Why Don't Wild Animals Have Floppy Ears and Curly Tails?

Domesticated Animals

Story at-a-glance

  • Domestication syndrome describes a group of distinctive genetic traits seen in domesticated animals, but not in their wild counterparts
  • Scientists have long wondered why domesticated animals have similar features and behaviors. Recently, a team of researchers discovered that the process of domestication seems to lead to genetic changes that affect a group of embryonic stem cells called the neural crest
  • Neural crest cells create a variety of tissue types, including pigment cells, parts of the head, and the adrenal glands. They are also indirectly involved in brain development
  • The researchers believe that when certain species were bred by humans for tameness, individuals with mild neural crest deficits were selected, resulting in smaller or slow-maturing adrenal glands, as well as certain physical abnormalities

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:

(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.”