by Ziya Tong
As a result, we have launched our own “Black Death,” a vicious chemical war against these tiny invaders. Globally, agro-chemicals and pesticides have become a multi-billion-dollar industry that grows year over year.*6 But in our efforts to stamp out unwanted pests, we pour over two million metric tons of pesticides onto our plants and soils every year. Unsurprisingly, we aren’t just harming the insects we don’t like; we are destroying the insects we do like as well.
Scientists tell us we are witnessing a catastrophic collapse of insect populations. A German study found that on protected nature reserves, insect numbers had plummeted by 80 percent. Rodolfo Dirzo, a Stanford University ecologist, has documented a 45 percent decline worldwide in insect populations over the last four decades. And on the International Union for Conservation of Nature (IUCN) Red List, of the 3,623 invertebrates being tracked, 42 percent are under threat of extinction.*7
In our desire to exterminate insects, we’ve lost sight of how critical they are to human survival, but the ripple effect runs right up the food chain. As British biologist Dave Goulson warns, we “are currently on course for ecological Armageddon. If we lose the insects, then everything is going to collapse.” That’s because insects not only help with pollination, they are nature’s garbage men and recyclers as well. As Goulson notes, “Most of the fruits and vegetables we like to eat, and also things like coffee and chocolate, we wouldn’t have without insects. Insects also help to break down leaves, dead trees and dead bodies of animals. They help to recycle nutrients and make them available again. If it weren’t for insects, cow pats and dead bodies would build up in the landscape.”
We won’t be alone in feeling the effects. Already, birds that feed on insects have begun to disappear. The number of birds in Europe plunged by four hundred million in the last three decades. Some migrating songbirds, like the meadow pipit, have seen their populations decline by up to 70 percent.
We do not see it happening, and this is potentially our fatal flaw: we tend not to notice that something is disappearing until it is gone.
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IN THE END, what killed the flea circus was the disappearance of its star. The little top reigned glorious for well over a hundred years but was forced to shut its tent flaps when the human flea proved no match, not for insecticides, but for the vacuum cleaner.*8 From a business standpoint, it was the cost of importing fleas that made it impractical. As Professor Tomlin, one of the last great flea trainers noted, “I have offers from all over the world to take my show, but you’re afraid of one thing, when you get out of the country can you get fleas? I went to Sweden and I had to send to Majorca in Spain to get fleas every fortnight.”
We have largely rid ourselves of the human flea, but our bodies continue to host many lesser-known species. Fortunately, both for them and for us, they make their livings quietly as tiny companions that we cannot feel or see. You may want to take a deep breath as you read this, but right now your face is crawling with Demodex mites, eight-legged arachnids whose closest relatives are spiders. One study found that by the age of eighteen, 100 percent of people tested are host to the mites.*9 Nestled in the beds of our pores and tucked into our eyelashes, the nocturnal creatures emerge each night, moving at a rate of eight to sixteen millimetres an hour, to feed and search for mates on our faces. Scientists still aren’t sure exactly what they eat. It could be the sebum, or oil, our pores secrete, or they could be feasting on meals of dead skin cells or bacteria on our skin. One thing scientists do know: while these mites have mouths, they do not have anuses, and the buildup of food means that when they die they explode a flush of material from their guts, which ends up on our faces. And this fecal matter serves as a home to ever-smaller species, because hitching a ride inside the mites’ guts are even more prolific life forms: bacteria.
A little face bacteria is nothing, however, when you consider that humans are covered head to toe in microbes. And the diversity of species is absolutely bewildering. Taking swabs from sixty subjects’ bellybuttons, researchers at North Carolina State University working on the “Bellybutton Biodiversity Project” found a veritable zoo of bacteria, a total of 2,368 different species, over half of which were previously unknown to science. One person’s bellybutton even housed a bacterium only known to exist in Japanese soil. He had never set foot in Japan, so how did it get there? Well, bacteria are world travellers. Even in drawing a single breath, as microbiologist Nathan Wolfe has observed, we are sampling a safari of microbial species from around the world: “Dust from deserts in China moves across the Pacific to North America and east to Europe, eventually circling the globe. Such dust clouds harbour bacteria and viruses from the soils where they originated, as well as other microbes they pick up from the smoke of garbage fires or from the mist above the oceans they cross.”
Air samples collected by scientists at Lawrence Berkeley National Laboratory found as many as 1,800 bacterial species in the air we breathe. These bacterial life forms are not just on us and around us, they are a part of us. Yale University engineers for instance, have found that a person’s “mere presence” in a room adds about thirty-seven million bacteria to the mix, every single hour. What we call our own bodies are in truth only half our own. And while the myth is that bacterial cells outnumber human cells ten to one, recent research has proved that we are a little closer to par. An average human body has thirty trillion human cells and about thirty-nine trillion bacteria cells, meaning we are only slightly outnumbered, by a ratio of 1.3:1.*10
This, of course, raises the question of who is in charge. Them or us?
