By Dr. Becker
Have you ever heard of “domestication syndrome?” If not, picture a wolf, and then picture a dog with floppy ears, a sweet little patch of white fur, and a baby (puppy) face.
According to a study published last year in the journal Genetics, domestication syndrome is a term Charles Darwin coined to describe his discovery that “domesticated mammals possess a distinctive and unusual suite of heritable traits not seen in their wild progenitors.”1
And domestication syndrome isn’t seen exclusively in mammals like dogs, rabbits, foxes, pigs, horses, or sheep. It has also been observed in domesticated birds and even fish.
Domestication Leads to Genetic Changes
Scientists, including Darwin, have long been puzzled by why domesticated animals have many similar features and behaviors. These include:
Depigmentation
(white patches, brown regions)Floppy ears Smaller ears Shorter muzzles Smaller teeth Docile behavior Smaller brain or cranial capacity More frequent estrous cycles Juvenile behavior Curly tails According to the authors of the Genetics study, when certain species are domesticated with the goal of taming them, it leads to genetic changes that affect a group of embryonic stem cells called the neural crest.
Neural crest cells form near the spinal cord of early vertebrate embryos. As the embryo develops, the cells travel to other locations in the body and create different tissue types, including pigment cells, parts of the head (skull, jaws, teeth, ears), and the adrenal glands, which are responsible for the fight-or-flight response. Neural crest cells are also indirectly involved in the development of the brain.
Lack of Fear of Humans Had Its Start as a Cell Abnormality
According to co-author Adam Wilkins of Berlin’s Humboldt University:
“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. So, these animals were less fearful.”
The neural crest abnormalities Wilkins speaks of could also lead to physical signs of tameness – and not all of them good. For example, floppy ears are an appealing feature on dogs and rabbits, but unfortunately, they’re actually the result of deformed ear cartilage. Animals with ears flopped over and hanging alongside their faces presumably don’t hear as well as those with erect ears.
Domesticated animals also appear to have smaller brains than their counterparts in the wild. The decreased size of the forebrain seen in most domestic animals could be indirectly related to neural crest changes.
According to Wilkins, “Animal domestication was a crucial step in the development of human civilizations. Without these animals, it’s hard to imagine that human societies would have thrived in the way they have.”