The dubious winners of the agricultural revolution, by and large, are obvious. Living in the world today are 30 billion chickens, 1 billion cows and almost 800 million pigs.
While the dawn of agriculture was 8,000 to 10,000 years ago, in the last century or so humans’ relationship to farming and farm animals has changed dramatically.
Changes and challenges
“From the use of animals mainly for traction and small farming—chickens in the backyard and a few pigs in a pen—to industrial farming,” said Laurent Frantz, professor of paleogenomics. in animal science at the Ludwig Maximilian University of Munich, Germany.
Not only did the scale of agriculture change, the farm animals themselves changed dramatically. This morphing over time can sometimes be seen in their skeletons.
Now scientists are trying to better understand the process by sequencing ancient animal DNA—and from that learn how to make modern livestock stronger.
Domestication began when animals and plants began to adapt to living in environments altered by humans. Then humans began to selectively breed animals with particular traits that made them useful for humans.
These characteristics can be from a favorable size to a natural relationship with people. The process of domestication dramatically changed the appearance and behavior of animals, for example becoming more docile and tolerant of humans.
Some periods reveal visible physical changes such as the increase in livestock size during the Roman period.
Pigs and cattle generally became smaller over the next several centuries until the Black Death in the 1300s, when the animals began to grow again. While these changes are evident in the archaeological record, researchers are still investigating what may have caused them.
Frantz has long been fascinated by the history of domestication. He investigated livestock genetics over the past 3,000 years in the PALAEOFARM project.
Pigs are probably the only animal domesticated not once but twice—in the Middle East and in China, according to Frantz.
Gene pools
For millennia, pigs were largely allowed to roam, free-style, in Europe and interbreed with local wild boar. But in the 19th century, Chinese pigs were imported to Europe.
These pigs probably went through an earlier process of selection and domestication than in European countries and are more productive.
Cows are different. Their gene pool was smaller to begin with and it was less likely that humans bred cattle with their more formidable wild ancestor, the extinct auroch. The auroch bull usually stands 1.8 meters at the shoulder and has longer horns.
“Wild bovids are aggressive,” Frantz said. “People use cattle primarily for traction to pull a plow and are less inclined to breed them with wild aurochs.”
He collected ancient bones from archaeological digs and sequenced their genomes as part of PALAEOFARM, which runs for five years until August 2025.
Sites include the medieval city of Lübeck, once the capital of the Hanseatic League in modern-day Germany, and Viking and Anglo-Saxon settlements around the city of York in England.
Frantz compared this ancient genetic information with DNA sequences from modern breeds of cattle, pigs and chickens.
Pest control
He is especially interested in animal diseases. Mass burials of hundreds of cattle occurred in northern Europe in the 16th, 17th and 18th centuries. The cause was probably rinderpest, a viral disease derived from the German word meaning cattle plague.
Whenever a disease kills many pigs or cattle, some always survive. Frantz wants to understand the genetics of those who died and those who survived, as well as which bacteria or viruses caused the disease.
This knowledge helps in the treatment of modern animal diseases.
For example in Scotland, researchers have gene edited pigs to resist a deadly respiratory virus. Ancient DNA can provide insights into which parts of an animal’s DNA can be modified for disease resistance.
This is also a reason to preserve unique breeds of pigs and cattle because they can carry gene variations that provide resistance to certain diseases.
“With cattle, this is especially important for the future, for potential resistance to infectious disease and drought,” Frantz said.
Their small population size and intensive selection mean that there is generally less genetic variation in large animals such as cattle compared to small pets.
Playing chicken
The chicken probably evolved from the red junglefowl, which roamed the villages and towns of Southeast Asia along with rice farming.
The bird eventually arrived in Europe around 800 BC and was then bred by the Romans.
Farmyards in the late 19th and early 20th centuries must have echoed with the calls of bright birds with a body that still resembled the more slender birds of the forest.
In contrast, today’s birds are lumpy. Breeding over the past 70 years has changed the bird for factory farming.
“Chickens grow three times faster than 50 years ago,” said Frantz.
Wild birds are more colorful and smaller, according to Ophelie Lebrasseur, a zooarchaeologist at the Center for Anthropobiology and Genomics in Toulouse, France.
Keenly interested in the history of chickens, he traced the introduction of chickens to Europe and studied their evolution into modern times.
Now Lebrasseur continues their angry roots in South America with the ARAUCANA project, which ended this September after two and a half years.
“It appears that, today, South America is a melting pot of European, Polynesian and Asian chickens,” he said.
Puzzle of South America
However, how and when chickens first arrived on the South American continent remains a puzzle.
In the late 15th century, Christopher Columbus brought chickens there, “but they were all eaten because of hunger,” Lebrasseur said.
Europeans brought chickens back to South America in the 16th century, but it is uncertain whether Polynesian chickens arrived first.
Lebrasseur sequenced ancient DNA from chicken bones found at archaeological sites in South America, particularly in Argentina. He hopes to find a trace of DNA that tells him where their ancestors came from.
Lebrasseur is also interested in backyard chickens in South America and the possibility that some are better adapted to their local environment.
“In Europe we don’t have these backyard chickens that you find in some countries in Africa and South America,” he said.
Chicken virus
Today, farmers choose modern productive chicken breeds, but this reduces their diversity and makes them susceptible to disease.
One solution is to introduce genes from traditional breeds, especially those potentially useful in fighting a disease.
Frantz was particularly interested in Marek’s disease, a fatal condition caused by a highly contagious herpes virus. Affected birds suffer from enlarged veins and tumors.
“The industrial production of chickens plays a role in the evolution of the virus,” he said.
His research revealed older strains of the virus that were less lethal and, importantly, chicken genes that provided defense against the virus.
“Maybe we can develop new ways to fight this modern disease or maybe improve vaccines,” Frantz said.
Provided by Horizon: The EU Research & Innovation Magazine
Citation: Ancient chickens, cows and pigs may hold secret to modern animal diseases (2023, June 29) retrieved on July 4, 2023 from https://phys.org/news/2023-06-ancient-chickens -cows-pigs-secrets.html
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