The cat hunts again, dines on infected prey, and the odd hypnotists thrive. Only cats further the parasite’s agenda, but other animals can sometimes ingest the eggs without knowing it and become dead-end hosts. That’s why pregnant women are warned not to empty kitty litter or handle cat bedding. Exposure to Toxoplasma can derail a fetus, leading to stillbirth or mental illness. Some studies link Toxoplasma and schizophrenia. Infected women have a higher risk of suicide than parasite-free women. According to Oxford researchers, it can doom children to hyperactivity and lower IQs. And, for some reason, over twice as many pregnant women infected with Toxoplasma give birth to boys.
But these new rat–cat findings are only the beginning of an Orwellian saga steeped in irony and intrigue. Worldwide, scientists are posing questions both eye-opening and creepy. If Toxoplasma can enslave the minds of rats—animals often studied to test drugs for humans—can it also alter the personality of humans? What if that yen to go rock-climbing or change jobs isn’t a personal longing at all, robust and poignant as it may feel, but the mischief of an alien life form ghosting through your brain? Is Toxoplasma to blame for a hothead’s road rage? How about a presidential hopeful’s indiscreet liaisons, or a reckless decision made by a head of state? Could a lone parasite change the course of human history?
So when is a whim not a whim? It feels like we have free will, but is a tiny puppeteer pulling the strings of billions of people? For the longest time philosophers, theologians, and college students debated such questions, then neuroscientists joined the fray, and now a body of parasitologists.
When Jaroslav Flegr, of Charles University in Prague, surveyed people infected with Toxoplasma, he found clear trends and surprising gender differences. The women spent more money on clothes and makeup and were more flirtatious and promiscuous. The men ignored rules, picked fights, dabbled in risk, and were nagged by jealousy. Both sexes got into more than twice the average number of traffic accidents—as a result of either impulsivity or slowed reaction time.
Rats have proclivities and tastes. Humans have those in spades, as well as sentiments and reveries. But mindset doesn’t matter. All warm-blooded mammals respond to thrill, anticipation, and reward—especially if that includes a wallop of pleasure. Many of the odd behavioral changes scientists attribute to Toxoplasma tap the brain’s dopamine system, and that’s what Toxoplasma zeroes in on, rewiring networks to favor its own offspring, even if that means death for the host. Cocaine and other euphoriants use the same dopamine system. As the Stanford neuroscientist Robert Sapolsky explains, “the Toxoplasma genome has the mammalian gene for making the stuff. Fantastic as it sounds, a humble microbe is fluent in the dopamine reward system of higher mammals.
“This is a protozoan parasite that knows more about the neurobiology of anxiety and fear than twenty-five thousand neuroscientists standing on each other’s shoulders,” Sapolsky adds, “and this is not a rare pattern. Look at the rabies virus; rabies knows more about aggression than we neuroscientists do. . . . It knows how to make you want to bite someone, and that saliva of yours contains rabies virus particles, passed on to another person.” It’s an extraordinary genetic tool for a witless one-celled creature to wield.
Marine mammals and birds are spreading the parasite via water currents and ribbons of air. How many of us may already be unwilling hosts? According to the Centers for Disease Control and Prevention, 10 to 11 percent of healthy adults in the United States tested positive for Toxoplasma, and the true figure (most people haven’t been tested) is thought to be 25 percent of adults. Some scientists estimate that in Britain, a decidedly cat-loving country, half the population has been infected, in France and Germany 80 to 90 percent, and in countries that favor undercooked meat even more, with nearly everyone an unwitting mark—destiny’s child, to be sure, but also Toxoplasma’s zombie.
According to Nicky Boulter, an infectious disease researcher at Sydney University of Technology, eight million Australians are infected, and “infected men have lower IQs, achieve a lower level of education, and have shorter attention spans. They are also more likely to break rules and take risks, be more independent, more antisocial, suspicious, jealous, and morose, and are deemed less attractive to women.
“On the other hand, infected women tend to be more outgoing, friendly, more promiscuous, and are considered more attractive to men compared with noninfected controls. In short, it can make men behave like alley cats and women behave like sex kittens.”