In this instance, the human-microbe relationship is not so much parasitic as it is symbiotic. Despite the bad press some germs get, we’ve learned to live together, for the most part, in relative harmony.*11 At birth, however, we are largely bacteria-free*12 and acquire the majority of microscopic hitchhikers along the way in life. This is why, if you take a microbial sample from identical twins, you’ll find the microbes that inhabit them have different DNA.
It’s becoming apparent that without bacteria, our lives would be at risk, because what we call “good microbes,” like probiotics, are necessary for a healthy immune system. A species known as Bacteroides fragilis, for instance, is found in abundance in the guts of most mammals, including 70 to 80 percent of humans. A molecule on the cell surface, called polysaccharide A, boosts regulatory T-cell production, which in turn prevents inflammation in the gut. Scientists working with mice that were specifically bred to be germ-free found them to have poorly functioning regulatory T-cells, but as soon as B. fragilis were introduced to their systems, their health improved and their immunity was restored.
We also call on bacteria to help us perform vital survival tasks like eating. If you’re a fan of pasta, pies, or french fries, then pat your belly in thanks to Bacteroides thetaiotaomicron. In much the same way that cows have bacteria in their rumens that help them digest the cellulose in grasses, humans rely on B. thetaiotaomicron to create the enzymes that let us process starchy plant foods.
But bacteria aren’t just in charge of regulating our bodies; they have bigger duties as well. As Rick Stevens, a founder of the Earth Microbiome Project, has observed, “Fifty percent of life on Earth is ‘invisible’ yet responsible for making the planet habitable.” Scientists now know that the smallest life forms on Earth are responsible for engineering planetary-scale systems, including the very air we breathe and the food we eat. And while humans walk around like we’re the most powerful creatures on the planet, in reality it is the microbes that are running the show.
For starters, they produce the gas that is vital for multicellular life—oxygen. And while we are taught that oxygen is exhaled primarily by trees, in fact, only 28 percent of the gas is exhaled from rainforests. The vast majority of oxygen is created in the ocean, by phytoplankton and algae. The source of this photosynthesis is one and the same, however, as both land plants and algae have something in common: they were once hijacked by bacter
ia.
More than two billion years ago, cyanobacteria evolved an extraordinary superpower: the ability to turn sunlight into food. Using the energy from our nearest star, they began converting water and carbon dioxide into sugars, splitting the remaining oxygen off as by-product. Over time, some species of these cyanobacteria remained aquatic and stayed free-living and independent in the ocean,*13 while others were absorbed by algae and became permanent residents housed inside their organelles, known as chloroplasts.*14 As algal species evolved and migrated onto land, they became the ancestors of modern trees and plants. Which means that these tiny and very ancient engineers sit at the controls of all photosynthesizing plants. And it is they who are responsible for all of the oxygen we breathe.
At our feet lies another wildly overlooked ecosystem. Soil is home to a third of all life on the planet, and it is buzzing with biodiversity. Just a single teaspoon of garden soil contains a population of about a billion bacteria. In terms of biomass, that’s the equivalent of about two cows per acre. One handful of forest soil contains more microbes than there are people on Earth, and one kilogram of healthy soil contains more microbes than all the stars in our galaxy. Van Leeuwenhoek could never have dreamed how vast the universe under the microscope would prove to be. But even today, more than three centuries after Van Leeuwenhoek’s first discovery, much of this subterranean cosmos of bacteria, archaea, fungi, protozoa, algae, and viruses remains unexplored. So far, only 0.001 percent of microbial species are known to science.
Soil, of course, is critical for food. Without good soil we’d starve. And today, we understand one of the key roles certain bacteria play with respect to plant growth. That’s because plants, like all living beings, need nitrogen for their DNA. In the soil, these bacteria have the ability to take atmospheric nitrogen, which is a gas, and “fix” it so that it turns into a form, like ammonia, that plants can use. In essence, nitrogen-fixing bacteria are like tiny “soluble bags of fertilizer” in the soil, feeding the plants their chemical nutrition and in turn enriching every animal on the food chain.
Beyond their habitats on land and in the oceans, bacteria have also been found swirling high up in the atmosphere. Travelling with NASA’s hurricane researchers, scientists sampled a cubic metre of air at 33,000 feet and netted over 5,100 species. Our planet is surrounded by a literal bubble of bacteria. Right now, we are only just beginning to find out what these tiny beings are doing up there. Some scientists believe they play an active role in creating clouds and seeding rainfall, while others say they may be recycling nutrients high up in the atmosphere. There is one thing at least we know for certain: far from being insignificant, the smallest life forms on Earth play a critical role in engineering the planet’s life-support systems. We have long been blind to the invisible services that bacteria provide, but in truth, we owe them our lives.
