Lesser Beasts: A Snout-to-Tail History of the Humble Pig

by Mark Essig

  Whereas other hoofed mammals gave up those generalized skills, pigs stayed true to the forest-dwelling first mammals. They kept shorter limbs, the better to scoot through the brush. Since pigs lived in dense thickets, they didn’t need good eyesight, so their eyes remained small. Since good hearing was an advantage, their ears remained large, and they learned to communicate through a wide variety of grunts and squeals. Adapted to moist, shady environments, they have few sweat glands and cool themselves with a wallow in the mud. Pigs are not good at standing in a field in the hot sun. That is a job for cows.

  The pig’s most specialized and distinctive feature, the snout, allows it to take advantage of the forest environment. In humans, the somatosensory cortex—the part of the brain responsible for sensation—is wired primarily to the hands. In pigs, nearly all the touch-sensitive nerves terminate in the nose. It’s best to think of a pig snout not as a nose at all but as something like an elephant’s trunk, a miraculous fifth limb that allows the pig to react to its world in ways unknown to other hoofed mammals. A tough cartilage nasal disk allows the pig to plow into rock-hard ground, while a fine mesh of snout muscles lets the pig make delicate rooting motions without moving its head. Other muscles clamp the nostrils shut to keep out dirt while still allowing puffs of air to enter, so that the pig’s exquisite sense of smell can determine whether a hard, round object is a rock to be nudged aside or a nut to be cracked open. Despite constant rough use, the snout remains, in the words of one pig observer, “art-gum-eraser tender,” as sensitive and finely tuned as a safecracker’s fingertips.

  Like humans, pigs (bottom) have molars, premolars, canines, and incisors that allow them to slice, rip, and grind a wide variety of foods, from tender plants to the tough flesh of large animals. By contrast, cows (top) have incisors and molars, suitable only for cropping and chewing grass and leaves.

  Like the multichambered stomach that allowed other artiodactyls to eat grass, the pig’s nose marked an immense evolutionary leap. The snout opened the underground realm to the pig, vastly increasing the amount of food available to it. Subterranean roots and tubers were relatively unaffected by forest fires, drought, or overgrazing by ruminants, giving pigs an advantage over other ungulates during hard times.

  Those roots suited the pig’s digestive system well. Compared to those of ruminants, the pig’s intestines had a limited array of bacteria to ferment plant matter, so grass and tough leaves were off the menu. Pigs instead ate bulbs, tubers, seeds, nuts, and fruits, which are packed with easily digestible simple sugars and proteins. They also ate tender plants, fungi, insects, worms, grubs, snakes, lizards, ground-nesting birds, small mammals, fish, clams, and carrion. This diet required an anatomy rather different from that of cows. Rather than a complex gut and single-purpose teeth, pigs went with a simple gut and multipurpose teeth.

  Because the pig evolved into a dietary generalist, its digestive system greatly resembles that of a person. Herbivores have turned their guts into giant fermentation tanks to allow them to eat leaves and grass, and carnivores such as lions have powerfully muscled stomachs that can churn up large chunks of meat into small bits of usable protein. But the pig developed no such skills. Its simple stomach chops up proteins, its small intestine absorbs sugars and other nutrients, and its colon sucks up water and does its best to ferment any plant material. Roughly speaking, that’s the same gut design found in humans, chimpanzees, and orangutans, not to mention a fair number of lower primates. Like pigs, all of these animals eat nuts, fruits, tender leaves, insects, and meat. This type of gut is remarkable for its lack of specialization: it can adapt to nearly any circumstances.

  An expansive menu requires enhanced intelligence. One scientist who studies pig cognition complained that no one was surprised by his findings: “I would recommend that somebody study sheep or goats rather than pigs, so that people would be suitably impressed to find out your animal is clever.” The flaw in that plan is that sheep and goats aren’t terribly clever; animals whose only dietary task is to spot something green and start chewing have little need of higher mental powers. Omnivores, by contrast, face difficult choices. They must be open to novel foods because individuals hardwired to discover new sources of nutrition tend to thrive and pass on their genes. But indiscriminate snacking poses dangers: pigs that eat toxic mushrooms don’t leave many offspring. We might think of the pig as a judicious risk taker, open to the new but capable of assessing potential threats. In that quality, pigs are much like people.

