Published in the journal Genetics*, this study focuses on a phenomenon known as “domestication syndrome”. For a long time, scientists have observed that many domesticated species have commonalities. In addition to being more docile, they often have drooping ears, a shorter muzzle, smaller teeth, white spots on their coat or even a more curved tail.
The researchers wanted to understand if all these traits could have a common origin. To do this, they relied on available knowledge in developmental biology, genetics and evolution. Their work is not based on a new experience, but on the analysis and reconciliation of numerous studies carried out on different species of domesticated mammals.
Their hypothesis concerns neural crest cells. Present in the embryo, these cells then migrate throughout the body to form several tissues. They participate in particular in the development of facial bones, ear cartilage, cells responsible for coat color, adrenal glands and part of the nervous system.
According to the authors of this study, when humans selected, generation after generation, the least fearful and least aggressive animals, this selection would also have modified the functioning of these cells.
Drooping ears in many dogs
Researchers believe that a slight decrease in the number or activity of neural crest cells could explain many of the characteristics seen in domestic animals.
In the case of the ears, these cells participate in the formation of cartilage. If their development is reduced a little, the cartilage becomes less rigid. The ears then have a greater tendency to droop, as is the case with many dog breeds. Conversely, the wolf retains erect ears, because it has not been subjected to this long selection for docility.
This same explanation could also shed light on other differences. The adrenal glands, which play an important role in the stress response, are also partly derived from neural crest cells. A slight reduction in their development could contribute to making animals less reactive to stressful situations. This corresponds precisely to the main criterion used by humans during domestication.
The authors also point out that variations in coat color could result from the same phenomenon. The cells that produce pigments also come from the neural crest. Less migration of these cells could lead to the appearance of white areas on the body, a common trait in several domestic species.
This theory thus offers a unique explanation to changes which until then seemed unrelated. It shows that behavioral selection can have consequences on many aspects of appearance.
The researchers nevertheless point out that not all species have exactly the same characteristics, and other genetic mechanisms are undoubtedly involved depending on the case.
* “The “Domestication Syndrome” in Mammals: A Unified Explanation Based on Neural Crest Cell Behavior and Genetics”, Adam S. Wilkins, Richard W. Wrangham, W Tecumseh Fitch, Genetics, 2014.