About 8,000 years ago, Southeast Asian nomads began to breed the Banquiva Rooster, a tropical bird with bright plumage that still inhabits Southeast Asia’s forests and mangroves.
The descendants of these birds, the chickens, can be found on farms — and dinner plates — all over the world.
In his laboratory at Linköping University in Sweden, Per Jensen, a professor of ethology, is trying recreate this domestication process in record time.
When crossing Banquiva Roosters that show less fear of humans, in just 11 generations he noticed a notable difference.
His experiments also revealed how proximity to humans can have a dramatic effect on animal behavior.
“If you go into a henhouse of wild grouse, they try to escape and go to the back of the henhouse, flapping their wings in desperation,” says Jensen.
“The domesticated birds we raise come to you and peck at your shoes—they want to interact with humans.”
Banquiva Roosters have changed in other ways too.
They are more sociable with their packmates and tend to be more interested in exploring their surroundings. They are also larger in size, females lay larger eggs and have smaller brains than their wild cousins—differences that are also seen in chickens.
Humans have a long history of domesticating animals, a process that spanned thousands of years.
Charles Darwin was the first to note that domesticated animals, such as pet cats, dogs and rabbits, share certain characteristics in addition to “meekness”.
Pets tend to have droopy ears and more curled tails than their wild ancestors.
They also have smaller jaws and teeth, white patches on their fur, and breed more often.
This phenomenon is known as ‘domestication syndrome’.
The most famous example of domestication syndrome goes back to a 1959 experiment in which Soviet biologists Dmitri Belyaev and Lyudmila Trut took a few dozen wild silver foxes from a fur farm in Siberia and began selectively breeding the tamer animals. .
Incredibly, in just a few generations scientists have bred docile and friendly foxes.
And it wasn’t just their behavior that had changed; the foxes also looked different. They had shorter snouts, drooping ears, mottled spots, and curled tails that wag.
Although the reason for this is unknown, a popular theory is that when humans cross animals to domesticate, they may inadvertently select individuals with underdeveloped adrenal glands.
growth and reproduction
The adrenal or adrenal glands are responsible for the “fight or flight” response, so animals with smaller adrenal glands are less afraid.
The embryonic stem cells that form the adrenal glands also develop into pigment cells and parts of the skull, jaw, teeth and ears.
Therefore, the domestication syndrome may actually be an accidental side effect of crossing tame animals.
In the case of Jenson’s Banquiva Roosters, one of the biggest differences between wild and domesticated birds is the size of the brain stem, an ancient part of the brain involved in stress reactions.
“The brain is a very expensive organ, consuming 25% to 30% of mammalian energy,” says Jenson.
“If you select animals that grow faster and have a higher reproductive rate, you’re putting demands on the way these animals use energy. Chickens don’t have to deal with many complex issues that wild animals do, so they can use that energy to increase growth and reproduction.”
The domestication syndrome may also not be limited to just animals that humans have deliberately bred.
The mouse probably entered its first pantry 15,000 years ago, according to a study by Lior Weissbrod, a zoo-archeologist at the University of Haifa in Israel.
Weissbrod discovered rodent teeth in settlements left by the Natufian hunter-gatherer culture of the Eastern Mediterranean around this time.
Since then, the mouse has traveled to all corners of the world, making its home wherever humans live.
And there is evidence that living with humans for so long changed the mice’s own DNA.
Researcher Anja Guenther, from the Max Planck Institute, in Germany, gathered 150 specimens from three different subspecies of mice.
Each of the subspecies began to live with humans at different times in our evolutionary history.
Mus musculus domesticus started living with humans 12,000 to 15,000 years ago, M. musculus musculus has lived with us for 8,000 years, and M. musculus castaneus only recently started a relationship with us — about 3,000 to 5,000 years ago.
Guenther has bred mice for several generations in the laboratory. She took the descendants of the original rodents and experimented with them using seven different food puzzles.
Inside each puzzle was a mealworm, which the mouse could only catch by pushing or pulling a lid, extracting a paper ball from a tube, or opening the window of a Lego house.
Incredibly, mice whose ancestors had lived the longest with humans were the best at solving the food puzzles.
“It must be evolution on the scene because the animals we use have been kept in standard laboratory conditions over the generations,” says Guenther.
“The mice we tested had never lived with humans, but their ancestors did. Living close to humans altered the mice’s genetic makeup.”
Guenther believes that mice evolved to become better at solving problems because humans hid their food from them.
This battle of minds made the rats more cunning over time.
“It’s like an arms race. As we started hiding our food from them, they had to be more creative to find it.”
While living close to humans may have made some animals (such as mice) more intelligent, it may have had the opposite effect on the fruit fly, Drosophila melanogaster.
D. melanogaster probably first lived with humans at least 12,000 years ago, when, attracted by the smell of fruit, it flew into the caves of ancient peoples living in southern Africa.
The flies then followed us and our garbage around the world.
More than a century ago, these insects were chosen as genetic models to analyze both their short life and ease of reproduction.
Since then, D. melanogaster has become an indispensable laboratory model used to treat a wide variety of biological issues.
Among geneticists working with fruit flies, it is well known that laboratory strains are much less active than their wild cousins.
Catching a runaway fly that has been bred in the laboratory requires relatively little skill compared to catching a fly buzzing around a cup of Cabernet Sauvignon.
“Anyone who’s ever worked with laboratory flies knows that if one escapes the vial, it’s very easy to catch, just tap the head and it falls,” says Rob Kulathinal, an evolutionary geneticist at Temple University in Philadelphia, USA .
To find out if there was anything else going on, Kulathinal compared the genomes of wild drosophila and laboratory flies.
He not only confirmed that laboratory strains are significantly less active and interactive with other flies than their wild cousins, he also found evidence that, over the past 50-100 years, laboratory-dwelling flies have undergone rapid evolutionary changes.
Instead of finding changes in just one or two genes, Kulathinal found changes in an entire complement of genes, particularly those involved in the formation of new neurons in the brain.
These changes may contribute in some way to explain the different behavior of laboratory flies.
We don’t know why this happened, but Kulathinal has an interesting theory.
“In research labs, you have to transfer your flies to a different container every two weeks. When you turn the flies, the fast ones escape, and the donkeys remain. , instead of the fast ones that manage to escape.”
So what unites the dog, the chicken, the fox, the mouse and the fly?
Whether they chose it or not, each of them has become intimately connected with us.
By sharing our lives and rummaging through our remains, each of these species had to overcome their fear of humans to survive.
“When you start thinking about the early stages of domestication that go back thousands of years, the absolute first step must have been to reduce the fear of humans, as animals in fear cannot thrive and reproduce,” explains Per Jenson.
What our hunter-gatherer ancestors didn’t know is that a host of other changes would free ride on the journey of ‘domestication’.