What does it take to slant an opinion? Advertising, group pressure, financial gain, a charismatic leader? How about a real lowlife, a wheeler-dealer who delights in messing with your mind and harbors primitive drives? Enter the saboteur skillful enough to slowly and subtly change the personality of whole nations—a humble microbe. Some researchers speculate that between a third and half the people on Earth now have Toxoplasma in the brain. And it’s only one of the many microbes that call us home. Is it possible that what we chalk up to cultural differences may be different degrees of mass infection by a misguided parasite? Kevin Lafferty, a parasite ecologist with the U.S. Geological Survey, also theorizes that cultural identity, at least “in regard to ego, money, material possessions, work, and rules,” may reflect the amount of a parasite in a population’s blood.
If you’re now eyeing your tabby with raised eyebrows, there’s no need to panic. Even invisible dictators can be deposed, and Toxoplasma responds well to antibiotics. In any case, would it have a greater influence than family dramas, pharmaceuticals, TV, college, climate, love, epigenetics, and other factors in human behavior? It’s probably one spice among many. After all, a slew of elements and events influence us from day to day, changing us in cumulative and immeasurable ways. Toxoplasma may be but one, and it doesn’t lurk in all cat owners or devourers of steak tartare. It may ring its changes only in the presence of certain other microorganisms. How can you tell the dancer from his dance of microbes?
In the garden, all the plants and animals have their own slew of microbial citizens, some sinister, others helpmeets. That takes some getting used to. It’s a big paradigm change, one future generations will understand from childhood and capitalize on. In health and medicine, they’ll focus on the human ecosystem, our whole circus of human cells, fungi, bacteria, protozoa, and archaea working together, untidily perhaps, but in concert.
When I was growing up, scientists only grew microbes in small petri dishes in their labs, and all bacteria were nasty. In just a decade, we’ve begun seeing the big mosaic and we’re even starting to think in terms of microbes for improving the planet in precise ways: fixing the health of endangered species with wildlife probiotics, ousting invasive species using certain bacteria, sweetening groundwater that’s been tainted by pollutants, cleaning up oil spills with voracious grease-loving microbes, helping agriculture feed more people without fertilizers by employing bacteria that make the crops grow faster and more robustly.
The hope is that, just as with genes in the Human Genome Project, if researchers can identify the core microbes that most humans share, then it will be easier to divine which species contribute to specific complaints. This offers a new frontier for fighting illness, one easier to manipulate than the genome, and safer to barge in on than deeply embedded organs like the heart or liver.
New studies suggest that a single pathogen is rarely enough to trumpet disease, because different microbes form alliances. “The real pathogenic agent is the collective,” says David Relman, an infectious disease specialist at Stanford University. This has sparked a new way of thinking about illness called “medical ecology,” which recognizes the collective as the key to our health. In the past, we thought of all bacteria as bad, a contagion to be banished, a horde of invisible dragons. Ever since the end of World War II, when antibiotics arrived like jingle-clad, ultramodern cleaning products, we’ve been swept up in antigerm warfare. But in a recent article published in Archives of General Psychiatry, the Emory University neuroscientist Charles Raison and his colleagues
say there’s mounting evidence that our ultraclean, polished-chrome, Lysoled modern world holds the key to today’s higher rates of depression, especially among young people. Loss of our ancient bond with microorganisms in gut, skin, food, and soil plays an important role, because without them we’re not privy to the good bacteria our immune system once counted on to fend off inflammation. “Since ancient times,” Raison says, “benign microorganisms, sometimes referred to as ‘old friends,’ have taught the immune system how to tolerate other harmless microorganisms, and in the process reduce inflammatory responses that have been linked to most modern illnesses, from cancer to depression.” He raises the question of “whether we should encourage measured reexposure to benign environmental microorganisms” on purpose.
A baby is born blameless but not microbe-free. Mom coats her with helpful microbes as she squeezes down the birth canal, including Lactobacillus johnsonii (a bacterium one expects to find in the gut, not the vagina), a bug essential for digesting milk. I was bottle-fed formula, but breast-milk-fed babies grow stronger immune systems because breast milk, often the first source of nourishment, teems with more than seven hundred species of hubbub-loving, life-enhancing bacteria. Researchers are thinking of cobbling them into infant formula to help ward off asthma, allergies, and such autoimmune triggermen as diabetes, eczema, and multiple sclerosis. Babies pick up other useful bacteria in Mom’s dirt-and-crumb-garlanded home and landscape. At least, they should.
