by Riskin, Dan
Plants and animals make us healthy because our bodies have evolved in direct response to the plants and animals we eat. We’ve been killing and eating nature’s bounty for millennia, so human bodies are built to thrive on precisely those kinds of foods. To say nature is there to make us healthy has it backward. Our bodies are built to steal from the other bodies around us: we can only survive by eating plants, animals, and fungi.
But we’re not the only ones out there with an appetite. To get a clear perspective on our own gluttony, it helps to first see how intense gluttony can get in nature. That’s what this chapter is about—gluttony in the natural world—starting with plants that make their own food, moving up through the plant-eating animals, the animal-eating animals, and finally to the animals that dine on the corpses that are left behind in the carnage. Gluttony abounds.
There’s a man in India named Prahlad Jani who has consumed neither food nor water since he was eleven years old, in 1940. How do we know this? Because he says so. Mr. Jani says he gets all his energy from the sun.
That seems like it should be impossible, but there’s a physician in India, a neurologist in fact, named Dr. Sudhir Shah, who has verified Mr. Jani’s claim on two separate occasions. Over the course of ten days in 2003 and fourteen days in 2010, Dr. Shah and his team watched Mr. Jani carefully and confirmed that he survived with no food or water.
Well . . . no water except the water he got each day to rinse out his mouth, but he promised not to swallow any of that. Also, he got to bathe himself, but other than those two minor details, he had absolutely no food or water at all over the course of those two studies.2
Now, for reasons you might be able to guess, neither of Dr. Shah’s studies has quite made it into a scientific journal, but Dr. Shah has published a PDF on his website, explaining how Mr. Jani might have turned himself into a “kind of solar cooker” with “solar batteries.” 3 This story has been covered by newspapers and TV programs around the world, and some people actually believe it’s true.
Of course it’s not, though.
I don’t know if Mr. Jani is a fraud or if he is suffering from a mental illness that makes him unaware that he eats and drinks, but I do know that humans use energy to stay alive, and I also know there’s no way for a human to get energy from a beam of sunlight.
As for Dr. Shah, he’s either in on the lie or he’s not a very good doctor (or both, I suppose). A human cannot go decades without food or water. That seems like the kind of basic fact about humans that a doctor should know. I don’t think I’m being unfair about this.
Humans need water. A person with no access to water at all may die in less than a week. Our bodies are mostly made of water, not 99 percent as the urban myth goes, but closer to 60 percent (the proportion changes slightly with health and age).4 And that water is constantly streaming out of us: as urine, feces, sweat, tears, the humidity of our exhaled breaths, and for women, during menstruation. With so much water leaving the body, our food and drinks need to bring in at least 2 to 3 liters of water per day (that number can vary, but 2.6 liters is the number scientists have used when trying to estimate how much water astronauts will need).5 That’s about five and a half pounds. During heavy exercise or in hot climates, those water needs can more than double.I
In addition to water, humans also need food, because that’s where we get our energy. A person on a hunger strike (drinking only water) usually dies after a month or two, having burned up all their energy reserves. Even just sitting around, a person burns through the equivalent of around 580 AA batteries each day.6 With daily activities factored in, like walking, talking, working, and all the other things a person does, daily energy costs can be two to three times higher than that. It’s simple physics. Energy cannot be created or destroyed. Since Mr. Jani’s body uses energy, he has to consume energy.
Mr. Jani’s claim is that he gets his energy from sunlight. Plants can do that, but animals like Mr. Jani cannot. The process by which plants do that is called photosynthesis.II Photosynthesis first evolved about 2.4 billion years ago, so long ago that everything living on Earth still had only one cell and lived in the water.7 Those first photosynthetic organisms therefore weren’t plants as we know them today but single-celled algae, like those that make up the mat you might see on the surface of a polluted pond, for example. Many kinds of single-celled algae are still around today, but one lineage of algae has changed a lot since then, becoming multicellular, adapting to life on land, and becoming the plants we know and love. (In other words, plants are specialized kinds of algae.)
