We contain multitudes (2007)
While walking to work one day, anthropologist and essayist Loren Eiseley tripped and fell, hitting the pavement with great force. He recalled the accident in his book The Unexpected Universe, published in 1969.
“Under my face a steady of rivulet of blood was enlarging to a bright pool on the sidewalk. It was then, as I peered nearsightedly at the ebbing substance there in the brilliant sunshine, that a strange thing happened. Confusedly, painfully, indifferent to the running feet and the anxious cries of witnesses around me, I lifted a wet hand out of this welter and murmured in compassionate concern, “Oh, don’t go. I’m sorry, I’ve done for you.”
He noted: “A great wave of compassionate contrition, even adoration swept through my mind, a sensation of love on a cosmic scale, for mark that this experience was as vast a catastrophe as that of a galaxy consciously suffering through the loss of its solar systems.”
It may have been as much concussion as compassion, but Eiseley hit on something big with his curbside revelation about an in-house cosmos. According to Eiseley, each one of us is a commonwealth of microorganisms, with trillions of nano-sized citizens working non-stop maintaining that vast, sentient being called “I.”
Eiseley was more right than he knew about an unexpected universe. Three decades after his death, scientists have determined that 90 percent of the cells in the human body are bacterial. Only five percent of the cells in your body constitute “you,” in the sense of your genetic heritage. In relative scale, bacteria are much smaller than your own cells, so they account for only a small fraction of your body weight. Nearly all of these microbes are located in your gut, where they keep you working at optimal health.
There’s a new paradigm in microbiology emerging, in which bacteria are no longer seen exclusively as disease-causing killers, but rather as lifelong partners. In a certain sense, they’re the immigrants, doing the work the rest of the community isn’t up for.
Many of these one-celled fellow travellers are introduced soon after birth. Breast-fed, versus formula-fed, infants show a marked difference in the predominant microflora in their GI tracts. LivingWell Communications president Victoria Shanta Retelny writes in For the Record: “The fecal flora of breast-fed infants is so heavily dominated by the probiotic genus, bifidobacterium, that it is considered the “gold standard” type of gut flora, which imparts excellent resistance to infection.” On the other hand, “In formula-fed infants, no one microbial group predominates, rendering the system less able to fight infection,” she notes.
Over the past decade, physicians grudgingly recognized the health benefits of microflora, such as acidophilus. For years, they had been scribbling prescriptions for antibiotics, even for viral infections, apparently in the lazy hope that patients would benefit from the placebo effect. The law of unintended consequences followed with depressing predictability, evidenced by opportunistic infections in GI tracts from fungi and other pathogens and the emergence of antibiotic-resistant strains of bacteria.
With the new medical paradigm, physicians now understand the value of introducing bacteria into the diet. “Probiotics” can prophylactically manage acute and chronic gut disorders, by reducing the activities of other pathogens already present, or those that have been transmitted by food and water.
Young kids are forever sticking things in their mouths, but there’s a reason for that. A study in the New England Journal of Medicine indicates that early exposure to dirt, dust and bacteria actually helps childrens’ immune systems develop more effectively. The concept has been coined the “hygiene hypothesis.” One study concluded that children who grew up on farms had fewer allergies than their counterparts in urban areas. Conversely, health studies have shown that mothers who kept their children in antiseptic environments were actually compromising their health. Children need to be exposed to the natural environment of threats and benefactors so their immune systems learn to distinguish between the two.
While most doctors aren’t likely to encourage parents to let their kids eat mouthfuls of dirt, an occasional nip of soil is probably beneficial. As for scouring the home twice a week, there’s probably a greater health threat to young children from industrial cleansers than there is from exposure to a moderate amount of bacteria.
For millions of years, animal immune systems have coevolved with Earth’s smallest habitants. These arrangements run the range from symbiosis – benign, mutually beneficial relationships – to parasitism, in which only one party benefits. While there is plenty of evidence to support that the body’s outside contractors, such as bifidobacterium, provide health benefits, scientists aren’t quite ready to romanticize microbes, at least not after recent research conducted on a parasite common to housecats.
