The humble chicken has had a hell of a journey. After being domesticated from jungle fowl in Southeast Asia some 6,000 years ago for cockfighting, they went on to become egg providers and religious oracles for numerous cultures across the world. They even accompanied Roman armies into war because they were thought to be such good fortune tellers.
Somewhere along the line, they became the modern-day chicken we all know, love, grow in factory farms, and put in a bargain bucket.
New DNA evidence gathered from nearly 100 ancient chicken bones, and published in the journal Molecular Biology and Evolution, suggests that the genetics of the chicken underwent a considerable change in the High Middle Ages around 1000 CE. This shift also coincided with increasing urbanization and some unique Catholic fasting practices across Northern Europe.
Genetic variants in two genes are believed to “make” the modern chicken. Firstly, TSHR is a gene thought to lead to a loss of seasonal reproduction in many domestic animals. This also tends to make birds lay more eggs year round, be less aggressive, and friendlier to people. The other, BCD02, affects skin pigmentation in birds.
The red jungle fowl, aka the Thai chicken, the wild ancestors of all domestic chickens. mooninblack/Shutterstock
Using a new form of genetic mathematical modeling, the researchers discovered that selection of the TSHR gene began to boom around 920 CE. As archeological evidence has shown, this was also a time when chicken consumption intensified across Europe.
"With our new method we see that the time of selection coincides with an increase in the amount of chicken bones in the archaeological records across Northern Europe," study author Anders Eriksson explained in a statement.
“Intriguingly, they also coincide with several socio-cultural changes, including a general increase in the popularity of Christian beliefs, new religious dietary rules and increase in urbanization (favoring traits that mean that animals could be kept in small spaces)."
Along with this, a monastery of Benedictine monks around 1000 CE propagated fasting practices that banned eating four-legged animals during certain days. This obviously didn’t include the chicken. This period, therefore, witnessed an intense rise in poultry farming, complete with these selection pressures for genes that meant productive and friendly chickens.
"We tend to discount how selection pressures on domestic plants and animals varied through time in response to different preferences or ecological factors," said author Greger Larson. "This study demonstrates just how easy it is to drive a trait to a high frequency in an evolutionary blink of an eye, and suggests that simply because a domestic trait is ubiquitous, it may not have been a target for selection at the very beginning of the domestication process."