Plants and algae can photosynthesize because they’re direct descendants of those first photosynthetic organisms and have inherited the complex machinery required to harness the sun’s energy. Animals can’t photosynthesize because they don’t have the equipment. The idea that Prahlad Jani suddenly just happened to be able to make sugars from sunlight would be like discovering one day that a brick factory could suddenly make sports cars.
You can’t harness the power of the sun by closing your eyes and having warm thoughts. It’s a precise chemical process. Photosynthesis requires dozens of incredibly specialized proteins that humans don’t have, all working together in perfect synchrony, like robots on a microscopic assembly line. A beam of sunlight penetrates the surface of a leaf, exciting a special molecule inside it, called chlorophyll a. Left alone, that excited molecule would give off some of that energy as light, glowing red as the energy dissipated. But in the leaf, it doesn’t glow, because crowds of orderly proteins around that molecule immediately jump into action, harnessing its energy to rip molecules of water (H2O) and carbon dioxide (CO2) apart, then rebuild their constituent atoms to make sugars (C6H12O6).
Oxygen (O2) molecules, by the way, are released from this process as a waste by-product, the result of the plant’s having extra O2 left over from the breakdown of the H2O and CO2. But one life form’s trash is another life form’s treasure: oxygen is a waste product we’ve built our lives on. (More about that in the chapter on wrath.)
Have you ever played with those halves of hollow rubber balls that you can flip inside out and then place on a table, until a few seconds later they spontaneously pop back into their previous shape and go flying into the air? That’s how I like to think of sugars. It takes energy to bend a half ball into that inverted shape, and that energy is physically stored within the structure of the half ball itself. When the half ball pops, the energy is released as the object relaxes to a more “comfortable” shape. Sugars basically work just like that. It takes energy for a plant to load atoms into a sugar, and that energy can sit there, inside the sugar, to be released later on. When a sugar is broken back down to water and carbon dioxide, the energy comes popping out. Plants build sugars so they can use the sun’s energy later on—for growth, reproduction, and whatever other processes are required for staying alive. But if an animal steals a sugar by eating part of a plant, the animal can break the sugar down itself and use the energy for its own purposes.
As you read this book, your eyeballs move from side to side because they’re pulled by muscles. The energy burned by those muscles originally came from plants. It’s kind of a shame, when you think about it. All this energy rains down on us from the sun each day, but as animals we can’t tap into any of it. Instead, we let plants do that work, and then we eat the plants. It’s as if instead of bringing lunch money to school, we beat up the kids who bring their own lunch each day, and take theirs.
Whole ecosystems work this way. The energy inside a deer came from solar-powered plants. When a cougar kills a deer, the plant energy is passed on—to the cougar, but also to the cascade of small mammals, birds, insects, fungi, and bacteria that clean up the bits of carcass left behind by the cougar. All those living things (and their parasites, by the way) constantly fight one another to get energy into their bodies. Then the game becomes one of making sure no other animals steal the energy from them. Energy is constantly flowing through nature, and gluttony is the mechanism by which it does so.II
I
As the nozzle through which energy flows into ecosystems, plants have it pretty rough. There’s an endless parade of animals, from aphids to zebras, constantly trying to take a bite out of them. Plants can’t run and hide, so they have to hunker down and defend themselves. As a result, plants make up some of the most violent, ruthless, and lethal instruments you’ll ever find in nature’s arsenal.
It’s easy to think of plants as harmless, as we look around the produce section of the grocery store, but of course that’s because none of the dangerous plants are there. In the past, foraging for fruits and vegetables meant hunting among hundreds of inedible plant species for something edible. There are more than 250,000 kinds of plants in the world, but we humans get more than 90 percent of our calories from just fifteen of them. That’s around a 160th of 1 percent.IV Most of those plants have been cultivated by humans for thousands of years to make them better for us than nature originally made them, or at least more appealing or easier to eat. Grocery store advertisers may use the word natural to describe their foods, but the produce section of the grocery store is a far cry from walking across the African savannah looking for something to eat.