The bizarre life cycle of toxoplasma gondii recently made front page news. Science writer Carl Zimmer, author of Parasite Rex, writes in his blog:
“This single-celled parasite lives in the guts of cats, shedding eggs that can be picked up by rats and other animals that can just so happen be eaten by cats. Toxoplasma forms cysts throughout its intermediate host’s body, including the brain. And yet a toxoplasma-ridden rat is perfectly healthy. That makes good sense for the parasite, since a cat would not be particularly interested in eating a dead rat. But scientists at Oxford discovered that the parasite changes the rats in one subtle but vital way.”
The scientists put the rats in a six-foot-square outdoor enclosure, which they turned into a brick-lined maze. In each corner, they put a nesting box along with food and water. One box was scented with raw, straw bedding; another had the scent of a rat’s nest; yet another had the scent of rabbit urine and one had the scent of cat urine. When the rats were put into the maze, they sniffed about curiously, investigating the nests. The healthy ones avoided the nests with the cat odour and refused to return to them.
“This was no surprise,” writes Zimmer. “The odour of a cat triggers a sudden shift in the chemistry of rat brains that brings on intense anxiety. (When researchers test anti-anxiety drugs on rats, they use a whiff of cat urine to make them panic.) The anxiety attack made the healthy rats shy away from the odour and in general makes them leery of investigating new things. Better to lie low and stay alive.”
The researchers then put the toxoplasma-carrying rats in the enclosure. The infected rats were indistinguishable from their healthy brethren. They could feed themselves and competed for mates just as well. But there was one big difference: they were more likely to get killed. The cat odour didn’t faze them and they sniffed around without a trace of anxiety. In fact, researchers found they took extra interest in the spot and returned to it over and over again.
The theory behind the rats’ behaviour is that toxoplasma somehow alters the neural activity of rats. Through natural selection, parasites that ended up in cats – via the unafraid rats – were more likely to leave offspring.
Humans can be hosts to toxoplasma too, thanks to housecats. In fact, it’s estimated that about half the human population is infected with the one-celled parasite. For the most part, the microbe is only a concern for people with weak or compromised immune systems, which is why pregnant women are advised not to handle kitty litter, and why toxoplasma are a health risk for people with AIDS. But for healthy people with the parasite, it poses no great risk, residing quietly in their bodies and brains.
Because human and rat brains function with roughly the same anatomy and use the same neural transmitters, some scientists are now questioning whether toxoplasma could alter human behaviour as well. “Obviously, this manipulation would not do the parasite any good as an adaptation, since it’s pretty rare for a human to be devoured by a cat. But it could still have an effect,” Zimmer writes.
In fact, some scientists believe that toxoplasma slightly changes the personality of its human hosts, effecting men and women differently. Parasitologist Jaroslav Flegr of Charles University in Prague administered psychological questionnaires to both a control group and a group of people infected with toxoplasma. Zimmer notes: “Those infected… [Flegr] found, show a small, but statistically significant, tendency to be more self-reproaching and insecure. Paradoxically, infected women, on average, tend to be more outgoing and warm-hearted than controls, while infected men tend to be more jealous and suspicious.”
While the research is still controversial and has been disputed by some scientists, E. Fuller Torrey of the Stanley Medical Research Institute in Bethesda, Maryland, has noted some intriguing links between toxoplasma and schizophrenia. He and his colleagues have discovered that toxoplasma infection is associated with damage to a certain variety of neurons – the same ones damaged by schizophrenia. Most tellingly, pregnant women with high levels of toxoplasma antibodies in their blood were more likely to give birth to children who would later develop schizophrenia.
Zimmer’s conclusion: “It’s conceivable that exposure to toxoplasma causes subtle changes in most people’s personality, but in a small minority, it has more devastating effects.”
Is it possible that microbes mediate some mental conditions? And do these disabilities confer any survival value for human beings? An upside to schizophrenia seems unlikely, but it may not be nil. Psychologists have determined that during periods of war, for example, schizophrenics do not develop hysterical conditions – the “normal” shutdown reaction of otherwise mentally healthy people.
There’s a persistent notion, fed by advertisers, that we should all be slim, gorgeous, healthy and happy, right into our golden years. After all, isn’t this what Darwin’s survival of the fittest is supposed to mean? In this view, disease is an existential scourge, which must be defeated by invasive medical procedures and powerful drugs. This monolithic but immensely profitable viewpoint has been both a boon and a bludgeon to people’s health the world over. Now, a more balanced viewpoint is emerging, in which disease is seen in an evolutionary context.