Doctors are embracing the idea of personalized medicine based on a patient’s uniquely acquired flora and fauna, as revealed in his or her genome, epigenome, and microbiome. No more antibiotics prescribed by the jeroboam on the off chance they might prove useful. Instead, try unleashing enough beneficial bacteria to crowd out the pathogen. No more protecting children from the hefty stash of derring-do white-knight bacteria they need but we’ve learned to regard as icky.
Patients whose gut flora have been wiped out by certain antibiotics are prey to Clostridium difficile, an opportunistic weasel of a bug that causes severe, debilitating diarrhea. Once it has taken up residence, it’s miserably hard to expel it and restore the good bacteria. What does seem to help, though it’s not an image to dwell on, is fecal transplants from a healthy person—an enema full of bacteria to recolonize a stranger’s intestines, join the Darwinian fray, and triumph over the pathogens by acting like sailors on leave.
When Kathy Lammens, a stay-at-home mom with four young children, learned that her nine-year-old daughter’s battle with colon disease might lead to a colostomy bag, she began looking for alternative therapies. After much research, she decided on do-it-yourself home fecal transplants, tendering one five days in a row. Twenty-four hours after the first, all of her daughter’s symptoms improved. Now Kathy, a robust believer, offers a YouTube video with instructions.
One study has revealed that mice with autism don’t host the same gut microbes that mice without autism do, and they seep behavior-altering molecules through the body and brain. But researchers find that dosing the mice with the beneficial bacterium Bacteroides fragilis eases the symptoms, and so human trials will follow. Another study discovered that if heart patients don’t eat enough protein, the good gut microbe Eggerthella lenta will steal some of a patient’s dose of digoxin, an important heart stimulant.
Some of global warming’s unwelcome guests are tiny winged buccaneers carrying invisible stoles of misery. Mosquitoes in Africa and South America are rambling farther north, injecting dengue fever, malaria, West Nile virus, and yellow fever into parts of the world unfamiliar with such scourges. Perfusing our clothes and bedding with insecticides isn’t safe, but the diseases infect hundreds of millions of people each year. So the Michigan State microbiologist Zhiyong Xi has been working on the problem in a novel way, by rearranging microbes. When he noticed that mosquitoes carrying dengue fever and malaria were missing the mosquito-loving bacterium Wolbachia, he tried infecting the mosquitoes with a heritable strain of Wolbachia, and sure enough, the next generations didn’t carry either illness, and the lifesaving trait was passed on to their offspring.
It’s intriguing to imagine the role a simple microbe may play in someone’s relationships and career, and it reminds us that nothing life ever does is simple, or boring. How many threads weave a fleeting thought, let alone a hankering? It also reminds us of the fierce beauty of Earth’s organisms, whatever their size, creatures unimaginably complex, breathtakingly frail and yet sturdy, durable, filled with the self-perpetuating energy we call life. A big brain isn’t required to concoct sly, world-changing strategies.
AS I GLANCE out at the yard, I’m charmed by nature’s details: the magnolia tree’s fuzzy buds fattening up for spring; the melting snow on the lawn that’s left hundreds of grass follicles; long arcs of wild raspberry canes covered in their chalky lavender winter mask. But I’m also struck by the everythingness of everything in cahoots with the everythingness of everything else. When I look at my hand now, I scout its fortune-teller’s lines, and the long peninsulas of the fingers, each one tipped by a tiny weather system of prints; I see it whole, as one hand. But I also know that only a tenth of what I’m seeing is human cells. The rest is microbes.
When all is said and done, both our parasites and we their innkeepers are diverse—no one hosts the same reeking and scampering microbial zoo. Our microbes can change either in ratio or in kind at the drop of a cookie or in the splash from a locker-room puddle or through an ardent kiss, and then we have to adapt quickly. So it’s possible that some diseases really are inherited, but the genes that bestowed them were bacterial. When you think about it, for a major trait to evolve—something grand like the advent of language or the urge to explore—only one gene has to change on the Y chromosome of one man. That would be enough, over many many generations, to create a predisposition or a trend in an entire culture. It all depends on the highjinks of the maddening microbe.
