In a new experiment by scientists from Linköping University, a process suggests that junglefowl commonly found in the rainforests of Southeast Asia might become similar to domesticated chickens seen today.
Their experiment involved selectively breeding junglefowl by choosing those with the least fear of humans. After ten generations, the scientists discovered that the offspring have smaller brains compared to their ancestors.
The researchers believe that the change in the birds' brain sizes might have something to do with their change in behavior, such as becoming accustomed to frightening but non-hazardous events. Their new experiment may have shed a new light of understanding of how domestication may have influenced the changes found in animals within such a short time.
Domestication of Animals May Have Led Some of Them to Develop Smaller Brains
Breeding Selected Junglefowl More Suited for Life with Humans
For thousands of years, humans have learned to domesticate chickens. They can now be found in almost all continents of the world, making them the most common and perhaps most famous birds on the planet with a population of more than 20 billion and counting.
They all came from the Red Junglefowl, which were originally found in Southeast Asia. Approximately 10,000 years ago, humans started to tame and domesticate them.
Ancient humans have selected the tamest junglefowl for breeding, and perhaps at that time, they unknowingly selected those birds with different brains, one that may have been best suited to a life with humans, the researchers wrote in their findings published in Royal Society Open Science.
To test this, researchers Per Jensen and Rebecca Katajamaa bred a group of Red Junglefowl. They selected those that showed the least fear of humans and conducted the experiment until the 10th generation.
They assigned the offspring who showed the greatest fear of humans to the second group. In that way, they had imitated the most important factor when domestication started, proving that animals can be tamed.
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Difference in Brain Size of a Domesticated Chicken and Junglefowl
The researchers found that the offspring in their breeding experiment have relatively smaller brains, which mirrors what has happened to chicken during domestication.
Most specifically, the brain stem seems to be smaller in animals that are not overly timid. The brain stem is the primitive part of the brain responsible stress reactions and other important functions.
The scientists tested the animals in two behavioral tests to determine if the change in brain size has affected the animal's ability to learn. One of these tests investigated how the fowls would react to a frightening but non-hazardous event. They found that the birds became rapidly accustomed and stopped responding to the stimulus.
The researchers believe that this characteristic is beneficial for birds living with humans as a frightening but non-hazardous stimulus is a part of everyday life.
They also investigated if the birds differ in associative learning, which is if the birds differ in their ability to learn to associate two different objects. They found no differences at all.
But these differences in behavior that they found do not directly connect the difference in brain size. It is a matter that the researchers want to investigate further.
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