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Chicken reigns in the 21st century. (Tim O’Brien)

How the Chicken Conquered the World

The epic begins 10,000 years ago in an Asian jungle and ends today in kitchens all over the world

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The chickens that saved Western civilization were discovered, according to legend, by the side of a road in Greece in the first decade of the fifth century B.C. The Athenian general Themistocles, on his way to confront the invading Persian forces, stopped to watch two cocks fighting and summoned his troops, saying: “Behold, these do not fight for their household gods, for the monuments of their ancestors, for glory, for liberty or the safety of their children, but only because one will not give way to the other.” The tale does not describe what happened to the loser, nor explain why the soldiers found this display of instinctive aggression inspirational rather than pointless and depressing. But history records that the Greeks, thus heartened, went on to repel the invaders, preserving the civilization that today honors those same creatures by breading, frying and dipping them into one’s choice of sauce. The descendants of those roosters might well think—if they were capable of such profound thought—that their ancient forebears have a lot to answer for.

Chicken is the ubiquitous food of our era, crossing multiple cultural boundaries with ease. With its mild taste and uniform texture, chicken presents an intriguingly blank canvas for the flavor palette of almost any cuisine. A generation of Britons is coming of age in the belief that chicken tikka masala is the national dish, and the same thing is happening in China with Kentucky Fried Chicken. Long after the time when most families had a few hens running around the yard that could be grabbed and turned into dinner, chicken remains a nostalgic, evocative dish for most Americans. When author Jack Canfield was looking for a metaphor for psychological comfort, he didn’t call it “Clam Chowder for the Soul.”

How did the chicken achieve such cultural and culinary dominance? It is all the more surprising in light of the belief by many archaeologists that chickens were first domesticated not for eating but for cockfighting. Until the advent of large-scale industrial production in the 20th century, the economic and nutritional contribution of chickens was modest. In Guns, Germs, and Steel, Jared Diamond listed chickens among the “small domestic mammals and domestic birds and insects” that have been useful to humanity but unlike the horse or the ox did little—outside of legends—to change the course of history. Nonetheless, the chicken has inspired contributions to culture, art, cuisine, science and religion over the millennia. Chickens were, and still are, a sacred animal in some cultures. The prodigious and ever-watchful hen was a worldwide symbol of nurturance and fertility. Eggs hung in Egyptian temples to ensure a bountiful river flood. The lusty rooster (a.k.a. cock) was a universal signifier of virility—but also, in the ancient Persian faith of Zoroastrianism, a benign spirit that crowed at dawn to herald a turning point in the cosmic struggle between darkness and light. For the Romans, the chicken’s killer app was fortunetelling, especially during wartime. Chickens accompanied Roman armies, and their behavior was carefully observed before battle; a good appetite meant victory was likely. According to the writings of Cicero, when one contingent of birds refused to eat before a sea battle in 249 B.C., an angry consul threw them overboard. History records that he was defeated.

But one major religious tradition—ironically, the one that gave rise to matzo-ball soup and the Sunday chicken dinner—failed to imbue chickens with much religious significance. The Old Testament passages concerning ritual sacrifice reveal a distinct preference on the part of Yahweh for red meat over poultry. In Leviticus 5:7, a guilt offering of two turtledoves or pigeons is acceptable if the sinner in question is unable to afford a lamb, but in no instance does the Lord request a chicken. Matthew 23:37 contains a passage in which Jesus likens his care for the people of Jerusalem to a hen caring for her brood. This image, had it caught on, could have completely changed the course of Christian iconography, which has been dominated instead by depictions of the Good Shepherd. The rooster plays a small but crucial role in the Gospels in helping to fulfill the prophecy that Peter would deny Jesus “before the cock crows.” (In the ninth century, Pope Nicholas I decreed that a figure of a rooster should be placed atop every church as a reminder of the incident—which is why many churches still have cockerel-shaped weather vanes.) There is no implication that the rooster did anything but mark the passage of the hours, but even this secondhand association with betrayal probably didn’t advance the cause of the chicken in Western culture. In contemporary American usage, the associations of “chicken” are with cowardice, neurotic anxiety (“The sky is falling!”) and ineffectual panic (“running around like a chicken without a head”).

The fact is that the male of the species can be quite a fierce animal, especially when bred and trained for fighting. Nature armed the rooster with a bony leg spur; humans have supplemented that feature with an arsenal of metal spurs and small knives strapped to the bird’s leg. Cockfighting is illegal in the United States—Louisiana was the last state to ban it, in 2008—and generally viewed by Americans as inhumane. But in the parts of the world where it is still practiced, legally or illegally, it has claims to being the world’s oldest continual sport. Artistic depictions of rooster combatants are scattered throughout the ancient world, such as in a first century A.D. mosaic adorning a house in Pompeii. The ancient Greek city of Pergamum established a cockfighting amphitheater to teach valor to future generations of soldiers.

