2019-07-22 00:42:26
Humans have greatly influenced the evolution of domesticated animals. Domestication has even caused a set of symptoms, called domestic animal syndrome, discovered by Charles Darwin himself, with similar characteristics in all species of domesticated animals. These include: docility, changes in coat color, smaller teeth, floppy ears, twisted tails, increased frequency of reproductive cycles, alteration in some neurotransmitters and levels of stress-related adrenal hormones, youthful behavior in age adult and smaller brains.
In no species is pet syndrome more evident than in dogs. Of course, the bond between humans and dogs is more intense than that which can be established with any other animal species, even, in some cases, with humans themselves. This loving and intensely emotional relationship began around 33,000 years ago, when the first wolves began to be domesticated.
While the domestication of farm animals resulted in the selection of the best specimens to be used in agricultural work (as “pata de obra”) or as a source of food, the domestication of dogs was not motivated by the same objectives. In this case, the behavior was selected. Animals with the greatest loyalty, courage, and intelligence were chosen over those without those qualities. Perhaps the most favored quality was the ability to understand human communication, both verbal and non-verbal. Dogs are far superior to other domesticated animals in this ability, including animals raised in contact with humans, closely related to us and highly intelligent, such as chimpanzees. The evolution of dogs in the company of humans managed to achieve a capacity to understand us at a level never achieved by any other species.
Recent studies have shown that eye contact, previously a sign of threat among wolves, became a fundamental part of the close and friendly interaction between dogs and humans. Eye contact is, in fact, a fundamental feature of human communication, and our eye has even evolved in a way that makes it easy for others to accurately identify where or what we are looking at. This is the reason why our eyes have a colored center, the iris, surrounded by the sclera, better known as “the white of the eye.” Eye contact helps them know if the communication is directed towards them, since it has been shown that dogs tend to ignore gestural signals when the eyes of humans are not visible to them.
muscle evolution
Dogs’ tendency to make eye contact with humans appears to be a genetically determined trait, as they seek to make eye contact very early in life and without receiving any particular training to trigger this behavior. The insistence with which dogs seek eye contact with humans is related to the intensity of the dog’s emotional attachment to a given person. This is undoubtedly a characteristic that has increased during the evolution of dogs, and that has probably been selected, consciously or unconsciously, by humans.
Even more surprising is the fact that the bond between dogs and humans appears to be physiologically related to the bond between mother and child, that is, it is based on similar biochemical mechanisms, in particular the hormone oxytocin is released in both species. Oxytocin is a hormone involved in the early bonding between mother and child and is also involved in the feeling of trust between adults. The release of oxytocin initiates a positive feedback loop, since high levels of this hormone stimulate the search for the gaze of the other, in whom we trust more and more.
All this indicates that, during the evolution of dogs, those that induced a more affectionate response from humans were preferentially selected to reproduce. It is possible that the selection was not conscious on our part, but simply motivated by the positive emotions provoked by some dogs, although not by others.
What characteristics of the dogs facilitated eye contact and triggered those emotions? Based on the study of human preferences on the expressions of dogs, it has been shown that humans prefer dogs with characteristics of very young animals. One particular feature that is very attractive to humans is the ability of dogs to raise their eyebrows intensely. This simulates the face of a baby and gives the impression that the dog is experiencing sadness or some kind of anguish, and triggers an emotional response in us.
Brow elevation is only possible thanks to the function of a specific muscle. For this reason, a group of scientists has studied the anatomy of the dog’s face and compared it to that of the wolf. They discover that the muscle that raises the eyebrows is very well developed in dogs, but has only sparse fibers in wolves. The only species of dog without this well-developed muscle is the Siberian husky, one of the oldest dog breeds.
When exposed to the presence of a human for two minutes, dogs raise their eyebrows more frequently and intensely than wolves. These findings suggest that dogs may have evolved their expressive eyebrows as a result of artificial selection by humans who experienced positive emotions triggered by dogs. These emotions cause, in most humans, affectionate behavior to feed them, protect them and give them a ride. Who is the real master?
References:
Juliane Kaminskia et al (2019). Evolution of facial muscle anatomy in dogs.
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