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Domestication Syndrome

Domestication Syndrome Photo Credit: Clipart.com

A new hypothesis ties domestication in mammals to “cute” physical features.


Transcript

Domestic mammal syndrome. I’m Bob Hirshon and this is Science Update.

Domesticated animals, including dogs and rabbits, may have a developmental deficit that makes them both tame and cute. This according to Adam Wilkins, an evolutionary biologist at Humboldt University in Berlin. He notes that researchers going back to Darwin have noticed that domesticated animals are not only friendlier and less fearful, but have distinctive features, too:

Wilkins:
Smaller jaws, hence rounder faces; smaller teeth as part of that; floppy ears; and pigmentation changes, with either white or brown patches on the fur coats.

He and his colleagues report that all these traits can be linked to neural crest cells. Those are stem cells that form near the spinal cord and migrate to other parts of a developing animal. They suggest this process may be stunted in domesticated animals, resulting in traits that humans find appealing. I’m Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

Over 140 years ago, none other than Charles Darwin himself noticed that domesticated animals looked different from their wild counterparts, and in consistent ways. For example, compare domesticated dogs and their wild cousins like wolves and coyotes. Although domesticated dogs vary a lot in appearance, in general, they're more likely to have rounder faces, smaller jaws, floppier ears, and patchy fur than wild canines. Those are all characteristics of animals we describe as “cute.” 

It may be no coincidence that animals that have been bred to be friendlier, more loyal, and more cooperative with humans may also look more adorable. According to Wilkin's hypothesis, all these traits can be traced back to the development of neural crest cells. Neural crest cells are a type of stem cell, a general term for cells that can develop into other, more specific cell types.

During the embryonic development of all vertebrates (animals with backbones), neural crest cells first form near the spinal cord and then migrate to different parts of the body. In researching the fate of neural crest cells, Wilkins found that they influence most of the behaviors and physical features we associate with domestication. Wilkins proposes that domesticated animals have been bred (unknowingly, of course) so that their neural crest cell development is actually impaired.

For example, neural crest cells eventually form part of the adrenal glands. Adrenal glands produce a hormone adrenaline (also known as epinephrine), a central driver of the body's “fight-or-flight” response. Underdeveloped adrenal glands may explain the muted levels of fear and aggression found in domesticated animals. Neural crest cells also affect the animal's forebrain development, and a smaller forebrain in turn may lead to a smaller skull size.

Neural crest cells also directly affect the physical features we associate with domestication, including pigmentation (skin and fur color) as well as ear, tooth, and jaw development. Spotty pigmentation can result in white patches; underdeveloped ear cartilage can make ears more floppy; smaller teeth and jaws create an animal with a rounder, more appealing face (not to mention a less dangerous bite).

Although Wilkins' hypothesis is built on many separate pieces of scientific evidence, it would take further research to actually prove that the development or underdevelopment of neural crest cells directly affects these “domesticated” qualities in individual animals. Still, it's a significant step toward answering a question first posed by the founder of modern evolutionary biology—and understanding the nature of our closest animal companions.

Now try and answer these questions:

  1. What are the behaviors and physical features associated with domestication in mammals?
  2. What does Wilkins suggest as an underlying influence on those features?
  3. Why does Wilkins point to the infuence you named in your answer to #2? Give specific examples of how this may create animals that look and act domesticated.

You may want to check out these related resources:

The Science Update Ancient Cat History documents evidence of human-cat interactions over 5,000 years ago.

The Science Update Dog Breeds answers a question about whether cross-breeding dog types has its limits.


Going Further


For Educators

The Science Update lesson Ancient Cat History documents evidence of human-cat interactions over 5,000 years ago.

The Science Update Dog Breeds answers a question about whether cross-breeding dog types has its limits.


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