Why Did the Chicken Cross the World?

by Andrew Lawler

  In 1868, a few months before Variations came out, the naturalist packed up all his chicken skeletons in his Down House study and donated them to London’s Natural History Museum. “He got rid of them even before he published—you get the sense he was relieved to be done with them,” Cooper says as she leads me down a flight of stairs to the skeleton depository, also filled with identical storage cabinets. She motions for me to wait at a long table against one wall. Returning, Cooper looks like a waitress bussing a busy cafeteria. She carries a large tray of a half-dozen chicken carcasses that have been picked clean.

  Each is in its own rectangular plastic case that seems only slightly more substantial than the plastic cases of whole roasted chickens at the supermarket. She sets each on the table and goes back for more. I stare at the bones through the plastic. Some are marked with numbers and names. “That’s his writing,” Cooper says as she returns to set down another tray of boxes. Here is the rooster that arrived at Down House from Sierra Leone a century and a half ago. There is the Cochin hen, the rumpless fowl, and the Malaysian hen along with fighting cocks and little bantams. And on the far end is a box with a skeleton noticeably smaller than that of most of the other domestic birds. I open the plastic top and peer inside. There’s a small note, the ink still dark and the writing elegant. “Skeleton of Bengal Jungle cock for C. Darwin Esq.,” it reads. It is signed by Blyth. On a leg bone, Darwin has etched in tiny characters a single word, “Wild.”

  Many poultry fanciers derided Darwin’s assertion that a tiny Sebright bantam and a giant Chinese Silkie descended from a single ancestor. As recently as 2008, one headline insisted “Darwin Was Wrong About Wild Origin Of The Chicken, New Research Shows.” A team that included Leif Andersson from Uppsala University—his lab is just down the street from Linnaeus’s home—found that yellow skin in domesticated chickens can be traced to the gray and not the red jungle fowl. Since that trait might have been added long after initial domestication took place, Darwin may still have gotten it right.

  Pinpointing the chicken’s ancestor still left a host of mysteries unsolved. Was it domesticated once or many times? Where? When? And why? A century and a half later, these points remain hotly debated, and reflect larger unanswered questions about humans. For example, if domestication occurred only once and then spread across South Asia and the world, it could tell us that humans were busy trading goods and ideas as well as animals long before the advent of cities and caravans. If, however, chickens and our species forged partnerships in different times and places—Vietnam, Malaysia, India—then prehistoric peoples may have relied more on their own homegrown technologies than those produced elsewhere.

  China, India, and Southeast Asian nations all proudly claim to be the original chicken’s homeland. Actual ancient chicken bones could settle the dispute. Archaeologists can use radiocarbon techniques to date an old bone to within a few centuries, but the wet and acidic soils of Southeast Asia so far have revealed no chicken remains older than two millennia. The bone and textual data supporting a domesticated chicken at least four millennia ago is found thousands of miles to the west in what is now India and Pakistan.

  Comte de Buffon was skeptical that the chicken’s origins could ever be settled and Darwin himself was pessimistic. Biologists today, however, are armed with far more powerful tools than his rulers and calipers. Decoding the genomes of living creatures provides long-hidden information on the origin and changes of species over time. The first serious attempt to use genes to unravel chicken history was made in the 1990s by the second in line to the world’s oldest hereditary monarchy.

  Like his father, the late Japanese emperor Hirohito, Akishinonomiya Fumihito is a biologist. While Hirohito specialized in jelly­fish predators, his second son became fascinated at an early age with the chickens that the empress first acquired in the aftermath of World War II to help feed the royal household. After conducting field research in Southeast Asia, the prince and his collaborators extracted sections of red jungle fowl mitochondrial DNA, the genetic code passed down by the female that serves as a historical tracer of a species.

  The team’s 1994 conclusion was that chickens were domesticated only once, in Thailand. The work formed the basis of Fumihito’s doctoral dissertation and an independent research group confirmed these conclusions eight years later, but two decades after that, this theory unraveled. The American ecologist I. Lehr Brisbin noted that the red jungle fowl used as their wild sample came from a Bangkok zoo and likely was a domesticated hybrid.

