A team of researchers has proposed a new theory that could explain why domestic animals display characteristics that would have been mostly alien to their wild ancestors.

According to researchers, household pets tend to display a set of unique characteristics, such as floppier ears, patches of white fur and more juvenile faces with smaller jaws, something that Charles Darwin noticed about domesticated mammals more than 140 years ago. These diverse traits could be the result of a group of developing stem cells called the “neural crest,” which could be linked to the domestication of the animals, the researchers said in a new study, published in the journal Genetics.

“Because Darwin made his observations just as the science of genetics was beginning, the domestication syndrome is one of the oldest problems in the field,” Adam Wilkins, from the Humboldt University of Berlin and a co-author of the study, said in a statement. “So it was tremendously exciting when we realized that the neural crest hypothesis neatly ties together this hodge-podge of traits.”

According to the theory, which is yet to be tested, the hypothesis applies not only to mammals like dogs, pigs, horses, sheep and rabbits, but it may also explain similar changes in domesticated birds and fish.

Neural crest cells are formed near the developing spinal cord of vertebrate organisms in the early stages of life. As the organism matures, the cells migrate to different parts of the body and create many tissue types, including pigment cells and parts of the skull, jaws, teeth, ears and adrenal glands, the researchers said, adding that the neural crest cells also indirectly affect brain development.

According to the new hypothesis, domesticated mammals may show greater impairment in the development and migration of neural crest cells compared to their wild ancestors.

“When humans bred these animals for tameness, they may have inadvertently selected those with mild neural crest deficits, resulting in smaller or slow-maturing adrenal glands,” Wilkins said. “So, these animals were less fearful.”

In addition, neural crest deficits can also cause white patches in some areas of the skin, tooth anomalies and malformed ear cartilage, all of which are considered as “domestication syndrome” by the researchers.

"This interesting idea based in developmental biology brings us closer to solving a riddle that's been with us a long time. It provides a unifying hypothesis to test and brings valuable insight into the biology of domestication," says Mark Johnston, the editor-in-chief of Genetics, said in the statement.