The domestication syndrome is a key aspect of social evolution. It explains why some animals that live with humans acquire unique characteristics, such as those seen in dogs and cats. Let's dive into this syndrome.
What is the domestication syndrome?
The domestication syndrome is a process by which a species develops certain physiological, morphological, and behavioral traits as a result of prolonged interaction with humans.
This syndrome is one of the biggest puzzles in genetics. Charles Darwin started studying this phenomenon over 140 years ago when he noticed that domestic animals have certain characteristics that wild animals don't. For example, lop ears, docility, curved tails, short, baby-like faces, and smaller jaws.
Why does the domestication syndrome arise?It is not completely clear what biological mechanisms produce the domestication syndrome, but there is some evidence. For example, that many domestication traits are common in young animals.
But when talking about domestication, we are not only referring to what are now our pets. We can also talk about the human being himself, as while some species have been domesticated by us, others have domesticated themselves, such as humans. For example, by reducing our aggression.
Adams Wilkins, R. Wrangham, and Tecumseh Fitch, proposed that the most distinctive traits of the most domesticated species arose from a group of embryonic stem cells: the neural crest.
But before seeing exactly what the neural crest has to do with the domestication syndrome, let's see what those distinctive traits are:
- Lower rate of aggression compared to that of wild animals.
- Short face.
- Smaller teeth.
- Smaller brain.
- Reduction of sexual differences.
Now let's see what the neural crest is and how it influences this syndrome.
What is the neural crest?
The neural crest is a structure that forms in vertebrates, near the spinal cord of each embryo.
As the embryo develops, the cells spread to different parts of the body, giving rise to various tissues, such as jaws, ears, teeth or different parts of the skull, but also to the adrenal glands. These are the ones that control the fight or flight reactions.
According to experts, domesticated mammals could present some problems in the development of the neural crest. They have determined that when breeding these animals, humans have probably been unconsciously selecting those with alterations in the neural crest.
Specifically, those with smaller adrenal glands and, therefore, a more docile and less fearful behavior.
In addition, other consequences of the deficient neural crest would be:
- Dental abnormalities.
- Changes in the jaw.
- Malformations in the ear cartilage.
- Depigmentation of some areas in the skin.
But, how does the domestication syndrome occur? A Spanish study was able to answer this question.
How does the domestication syndrome occur?
Researchers from the Institute of Marine Sciences of the Barcelona Higher Council for Scientific Research, Francescs Piferrer and Dafni Anastasiadi, confirmed the neural crest hypothesis and were able to describe the mechanism behind the syndrome's development.
Piferrer and Anastasiadi compared wild sea bass with farmed ones in the early stages of domestication and found that the syndrome occurs through epigenetic changes in the DNA methylation of genes related to early development, specifically from the neural crest.
What is methylation?
Methylation is an epigenetic mechanism where a wild and a domestic animal can have genes with the same genetic sequences, but environmental factors can cause changes in DNA methylation, modifying the way genes are expressed and, in turn, the phenotype.
The researchers found that changes in DNA methylation during embryonic development persist into adulthood and affect genes whose expression is altered, leading to phenotypes associated with the domestication syndrome, such as pigmentation changes or jaw deformities.
Since DNA methylation increases the chances of mutation, the results suggest that after several generations, these epigenetic changes may become integrated into the genome. The experts also found that many of the genes that present these modifications coincide with the same variants in domestic mammals and birds, such as dogs, rabbits, cats, horses, and ducks, among others.