Among all domestic animal species, chickens have a special place in the history of human civilizations and on our dinner plates.
Chickens were domesticated from wild jungle fowl that lived in the forests of southeastern Asia and spread via trade routes into the Middle East, Europe and Africa. During the establishment of European colonies worldwide, chickens, along with other domestic animals, were introduced with settlers.
By weight, there are more chickens than all other bird species on Earth combined. As of 2016, there were more than 65 billion chickens slaughtered worldwide, representing more than 100 million tonnes of meat. Globally, chicken is the most commonly consumed meat.
In comparison, there are about 300 million each of turkeys and geese. As for wild birds, the second most common species is the globally invasive house sparrow. Even though people have spread this small bird worldwide and it readily adapts to life in cities, there are a comparatively meagre 500 million of them. If you’ve ever wondered about chickens and their eventual world domination, there is now scientific proof.
A study published in the journal Royal Society Open Science in November, sought to better understand how chickens have changed to assume this role in global animal domination. A team of researchers in the United Kingdom measured 486 chicken leg bones found in 74 excavation sites across London, and compared these to modern chickens and the wild guinea fowl relatives. The study, whose lead author is Carys Bennett of the University of Leicester in England, used these measurements to consider how chickens have changed over the years. The earliest chicken bone specimens used in the study dated back to the Roman occupation of London.
According to Richard Thomas, one of the researchers on the study who is investigating the archaeology of chickens, the idea arose from an informal chat with scientists who study geology.
One of the study’s most striking observations is that the leg bones of modern chickens are more than twice the size of their wild fowl counterparts. Modern chickens are capable of tremendously rapid growth — more than three times faster than jungle fowl.
The study also supports the idea that humans have had a huge influence on chickens by selecting for larger body size and faster growth. Changes to chicken bodies over the years were gradual until around the 1950s, when genetic selection for breast meat and rapid growth took off.
Today, modern broiler chickens go from hatching to slaughter weight in six weeks or less.
The study demonstrates how humans can bring about unprecedented change to the landscape, environment and animals.
As we have modernized chicken production with intensive agriculture production systems, the number of chickens has increased while the number of wild birds has decreased.
The authors point to other research that shows that the combined mass of humans and our domestic animals, including chickens, is greater than all wild vertebrates combined.
The authors emphasize that the sheer biomass of chickens compared to other species is unprecedented in history. They also build a case that chicken bones will be a key archeological marker of our current phase in geological history — deposits of chicken bones in landfills worldwide will be useful to distinguish our current times from those of earlier human history.
Every time you munch on a wing or drumstick, you are adding to the geological record, one that is increasing defined by the domestic chicken.
Dr. Jamie Rothenburger, DVM, MVetSc, PhD, DACVP, is a veterinarian who practices pathology and is an assistant professor at the University of Calgary’s Faculty of Veterinary Medicine.