Why Did the Chicken Cross the World? (21 page)

Darwin tackles the perplexing question of how chickens could have such outrageous variations and still be descended from the same ancestor. Since ancient times, breeders have known how to select the best birds in order to improve their stocks. Fashions came and went in animals as well as clothes. Love of novelty led some Britons to develop “rumpless” fowls lacking a final vertebra, while Indians bred for a frizzled feather look. Some of the novelties would be prized and carefully preserved. Ancient Romans, for example, liked their chickens with an extra toe and white ear lobes that persist to this day. Such breeding didn't require written records or fancy poultry experts. In the Philippines, Darwin notes, “no less than nine sub-varieties of the gamecock are kept and named, so that they must be separately bred.”

Human control is limited, and enthusiasts like Dixon had over
looked unconscious or unmethodical selection. Birds escape their coops and mate while farmers are asleep. This takes place even in the best-controlled research facilities. And natural selection, the spinning of the genetic dials, can alter how a creature looks and behaves, a process that continues to function even in the barnyard. The occasional bird will be born with what Darwin calls “abnormal and hereditary peculiarities.” Humans might make the most of that new trait, spinning off yet another variety of fowl, or they might decide to not let that characteristic propagate. Darwin summarizes that “there is no insuperable difficulty, to the best of my judgment, in believing that all the breeds have descended from some one parent-source.”

The
Gallus gallus
bankiva
, the subspecies of red jungle fowl that Wallace collected in Malacca, is the best candidate for the ancient chicken's ancestor, Darwin concludes. The domesticated birds that most nearly resemble this wild fowl, he notes, are the gamecocks of Malaya and Java, which are close in size, color, and skeletal structure and even in their crow to the local red jungle fowl. People in the region keep wild cocks to fight their domesticated ones, and the bird may have been first domesticated in Malaya and exported to India. Chinese texts consulted by the naturalist in the British Library support this idea, since they hint at a Southeastern Asian origin for the domesticated bird. Darwin not only pinpoints the ultimate ancestor of the chicken, he also names the region where humans likely domesticated the wild creature. He ruefully acknowledges, however, that “sufficient materials do not exist” to reveal the complete history of the bird.

Just as Dixon used Darwin's data to argue that species don't change, Darwin used Dixon's data to show the opposite. The rector's experiments demonstrated that crossbreeding other jungle fowl with the red led to infertile progeny. In a later and larger experiment involving five hundred eggs made by crossing gray and red jungle fowl at London's Zoo, the handful that were raised proved sterile, but the red could cross with domesticated chickens and produce fertile birds. “Hence it may be safely ranked as the parent of this, the most typical domesticated breed,” Darwin concluded.

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 Mwa
charo 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 thousand 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.