Some experts say we are now in the era of the “Anthropocene,” a term used to describe humans’ unprecedented influence on the planet. When our civilization is long gone, the Earth will continue to bear the effects of the time we spent here—effects like nuclear isotopes in sedimentary rock, and the fossilized remains of plastic on the ocean floor and concrete on land. But perhaps more than anything else, according to a new study, the great legacy of our time will be chicken bones. Lots and lots of chicken bones.
Writing in Royal Society Open Science, a team of researchers argues that the remains of domesticated chickens (Gallus gallus domesticus) will be a major and unique marker of our changing biosphere. For one thing, there are just so many of them. With a standing population of more than 22.7 billion, domesticated chickens far outnumber the world’s most abundant wild bird—the red-billed quelea, which has a population of about 1.5 billion. According to James Gorman of the New York Times, if you combined the mass of all these chickens, it would be greater than that of all other birds.
The world is home to such a huge number of chickens because humans can’t stop eating them. Chicken consumption is growing faster than the consumption of any other type of meat—more than 65 billion chickens were slaughtered in 2016 alone—and it is on pace to surpass pork soon as the world’s most consumed meat.
With an abundance of chicken dinners comes an abundance of chicken remains. In the wild, bird carcasses are prone to decay and are not often fossilized. But organic materials preserve well in landfills, which is where many chicken remains discarded by humans end up. Thus, these chicken bones don’t degrade, according to the study authors—they mummify. For this reason, lead study author Carys E. Bennett tells Sam Wong of New Scientist that chickens are “a potential future fossil of this age.”
The modern chicken’s strange and singular features also make it a good candidate to represent the current era of human-directed change. The domestication of chickens started around 8,000 years ago, but humans have come up with a number of innovations to feed our growing hunger for chicken products. Modern broiler chickens, which is the variety farmed for meat, are bred to be four or five times heavier than they were in the 1950s. They are transported to slaughterhouses once they reach an age of between five and seven weeks, which may seem like a short lifespan, but in reality, they would not be able to survive much longer.
“In one study, increasing their slaughter age from five weeks to nine weeks resulted in a sevenfold increase in mortality rate,” the study authors write. “The rapid growth of leg and breast muscle tissue leads to a relative decrease in the size of other organs such as the heart and lungs, which restricts their function and thus longevity. Changes in the centre of gravity of the body, reduced pelvic limb muscle mass and increased pectoral muscle mass cause poor locomotion and frequent lameness.”
These chickens are, unsurprisingly, unlike any the world has seen before. The study authors compared data on modern broilers to zooarchaeological information recorded by the Museum of London Archaeology. Today’s domestic chickens are descended from a bird called the red junglefowl, Gallus gallus, and related species that might have bread with G. gallus, Andrew Lawler and Jerry Adler explain for Smithsonian magazine. The researchers found that between the 14th and 17th centuries, domestication caused chickens to become noticeably larger than their wild progenitors. But those chickens had nothing on the fowls of today. “There has been a steady increase in growth rate since 1964,” the study authors write, “and the growth rate of modern broilers is now three times higher than that of the red junglefowl.”
So the next time you tuck into a plate of drumsticks or wings, remember: archaeologists of the future may one day be able to find and identify your meal.