  Many developments set humans apart from their more apelike ancestors. The first important shift was bipedalism: 4 million years ago, our ancestors developed a skeleton adapted to walking upright rather than climbing trees. They started using stone tools 3 million years ago. Along the way they developed more acute vision, lost much of their body hair, and evolved more efficient sweat glands. The most important changes, however, involved the brain and the gut.

  Digesting and thinking are the most energy-intensive processes in animal physiology. According to what scientists call the “expensive-tissue hypothesis,” before an animal can develop a big brain, it must first lose its large gut, because having both would exact an enormous cost in calories. The only way to shrink the gut is to subsist on higher-quality food—not grass but nuts, fats, and meats. In the human lineage the crucial shift took place about 1.8 million years ago, when Homo erectus appeared. Compared to their most immediate predecessors, these human ancestors had bigger skulls, smaller teeth, and a smaller rib cage and pelvis—the last two providing evidence of a smaller gut. Most likely, these changes were linked not simply to eating nutrient-rich foods but to cooking them, which made digestion even more efficient. By cooking their meats and roots, our ancestors freed up energy that otherwise would have gone to digestion, allowing it to be redirected to the growth of a bigger brain.

  Scientists developed the expensive-tissue hypothesis to explain human evolution, but it might also account for why pigs are smarter than cows. The enormous guts of ruminants, required to ferment grass into digestible sugars, spare few calories for the brain. Pigs, with simple guts and calorie-intensive diets, can devote more metabolic energy to thinking.

  The ancient fossil beds of the world are littered with the skeletons of barrel-bodied, short-limbed, piglike creatures. Only two families—pigs (Suidae) and peccaries (Tayassuidae)—survive today. Their evolutionary lines split more than 35 million years ago in Asia. The Suidae line stayed in the Old World, evolving into the wild boar of Eurasia (ancestor of the domestic pig), the warthog of Africa, the babirusa or “pig deer” of Indonesia, and a dozen or so other species. Members of the Tayassuidae line live only in the Americas. The peccary’s head is a bit shorter than the pig’s, its tusks point down rather than up, and it runs faster. Otherwise pigs and peccaries are remarkably alike. Thick body, small eyes, probing snout, multipurpose teeth—all are adapted to omnivorous life in the bush.

  Pigs are often described as the most “primitive” of the artiodactyls. In a sense, they are: they have the full range of teeth and the simple guts of early mammals. In this sense, however, people too are primitive. Sometimes the simplest tools are the best. An ecological niche, at root, is just a source of energy, a place in the world where a plant or animal can find enough food to sustain itself. Pigs and people, both expert at evaluating new foods, quickly colonized every remotely viable niche.

  Some 31 million years after the pig’s Suidae ancestors split off from their Tayassuidae cousins, the family divided again, forming a new species. The Eurasian wild boar—classified as Sus scrofa, Latin for “breeding sow”—first evolved in Southeast Asia 4 million years ago and then radiated throughout the continent. Today the natural range of the Eurasian wild boar stretches from northeastern Europe to Southeast Asia, from 13,000-foot mountains to swamps to near desert. Pigs, like people, are everywhere, and for many of the same reasons: they have clever brains, omnivorous appetites, and general-purpose teeth and
guts.

  The Eurasian wild boar did very well in the wild, but it thrived as never before when, about 10,000 years ago, certain members of the species took one further evolutionary step: they gave up their independent ways, moved into town, and domesticated themselves. Pigs and people threw in their lots together, and that proved a wise evolutionary strategy for both species.

