Adapted from Why Did the Chicken Cross the World?: The Epic Saga of the Bird That Powers Civilization, out now from Atria Books.

The World Slasher Cup is the Super Bowl of cockfighting, a five-day series of 648 matches held in a coliseum in downtown Quezon City in metro Manila. Outside the sleek chrome entrance, a 30-foot-high inflated rooster sways in the hot breeze, advertising a formula feed. Next to the event poster featuring two cocks in combat hangs a bill announcing the Miss Philippines contest, displaying a woman in a teal-blue low-cut dress. Ice Capades just finished a run at the coliseum, and Dionne Warwick will be coming soon.

But for now, the 20,000-seat arena where Joe Frazier once fought Muhammad Ali for the world heavyweight title belongs to the Filipinos’ favorite traditional pastime. Cockfighting is also the world’s oldest sport after boxing, and one of humanity’s most ubiquitous gambling games. Though now illegal around much of the world, you can still find cockfights in Appalachian farmyards, Venezuelan favelas, and Pakistani back lots. This sport, in fact, may be responsible for creating the bird that today is the world’s single most important source of protein.

Inside the Araneta, big screens make it easy to watch the birds battle each other with steel spurs. When I take my seat, there are four men in the ring, two of them calmly squatting, each with a cigarette between his lips and a chicken between his legs. The other two are referees. Thousands of spectators, all men, are standing and shouting, making distinctive hand gestures to one another around the vast space, each gesture part of an intricate system for betting on the birds below. The noise is deafening.

Suddenly, the squatting smokers release the birds, and the roosters approach each other at a wary angle, hackles rising like rainbow-colored umbrellas from their necks. As they explode forward with the speed and aim of heat-seeking missiles, the clamor outside the ring abruptly halts. Feathers, legs, and a flash of steel fill the screens. The only sound is the vibration of pounded air from hard-flapping wings. In less than a minute, it is over. The white-feathered victor sends up a triumphant crow next to the still body of its dead opponent. Losers pay up their bets in a rain of folded peso notes as the loudspeaker blares the pop tune “Eye of the Tiger.”

“Here in the cheap seats, they are betting 10 to 100 dollars a match,” says Rolando Luzong, my cockfighting guide and a journalist, industry consultant, and public relations specialist. We are sitting halfway up, where the crowd thins out. “But there in the preferencia”—he points at the VIP bleachers next to the ring—“they are betting 1,000 to 10,000 dollars.”

The cup is the high end of global cockfighting. To enter a single bird in the competition costs $1,750, more than half a year’s salary for the average Filipino. Wealthy owners often have more than just the money; they have dedicated farms and full-time trainers caring for hundreds of fowl that could sell for well over $1,000 apiece. Vaccines, antibiotics, vitamins, and supplements are all part of the modern game fowl’s life. Traditional methods of revving up your bird for a fight, like slipping cayenne up its anus, have given way to pricey steroids and other powerful drugs.

Like American baseball or the Tour de France, modern Filipino cockfighting is caught in a tangle of corporate sponsors and performance-enhancing drugs. The brightly lit concession stands, the blaring canned music, and the rows of clean toilets in the restrooms give the event a depressingly modern feel. Still, the people in the cheap seats are the working-class men that you would find at any Canadian hockey game, British rugby match, or Brazilian soccer contest. The real draw, though, seems to be in the gambling outside the ring rather than in the combat inside.

Luzong insists that cockfighting is a much less corrosive form of gambling than what takes place in the flashy casinos springing up across Manila. “Here, you only choose between two birds; you have a 50-50 chance,” he says as another shower of peso notes sprinkles through the air at the conclusion of a match. “You can cancel your bet before the roosters are released. When the birds are released, there is no human intervention. And you can leave whenever you want.”

There are, of course, other stories. There is the young villager who spent all his hard-earned money saved from an overseas job, and the children who suffer from malnutrition while their father’s roosters live a well-fed life. For the millions packed into Manila’s sprawling slums, cockfighting offers a fast way up the socioeconomic ladder or a quick tumble into indigence. And while the birds are famously pampered outside the ring, most end up dead inside it.

