Biology

How medieval Christian monks helped make the modern chicken

A new study suggests that Christian religious practices influenced the evolution of our modern chicken
A new study suggests that Christian religious practices influenced the evolution of our modern chicken
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A new study suggests that Christian religious practices influenced the evolution of our modern chicken
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A new study suggests that Christian religious practices influenced the evolution of our modern chicken

For about 6,000 years, humans and chickens have led an interconnected existence, with the latter serving the former a regular supply of nourishing meat and eggs. Evolving from an Asian species of red jungle fowl, our modern domesticated chicken is remarkably passive, can lay many eggs quickly, and has little fear of humans. But these traits were not always common in the animal, and a team of scientists has recently managed to pinpoint the time in history when chickens went through their major evolutionary shift.

The international research team built its study off previous discoveries that focused on a specific genetic variant that looked to be indicative of selective evolutionary pressures. The thyroid-stimulating hormone receptor (TSHR) is understood to be significant in enabling faster egg-laying and reduced aggression.

Archaeological records have long shown an increase in the volume of chicken bones from the 9th century CE onwards. The research team took these historical records and developed a new mathematical model to study chicken DNA. This approach allowed them to pinpoint when the TSHR variant in chickens started to appear with greater frequency.

Their study showed that from about 920 CE, selection on the TSHR variant began to notably appear. While virtually 100 percent of modern domesticated chickens display the TSHR variant, around 1,100 years ago only 40 percent of chickens were estimated to carry it.

It became clear to the researchers that between the 9th and 12th centuries, chickens underwent a dramatically fast evolutionary process developing traits that made them increasingly more useful and manageable to humans. Naturally, the researchers looked to understand the social and historical factors at play over that time to try to understand what was pushing this speedy evolutionary shift.

"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," says study author Anders Eriksson. "These dietary rules were adopted across Europe and applied to all segments of society around 1000 AD."

The team add that increased urbanization was a factor in the growing trend to consume chicken and eggs across that time period.

"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", says Greger Larson, who led the research team.

The research also fascinatingly highlights how brief social and cultural changes in human society can profoundly affect the natural and artificial pressures on domestic plants and animals.

The team's research was published in the journal Molecular Biology and Evolution.

Source: Oxford University Press via EurekAlert

6 comments
Robert Walther
Sooo, the evolution of chickens has been directed by humans. Doesn't that make our poultry GMO?
Douglas E Knapp
Robert Walther, no it does not. The DNA was not spliced with the DNA of another creature. The danger of GMO is not the change in the DNA as much as the change is a way that is harmful to the eater. For example some humans die when they eat peanuts. So lets say I take a farmed fish and splice in a peanut DNA and then feed it to everyone without testing or labeling. Then I am risking people's lives. Sadly this is the normal way it is done. The companies have had laws made so that labeling and testing are not rigorously done or even allowed in some cases. Could a problem crop up from just normal evolutionary changes? Sure, but it is not likely. The problem with GMO lies in the testing and disclosure, not so much the act itself.
Karmudjun
Mr. Walther - You may remove your tongue from your cheek. GMO as used by the world - and associated country's governing bodies that attempt to regulate such things - defines GMO as the organism altered by techniques of genetic engineering "so that its DNA contains one or more genes not normally found there." http://www.dictionary.com/browse/gmo If you will scan the article again, you will notice that estimates of 40% or the chickens prior to 920CE had the variant - ergo it is normally found in nearly 40% of the previously existing chickens. But funny insight, since the evolution of many creatures, plants, and even species has been due to genetic modification & evolutionary pressures that Darwin & others have studied. Are you pointing out the fallacy of human's labeling skills which usurp the evolutionary genetic modification process, a macro level "Mendelian pea study" type gmo by qualifing "GMO" as the above defined laboratory manipulation of the genome (in the micro-level of modification process).
Bruce H. Anderson
This was not so much evolution as it is adaption, and maybe not even that. The genes existed already. When someone has an obstreperous chicken they can be quickly be removed from the gene pool, eaten for dinner perhaps or left to wander among the coyotes. Thus the more cooperative chickens remain and are nurtured. No different than any other species, including us.
Koolski
Bruce is right. This isn't evolution. It's breeding for specific traits. We do it all the time with cattle, sheep, horses, dogs etc... as well as every crop grown purposefully. We "engineer" the outcome through controlling the breeding/pollenization process rather than directly manipulating DNA. Definitely not evolution because we are choosing the genetic the winners and losers.
Expanded Viewpoint
No, Robert, it does not. No one back then was using any restrictor nucleases to cut any DNA strands and then put them back together again like we have since the early 1980s. THAT is what makes an organism GMO. When the Russians took some wild foxes and bred them selectively in the 1940s, taking their wildness out of the genetic line for the fur trade advantages, after about 30 generations or so, they suddenly developed floppy ears and a spotted coat! That is FORCED genetic evolution, not natural selection. Same way with the Pluot, the result of many years of cross breeding two different species, the plum and the apricot. Ligers and Tions are both large cats, but no one went in and chemically altered any DNA strands.
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