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The chicken age: Will finger lickin’ fossils define our geological era?

Why We Wrote This

Over the past several decades, humankind has reshaped the domestic chicken into a creature highly tailored to our needs – so much so that its fossils may prove to be the defining markers of our geological era.

Melanie Stetson Freeman/Staff/File
Chickens are raised at a California poultry farm. Because of intensive breeding programs and high-tech rearing, the average contemporary chicken is five times as heavy as its predecessor in 1961.

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Geological periods are frequently marked by the fossilized creatures that they feature. The Jurassic Period had dinosaurs. The Pleistocene Epoch had woolly mammoths. For us, in the modern Anthropocene Epoch, the defining animal may prove to be the chicken. That’s what a group of British scientists argues in a recent study. They say that the Anthropocene – characterized primarily by the huge impact humans are having on their planetary environment – will be clearly demonstrated in the changes wrought in the humble chicken over the past several decades. Subjected to intensive breeding programs and high-tech rearing farms, the average contemporary chicken is much taller and five times as heavy as its predecessor in 1961. Today’s birds are not just fatter; their bigger bones have completely different genetic and biochemical structures from their antecedents just seven decades ago. And there are a lot of chickens: The world eats more than 60 billion chickens a year, and the standing population is around 23 billion. “Broiler chicken fossils will be abundant worldwide and recognizable as new and distinct,” says Jan Zalasiewicz, one of the researchers. “That makes them good candidates” to mark the dawn of the Anthropocene Epoch.

Most people, when they take a broiler chicken from their supermarket shelf, don’t give much thought to what kind of a fossil the bird’s bones will one day make.

But Jan Zalasiewicz does. And he is part of a group of British scientists who believe those fossilized bones will provide future paleontologists with a key hallmark of our society as mankind moves into a new geological epoch.

The Jurassic Period had dinosaurs. The Pleistocene Epoch had woolly mammoths.

We, it seems, have chickens.

For one thing, there are a lot of them. The world eats more than 60 billion chickens a year, and the standing population is around 23 billion, according to a University of Leicester paper published recently by Professor Zalasiewicz and a team of colleagues.

And today’s broilers are nothing like the chickens our grandparents ate. Subjected to intensive breeding programs and high-tech rearing farms, the average contemporary chicken is much taller and five times as heavy as its predecessor in 1961.

“Broiler chicken fossils will be abundant worldwide and recognizable as new and distinct,” says Zalasiewicz. “That makes them good candidates” to mark the dawn of the Anthropocene Epoch, he adds.

The Anthropocene, many scientists suggest, is a new unit on the geological timescale, characterized primarily by the huge impact humans are having on their planetary environment. They date its beginning to the mid-20th century.

The humble domestic chicken is a good example of that, the University of Leicester team says. The denizens of modern battery farms would barely be recognizable as Gallus gallus domesticus to ancient Roman farmers, or indeed to American farmers before 1948.

That was the year the US Department of Agriculture organized the “Chicken of Tomorrow” contest among poultry breeders, with the goal of “one bird chunky enough for the whole family – a chicken with breast meat so thick you can carve it into steaks,” as The Saturday Evening Post put it.

That launched the modern global poultry industry that has made the broiler chicken the most numerous bird species on earth (40 times as large as the global sparrow population) and probably the most numerous in history.

It also led to “the most extreme and rapid change ever seen in the body of an animal,” says Zalasiewicz. “Evolution normally takes millions of years; this has taken just a few decades.”

That is because of the technology brought to bear – computers controlling broiler farms’ heat, humidity, light, and grain distribution to maximize growth rates in carefully bred birds. “Left alone these chickens couldn’t survive,” points out Carys Bennett, lead author of the University of Leicester paper. “Their body mass is too much for their legs and their hearts.”

Today’s birds are not just fatter; their bigger bones have completely different genetic and biochemical structures from their antecedents just seven decades ago.

That will be clear to future scientists digging through geological strata, and their job will be made easier by the manner in which we dispose of chicken bones.

Wild bird carcasses are scavenged and generally disappear from the geological record. But most chicken bones are thrown into plastic-lined landfills, an anaerobic environment in which organic material tends to mummify, rather than decay, which means it will eventually fossilize.

Chicken bones will not be the only markers of the putative Anthropocene Epoch. The Earth, and we ourselves, have all become slightly radioactive since the United States and other powers began staging atmospheric nuclear tests in the 1950s. Plastics have also become a ubiquitous marker of the modern age; most handfuls of beach mud and other sediments now accumulating contain plastic microfibers.

But “chickens are the only example of a new and distinct future fossil coincident with the Anthropocene,” Zalasiewicz says. They are also “pretty symbolic” of mankind’s priorities, he adds. The poultry industry “shows the scale of our transformation of our biosphere. We’ve converted it into feedstock for humans.”

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