by Rob Dunn
Do I think that snakebites are or were common enough to favor individuals with better vision, vision for seeing still and camouflaged objects? Maybe, especially when one considers the small size of many of our early ancestors and for that matter, their children. As Isbell points out, one of the earliest of our primate kin, Eosimias, weighed about a quarter pound, small enough to put between two buns with some lettuce. For such bite-sized ancestors, deaths owing to snakes would have been common, all too easy a way to go. If there was anything different about the genes and traits of those individuals who survived, it would be favored generation after generation. It seems very plausible that what would be different is the quality of the vision and ultimately the brains of those who lived.
In short, I would go so far as to say that Isbell’s reading of the history of primates and their vision is both wild and plausible. And, in any case, for my own broader thesis about the consequences of our interactions, it almost doesn’t matter. Any answer almost inevitably has to invoke interactions with other species, whether they are snakes, fruits, or something else. I vote for the snakes. Close your eyes and imagine Geerat Vermeij out in the jungle walking down a trail. Beside him is someone with vision. Who do you think is more likely to die of snakebite? Almost inevitably, Vermeij, who can feel trees and know their type, can smell fruits and listen for leopards, but is unable to notice snakes. Unless he can grab them, which is ill-advised, they are not part of his perceptual world. Vermeij has almost been killed by a variety of dangerous animals, for just this sort of reason. He once grabbed a venomous fish, only to have the reality slowly dawn on him as he fumbled with its texture. He also, when reaching for shells, once put his hand onto a stingray’s tail. Vermeij, like the lemurs in Madagascar, was fortunate enough to be born where death by snakes is rare enough that he can thrive by feeling his way. Across most of the long history of predators and poor besieged monkeys, he would not have been so lucky.
Once we had better eyes, the aspects of the world that were apparent to us changed, and as they did, the world itself changed. Our vision may have been shaped when we were prey, but its greatest effects came once we had turned into predators. Its effects included nearly everything, good or bad, that we would have done to the world, including the changes we have instigated in our relationships with predators and snakes themselves. When crabs and their claws evolved, the rest of the sea’s creatures changed in response. When Eve looked at the snake, it tempted her to the apple and then, ultimately, to both knowledge and choices about the fate of others. When we evolved to be able to see the snake, we too found the apple, or at least the road to consciousness, tools, power, and consequences. When combined with our preferences, our senses are what frame many of the decisions we make in the world. Even these preferences evolved to help us survive in a world of species that mean to do us harm. They rise up out of the deep well of history and help us choose among the things we perceive. Our preferences are not usually conscious and yet determine much of how we act. We and our actions are tethered to who we were, pulled this way and that among the scenes our eyes relay, colorful scenes no longer filled with snakes and yet still shaped by them, regardless of who we are, every day. It is our senses and preferences that would, in the end, lead us to begin killing snakes. We kill them regardless of their danger because we see them. They suffer from what they have done to us, letting us see, however unclearly. In some places we learned to distinguish the deadly from the innocuous or, more simply, to avoid snakebites (the invention of rubber boots saved many lives). But in other places we thrash blindly with our shovels and machetes, and so the snakes suffer the consequences of who we were. We gave not into temptation, but instead into our senses, led by our eyes this way and that through the apparent world.
12
Choosing Who Lives
A handful of scientists spend their days trying to identify things universal to all human cultures that have ever existed. They paw through ethnographies and search anthropological studies for the differences between one tribe and another, but also for those things that are not different. They look for the ways that they themselves are similar to people in Tahiti or Timbuktu. These scientists have compiled a list of a few hundred or so attributes of humans that apply to very nearly all of us, whether we live in a tree house in Papua New Guinea or in an apartment overlooking Central Park. These similarities are at the core of what unites us, despite our differences. Among these universals is a tendency toward wariness around snakes. But there are others too. We all seem to be fond of sweets, salt, and fat, and have an aversion, at least at birth, to bitter foods. Even more intriguingly, most humans appear to prefer scenes with a bushy tree out on an open plain with a little water somewhere in the distance. Most, and perhaps all of these universal preferences relate to our evolutionary past where such fondnesses evolved and made sense, even if they no longer do. These universals follow from the ways in which our senses affect our perception. Universals would be quaint if they had not shaped the version of the living world we have constructed around ourselves. They would be quaint, that is, if they were not the source of many of our real problems, especially those associated with how we have changed the world.
As we walk past each other on the street or look through each other’s car windows in passing, we tend to assume that other people are like us. The very similarity of what we see others doing, relative to what we do—walking, driving, spitting, and grimacing—suggests our deep sameness as does the sensation we derive from reading a familiar poem. In the ancient cave paintings of Namibia, one finds hunters chasing prey. These hunters have bodies like our bodies. We cannot help but feel that the person who created this, and his or her intended audience, was very much like us. We feel connected in our essential humanness. Yet the truth is that most attributes of our thoughts and behaviors that one can enumerate differ from person to person, or culture to culture. Some of us have gods. Others do not. Some of us have a single wife or husband. Others have many. In some places, violent reactions to affronts to one’s pride are the norm. In others, pride scarcely exists. In some places, fat ankles are beautiful, in other places fat behinds. In relatively few cultures, thinness is sexy. We are all the same species and yet, because of the speed with which culture changes, the variety of our settings, and the whimsy and idiosyncrasy of history, we do and like different things. In fact, the most remarkable thing about universals is that they exist at all, so much do cultures vary from one place to the next. Relatively few of the truths we hold to be self-evident are held to be so everywhere.
