Domestication syndrome: what is it and how is it expressed in animals?

Droopy ears, short skull, peaceful behavior... characteristics associated with domestication.

Do you know why some animals, when living with humans, acquire certain distinctive characteristics, such as cats or dogs? This is explained by the domestication syndrome, a fundamental process in social evolution..

This phenomenon was originally studied by Charles Darwin, but recently, researchers Adam Wilkins, Richard Wrangham and W. Tecumseh Fitch, returned to study the phenomenon. Five years ago, in 2019, they published the results of their studies in the journal Genetics.

Let's learn what this phenomenon consists of and how it appeared in evolution.

Domestication syndrome and Charles Darwin's studies.

The domestication syndrome is considered one of the greatest mysteries of genetics. It is the process by which a species acquires certain morphological acquires certain morphological, physiological and behavioral characteristics as a result of prolonged interaction with humans..

More than 140 years ago, Charles Darwin began to study this phenomenon when he noticed that domestic animals shared a variety of peculiarities not found in wild animals, such as white spots on their fur, droopy ears, a short face, juvenile faces, a curved tail and smaller jaws. He also noted, when comparing the domesticated animals to their wild relatives, that they were more docile.

Despite Darwin's observations, it was difficult to explain why this pattern occurred.

Characteristics of the syndrome

British anthropologist and Harvard University researcher Richard Wrangham also speaks of this concept of domestication syndrome to refer to the fact that humans exhibit a number of Biological characteristics more typical of pets than of wild animals. One of these, for example, is the very low rate of face-to-face aggression that we manifest.

R. Wrangham states that we share with our pets and farm animals some of their characteristics.. These traits are unusual among wild animals and common among pets. In addition, Darwin states that humans did not choose their pets specifically for having these traits.

In addition, R. Wrangham states that our skeleton has many peculiarities characteristic of pets. In addition, according to him there are four characteristics that we have related to pets that wild animals do not have; a shorter face, smaller teeth, reduction of sexual differences with males becoming more feminine; and finally, a smaller brain.

In relation to the latter, it is worth mentioning that the natural evolution of the species has always been a trend towards a continuous increase of the brain; however, this trend has been reversed in the last 30,000 years. The domestication process began to develop about 300,000 years ago, and brain size only began to decrease at the end.

How did the domestication syndrome appear?

Still is not yet clear what biological mechanisms produce the domestication syndrome.But there is some evidence, for example, that many of the domestication traits are typical of young animals.

While some species have been domesticated by humans, others have been domesticated on their own, for example by reducing their aggressiveness, such as us humans.

R. Wrangham, together with Adams Wilkins (Humboldt University in Berlin) and Tecumseh Fitch (University of Vienna), proposed that these distinctive traits mentioned in the "domesticated" species arose from a group of embryonic stem cells, the neural crest.

The neural crest is a structure that forms in vertebrates near the spinal cord of the embryo.. As it develops, the cells migrate to different parts of the body, giving rise to different tissues such as parts of the skull, jaws, teeth and ears, as well as the adrenal glands that control the "fight or flight" reaction.

According to these researchers, domesticated mammals could present problems in the development of the neural crest. They argue that in breeding these animals, humans have probably been unconsciously selecting for those with neural crest alterations, with smaller adrenal glands and less fearful and more fearful behavior. behavior less fearful and more docile and prone to collaboration..

Consequences of a deficient neural crest

Some of the consequences of this deficient neural crest can be depigmentation of some areas of the skin, dental anomalies, malformations in the ear cartilage, and changes in the jaw. These alterations appear in the domestication syndrome.

Domesticated animals in nature

For example, we find among our closest relatives the bonobos. They are animals very similar to chimpanzees, but their skulls have characteristics of domestication (a shorter face, smaller teeth, a smaller brain and reduced differences between the sexes). They are also less aggressive, more peaceful.

R. Wrangham states that the bonobo females probably domesticated the malesbecause bonobos live in a habitat that allows females to travel together all the time, unlike chimpanzees. This has favored social alliances between females.

The case of humans

In the case of human beings, however, it cannot be affirmed that women "domesticated" or civilized men as well; it is true that there has been a lot of mythological tradition that held that power was in the hands of women, but currently there is no matriarchy anywhere in the world (in fact, the opposite system, patriarchy, still exists) and there is no evidence to support it either.

If women were not the ones who "tamed" men, we ask ourselves.... Who did? But this is all speculation, since the fossils do not tell us exactly what happened. According to the author, we should look at how hunters and gatherers today deal with people who behave aggressively.

In communities where there are no prisons, no military and no politics, they just find a way to defend themselves against the perpetrator. only one way to defend themselves against the determined perpetrator of the aggressive behavior: execution.. Thus, the killing is done by agreement among the other members of the society.

Today, it is known that without domestication, human societies would not have evolved and progressed in the same way.

Bibliographical references:

• Adam S. Wilkins, Richard W. Wrangham and W. Tecumseh Fitch. (2014). The "Domestication Syndrome" in Mammals: A Unified Explanation Based on Neural Crest Cell Behavior and Genetics. Genetics, 197(3), 795-808.
• Grolle, J. (2019). The Emergence of Homo Sapiens 'Those Who Obeyed the Rules Were Favored by Evolution'. Spiegel Online, interview with Richard Wrangham.