. While it pupates, the host protects it from predators. When the grown wasp hatches, the host dies. [5]

A ladybug standing on a cocoon of a parasite that took away her free will when it parasitized her

Fungi, too, influence our behavior. The Massopora fungus infects male cicadas, devouring the insect’s hindquarters, but leaving it with an insatiable sex drive. Though physically damaged, it will be so eager to mate, it will even mount other males. Unable to consummate the act, these infected cicadas aren’t so good at perpetuating their species, but they’re great at spreading spores. [6]

So are ants colonized by the Cordyceps mycelium. When a carpenter ant ingests the fungus, it gradually becomes consumed by it. Finally, the fungus forces the insect to climb to the highest place it can find, where it collapses and dies. From the ant’s head grows a mushroom that soon explodes, ballooning its spores throughout the area. [7]

The Influence on Humans

Lest one think such things don’t affect humans, consider the Taxoplasma gondii parasite. This creature lays eggs inside a cat’s belly the way the Diplostomum does in birds. Also like the Diplostomum, it spreads through the feces. That’s why pregnant women are told to avoid cleaning cat boxes, for although the Taxoplasma gondii is not a problem for most human adults, developing fetuses can be seriously damaged by it.

What matters for us in this moment, though, is that the intermediate host for Taxoplasma gondii is a rodent. When infected with the parasite, rats and mice become careless. They lose their fear of the smell of cat urine and start drawing attention to themselves the way parasite-ridden fish do.

From the Taxoplasma gondii, we can develop taxoplasmosis. This disease doesn’t do much to our bodies, but it does influence our behavior. Infected women tend to be more intelligent, dutiful, conforming, warm, attentive to others, and outgoing than those without taxoplasmosis antibodies. Infected men, on the other hand, are less intelligent, dutiful, and conforming, and more rigid and stoic. Both genders with taxoplamosis tend to be apprehensive and insecure. [8]

The Influence of Microbes

Then there are bacteria and other microbes. The ones in our gut allow us to digest food. They have a lot to do with our physical health, but they also influence our behavior. They impact our brain development, our ability to handle stress, and our sociability. [9]

Skin bacteria may also influence our emotions and behaviors. We have long known that growing up in urban areas leads to an increased risk of anxiety disorders, reactive stress responses, schizophrenia, depression, impaired emotion regulation, and decreased gray matter. It’s assumed this is due to the stress of urban living itself, but since the bacteria we coexist with in the country is different from that found in urban dwellings, some researchers suspect that this difference has something to do with the impaired emotional, cognitive, and mental health of city kids. [10]

The Influence of Addiction

Clearly these parasites, fungi, and bacteria are not the only influences on our personality. Our genes determine a large part of who we are at birth, and we are shaped by our environment and culture. But knowing this, how can we trust that our actions, or even our thoughts, are fully our own?

We have a clear example of this in our addictions. According to twelve-step communities, an addiction is “unmanageable.” By its very definition, it assumes a lack of control. After all, if damaged relationships, impaired health, mental confusion, legal consequences, and tattered lives aren’t enough to get us to stop injecting or gambling or otherwise numbing ourselves, then something other than reason and free will are affecting us.

Yes, if the pain gets bad enough, most people manage to change their behavior, at least for a little while, but never by themselves. When we stop “cold turkey,” without the help of medication or community, we often find that another addictive process, or a clinging to rigidity or anger, takes that addiction’s place. The irony is that when we are under the influence of our drug of choice, whether a substance or a behavior or an experience, we tend to believe we are making rational decisions. Generally we aren’t.

Indeed, it’s rare that we don’t think we’re making decisions based on the will of our brain or of our informed heart. We assume we are free to choose the right and the good, or not. After all, we know what we should do, so if we aren’t doing it, it must be a defect of our will. That means we just need to try harder.

The Illusion of Independence

This illusion of control has something to do with our ego, that part of us that identifies as separate and immutable. To live embodied in a world, we need egos. They allow us to earn money and manage our daily affairs, in as much as we do. When healthy, our egos encourage us to live according to the rules of our community. They guide us as we play the social games that living in relationship require.

Even so, our egos do not see the world as it is. They encourage us to believe in the power of our individuality. At least in the Western world, we forget that if we are independent at home and at work, it is only because we of others who built our towns, who taught us, who trade and farm and truck for us, who lived before us and created everything we use, and who formed a culture that has given us a place, even if that place is not one we would have chosen if we did have free will.