  In 2006, a team led by Yi-Ping Liu of China’s Kunming Institute of Zoology found nine separate clades—that is, groups descended from a common ancestor—in the mitochondrial DNA of a large sample of red jungle fowl and domestic chickens. The distribution of these clades suggested several domestications rather than just one. Ancient peoples in southern China, in Southeast Asia, and on the Indian subcontinent separately bred red jungle fowl, they argued, creating distinct lineages with their own genetic signatures. A 2012 study that used nuclear DNA, which provides more detailed data on an organism than the mitochondrial sort, supported the claim of multiple origins of the chicken.

  Fumihito himself is convinced by the new data. He could not speak with me, since an interview with any member of the Japanese royal family is difficult to arrange, but a person familiar with his views did say this: “Earlier I thought domestication of the chicken took place in continental Southeast Asia and chickens dispersed from there. Based on recent studies, however, it is more likely that the chicken was domesticated in multiple locations, such as in India, in southern China, and perhaps also in Indonesia. In any case, I don’t think it was a single event.”

  Other geneticists, however, may vindicate the prince’s original view. They claim that extensive analysis shows that the chicken indeed originated in Southeast Asia and spread from there to other parts of Asia and then the rest of the world. Olivier Hanotte, a biologist at the University of Nottingham in Britain, and his young colleague Joram Mwacharo have spent the past few years analyzing blood samples from thousands of village chickens across Asia, Africa, and South America. With the help of other colleagues and village children capable of catching the hard-to-get birds, Hanotte and Mwacharo have assembled more than five thousand genetic sequences of modern chickens.

  Tracing the chicken’s history through the bird’s blood is immensely complicated since the bird’s genome is scrambled from being moved back and forth across oceans and continents for millennia, its sequences mixed and remixed. In their Nottingham lab, Hanotte and Mwacharo show me a PowerPoint presentation that lays out that complexity. Their genomic maps show a half-dozen major haplotypes, or genetic groups, connected by a confusing array of arrows and bars. “How do you reconcile huge diversity with a single domestication?” asks Hanotte, a rangy man who speaks rapidly with a musical accent. The complexity of the chicken genome points to multiple domestications in different places.

  Hanotte believes that this complexity actually stems from several wild subspecies of the red jungle fowl mating and occasionally producing hybrids. Three of the five subspecies of red jungle fowl are Southeast Asian. Also, the greatest variety of domesticated fowl are found there as well. As one moves west, toward the red jungle fowl’s western terminus in Pakistan, those distinct varieties decrease. This is why chickens from Britain’s lands on the Indian subcontinent didn’t dazzle Queen Victoria, fascinate Dixon, or intrigue Darwin the way that those from Southeast Asia and southern China did.

  This genetic diversity in both wild and domesticated varieties is a strong indicator that this region is the original homeland of chicken domestication. Hanotte and Mwacharo also pinpointed what biologists call a “population bottleneck” in the same region. That is, the bird’s genetic diversity suddenly decreased in the distant past, a sign that an early domesticated bird radiated from some point in Southeast Asia across the region. Hanotte estimates that the bottleneck began from eighteen thousand to eight tho
usand years ago. The newly domesticated bird may have moved in small numbers to villages in Southeast Asia and eventually spread to the Indian subcontinent. Then, about five thousand years ago, he believes, the chicken population increased rapidly throughout South Asia and then beyond.

  This suggests that the bird and humans originally made common cause for very different reasons than why we keep chickens today. At first, the domesticated animal was not bred for meat and eggs. “There does not seem any ground for believing that an attempt was made at this early period to domesticate them for purposes of food,” a group of poultry scholars noted as early as 1854.