The domesticated chicken has a genealogy as complicated as the Tudors, stretching back 7,000 to 10,000 years and involving, according to recent research, at least two wild progenitors and possibly more than one event of initial domestication. The earliest fossil bones identified as possibly belonging to chickens appear in sites from northeastern China dating to around 5400 B.C., but the birds’ wild ancestors never lived in those cold, dry plains. So if they really are chicken bones, they must have come from somewhere else, most likely Southeast Asia. The chicken’s wild progenitor is the red junglefowl, Gallus gallus, according to a theory advanced by Charles Darwin and recently confirmed by DNA analysis. The bird’s resemblance to modern chickens is manifest in the male’s red wattles and comb, the spur he uses to fight and his cock-a-doodle-doo mating call. The dun-colored females brood eggs and cluck just like barnyard chickens. In its habitat, which stretches from northeastern India to the Philippines, G. gallus browses on the forest floor for insects, seeds and fruit, and flies up to nest in the trees at night. That’s about as much flying as it can manage, a trait that had obvious appeal to humans seeking to capture and raise it. This would later help endear the chicken to Africans, whose native guinea fowls had an annoying habit of flying off into the forest when the spirit moved them.

But G. gallus is not the sole progenitor of the modern chicken. Scientists have identified three closely related species that might have bred with the red junglefowl. Precisely how much genetic material these other birds contributed to the DNA of domesticated chickens remains a matter of conjecture. Recent research suggests that modern chickens inherited at least one trait, their yellow skin, from the gray junglefowl of southern India. Did a domesticated breed of G. gallus spread initially from Southeast Asia, traveling either north to China or southwest to India? Or were there two separate heartlands of domestication: ancient India and Southeast Asia? Either scenario is possible, but probing more deeply into chicken origins is hindered by an inconclusive DNA trail. “Because domesticated and wild birds mixed over time, it’s really difficult to pinpoint,” says Michael Zody, a computational biologist who studies genetics at the Broad Institute of Harvard and MIT.

The chicken’s real star turn came in 2004, when an international team of geneticists produced a complete map of the chicken genome. The chicken was the first domesticated animal, the first bird—and consequently, the first descendant of the dinosaurs—thus honored. The genome map provided an excellent opportunity to study how millennia of domestication can alter a species. In a project led by Sweden’s Uppsala University, Zody and his colleagues have been researching the differences between the red junglefowl and its barnyard descendants, including “layers” (breeds raised to produce prodigious amounts of eggs) and “broilers” (breeds that are plump and meaty). The researchers found important mutations in a gene designated TBC1D1, which regulates glucose metabolism. In the human genome, mutations in this gene have been associated with obesity, but it’s a positive trait in a creature destined for the dinner table. Another mutation that resulted from selective breeding is in the TSHR (thyroid-stimulating hormone receptor) gene. In wild animals this gene coordinates reproduction with day length, confining breeding to specific seasons. The mutation disabling this gene enables chickens to breed—and lay eggs—all year long.

Once chickens were domesticated, cultural contacts, trade, migration and territorial conquest resulted in their introduction, and reintroduction, to different regions around the world over several thousand years. Although inconclusive, evidence suggests that ground zero for the bird’s westward spread may have been the Indus Valley, where the city-states of the Harappan civilization carried on a lively trade with the Middle East more than 4,000 years ago. Archaeologists have recovered chicken bones from Lothal, once a great port on the west coast of India, raising the possibility that the birds could have been carried across to the Arabian Peninsula as cargo or provisions. By 2000 B.C., cuneiform tablets from Mesopotamia refer to “the bird of Meluhha,” the likely place name for the Indus Valley. That may or may not have been a chicken; Professor Piotr Steinkeller, a specialist in ancient Near Eastern texts at Harvard, says that it was certainly “some exotic bird that was unknown to Mesopotamia.” He believes that references to the “royal bird of Meluhha”—a phrase that shows up in texts three centuries later—most likely refer to the chicken.

Chickens arrived in Egypt some 250 years later, as fighting birds and additions to exotic menageries. Artistic depictions of the bird adorned royal tombs. Yet it would be another 1,000 years before the bird became a popular commodity among ordinary Egyptians. It was in that era that Egyptians mastered the technique of artificial incubation, which freed hens to put their time to better use by laying more eggs. This was no easy matter. Most chicken eggs will hatch in three weeks, but only if the temperature is kept constant at around 99 to 105 degrees Fahrenheit and the relative humidity stays close to 55 percent, increasing in the last few days of incubation. The eggs must also be turned three to five times a day, lest physical deformities result.

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