SWEDISH SAVANTS FIND DOMESTICATED CHICKENS HAVE SMALLER BRAINS

Researchers from Sweden’s Linköping University suggest a process by which the timid junglefowl from the rain forest could have become today's domesticated chicken. When the scientists selectively bred the junglefowl with least fear of humans for 10 generations, the offspring acquired smaller brains and found it easier to become accustomed to frightening but non-hazardous events. The results shed new light over how domestication may have changed animals so much in a relatively short time, ScienceDaily reported on August 27, 2020. 

Chickens are the most common birds on Earth. There are currently more than 20 billion individuals on the planet. All of them have come from the Red Junglefowl, originally found in Southeast Asia. This species was tamed and domesticated by humans approximately 10,000 years ago. The results of the current study show that when our ancestors selected the tamest individuals for breeding, they may at the same time have unconsciously selected birds with a different brain -- one that may have been more suitable for a life among humans. The findings are published in Royal Society Open Science.

Researchers Rebecca Katajamaa and Per Jensen started with a group of wild Red Junglefowl and selected as parents the birds that showed least fear of humans in a standard test. The breeding experiment was conducted for 10 generations. The birds that showed greatest fear of humans were placed into a second group. The researchers believe that they have in this way imitated the factor that must have been the most important during early domestication, namely that it was possible to tame the animals.

A somewhat unexpected result of the breeding was that the brains of the domesticated birds gradually became smaller relative to body size, which mirrors what has happened to modern domesticated chickens during the domestication process. The change was particularly pronounced in the brain stem, a primitive part of the brain that is involved in, among other things, certain stress reactions. The brain stem was relatively smaller in animals that were not overly timid. The scientists carried out two behavioral experiments, to determine whether the difference in brain size and composition affected the ability of the fowl to learn. One test investigated how rapidly the birds became accustomed to something that could be experienced as frightening, but which was actually non-hazardous, in this case a flashing light. The tame birds became accustomed and stopped reacting to the stimulus significantly more rapidly.