  TWO

  Out of the Wild

  In 1989 archeologists discovered a tiny ancient village in the foothills of the Taurus Mountains and began digging with haste: the Turkish government was building a dam on the nearby Batman River, a tributary of the Tigris, and the area would soon be inundated. The site, known as Hallan Cemi, dated to about 11,000 years ago. Most of the buildings the archaeologists excavated were tiny round huts of wattle and daub, just six feet in diameter, though there was one larger ceremonial building with a cattle skull mounted on the wall. Among the debris were beautifully carved sandstone bowls, decorated grinding stones, and obsidian tools.

  The villagers of Hallan Cemi had formed a complex society with a rich cultural life, but they were hunter-gatherers, not farmers. They ate wild lentils, bitter vetch, almonds, plums, and pistachios. They hunted sheep, goats, deer, and pigs. The first three were unquestionably wild animals. The site’s pig bones, however, told a more complicated story.

  Nearly half the pigs eaten at Hallan Cemi were killed at less than a year old, a profile very different from the broad age range found in hunted animals. The bones also were overwhelmingly male, suggesting that the villagers had spared females to serve as breeding stock. During the time that Hallan Cemi was occupied, moreover, deer bones became less common while pig bones increased in number. Both deer and wild pigs are forest-dwelling creatures, so if the pig bones at Hallan Cemi came from wild animals, their numbers should have declined along with those of the deer. The fact that they did not makes it likely that the destruction of forests killed off the deer, while pigs found a new habitat, living alongside humans in the village.

  The changes at Hallan Cemi form one small part of the most significant event in human history: the invention of agriculture. This era, known as the Neolithic or New Stone Age, arose independently, and at very roughly the same time—10,000 to 5,000 years ago—in Asia, the Near East, the Americas, and Africa. Given how widespread it was, the rise of farming was likely triggered by a single phenomenon: the end of the ice ages and the warming of the climate. But many mysteries remain. Why would anyone choose the rigors of agriculture over the comparatively easy life of hunting and gathering? Why did prehistoric humans domesticate some animals and plants but not others? And how did the process of domestication take place?

  Hallan Cemi lets us begin to answer some of those questions, at least with regard to pigs. The archaeological record suggests that Sus scrofa took up life in villages because, as omnivores, they were biologically equipped to eat the garbage generated by newly sedentary humans. Most hunter-gatherers, after all, moved on to a fresh campsite before the stench grew too foul. In the first permanent settlements, pigs acted as sanitation service and food source, transforming butchery waste, rancid almonds, and moldy wheat into meat. Pigs proved useful to people—but that doesn’t mean the relationship developed solely because of human intention.

  It’s commonly held that humans domesticated pigs, but that’s not quite right. Wild boars, in adapting to the new niche created by human settlements, evolved in ways that made them capable of living in close proximity to people. Pigs, in other words, domesticated themselves.

  Anatomically modern humans, Homo sapiens, arose about 250,000 years ago in Africa. Between 60,000 and 130,000 years ago—there is much disagreement on timing—they crossed the Red Sea, entered the Arabian Peninsula, and from there spread all over the world. That means the Eurasian wild boar and modern humans first crossed paths in the Near East, that confluence of continents in the eastern Mediterranean.

  The eastern Mediterranean is generally an arid land, but coastal marshes and the riverbanks provided habitat for pigs. The amount of good habitat available varied considerably, because over the last 2 million years the Earth’s climate has shifted from warm and wet to cold and dry every 100,000 years or so. About 20,000 years ago—some 9,000 years before people settled at Hallan Cemi—the Earth was in the grip of the last great ice age. Rivers dried up, and ice locked up so much of the Earth’s water that the coast of the Mediterranean Sea was five or ten miles from its current location. Steppes covered with grass and scrubby brush dominated the landscape, and forests survived only in the uplands. Humans in the region, like those everywhere else in the world, lived as hunter-gatherers. They collected wild grains, beans, and nuts and used stone-pointed arrows and spears to kill game.

  The wild boar emerged in Southeast Asia about 4 million years ago and then colonized nearly every corner of Eurasia, from mountain to desert to jungle. When the first groups of Homo sapiens ventured out of Africa into the Near East some 60,000 years ago, Sus scrofa was already there waiting for them.