Given that there are nearly 7 billion of us on Earth with an infinite capacity for variety, that few of our attributes are truly universal is interesting. These attributes must ultimately follow from our biology. If any of our universals were within our conscious control or could drift with the shifts among cultures, they would have varied by now from place to place, even if only because of rebelling teens. That a few have withstood the chaotic consequences of our variety suggests they are both genetic and, in some deep and primitive way, beyond our ability to change.
Our visual preferences, those shaped by the influence of predators and snakes, are the most pervasive in their influence. But they are also complicated. Perhaps the most straightforward of our evolutionary preferences is taste. If we understand taste, we can use it as a kind of model for beginning to understand vision. Stick out your tongue and touch your finger to it. You will feel two things at once: Your finger will feel your tongue. In turn, your tongue will feel and taste your finger. Just which tastes it picks up depends on your finger. Five basic possibilities—sweet, salty, bitter, umami (savory), and sour—can come together to yield more nuanced impressions (index finger with a hint of peanut butter, perhaps?). The taste buds themselves look like brain corals at the center of which are the sensitive tips of taste cells, each of which ends in a thin hair. When you eat, little particles of food are washed over these hairs. If a sugar washes over a sweet taste bud’s hairs, a signal is sent by th
e nerves under the taste bud to your brain. The hairs are stimulated and the chemical chain is yanked until it rings somewhere in the space between your ears, “sweet.” At least two kinds of signals are sent when “sweetness” is sensed. One signal is sent to your conscious brain that triggers the sensation you think of as sweetness. Separately, a signal is sent subliminally to your older, deeper reptilian brain, where it stimulates hormonal changes in your body in response to having received sugar.
With its taste buds, the tongue is a gourmand’s muscle. We have grown used to our tongues and what they do. We take them for granted, leaving them to wallow for whole afternoons in coffee or bad wine. To me, though, what is most interesting about our tongue is that it influences us, in the way that a political tail can sometimes wag the dog. After all, the sensation of taste is a trick. The categories of chemicals our tongues distinguish (sweet, sour, etc.) and how they “feel” to us are produced in our mind. Cats, be they domestic or wild, have a nonfunctional gene for the receptors associated with sweet food and so they never experience the sensation of sweetness. We might have evolved to detect different groups of compounds with our tongues. Or our perception of those compounds that we do detect might have been very different. Nothing about sweet foods gives them an inherently sweet taste. The entire concept of sweet and its taste is an evolved product of our mind. But why? Why have some of our taste buds evolved to signal tastes that our minds experience as pleasurable (sweet, umami, and salty) while others signal something more ambiguous (sour) or even downright bad (bitter). Why do our taste buds produce the sensation of taste at all?
One could imagine, as a thought experiment, scenarios in which our taste buds might produce no conscious sensations. If their only purpose were to modulate our internal hormones and digestive enzymes our taste buds would have no reason to notify our conscious brain that something had been tasted at all. This is just what happens in our guts. As late as 2005, no one knew we had taste buds in our guts. It now appears that that is where most of our taste buds, or at least taste receptors, reside.1 Those receptors are identical to the ones in our mouths with two exceptions—they are arranged in smaller and more diffuse clumps, and they are not wired to our conscious brain. As a result, they send all of their signals to the subconscious part of our nervous systems and bodies more generally. When food makes contact with them, the taste receptors in our guts initiate waves of response around our bodies. They can trigger salivation, but also other diverse consequences.
Although they are triggered subconsciously, the effects of the taste receptors in our guts are visible to us. We can see them at work when we eat noxious foods that make us vomit. The reflexive opening of our mouths and expulsion of food can be triggered by the response of the bitter taste buds in the stomach that respond to tastes they interpret as toxic. None of this surfaces on our conscious minds until we find ourselves facedown in a toilet. The taste receptors in our guts are evidence of the ways in which all of our taste receptors and buds might have worked. That the taste buds in our mouths lead us to become pleased or displeased is because of our ancestors. Those ancestors whose taste buds triggered a pleasant sensation when they ate foods they needed to find more of were more likely to survive. The reverse holds for dangerous foods and unpleasant sensations. Like lab animals, our ancestors were trained by their sensations to chase after some things and flee others. Their tongues praised them into the right decisions: “Look for more of this sweet and you will be rewarded!” But they also scolded them out of wrong ones: “Put that plant in your mouth again and I’ll make you suffer. I swear to god I may even make you puke.”
