Lesser Beasts: A Snout-to-Tail History of the Humble Pig (2 page)
Read Lesser Beasts: A Snout-to-Tail History of the Humble Pig Online
Authors: Mark Essig
Few religious rules govern the consumption of vegetables; taboos and regulations cluster around meat. Such rules may
have functioned as public health measures—meat is more likely to harbor parasites and lethal bacteria—but they also acknowledged the significance of taking life. Killing an animal and eating its flesh traditionally has been considered a sacred act, which is why—in ancient Greece, Israel, and many other cultures—the roles of butcher and priest often blended together: holy men killed animals at the altar according to sacred protocols, offered burnt offerings to their God or gods, and then distributed the remaining meat to the crowd. Ritual sanctified the spilling of blood.
It also offered distraction from an uncomfortable fact: the substance we call meat is virtually identical to the flesh on our own bones. Pork presents this problem in acute form. People and pigs share roughly similar teeth, skin, and internal anatomy. Renaissance doctors dissected pigs as models for humans. Modern surgeons transplant pig heart valves into people.
Scientists are developing genetically modified pigs with “humanized” lungs for transplantation into people.
Pigs get ulcers, arthritis, and diabetes, just like we do. They’re also smart. They like to watch TV and drink beer, and, given the chance, they tend to grow fat and sedentary.
Confronted by this uncanny beast, humans have reacted with a blend of attraction and revulsion, hunger and disgust.
“Dogs look up to you, cats look down on you,” Winston Churchill once said. “Give me a pig—he just looks you in the eye and treats you as an equal.” We look back at the pig and see quite a bit of ourselves. And then, more often than not, we eat him.
I
n late February 1922, Henry Fairfield Osborn, head of New York’s American Museum of Natural History, received a molar in the mail. A fossil hunter named Harold Cook had unearthed the tooth while digging in the 10-million-year-old Snake Creek fossil beds of western Nebraska.
The tooth, Cook told Osborn, “very closely approaches the human type.”
The scientist agreed. “It is the last right upper molar tooth of some higher primate,” Osborn told Cook. “We may cool down tomorrow, but it looks to me as if the first anthropoid ape of America has been found.”
Osborn did not cool down. A month after first examining the tooth, he published a scientific article proclaiming that, millions of years ago, a human-like primate had walked the plains of North America. The
Illustrated London News
ran a fanciful drawing depicting a brawny, slope-shouldered, club-wielding ape-man. A worldwide mania for “Nebraska Man” commenced.
The timing could not have been better for Osborn, who was just then engaged in a public dispute with William Jennings Bryan, the great populist leader. Bryan had launched a campaign against Darwinism that would culminate a few years later with the Scopes Monkey Trial in Tennessee, which tested a law that banned the teaching of evolution.
The
New York Times
explained that the tooth provided “further evidence that Mr. Bryan is wrong and Darwin was right.” Even better, the fossil had been discovered in Bryan’s home state.
Osborn did not let the irony pass unnoted, suggesting in his journal article that the new ape-man “should be named
Bryopithecus
after the most distinguished primate which the State of Nebraska has thus far produced.”
The joke soured quickly. Further expeditions turned up more teeth that undermined Osborn’s claims. A retraction in the journal
Science
acknowledged that the tooth had come not from a man or an ape but from an extinct piglike creature.
The story of Nebraska Man is remembered today mostly by Bryan’s intellectual descendants, the creationists, who claim that Darwinists extrapolate wildly from slight evidence. And they seem to have a point: How could a great scientist confuse a pig tooth with a primate tooth?
As it turns out, the mistake was an easy one to make. The Nebraska fossil came from a peccary, close cousin to the pig. Pigs and peccaries have incisors for cutting, canines for tearing, and premolars and molars for chewing and grinding. The full set closely matches those of people, and that is what got Osborn into trouble. He erred by drawing his conclusion on the basis of an old tooth. Young molars have distinctive cusps that reveal the species of origin. Once those cusps wear away, the molars of pigs and people are nearly identical.
When Osborn confused those teeth, he may have rushed to scientific judgment, but he also exposed an important truth: pigs
and people have much in common. The two species have similar digestive systems, from teeth to stomach to intestines, because they have similar diets. Both are omnivores who thrive on meat, nuts, roots, and seeds. And because pigs and people eat the same foods, they evolved to form a symbiotic connection—a bond so tight that 10,000 years later, it remains unbroken.
The 1922 discovery of a fossilized molar prompted speculation that “Nebraska Man” once roamed the Midwest. It turned out that the tooth belonged to an extinct relative of swine. Pigs and people have much in common, especially their digestive systems, which explains why the two have formed such an enduring, albeit fraught, relationship.