Maybe this should also remind us how much of a pointillist jigsaw puzzle a personality really is. As a friend approaches with a smile, we greet a single person, one idiosyncratic and delightful being who is recognizable—predictable, even, at times. And yet every “I” is really a “we,” not one of anything, but countless cells and processes just barely holding each another in equilibrium. Some of those may be invisible persuaders of one sort or another: protozoa, viruses, bacteria, and other hobos. But I like knowing that life on Earth is always stranger and more filigreed than we guess, and that both the life forms we see and those we cannot see are equally vibrant and mysterious.
Where does your life story begin? When does the world start whittling your personality and casting your fate? At birth? In the womb? At the moment of conception, when DNA from your mother and father fuse, shuffling an ancient deck of genetic cards and dealing out traits at random from Mom or Dad? Long before womb-time, it would seem, much farther back, before your parents’ courtship, even before their parents’, in a crucible of choices, daily dramas, environmental stresses, and upbringing. Our genome is only one part of our saga. The epigenome is another. The birdlike microbes singing in the eaves of the body are yet another. Together, they’re offering a greatly enriched view of the terra incognita inside us. In the process, sometimes loud as headlines, but more often silent as the glide of silk over glass, how we relate to our own nature is subtly changing.
CONCLUSION:
WILD HEART, ANTHROPOCENE
MIND (Revisited)
NASA’s “Blue Marble” photograph of Earth from space gave us an eye-opening image of the whole planet for the first time. Forty years later, “Black Marble” was equally mind-altering, but in a different way: it introduced us to ourselves. Forging a new geological era, we are an altogether different kind of animal from any the planet has ever known, one able to reinvent itself and its world, and manage to survive, despite more twists and turns in daily life than any creature has ever had to juggle. We inhabit a denser mental whorl than any of our stout-hearted ancestors. We’re in the midst of a m
ajestic Information Age, but also an ingenious sustainability revolution, a deluxe 3D revolution in manufacturing, a spine-tingling revolution in thinking about the body, a scary mass extinction of animals, alarming signs of climate change, an uncanny nanotechnology revolution, industrial-strength add-ons to our senses, a biomimicry revolution—among so many other “new normals” that we sling the phrase daily.
We understand ourselves on many more spine-tingling levels: how we’re changing the planet, other creatures, and each other. This is not just the Human Age. It’s also the age when we began to see, for the first time, the planet’s interlaced, jitterbugging ecosystems—on the land, in the air, in the oceans, in society—and unmasked our own ecosystems. We’ve met many of our makers, the mad molecules.
Thanks to revelations in neuroscience, genetics, and biology we’re bringing the life and times of Homo sapiens sapiens into a much clearer focus. As the “Me” generation gives way to the “We” generation, we’re growing more aware of the ties that bind us—even if we’re less relaxed in face-to-face encounters.
We humans have so much in common that we can’t seem to speak of comfortably: a genetic code, a niche on a small planet in a vast galaxy in an infinite universe; the underrated luxury of being at the top of our food chain; a familiar range of passions and fears; a mysterious, ill-defined evolution from creatures whose thoughts were like a vapor, and before that bits of chemical and chance so small they pass right through the mind’s sieve without its being able to fully grasp them. We have in common, despite our extraordinary powers of invention, subtlety, and know-how, an ability to bore ourselves that is so horrifying we devote much of our short lives to activities designed mainly to make us seem more interesting to ourselves. We have in common a world our senses know voluptuously, from one splayed moment to the next, the wind touching one’s chapped lips, a just-forgotten chore, the small unremarkable acts of mercy and heroism parents and lovers perform each day, the collective sort of creatures we are, whose qualities embarrass us when we stumble upon them in ourselves, but which we’re glad to epitomize in movie stars, sports figures, and politicians—people like Neil Armstrong stepping onto the moon, or Thomas Edison spending the last of his days in Florida trying to make rubber from goldenrod. We have in common a fidgeting, blooming, ever-startling universe, whose complex laws we all obey, whether we’re born in Tierra del Fuego or Svalbard.