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OUR FIRST BLIND SPOT is that reality is not human-sized. What we call reality is only a tiny sliver in the grand scheme of things. And while we seldom think about size, size is arguably the most important attribute of an animal’s existence: it shapes where, how, and even for how long *15 we live on this planet. When it comes to life on Earth however, size does have its limits.
The parasitic wasp called a fairyfly, for instance, is just two hundred microns across. That’s about the size of an amoeba, meaning a family of five of these tiny wasps could fit comfortably on the period at the end of this sentence. But what’s incredible about the fairyfly is that, unlike an amoeba, it is not a single-celled organism. It’s a complex multicellular life form that has managed to squeeze an incredible amount of biological material into an unbelievably minute package. Inside their bodies, these animals have the basic biological architecture of a beating heart, wings, legs, a digestive system, and a functioning brain. So how does it all fit? For the fairyfly, being small comes at a hefty price, and they pay it in brain cells.
Scientists have discovered that by the time they’re adults, fairyflies have sacrificed the nuclei in 95 percent of their neurons, which is where the genetic material is stored in the cell. What that means is, for insects, going even smaller becomes next to impossible. For brainless bacteria, there is still space to shrink. While only five fairyflies could fit on a period at the end of a sentence, hundreds of thousands of single-celled bacteria could occupy the same space. When it comes to size, then, bacteria guard this final frontier. Multicellular life cannot get smaller because there’s not enough room for its essential ingredients: proteins and DNA. Meaning life, quite literally, cannot squeeze itself in.
On the opposite end of the spectrum there are the giants: the multicellular animals that operate at our size and the few that are even bigger. So, what then are the limits of large living things? Why are there no real-life King Kongs,*16 Godzillas, or fifty-foot women? The first person to tackle that question was, fittingly, a kind of Goliath himself: the famed stargazer and scientific revolutionary Galileo Galilei.
What Galileo realized was that size not only matters, it can be a matter of life or death. In Discourses and Mathematical Demonstrations Relating to Two New Sciences, he wrote, “Who does not know that a horse falling from a height of three or four cubits will break his bones, while a dog falling from the same height or a cat from a height of eight or ten cubits will suffer no injury? Equally harmless would be the fall of a grasshopper from a tower or the fall of an ant from the distance of the moon.” In essence: Why would a big animal fall to its death while a small animal could walk away without injury?
Galileo’s brilliance was in realizing that if you continued scaling an animal up, at a certain point it would begin to break under its own weight. Just as a tree would no longer be able to support the heft of its massive branches, a fifty-foot giant could not take a step without cracking the bones in her limbs.*17 For the behemoths on Earth, then, it’s the laws of physics, and gravity in particular, that puts a limit on things.
The observant among you however, must be thinking, what about dinosaurs, or whales? The biggest sauropods were as tall as a five-storey building, and even blue whales measure about the same as three school buses parked end to end. So how come they are so big? It turns out, these massive animals evolved some impressive workarounds.
Dinosaurs got around the heavy bone problem by becoming pneumatic. The titanic reptiles, like their bird descendants today, had light, hollow bones with large air pockets inside them. In fact, 10 percent of T. rex’s body volume was air, and in studying sauropod skeletons, scientists have discovered that their bones were up to 90 percent air by volume. Whales solved the problem by evolving in water. Like all living things, a whale’s cells contain saline. In the simplest terms, being primarily made of salty water and swimming in salty water allows these leviathans to grow to massive sizes and weigh up to 144 metric tons, because, living in the ocean, they’re essentially weightless.*18
There is, however, another invisible medium that can affect an animal’s size, and, like water for whales, it’s something we barely notice: the air. That vaporous cocktail we all breathe has changed significantly over the ages. And, along with it, so has the size of life.
If you could hop in a time machine and turn the dial back to between one hundred and four hundred million years ago, like Alice, you would emerge into a gargantuan Wonderland. Because this was the age of giants. In this ancient world, mushrooms rose to the height of houses, hawk-sized dragonflies swooped through the skies, and even dinosaur fleas were ten times larger than their modern counterparts.
Invertebrates were free to grow because for them the weight of bones was not an issue. But there was something else that limited their growth. Kirkpatrick Sale, the author of Human Scale, describes the problem like this: “If an earthworm were ten times bigger, its weight would be a thousand times greater, and its need for air a thousand times greater, but the surface area through which it absorbs oxygen would only be a hundred times greater, so it would get only a tenth of the air it needed and
would immediately die.” So how did prehistoric worms grow in size and still manage to survive? The answer was the concentration of oxygen. In our atmosphere today, oxygen makes up 21 percent of the air, but during the Carboniferous era *19 its concentration was much higher, at 35 percent. For animals like worms that breathe not through their mouths but through pores in their skin, each breath packed a more powerful punch and delivered enough oxygen for them to survive.*20