The ancient sport already obsessed native Filipinos when the first Europeans—the crew led by Ferdinand Magellan—arrived here in 1521. The new Spanish overlords encouraged the sport so they could tax it. The large and regular gatherings of men eventually gave revolutionaries a chance to organize their successful uprising against the colonial power. Later, pious American and then Japanese rulers tried but failed to stamp out cockfighting. By the 1990s, distractions like satellite television and shopping malls seemed destined to erode the sport’s popularity. Then, in 1997, the central government passed cockpit-licensing control to local authorities. “That opened the floodgates to more cockpits and more fights,” says Luzong. “There is both good tax money and under-the-table money.”

The Philippines today is to cockfighting what Switzerland is to secret bank accounts, a safe haven where you can operate without government interference. Wealthy Malaysians and Indonesians come here to gamble, and Americans come to sell their fighting birds. Cockfighting in the United States is against the law in every state, but the U.S. exports more game fowl than even the Philippines. “Most Americans are breeders who come here to promote their birds,” Luzong explains, nodding toward the VIP bleachers. “There are fewer diseases there. And the birds are tougher.”

The United Gamefowl Breeders Association in the U.S. claims thousands of members, who raise hundreds of thousands of gamecocks. Since they can sell for $1,000 or even $2,500, it is a multimillion-dollar business. Animal rights activists claim the organization collects money to defeat anti-cockfighting legislation, a charge that association representatives deny. Luzong estimates that about 100 Americans are in town for the World Slasher Cup, and most are breeders more than gamblers.

He ducks my request for an introduction, and the few I approach give me a wide berth. They have good reason to be fearful. Police arrested game fowl breeder Wally Clemons and seized 200 roosters on his Indiana farm a few years ago after he gave an interview with Pit Games, a Filipino cocker magazine. American cockers understandably like to keep a low profile.

Pitting two roosters against one another may seem barbaric and arcane, but it may be why the bird became so ubiquitous. Biological evidence suggests that thousands of years ago in South Asia, its ancestral home, the chicken existed only in small numbers. In other words, chickens weren’t kept for producing meat and eggs; there weren’t enough of them for that purpose. They must have had a specialized use, and some scholars believe that use was cockfighting.

It may have begun, like bull fighting, as a religious ritual. A clan or village may have pitted its sacred rooster against another group’s bird. In northern Thailand, for example, the faun phi ceremony honoring ancestral spirits entails cockfighting of a religious nature that may reflect ancient practices. And in Indonesia’s Bali, few religious rituals take place without a cockfight that spills blood into the soil, satiating earth demons. As the chicken spread, so did its use in ritual and gambling.

One of the earliest recorded cockfights took place in China in 517 B.C. The match was held in Confucius’ home province of Lu during the philosopher’s lifetime. The earliest unequivocal evidence of cockfighting in the West comes from this same era. In a tomb just outside Jerusalem, excavators found a small seal that shows a rooster in a fighting stance. The seal was owned by Jaazaniah, who is called “the servant of the king.” A man of the same name—Jaazaniah, the son of the Maakathite—is mentioned in the biblical books of Kings and Jeremiah as an army officer after the Babylonian attack on Jerusalem in 586 B.C., the battle that ended with the leveling of Solomon’s temple and captivity for the elite in Babylon.

From China to Britain, cockfighting transformed into a more secular event. The sport became a place for men of many classes to meet, take financial risks, and watch male animals demonstrate raw courage. Not until the 19th century, when cockfighting came to be viewed as a vice—not, generally, because of animal cruelty, but because it was seen as a low-class form of gambling—did it begin to lose its status. Outrage about the treatment of the cocks began to gather steam only in the 20th century. It was not until 2007 that the last U.S. state—Louisiana—banned the practice.

Cockfighting’s popularity for so long across every corner of the world—with the exception of more isolated parts of Central and West Africa—suggests that it spread with traders who carried game fowl on their long journeys. Today’s American game fowl breeders sitting on the Araneta bleachers likely had ancient counterparts who traveled long distances with their valuable animals. Chicken now is synonymous with a meal, and whether we treat our meat-and-egg birds better than Filipino fighting cocks is open to debate. And maybe there is still a religious aspect to cockfighting, a kind of sacrifice that still goes on even under the lights and on the big screens. As Luzong and I leave the coliseum into the steamy Manila night, he gestures at the milling crowds. “You can see we are a very loving people,” he says. “Maybe it has made us milder because we are able to let the birds do the bad things for us.”