A
giant meteor smashed into Earth about 65 million years ago. The meteor kicked up dust, the dust changed the climate, and the new climate killed off the dinosaurs. Onto the freshly cleared playing field stepped the mammals. These warm-blooded, lactating creatures had first emerged about the same time as dinosaurs, but for millions of years they had remained minor players, mouse-sized beasts scurrying about the forest floor.
When the dinosaurs died, mammals rose to the occasion, growing larger and filling just about every available niche.
About 10 million years after the meteor struck, the first hoofed mammals, or ungulates, appeared. One order of ungulates, called
Perissodactyla
, includes just a handful of living species, such as horses, rhinoceroses, and tapirs. The other order,
Artiodactyla
, is much larger and includes pigs, cows, goats, sheep, camels, llamas, giraffes, deer, antelopes, camels, hippopotamuses, bison, and water buffalos. Both orders of ungulates might be called tiptoers. Their hooves are actually outsized toenails, and they walk like ballerinas
en pointe
. The arrangement of those toes divides artiodactyls from perissodactyls. “Perissodactyl” means “odd-toed”: the foot’s axis cuts through the center of the middle digit, and the animals walk either on three toes, like rhinos and tapirs, or just one, like horses, zebras, and donkeys. “Artiodactyl” means “even-toed:” the first digit (the thumb or big toe) is absent, and the feet are symmetrical, with the axis running between the third and fourth digits (the equivalent of the human middle and ring fingers). As they evolved to move more quickly, their outer digits shrank or disappeared, letting the animals run on just the middle two digits. Thus they appear to have a single hoof split down the center, what the King James Bible describes as the “cloven foot.”
Subtropical forest dominated the Northern Hemisphere when ungulates first evolved, and they dined on tender leaves, seeds, and fruits. About 20 million years ago, the climate became cooler and drier, forests disappeared, and grasses spread over millions of square miles. Deprived of their old forest habitats, some hoofed animals adapted to the new circumstances. In forests, hiding was the key strategy to avoid predators, but grasslands offered little cover, so the bodies of many ungulates evolved: their eyes shifted farther to the back on their heads and became larger, allowing them to see predators more easily. And they became cursorial, or primed for running: free-swinging
knee joints and longer, stiffer leg bones gave these animals enough speed to outrun a big cat.
These graceful savannah creatures ate grass, which is rather like chewing on sandpaper. Grass cells contain minute glassy particles, and the blades often pick up an additional coating of grit from the dirt below. If humans tried to eat grass, they would wear their teeth down to the gums. To deal with the new diet, many ungulates evolved teeth that grow constantly, rather like mechanical pencils, with new material emerging from the gums as the top wears away.
Those newfangled teeth solved only part of the problem. Grass is heavy on cellulose, which consists of simple sugars bound together so tightly that no enzyme produced by mammals can break them apart. That process requires the assistance of bacteria, which live in the gut and break down cellulose through fermentation, making the sugars and other nutrients available to the animals. Cows and sheep—along with giraffes and deer—bite off and swallow large amounts of grass without chewing it, and it passes into the rumen, or first stomach, where bacteria begin to digest the cellulose. Then, when the animal is resting, it regurgitates the food and “
cheweth the cud” (as Leviticus tells us) before swallowing it again and allowing the grass to pass all the way through the alimentary canal.
These developments in many ungulates—rapid running, sharp eyesight, and the ability to eat grass—led to the extraordinary success of hoofed animals. Artiodactyls demonstrate especially beautiful and astonishing specialization: the gazelle bounding across the savannah, the giraffe grazing the tops of trees, the mountain goat scaling a vertical cliff, the powerful bison roaming the grasslands of America.
And then there are pigs. The pig and its close cousin, the peccary, are the odd men out, artiodactyls that didn’t become
ruminants. While their cousins signed up for the evolutionary fast track, moved to a new territory, and accomplished great things, the pig stayed at home in the forest. And that has been the key to its success.
Being a generalist has advantages. The very earliest mammals ate insects and had teeth like those of reptiles, simple spears for holding bugs until they could be maneuvered into position to be swallowed whole. The mammal jaw then evolved to become stronger and more dexterous. It could move side to side as well as up and down, allowing animals to chew a variety of foods and thereby get the process of digestion started earlier. Eventually, mammals developed a full complement of incisors, canines, premolars, and molars adapted to shearing, slicing, grinding, puncturing, and crushing. The more kinds of teeth you have, the more kinds of food you can eat.
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.