To defend themselves, many plants use thorns and spines. (Ever tried to chew on a rosebush?) Sharp, poking bits can make it painful to touch a plant—never mind eat one—and plants often make those spikes even more effective by filling them with noxious chemicals. That way, animals that try to eat the plant get blisters and sores to remind them not to do that again. However, by far, the most impressive set of spines on any plant has to belong to the bull’s horn acacia. Working on the principle that sometimes the best defense is a good offense, that plant has found a way to keep weapons inside the thorns that can crawl out to repeatedly sting anyone who comes too close. Even more incredibly, it does this by secreting a chemical that isn’t noxious at all. The acacia plant secretes a nectar.
That nectar is there to feed tiny, vicious, wasplike stinging ants that make their home inside the plant’s hollow branches and thorns. The ants live nowhere else—that’s why they’re called acacia ants. The ants don’t hurt the plant, but they get all their food from it. Acting selfishly, the ants defend that food source against other animals, and that works out very nicely for the plant. If some deer takes a bite of bull’s horn acacia, it ends up with a mouthful of stinging ants.8 And these ants’ stings are particularly painful (a “rare, piercing, elevated sort of pain,” as you will see in the chapter on wrath). Acacia ants can even turn elephants away.9
The ants aren’t parasites of the plant, since the plant gets a benefit. In biological terms, their relationship is called a mutualism: both parties benefit. The plant gets protection, and the ants get room and board. But it’s not all hugs and kisses between them. The two species have been working together so long that the ants no longer have the ability to find food anywhere else, and that gives the plant a lot of control in the relationship. For example, the amount of nectar the plant is willing to produce varies depending on how worried it is about herbivores. Over the course of the year, and even throughout the day, the plant gives up as little sugar as possible, only secreting more when it needs the ants to provide better protection. The number of ants that can live on the plant’s nectar rises and falls at the whim of the plant. You can think of the plant as a millionaire, paying a fleet of security guards as little as possible to defend its factory, with some dying in the fight against intruders, and others simply dying of starvation when layoffs happen during periods of low crime.
The bull’s horn acacia has turned acacia ants into a living, swarming defense weapon, and it decides when and where that weapon will be ready for use. In essence, the plant has enslaved the ant meat robots to work for its own DNA. From the plant’s perspective, the ants have pretty much become part of its own body.
Although enslaving ants is effective as a defense system, it’s a solution to herbivores that hasn’t evolved in most plants. Instead, the vast majority of plants do something simpler to deal with herbivores: they just make themselves poisonous. It’s estimated that plants have come up with more than 200,000 different chemical compounds, and the effects those chemicals have on the animals that eat them can be wonderfully brutal.10 One challenge with poisons, though, is that the poisons most lethal to animals are often also deadly to plants. That’s bad news for the plant. There’s no point in making poisons to keep animals from eating you if you’re going to kill yourself in the process.
For example, hydrogen cyanide is extremely lethal to animals. The lethal dose for a human is around half a milligram of cyanide per pound, so one hundred milligrams could take out a two-hundred-pound person. (For reference, a toothpick weighs around one hundred milligrams.)11 Hydrogen cyanide kills animals because it interferes with the molecular machinery used to get energy out of sugars. Since plants also get energy from sugars, hydrogen cyanide kills plants too. But despite that, more than 2,500 species of plants produce cyanide to deter herbivores.12 Somehow, though, the plants don’t succumb to their own poison, and the way they achieve that is brilliant: they basically pack hydrogen cyanide into bombs that will only go off if the plant gets eaten.
