In Yellowstone National Park, a lone wolf usually ends up dead. Gray wolves typically live and hunt in packs, but sometimes a pack member leaves its family group. Other wolves, protecting their own pack's territory, will kill the loner. One kick from an elk or a bison can be deadly. And then there are more prosaic threats, like getting hit by a car. So why would any wolf take the risk of striking out on its own?

The traditional answer: ambition. "Not a lot of wolves survive the process," says Kira Cassidy, a field biologist with the Yellowstone Wolf Project, which reintroduced wolves to the park in 1995. "But if you do, you have a good chance of starting your own pack." These are the top dogs, the theory goes, who slough off the strictures of bourgeoisie wolf society to make a name for themselves.

But what inspires a particular wolf to get up off its hindquarters and leave its pack behind? What is motivating them? Cassidy and her colleagues had a hypothesis: Maybe a parasitic infection was egging them along. Specifically, a microorganism called Toxoplasma gondii.

Toxo, as it's colloquially known, has a baroque life cycle. It reproduces in cat species (like the cougars in Yellowstone) but then leaps to other hosts, from rats and hyenas to people and wolves. And once it takes up residence in a new animal, Toxo is linked to all sorts of weird behavior — much of it spurred by a strangely elevated appetite for risk. Cassidy's team looked at blood samples taken from 229 captured gray wolves and compared them with the way the wolves fared in the wild. The results, published last month in the journal Communications Biology, were striking. Wolves that left their packs were twice as likely to be positive for Toxoplasma. And Toxo-positive wolves were 46 times as likely as uninfected wolves to become pack leaders.

"As we're watching them, we definitely see differences in what seems to be like personality — how shy they are, how bold they are, how willing they are to cross a road," Cassidy says. "A lot of things I may have chalked up completely to personality in years past, now I have to rethink some of that stuff. Now I think maybe part of that was because of the parasite."

Three wolves on a desolate winter backdrop in Yellowstone National Park. One stands off to the left; two others snuggle on the right.
When wolves in Yellowstone National Park get infected with a cat parasite called Toxoplasma gondii, they become more likely to leave their packs and start new ones.
Jim Peaco/National Park Service

If Toxo turns wolves into risk-takers, could it be having the same effect on us? It's primarily contracted from coming into contact with cat feces, contaminated water, or undercooked meat, and as many as 80% of humans may be Toxo-positive, most of them without even knowing it. And there's sketchy but tantalizing evidence that Toxoplasma alters our behavior, too — especially entrepreneurial behavior.

Which is to say, many members of our species who exhibit "alpha dog" tendencies in the business realm may be Toxo-positive. Feel like starting your own company? The Yellowstone wolf data hints that it's just the side effect of a protozoan inhabiting our brains in a failed attempt to make more protozoa. Maybe that business you admire wasn't founded by the Great and Powerful Oz, a heroic leader of epic proportions, but by the parasite behind the curtain.

The Toxo-entrepreneur link

Before wannabe Elon Musks in Silicon Valley start throwing Toxo parties, let me just say: Don't. Not only would it almost certainly not work, but it could almost make you really sick. "In academia, if we pursue interesting questions like this, maybe we're a little different, with screws slightly looser," says Dan Lerner, a business professor at IE University in Spain who studies Toxoplasma's link to entrepreneurship. "But to read the papers and think, 'Oh, yeah, let me go eat some cat droppings' would be a really shitty idea. No pun intended."

Toxoplasma reproduces by infecting cats, getting into their GI tracts, and then getting into their poop. There it assumes a whole other form that can infect pretty much any warm-blooded animal that comes into contact with it. That's when things get spooky. In non-cats, Toxo hangs out in the eyes and the brain. It seems to make infected rats more likely to venture into unfamiliar places and less afraid of the smell of cat pee — a "fatal attraction," as the classic study of the phenomenon called it, that would turn infected rats into easier prey. When a cat eats the infected rodent, the Toxo bits jump into their new host like ships fleeing a sinking rat, and the cycle starts all over again.

So why would any of this make an infected wolf want to start its own pack? No one's really sure of the mechanism by which Toxo affects behavior. Maybe it increases production of testosterone. Maybe the brain cysts it causes in a host mess with neurotransmitters like dopamine, altering the brain's reward system. Or maybe it's just a generalized inflammatory response to infection. But whatever the mechanism, don't think of it as, like, alien parasite zombification. Microbes don't "want" anything. They just reproduce. If they create any sort of push in a host, it's the barest of nudges, the gentle redirect of a mother guiding a toddler away from bonking into a table leg.

Except in this case, it could be guiding them toward a Series A round. Lerner and his colleagues have found that students positive for Toxo are significantly more likely to major in business, with a particular interest in entrepreneurship. Sampling the saliva of attendees at entrepreneurship events, they found that Toxo-positive people were more likely to have started their own businesses. And looking at national entrepreneurship data, countries with more business-starting action also have higher levels of Toxoplasma overall.

"Any one person, you would never say, 'Oh, this person has Toxoplasma and therefore they're going to be an entrepreneur," says Stefanie Johnson, the director of the Doerr Institute for New Leaders at Rice University and a frequent collaborator of Lerner's. "It's within populations. Our data were huge samples." The effects weren't as pronounced as with the wolf leaders. But they were there.

