This common parasite was found to make people more entrepreneurial. But how?

experiment parasite

When Daniel Lerner, a Professor of entrepreneurship at Madrid’s IE Business School, and colleagues examined the medical and professional histories of 74,291 Danish women, they discovered that those infected with the parasite Toxoplasma gondii were, on average, 29% more likely than others to have founded a startup, 27% more likely to have founded multiple ventures, and more than twice as likely to have founded their businesses alone.

In addition, their ventures were more successful, on average, than those launched by their uninfected counterparts. The conclusion: a common parasite can make people more entrepreneurial.

Professor Lerner, defend your research

Lerner: Behavior modification caused by parasites is a proven phenomenon. Scientists have shown that when Toxoplasma gondii infects rodents, it enters their brains and makes them less risk-averse. Specifically, the rodents become more active, are more inclined to explore new areas, have slower reflexes, and are less fearful of the smell of cats or cat urine. Novelty-seeking behavior, disinhibition, and reduced aversion to risk: Those sounded like entrepreneurial qualities to me. So my colleagues and I set out to assess a potential connection.

HBR: Hold on — are we talking about mice or men?

A: Both. Toxoplasma gondii, which is estimated to infect 10% to 50% of the human population depending on the country, also affects people’s brains, modifying the production and metabolism of neurotransmitters such as dopamine and serotonin and of hormones such as testosterone. Evidence is growing that those modifications can cause behavioral changes not unlike the ones observed in rodents. Even people with subclinical or latent infections — which account for the vast majority of cases — rate the odor of domestic cats as more pleasant relative to the way that uninfected people rate it. They become more extroverted. They’re also more likely to be involved in traffic accidents and to swim while intoxicated — behaviors that suggest they have an increased tolerance for risk.

Q: Given that the parasite can be transmitted to people from cats, are you sure you didn’t simply demonstrate that female cat owners march to the beat of their own drums and are therefore more likely than other people to start businesses?

A: Ah, the “crazy cat lady” stereotype! I highly doubt it. It’s true that TG reproduces only in feline intestines, making cats the ultimate hosts. But contrary to what many people believe, TG infections in humans don’t come very often from indoor cats. They’re more likely to come from consuming undercooked meat, unpasteurized dairy products, or unwashed vegetables, and occasionally they arise from exposure to feral cats or domestic cats that have been exposed to infected rodents. The overall link between TG and psychological and behavioral changes has been demonstrated in hundreds, if not thousands, of studies involving a wide variety of species.

Although studying TG’s effects in humans is, of course, complex, we are building a solid case. In previous research we took saliva samples from some 1500 university students and found that those who tested positive for TG were, on average, 1.4 times as likely as others to major in business and 1.7 times as likely to have an emphasis on or a concentration in management and entrepreneurship. In another study, this time of 200 professionals, we found that people infected with TG were 1.8 times as likely as others to be entrepreneurs.

Our new study builds on that research but on a much larger scale. TG causes serious illness in the immunocompromised and can even be fatal. In many countries, including Denmark, pregnant women are tested for it because acute TG infection during pregnancy can cause very serious birth defects.

Thanks to my Danish co-authors and to Denmark’s extraordinary record-keeping system and public data agency, we were able to compare individually linked but anonymised medical records with information on individuals’ economic activities — employment, business venturing, and other things — over more than a decade. We observed more than 74,000 women in all, of whom more than 7000 were TG-positive.

Q: Of necessity, your study included only women. Would you expect to find a similar effect among men?

A: The previous research on TG and entrepreneurship involved both men and women, so I would expect the general findings to be similar. However, it’s possible that the size of the effect might differ.

Q: Are you worried that some aspiring entrepreneurs might intentionally expose themselves to TG?

A: I certainly hope not; that would be very stupid. It is true that the mean performance of businesses started by the TG carriers in our study, as measured by profits, was about 8% higher than that of the noncarriers’ businesses. But individual performance was quite variable. There were plenty of impressive successes but a lot of flops as well. And the TG-infected entrepreneurs demonstrated less persistence than the uninfected founders did and were more likely to have founded their businesses alone. Persistence and the capacity to engage complementary co-founders are typically important qualities for an entrepreneur.

Most important, TG is a parasitic pathogen! It remains in your body forever. Even in latent form it can make you very ill if you ever become immunocompromised, say from cancer treatment or an organ transplant. And recent evidence suggests that TG can cause very serious mental problems among people with latent infections. For example, research has linked it to manic depression, schizophrenia, and dementia. My advice is to avoid the parasite by staying away from raw meat, thoroughly cleaning fruits and vegetables, and washing your hands should you come into contact with cat droppings or rodents.

Q: Could your findings be useful to venture capitalists when they’re sizing up possible investment targets? Maybe they could ask entrepreneurs to test for TG infection as a potential funding screen — a positive result being desirable from their point of view.

A: I’m all for more-rigorous and evidence-based assessments by venture capital firms, which could improve their financial returns and at the same time increase the diversity of founders they support and benefit the broader entrepreneurial ecosystem. But there are far better ways to do that than testing for this parasite.

Q: I find the whole notion of parasitic manipulation pretty creepy; it’s awfully close to suggesting that humans don’t really have free will. Is that what you believe?

A: Science shows that people’s behavior is influenced by innumerable things — for instance, research is emerging about how the bacteria in our guts affect our mental health. But I stop far short of arguing that we lack free will. You might recall that a similar concern arose decades ago, when scientists started learning about how genes influence our behavior. When it comes to both genes and parasites, we’re talking about probabilistic tendencies. Whatever effects TG has on our behavior, infection is not deterministic. Personally, I think it’s a good idea to keep one’s ego in check and be a bit humble about how well we understand our own motives, desires, and actions. But that doesn’t lessen my sense of autonomy and agency.

This article was first published by Harvard Business Review.

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