In his 2007 book Survival of the Sickest, Dr. Sharon Moalem writes of the surprisingly adaptive consequences of many forms of illness. According to Moalem, these conditions have lived on because they protected our ancestors from premature death, enabling them to live just long enough to procreate. Maolem, who holds a doctorate in neurogenetics, builds on the work of co-authors Randolph Nesse and George Williams, who introduced the revolutionary science of Darwinian medicine a decade ago. From diabetes to hemochromatosis, scientists have concluded that many debilitating, hereditary conditions have offered enough positive evolutionary advantages to offset the negative consequences. For example, sickle cell anemia, a condition afflicting people (or their descendants) from parts of the world, such as sub-Saharan Africa, persists because it conferred resistance to malaria.
In fact, every animal cell carries traces of a past as a bacterial hybrid, originating billions of years ago. Back in the 1970s, cell biologist Lynn Margulis theorized that the power plants of animal cells, the mitochondria, once existed as free-living bacteria that entered into a mutually beneficial relationship with larger host cells. These bacteria began to supply energy to the cells, in exchange for the security of habitation in the cell protoplasm. A similar dynamic is believed to have occurred with chloroplasts, the photosynthetic workhorses found in plant cells.
Viruses are little more than tiny strands of DNA coated in protein, existing on the boundary of living and nonliving. They may have an even closer evolutionary relationship with us than bacteria. In his book Viruses and the Evolution of Life, Luis Villarreal, director of the Center for Virus Research at the University of California at Irvine, distinguishes the familiar, deadly parasites like HIV from what he calls “persisting viruses.” These may have become partners in mammalian evolution, migrating into the genome over millions of years.
Astoundingly, some scientists theorize that as much as a third of human DNA could have originated from viruses. They may not only have sped up our evolution, but also influenced its direction. As Moalem insists, it’s not so much intelligent design as “infectious design.”
In this new, scientific worldview, there’s a blurring of biological boundaries between creatures multicellular and microbrial. It seems that nowhere in our shapeshifting world is there an absolute distinction between organism and environment. Across geological epochs, microbrial species act like travellers along a genetic Silk Road, trading bits of DNA back and forth like pots, pans and Persian carpets.
While this biological globalism may be unnerving for obsessive-compulsive homemakers, brandishing cleaners and solvents against invisible enemies, it’s the way the living world works. Luckily for us, and other creatures, the natural world is as much about alliances of convenience as it is about outright conquests (it’s usually only parasites poorly adapted to their hosts that kill them). And similar to toxoplasma, many pathogens become a real threat only when the host’s immune system is already compromised by environmental toxins, poor diet and other factors.
These discoveries should alert us to how shaky the concept of self really is – especially if it has been influenced across generations, Borg-like, by tiny hitchhikers. For all our pride in our clever ways, entities invisible to the human eye are the ones actually running the show on planet Earth. Ninety percent of the earth’s biomass is contained in the soil and oceans in the form of anaerobic and aerobic bacteria. Without this bacterial foundation, the chemical cycles of the biosphere would grind to a halt.
In H.G. Wells’ 1898 novel, War of the Worlds, human beings were saved when the alien invaders fell prey to the common cold. With his fictional finale, Wells perfectly captured the ambiguous relationship between beings big and small. We owe our continued survival to the toil of the world’s most primitive life forms, yet we could disappear as quickly as Wells’ tentacled invaders if we continue to threaten the planet’s ecological equilibrium. With fewer and fewer animal species available, infectious bacteria and viruses will do what they’ve always done: go where the meat is.
With these new, scientific discoveries, which are both sobering and liberating, we’re at last emerging from the lingering shadows of medicine’s Dark Age. We’re moving away from a worldview which sees nothing but implacably hostile microorganisms out to destroy us, which must be destroyed with equally hostile countermeasures. A more naturalistic and common sense viewpoint is emerging: that when we fall out of equilibrium with our environment, internal or external, we can expect unpleasant consequences.
Microbes‘R’us – we contain multitudes, as Loren Eiseley intimately knew after a violent fall to a curb. Will it take some equivalent trauma to fully awaken Western culture to the interdependence of all beings, and of community as life’s grand theme?