It might be tempting to think of this as an inherently male thing — that the urge to play a dominant role in the world is the result of an infection. Maybe toxic masculinity is literally toxic. But wolf biologists, it turns out, have been trying for decades to get people to stop using the phrase "alpha male." Wolf packs are usually led by both a male and a female, and the pack leaders don't act anything like Harvey Weinstein. They want to lead, but they're not jerks.

There's more: Toxoplasma affects females, too. One good database for human Toxo infection is pregnant women — they get tested for the parasite, because it can infect the fetus and cause severe harm. So for a paper published last year, Lerner and Johnson's team paired data on all the new businesses in Denmark started by women from 2005 to 2014 with data on Danish women's Toxoplasma status. They found that women who were positive for the parasite were almost 30% more likely to start a business.

A circular cluster of purplish bubbles floating amid a blue background dotted with other objects
When people become infected with T. gondii, thousands of the protozoan parasites cluster into cysts in the brain.
Jitender Dubey/US Agricultural Research Service

Now, let's not get too far out on a limb here. Other than starting a company, Toxo in humans has been correlated only to a handful of behaviors: elevated rates of schizophrenia and suicide, most notably, and an increase in the likelihood of getting into a car crash. I haven't been able to find studies linking it to any other alpha-sounding behaviors, like political leadership, military service, skydiving, or slapping Chris Rock. And all these human studies show correlation, not causation. Without a clear mechanism — without knowing how Toxo might be altering our behavior — the most you can say is that all of this is worth looking into further. Humans are, you know, complicated. "The way our mind is constructed, its range is like animals, but that range is off the chart," says Ajai Vyas, a neurobiologist at Nanyang Technological University in Singapore who studies Toxoplasma-host behavioral interactions. "I personally tend to be nondeterministic." 

Meaning, other factors could explain all those Toxo-infected entrepreneurs. Maybe the businesspeople infected with Toxo were already daredevils. In fact, that could be how they got infected in the first place, if they were more likely to travel the world and get exposed to contaminated water, or more likely to lick a cat's butt. Maybe their capacity for risk-taking is the cause, not the effect.

However Toxoplasma works, it can't make someone do anything they didn't have the capacity for. It's possible that Toxo just intensifies a person's baseline appetite for risk, sort of like turning up the volume on a song that's already playing. That's how Ajai Vyas views the studies that have been done in animals. "Probably there's a continuum of the behavior," he says, "and the parasite shifts it toward impulsivity and risk-taking."

Johnson and Lerner don't disagree. In the subjects they studied, Lerner says, the parasite seemed to be "reducing fear of failure." 

"Normally," he continues, "people are going to think about the risks, and here — I won't say it nudges them to do it, but it stops them from thinking about it."

How the high-T have fallen

It's common for germy things to affect behavior. There's a fungus that makes ants climb up to a high vantage point and then explodes out of them, to spread more widely. A species of worm makes grasshoppers jump into swimming pools in search of water. The microbes in the human gut can apparently affect our mood. And if Toxo alters behavior in humans, maybe we're full of other microorganisms that are doing the same thing. 

Which is a wild thought. Sum up all those effects and pretty soon you start to wonder: How much of what you do is you, and how much of what you do is them? If behaviors as complex as entrepreneurship can be spurred by a tiny parasite with, presumably, no interest in PNL, maybe all sorts of human activities are really just accidental, or incidental to microbial reproductive tides. That was the suggestion of an influential 2006 paper titled "Can the Common Brain Parasite, Toxoplasma gondii, Influence Human Culture?"

The magnitude of Toxo's effect in Yellowstone wolves surprised even that paper's author, a parasite ecologist with the US Geological Survey named Kevin Lafferty. "I'm just fascinated by the idea that this parasite, with no benefit to itself, can determine outcomes of social interactions," Lafferty tells me. "It's not just about, Toxo determines who's the alpha male."

Since 2006, Lafferty has gotten more and more interested in the way Toxo might affect people through testosterone levels. That idea won't come as any surprise to the "high T" bros who view their masculinizing hormone as the ghost in their high-performance machines. But Lafferty thinks it's more complicated than that. High testosterone levels, after all, don't provide an incontrovertible advantage. High T levels make you do dumb stuff and die sooner.

"Being an alpha male in a pack or any social system probably requires having testosterone well beyond the optimal," Lafferty says. "You might actually predict men could be less likely to be successful in those fields, if the testosterone boost is pushing them past the peak of performance for those traits." Just because Toxo might drive an alpha male to start a company, that doesn't mean it'll be a successful company. 

So yes, maybe launching a startup is "synonymous essentially with leading the pack," as Lerner puts it. But even he wonders whether that same trait might make the companies more likely to fail. "In terms of entrepreneurial success, the ability to get on with others is often a good thing and typically necessary," he notes. His collaborator, Johnson, is eager to compare the failure rate of businesses started by Toxo-positive people versus Toxo-negative people. "I don't think we were able to capture that," she says.

Cassidy, the Yellowstone biologist, hopes to ask the same things about her wolves. Her team looked at whether they were leaders, but not whether they were good leaders. How long is their tenure? What's the survival rate of the pack when they're in charge? "That will be one of the next steps for this study, to look at that," Cassidy says. "My inclination right now is that they might have shorter tenures."

Maybe Silicon Valley alpha-ness gets goosed, somehow, by this one weird microorganism. But if you want a high-quality, sustainable endeavor that builds value and changes the world? Well, let's just say neither alpha leaders nor the companies they start should be parasitic, inside or out.

Adam Rogers is a senior correspondent at Insider.