Here’s how the bombs work: Instead of making hydrogen cyanide ahead of time, the plant builds a bigger molecule that has hydrogen cyanide inside it. Because the hydrogen cyanide is stuck inside that larger molecule, it can’t perform the chemical reactions that would otherwise make it poisonous. That part is the bomb. Simultaneously, the plant builds an enzyme that can break that hydrogen cyanide free from the rest of that molecule. You can think of that enzyme as the bomb’s detonator. The plant stores the bombs in tiny walled-off sacs throughout its tissues and then surrounds those sacs with clusters of detonators. So long as the plant is uninjured, the chemicals stay separate, and no poison is ever made. But once a herbivore takes a bite of the plant, the sacs are mechanically broken by the predator, the detonators set off the bombs, and the lethal hydrogen cyanide is secreted right into the mouth of the herbivore. It’s a perfect system, and the real beauty of it is that the uninjured parts of the plant don’t get poisoned at all. Only those parts of the plant that are already being chewed on end up getting sacrificed.13
Not surprisingly, hydrogen cyanide creates problems for a lot of herbivores. Gorillas and rhinos, for example, eat plants that defend themselves with hydrogen cyanide, but they limit those plants to a small fraction of all the different foods they eat, presumably so that the poison dose stays small enough not to hurt them.14
Anyone who’s watched a James Bond movie or seen an Agatha Christie play knows that cyanide is deadly to humans, but humans routinely eat plants that produce hydrogen cyanide. Cassava (also called manioc) is a root, sort of like a potato, that is a staple in the diet of roughly 500 million people worldwide. It’s mostly eaten in Africa, the Philippines, and Brazil but also makes its way into kitchens in Europe and North America.15 The roots of that plant are deadly if eaten right out of the ground, which is part of the reason it works well as a crop: few animals can spoil the harvest by eating your crop beforehand. Humans get past the hydrogen cyanide in cassava by presoaking, fermenting, or cooking it, to break down the dangerous chemicals inside it. From time to time, though, people do die as a result of eating unprocessed cassava. It’s a sobering reminder that we survive by exploiting the plants and animals around us. Mother Nature isn’t trying to keep us healthy. We’re just taking what’s available in nature to look after ourselves.
The other strategy plants use to avoid self-poisoning is to make poisons that hurt animals but have no effect on plants. That way, the plant can produce those chemicals to its heart’s content without ever having to worry about getting hurt. Such chemicals usually work by focusing on animal body parts, like nerves, that plants don’t have. One plant, called zonal geranium, puts a drug in the petals of its flowers called quisqualic acid. Beetles that eat the petals feel fine at first but after about thirty minutes start to realize their hind legs don’t work so well, an
d before long they are totally unable to move. From tests in the lab, scientists know that the drug’s effects last only about twenty-four hours, but out in the woods where this plant grows, a beetle lying defenselessly on the ground for a day is almost always eaten long before its paralysis is over.16
Another great plant poison comes from the corn lily, which makes a chemical called cyclopamine. Cyclopamine doesn’t hurt the plant at all, but it has a very strange effect on sheep. I’ll give you a second to guess what that is. Your hint is that the name for cyclopamine comes from the one-eyed Cyclops of Greek mythology.
Got your guess? Okay.
Cyclopamine has no effect on an adult sheep, but if a pregnant sheep eats corn lily on the fourteenth day of fetal development (not before or after), the cyclopamine within the plant will block one particular set of genes from doing what it needs to do inside the sheep’s developing fetus.17 That’s it. That’s all this drug can do. One little step on one particular day in the fetal development of a sheep, but it’s a whopper. The fourteenth day of fetal sheep development happens to be the day when cells in the fetus’s head that will one day become eyeballs split into left and right halves. That step is controlled by the gene that is blocked by cyclopamine. What all this means is that if the mother eats corn lily on the fourteenth day of her pregnancy, then four and a half months later she will give birth to a one-eyed monster. As a result, any sheep flocks that try to stay in the corn lily’s area will be unable to reproduce and, within a few short years, will die off from old age and leave the plants alone.V
Did you guess right?
As wonderful as targeted drugs like cyclopamine are, they have the drawback that they might work on just a subset of the herbivores that are trying to eat the plant. Cyclopamine works on sheep, but it might not work on grasshoppers, for example. Many plants that use targeted poisons get around that problem by secreting a whole cocktail of them, with the hopes that something in there will hurt most herbivores somehow. Other plants use a more measured approach. They wait to see what kind of animal is eating them and then secrete the appropriate poison in response. It might seem incredible that a plant can do this, but it’s true. The chewing bite of a caterpillar on a leaf of barrel clover will make the plant produce jasmonic acid, whereas the tiny piercing bite of a spider mite will cause the plant to make salicylic acid instead.18 Plants might look like serene, inanimate objects, but they know how to get by in a world of gluttony.
