The domesticated chicken is now so widespread across the planet, that a new study published in Royal Society Open Science finds it could be seen as a defining feature of the Anthropocene–the proposed epoch that marks the unique and measurable changes that humanity is making to earth’s biosphere.
There are over 22 billion chickens at any given time on the planet, thanks to centuries of domestication that have enabled us to rapidly farm billions of these birds and mature them in just a few weeks for consumption. This quick turnover means that in 2016 alone, humans consumed almost 70 billion chickens globally. These huge numbers are also part of the reason why the biomass of humans and domesticated animals, combined, now outweighs that of all wild vertebrates on earth.
As well as this, the demand for chicken is growing faster than for any other type of meat. Considering the birds’ growing ubiquity, the University of Leicester-led researchers were curious about how our global appetite for chicken is shaping the planet–and what clues the mounds of chicken bones might leave behind for future archaeologists interested in humanity’s impact on the earth.
The researchers combined archaeological data with population estimates to understand how humanity’s relationship with chickens has changed over the ages. They showed that these birds were domesticated from the wild Red Jungle Fowl as far back as the 16th Century. But around the 1950s, the real changes began, with an intensive breeding program that created the bigger, meatier, heavier-boned chickens that are familiar to us today. This campaign was so successful that even just between 1957 and now, chickens have grown up to five times heavier than their ancestors 60 years ago. In fact, we’ve changed their morphology so much–favouring larger breast and leg muscles at the expense of smaller hearts and lungs–that few modern chickens could survive much longer than a few weeks after their slaughter.
An analysis of isotopes in chicken bones also revealed that from the mid-Century onwards, chickens were fed a diet that made them produce more meat–clear evidence of humanity’s ability to manipulate a species at a grand scale. As the researchers summarise: “Modern broiler chickens are morphologically, genetically and isotopically distinct from domestic chickens prior to the mid-twentieth century.”
These traits provide useful indicators of humanity’s ability to completely redirect the genetic course of a species–and through that, to alter the planet itself. Today, the production of feed for these ubiquitous birds produces more polluting nitrogen than the amount used to grow staple crops such as rice and wheat, the researchers found. And in Europe, for instance, it’s estimated that farming broiler chickens uses up more electricity and natural gas than the production of either beef or pork.
Together with the vast physical repositories of chicken bones spread across the planet in landfills, this provides compelling evidence that through chickens, humans have literally altered the face of the planet–helping to usher in the Anthropocene.
The researchers argue that just like plastic–now a hallmark of our irreversible impacts on the earth–similarly, we should see the chicken as a symbol of this new epoch. The fact that chicken bones can be preserved for a long time in the anaerobic conditions of landfills also means that one day far in the future, they could even provide way for archaeologists keen to understand how humans altered the face of the earth. “As the most numerous terrestrial vertebrate species on the planet, with a biology shaped by humans, modern chickens are a symbol of our changed biosphere.”
Source: Bennett et. al. “The broiler chicken as a signal of a human reconfigured biosphere.” Royal Society Open Science. 2018.