  The indigenous peoples of Southeast Asia retain a remarkably rich variety of traditions concerning the fowl. The Palaung people scattered through Vietnam, Laos, Burma, and southern China, for example, keep chickens but don’t eat the meat or eggs, instead using the bird’s intestines, organs, or bones for divination. Likewise, the Karen of northern Burma believe that they contact the powerful realm of invisible spirits by the angles that bamboo splinters make when inserted into a slaughtered chicken’s thighbones. The Purum Kukis, who live in India’s far northeast, close to Burma, recite prayers, sacrifice a cock, and judge by the way it falls whether the spot is a good place to build a village. Many tribes across the area practice an egg toss in which the resulting shell fragments will provide clear guidance for thorny situations. These beliefs in the magical nature of chickens may predate the arrival of agriculture, when people began to use the bird more commonly for food.

  At Uppsala University, Andersson and a team of collaborators recently found that several different populations of chickens share a mutant form of a gene absent in the red jungle fowl. This bit of DNA produces a particular hormone that stimulates the thyroid. A bird with this code could gain weight faster. This mutation may have been an important step in the evolution of the chicken. In some South Asian village long ago, a bird born with a proclivity to grow faster—and to procreate more frequently—was singled out for special breeding.

  But chicken as food may have been an afterthought. Long ago, when we first took or enticed it from its forest home, the bird was more than a cheap lunch. It was magical and practical at the same time. Along with its powers of divination, its delicate bones could be used for sewing or tattooing or to make small musical instruments. The rooster’s magnificent feathers could adorn ornamental clothing. The bird had well-known medicinal properties and its martial abilities provided entertainment. As a sacrifice to the gods, the small and fast-reproducing animal was ideal.

  Amid familiar mammals like dogs and cats and cows, however, the chicken retains an almost alien quality. The male can be fierce and even terrifying when defending its turf, all out of proportion with its small size, while the bird’s reptilian feet and downy feathers make for an unsettling combination. Jerky movements give the bird a disturbingly robotic quality, while its voracious appetite for sex with multiple partners is impressive to some and offensive to others. We veer between admiration and disgust and between fascination and fear in our long relationship with the chicken. This ambivalence mirrors our shifting attitudes toward God, sex, gender, and all that we consider both sensual and monstrous.

  8.

  The Little King

  Why are the cocks not crowing, he muttered to himself, and repeated the question anxiously, as if the cocks’ crowing might be the last hope of salvation.

  —José Saramago, The Gospel According to Jesus Christ

  The cock has no cock. That’s no Zen Buddhist riddle. The rooster lacks a penis. Or, to be more accurate, it lost it, which is a rather odd fact for the animal that more than any other is the zoological stand-in for the human male organ. The mystery of how the chicken phallus vanished was recently solved, although why it vanished remains a matter of some controversy among the small but dedicated band of bird-penis researchers.

  When chickens mate, a casual spectator might be forgiven for thinking that fowl sex is similar to that of mammals. The rooster mounts the hen, takes a firm grip of her back with his claws, and uses his beak to hold on to her head. Then he hops off. It is usually over in less time than a Filipino cockfight. Though it can be a similarly raucous affair, two birds have exchanged a cloacal kiss.

  The cloaca, from the Latin word for sewer, is a busy place. In the chicken—as well as all birds, reptiles, and amphibians—the cloaca is the single-lane end of the urinary and digestive tracts, and it also serves reproductive duties. Like human males, roosters have two testes, though these are internal organs tucked under the kidneys rather than dangling on the outside. A healthy rooster can produce more than 8 billion sperm in every ejaculation that are transferred into the hen when they invert their cloacae and press them together. It only takes a few seconds. The sperm in her oviduct can fertilize eggs in her single ovary for up to a month after they mate.

  A few species of birds, mainly waterfowl, do have penises. For example, ducks have long corkscrew-shaped peckers. A team overseen by Martin Cohn at the University of Florida, Gainesville, investigated why ducks and chickens differ in this respect. They cut small windows into eggs to view both male duck and chicken embryos, and found that both began to develop penises for the first nine days of development, after which growth in chickens stopped and the proto-organ shriveled up. On day nine, the chicken embryos began to manufacture a protein responsible for shriveling the would-be penis from the tip down. That protein also is tied to the loss of nascent chicken teeth during early development and it influences beak shape and feathers. It is essentially a chemical that kills off selected cells. When the researchers coated the would-be chicken penis with another protein that blocked the shriveling effects, it kept growing. Coating a duck penis with the cell-killing chicken protein reversed its growth.