It’s not hopeless, though. In Green’s book about Aza, we see her grow and learn. This is because, along with the untoward influence of parasites, microbes, and mushrooms, we are individuals with brains that do think, and we can learn. More importantly, we are part of a community. We have families, friends, counselors, teachers, and mentors. Music, paintings, and movies can change our minds and our lives. Religious communities like churches, covens, synagogues, and that temple in the wild, can all soothe us and help us grow.

Not So Free a Will

The bad news is that we’re a lot less self-determined than we think. Not only are we formed by our genetics, our nurture, the addictions that drive us, and the random experiences that punctuate a life, but we’re also influenced by the kinds of bacteria, parasites, and other microbes that inhabit our skin, our intestines, our blood, and our brains. Nowadays, technology, pollution, and climate change affect us, too.

It’s almost as if we were automatons with no thoughts of our own and no reason for breathing beyond supporting the creatures that live on and in us. That’s a depressing thought, and it would be bad news, indeed, if that were the totality of our life.

But it isn’t. There’s good news in this, as well. The knowledge that we are influenced by forces beyond our conscious awareness can change our approach to living, for when we understand this, we begin to see the ways we are interconnected. For instance, we stand on the shoulders of ancestors. We are beholden to the farmers and builders and teachers and plumbers and all who create and sustain our communities. Even the microscopic creatures that colonize our bodies are necessary, for they make life possible.

Choose Compassionate Community

We need one another. We are part of a whole. Even if our thinking is impacted by things and beings we can’t control, we can still learn, and in that learning, we can discover ways to collaborate for the good of us all.

If we can accept that within us exist competing and complimentary urges, mechanisms, and needs unnoticed by our conscious mind, perhaps we can find the compassion to forgive ourselves and others. This doesn’t mean we should excuse aberrant or harmful behavior. We can contain what needs containment and protect what needs protection without regressing to a simplistic and superficial morality that doles out punishment or reward according to rigid definitions of good and bad that assume an agency none of us possess. Even the sociopath is helpless to be anything but what he is in this moment of time. If we can remember this, then we might be able to create boundaries and limits with respect and dignity, if not affection.

We have less control over our choices than we like to think. So let’s practice compassion. Let’s learn to forgive. If we work together, we can build communities that encourage health and wellness. We can gently guide one another in the way we should go.

In faith and fondness,



  1. “Invictus” by William Ernst Henley
  2. Green, John, Turtles All the Way Down, New York: Dutton, 2017, 105.
  3. Editor, “Invasion of the Eye Flukes,” The Fish Site,February 28, 2006,, accessed 10/15/19.
  4. Green 106.
  5. “Behavior-Altering Parasites,” Wikipedia,, accessed 11/16/19.
  6. Yong, Ed, “This Parasite Drugs Its Host with the Psychedelic Chemical in Shrooms,” The Atlantic, July 30, 2018,, accessed 10/15/19.
  7. Pollan, Michael, How to Change Your Mind: What the New Science of Psychedelics Teaches Us About Consciousness, Dying, Addiction, Depression, and Transcendence, Penguin Press, 2018, 89.
  8. Lafferty, Kevin D., “Can the Common Brain Parasite, Taxoplasma gondii, Influence Human Culture?,” Proc Biol Sci, November 7, 2006, 273, (1602): 2749-2755, published online August 1, 2006,, accessed 11/16/19.
  9. Dinan, Timothy G., Roman M. Stilling, Catherine Stanton, John F. Cryan, “Collective Unconscious: How Gut Microbes Shape Human Behavior,” Journal of Psychiatric Research, vol. 63, April 2015, 1-9, published online March 2015,, accessed 11/16/19.
  10. Stamper, Christopher & Hoisington, Andrew & Gomez, O.M. & Halweg-Edwards, Andrea & Smith, D.G. & Bates, K.L. & Kinney, Kerry & Postolache, Teodor & Brenner, Lisa & Rook, Graham & Lowry, Christopher. (2016). The Microbiome of the Built Environment and Human Behavior: Implications for Emotional Health and Well-Being in Postmodern Western Societies. 10.1016/bs.irn.2016.07.006,, accessed 11/16/19.

Photo by Gilles San Martin from Namur, Belgium [CC BY-SA 2.0 (]

Copyright © 2019 Barbara E. Stevens All Rights Reserved

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