For the past six thousand years, humans and chicken have shared an intricate common existence. Today’s chickens provide us with plentiful meat and eggs and are the most common form of poultry consumed across the world.
Our current cultivated chickens descended from an ancestral species of Asian jungle fowl, bred to be very passive with little fear of humans and an ability to lay many eggs quickly. However, chickens were not always the easy-going birds they are today. If you can’t get enough of chicken or eggs, you should probably thank medieval Catholic monks.
Archaeologists have long noted an increase in the fossil record of chicken bones from the 9th century AD onward. A team of researchers from Oxford University set out to find the cause of this increase in the archaeological record. They first wanted to identify the difference between today’s modern chicken and the birds of yesteryear. In doing so, they identified the thyroid-stimulating hormone receptor gene, or TSHR gene for short, that is one of the primary causes of reduced aggression and increased egg-laying ability.
While nearly 100% of chicken’s today carry this gene, 1100 years ago less than half carried it. To figure out what caused this sudden dramatic shift, they looked at the years with an increase in chicken bones to identify what pressures selected for chickens with the TSHR gene.
In their study, they directly linked Catholic fasting practices of Benedictine Monks to the domestication of chickens, because during a fast meat from four-legged animals was not allowed while chicken was exempted from this rule. One author of the study, Anders Eriksson says:
“This significant intensification of chicken and egg production has been linked to Christian fasting practices, originating with the Benedictine Monastic Order, which disallowed the consumption of meat from four-legged animals during fasting periods, but the restrictions did not extend to birds or eggs. These dietary rules were adopted across Europe and applied to all segments of society around 1000 AD.”
Because Benedictine monks were allowed to consume chicken during their fasts, selective pressures on chickens who were easy to breed and not aggressive to humans rapidly caused them to shift towards carrying the TSHR gene. As the TSHR gene become predominant, the modern chicken of today appeared and the billions of people around the globe have monks to thank for it.