  Cohn thinks this organ loss was simply a consequence of dropping other body parts like teeth and limbs. This particular disruptive protein clearly plays a major role in bird evolution, and losing the penis was just a side effect. Other biologists suspect that the change is the result of female selection, which led to the evolution of the cooperative cloacal kiss over rougher penetrative sex. Male ducks are notorious for forcing copulation on uncooperative mates and sometimes even drown their mates in the process. Such battles of the sexes reduce the odds for fertilization. Over time, most bird species, including the chicken, may have selected males with smaller penises while others, notably ducks, geese, and swans, kept theirs.

  How the penis vanished in chickens—and most birds—could tell us much more about evolution, such as how snakes lost their legs and what causes birth defects in human genitalia, which are particularly susceptible to malformations in the womb. The research conceivably could lead to practical ways to correct those defects before birth. “Genitalia, dear readers, are where the rubber meets the road, evolutionarily,” wrote the biologist Patricia Brennan from the University of Massachusetts, Amherst, in Slate. She was responding to an outcry by some media commentators outraged that federal tax money would be spent on chicken penis research. “To fully understand why some individuals are more successful than others during reproduction, there may be no better place to look.”

  Losing the penis also might ultimately have given the chicken a slightly higher fertility rate than those other common farm birds outside the family of Galliformes. But in losing its cock, it is possible that the chicken may have gained the world.

  Biology can’t explain why our favored slang word for the male organ refers to a bird that lacks one. Americans blush at a word bandied about shamelessly by Canadians, Australians, British, and other English speakers, who still use it without hesitation when describing the male chicken. Eighteenth-century New England Puritans excised cock, a word that likely derives from the sound of a chicken—it comes from the ancient Aryan word kak, which translates as “to cackle”—from the American lexicon.

  These were, after all, people who punished those wicked souls who celebrated Christmas.
Puritans did not oppose sex and were harsh critics of celibacy for Roman Catholic clergy, but double entendres led the mind and body astray and therefore were not to be tolerated. Two centuries before, in Elizabethan times, one poem begins with the line “I have a gentle cock” and ends with: “And every night he perches in my lady’s chamber.” This bawdy tradition continued for centuries. The 1785 Classical Dictionary of the Vulgar Tongue notes that the phrase “cock alley” means “the private parts of a woman.”

  In the American colonies, the more anodyne rooster began to replace cock just before the revolution, starting in the north and spreading south. The term derives from an Old English word for the perch of a domestic fowl. In the young United States, haycocks became haystacks, weathercocks became weathervanes, and water cocks became faucets. Even cockroaches turned into just plain roaches. “Victoria was not crowned in England until 1838, but a Victorian movement against naughty words had been in full blast in this country since the beginning of the century,” H. L. Mencken notes sardonically in American Language. Cock had to go because it had acquired “an indelicate anatomical significance.” In Britain, the word continues to be used in all its glorious ambiguity. Well into the Victorian era, cock was still preferred among British doctors as a descriptor of the human organ over the more newfangled term penis, adopted from the French but originating in Latin.

  The cock most likely acquired this “indelicate anatomical significance” due to extremely randy behavior—and research demonstrates that the male chicken prefers new partners to familiar ones. Scientists call this salacious behavior the “Coolidge effect.” During separate tours of a chicken farm by President Calvin Coolidge and his wife in the 1920s, Mrs. Coolidge remarked on a rooster that was busy mating. She was told that this behavior took place dozens of times daily. “Tell that to the president when he comes by,” she said coolly. When the message was relayed, the president asked if the rooster mated with the same hen. He was told no, that the male preferred a variety of partners. “Tell that to Mrs. Coolidge,” he responded.