The reason, then, that taste buds elicit sensations in our conscious minds is to trigger preferences and ultimately actions. It is for this reason that our taste buds are so weighted to just a few good (sweet, savory); bad (bitter, sour); or slightly more complicated (salty) sensations. We all prefer sweet and savory foods because we all have those same taste buds. We all enjoy salt until it is too concentrated, for the same reason. Taste buds produce innate preferences because they evolved to help us to distinguish things that we needed from those we must avoid. Bitter and sour have long triggered aversion (whether in fruit flies or humans) while sweet, savory, and, for the most part, salty trigger us to find and eat more.
The problem with our taste buds—and, I will argue, the problem with most of our universal preferences—is that they evolved to favor things that were rare and necessary and to disfavor things that were bad, in a context far different from the one we now face. This system of goods and bads—a kind of sensory morality—worked for hundreds of millions of years. It is analogous to the systems bacteria use to move away from bad things and toward good ones. Like the bacteria, we moved toward sweet fruits, fatty meat, and salt (be it in dirt or anywhere else) and away from what was deadly or poisonous. What changed was that we invented tools and gained power over entire landscapes. We developed the ability to make common what was once rare. But it was not simply that we farmed. Other species farm, be they ants, bark beetles, or termites. We combined farming with the ability to process foods, to extract specific compounds and flavors and so to feed our taste buds in ways that stimulated the taste buds, without also bearing the nutrition such tastes once signaled. Consequences we were not smart enough to anticipate ensued, consequences like those that would befall an African bird, the honeyguide. Its small canary-sized body is a measure of a much broader problem—that of sweetness, desire, and the fate of the world.
The honeyguide lives in much of Africa, where it eats the wax, brood, and eggs of honeybees. In this, it is relatively unique. Wax is indigestible to most animals. The honeyguide has been simultaneously blessed with the ability to eat wax and cursed with the dilemma of how to obtain it. Honeyguide beaks are too small to break into beehives. Humans have a different problem. We crave beehives for their honey. We are willing to do almost anything to get to honey. In Thailand, little boys are sent a hundred feet up into trees with a smoking stick to do battle with three-inch-long giant bees and take from them their honey. All over the world children, men, and women have found themselves face-to-face with bees, deep in hives, covered in stings and yet, pleased with their sticky, sweet discovery. Honey, to paraphrase the anthropologist Claude Lévi-Strauss has “a richness and subtlety difficult to describe to those who have never tasted [it], and indeed can seem almost unbearably exquisite in flavour . . . [It] breaks down the boundaries of sensibility, and blurs its registers, so much so that the eater of honey wonders whether he is savoring a delicacy or burning with the fire of love.” The problem for humans, though, other than the stings (which we have learned to more or less avoid) is in finding hives. Together, honeyguides could find hives and humans could break them open, which could yield a sweeter life for both man and bird. So it was that over hundreds if not thousands or even hundreds of thousands of years, the honeyguide and East Africans came to realize each other’s talents and to depend on one another, bird and human.
Many bird biologists have watched the interaction between the greater honeyguide (Indicator indicator, the name itself an indication of its story) and humans. A honeyguide, when it has found a hive, will come to the nearest house or person. There it will call, “tiya, tiya,” flash the white of its tail, and fly toward whoever is lucky enough to look on. It will continue to do so until someone follows it to a hive. At the hive, it will call again and wait. With luck, the hive is low enough to be climbed to, whereupon the person, a gatherer of honey, finds a food that rewards his or her sweet taste buds and the honeyguide finds a taste that rewards its too (our taste buds are sufficiently ancient that we and the honeyguide have similar fondnesses).2 No other mammals are known to follow the honeyguide, and so every bit of its elaborate act seems to have evolved for us, that we might help it and it us to sate our respective taste buds. Then, very recently, everything began to change.
Thousands of miles away from the honeyguide in the year AD 350 (give or take), Indians figured out how to farm
sugar in the form of sugarcane. Over time, the process grew in sophistication until pure sugar-crystal sweetness could be extracted from the cane. It was, in the history of humans, a revolutionary process. What was once valuable because of its rarity became common as sugar cane and the ability to process it spread. Elsewhere, sugar beets were domesticated. Each year we have farmed more sugarcane and sugar beets. Now they are joined by corn farms. On such farms, a useful food (corn) is farmed to produce nutritionally useless sweet high-fructose corn syrup. In 2010, more than 400,000 square kilometers of Earth were dedicated to the farming of sugar beets and sugarcane,3 an area the size of California. A similar quantity of land is dedicated to the corn used to produce corn syrup.
When millions of humans continue to starve each year, the fact that we have allotted an area this large to a substance for which none of us has any real need (even without adding sugar, all of our diets now certainly have enough of the stuff) is a sign of just how beholden we are to our taste buds. We might see our investment in sugar agriculture as a choice, but it is just as reasonable to see it as an inevitable consequence of what our taste buds can perceive and what they tell us is “good.” Because we never, in our long evolutionary history, faced a situation in which we had too much sugar, we have no bell or whistle in our body that tells us that we have eaten too much. Our body’s demand for sugar is essentially infinite and irrational, but that was never a problem until we evolved the ability to wield tools and change the land.