  When the weather warmed about 15,000 years ago, the people of the Near East found themselves living in a world where food was abundant. They gathered nuts and fruit from forests of oak, pistachio, almond, and pear trees and harvested grains and legumes from huge stands of wheat, barley, rye, lentils, and peas. Hunting became easier because animal populations exploded in the warmer, wetter landscape.

  With nature so bountiful, there was no need to travel far in search of food. People built permanent dwellings in villages like Hallan Cemi. They used stone sickles to harvest wild grains and stored them in bins for the dry season. For grinding wild grains they invented stone mills, a heavy appliance that hunter-gatherers would have refused to lug to their next campsite. Technology thus reinforced the cultural transformation that initially began as a response to the changing environment.

  This village way of life spread throughout the region. The expansion was a simple matter of demographics: hunter-gatherers needed to carry not only their belongings but also their youngest children from camp to camp, which meant that they spaced offspring—perhaps through infanticide—at intervals of three or four years. Freed from this limitation, the population of settled villages exploded.

  The good times lasted a couple of thousand years. Then another cold spell arrived about 10,800 bc. Populations had boomed in warm weather, but now the wild sources of food that had sustained them disappeared.

  Faced with hunger, people realized that they didn’t have to wait for wild cereals to grow on their own: they could take the seeds they had gathered and stick them in the ground. The earliest known domesticated plant, rye, dates from 10,000 bc, in the midst of this cold snap. The newly arid climate also shrank the size of lakes and rivers, exposing thousands of acres of rich soils ready for planting. The people became farmers.

  Those of us on the far side of this shift might ask what took them so long. Anyone who’s spent time farming—let alone farming with stone tools—knows the answer: gathering food from the wild is far preferable to growing it. Farming is hard work. It also tends to lead to social stratification, famine, and epidemic disease. That’s why one scholar has labeled agriculture “the worst mistake in the history of the human race.” But the people of 10,000 bc couldn’t have predicted this. For them, farming was a matter of survival. When nature stopped providing, they provided for themselves.

  The cold spell ended about 9600 bc, and the global climate warmed again, entering a period of stability known as the holocene (which is now ending, some scientists propose, as we enter the anthropocene, an era of climate change caused by human activity). Once again, wild food flourished. People could have returned to the foraging ways of their ancestors, but they did not. Instead, they got more serious about farming. In the Near East, the period from 10,000 to 6000 bc witnessed the domestication of wheat, barley, lentils, and chickpeas, as well as pigs, goats, sheep, and cattle. Wheat remains one of the world’s staple grains (alo
ng with corn from the New World and rice from Asia), and the region’s domestic animals have become the primary sources of meat and dairy products all over the world.

  The success of farming in the Near East owed much to the weather. The climate was hot and dry in the summer, cool and rainy in the winter. Cereals and legumes grew in the winter and lay dormant in the soil during the hot, dry summer. That required large seeds, with a tough shell protecting a kernel of carbohydrates that served as the seed’s energy source. Those carbohydrates became food for the humans who harvested the seeds.

  Large grains were useful enough when collected from the wild, but once people started planting them, another change occurred. Wheat and other grains had evolved a seed head that shattered when ripe, scattering seeds to the ground. If the head didn’t shatter—which could happen as the result of a simple genetic mutation—the seeds remained high above the ground, unable to germinate, directed down an evolutionary dead end. But then humans came along. On a few occasions, they would have come across a stand of wild cereal after it had ripened, and the plants with this mutation would have made up a disproportionate percentage of the harvest. People would have kept these seeds to replant, thereby perpetuating the mutations. This reversed the course of evolution: an undesirable quality in nature became indispensable to human culture. Soon humans selected for other desirable qualities in the plants, such as increased seed sizes and thinner seed coats. Thanks to these first experiments in plant breeding, people enjoyed more bountiful crops that were easier to harvest, thresh, mill, and eat.

  Mutated wheat and barley was waiting for humans, ready to be plucked and planted, but animals were different. People could kill and eat them, but they couldn’t take wild beasts back to the village and commence a captive breeding program. Domesticating animals entailed a more complex process.