In search of the affectionate gene that turned some wolves into dogs

Some 14,000 years ago, a woman, a man, and a nine-month-old puppy were buried together near what is now the German city of Bonn. The archaeologists discovered that the animal was sick and suffered from ailments that it could only overcome with the care of humans. Around the same time, in the north of what is now Israel, a woman was buried, curled up, with one of her hands resting on the remains of a puppy of about four months, as if she were holding it.

These tombs are not only proof of the origins of the first domestication, that of dogs, but also of the ancient special connection between humanity and its “best friend”. A friendship that goes beyond a simple way of speaking and that some specialists dare to call love. In 2015, Japanese scientists showed that the more people looked into their dogs’ eyes, the more oxytocin production in their brains increased in both dogs. This hormone, a fundamental chemical ingredient of affection, is triggered between mother and child, comrades-in-arms and sexual partners.

Now, that same team of scientists, coordinated by Miho Nagasawa, from Azabu University (Japan), has taken another step in their search for the biological connection between sapiens and dogs. In a double experiment published in Scientific ReportsNagasawa and his team observed that the so-called ancient Japanese dog breeds – closer to the primitive wolf-dogs— had a lower ability to attend to human cues. Looking at the genetics of the more than 600 dogs involved in the study, they found a peculiarity in some of them related to the production of cortisol, a stress hormone.

Nagasawa assures by email that his results support the hypothesis that some wolves of those early settlements had genetic mutations that made them suffer less stress in contact with humans. And so the daily friction that ended in affection could begin. “Although it is not yet clear whether cortisol, a marker of stress, is actually lower in dogs than in wolves, it may provide clues as to how canine tolerance and the ability to easily adapt to human society were acquired,” he explains. the investigator.

Burial of a woman next to a puppy dog ​​found in northern Israel.
Burial of a woman next to a puppy dog ​​found in northern Israel.

This genetic predisposition of some wolves with little fear allowed them to approach humans and, as a consequence, they acquired the aptitudes that bind them to humans today. “Today’s dogs are less aggressive and fearful than wolves, and they have the ability to understand human gestures. As a next step, it is believed that humans and dogs have become more closely connected through humans’ use of this ability.”

That does not imply that there was a single genetic switch, be it stress or another, that caused the evolutionary jump. “I don’t think that’s possible,” says the researcher. “Domestication is a complex phenomenon that is the result of a combination of several factors.” For example, it is assumed that the way dogs were used as work animals, climate, culture, and other factors played a role in this selection. However, Nagasawa does believe in these stress-sensitive genetic mutations as a possible starting point for domestication: “In that sense, we believe that our results are important for understanding canine domestication.”

Other researchers do not see this work as robust, although it may fit into a plausible explanation. For example, the researcher Kathleen Morrill, from the University of Massachusetts (USA), considers that the ancient Japanese breeds are not an ideal of a primitive dog to suppose that they are more wolves than other dogs. Morrill, who has just published in Science a macro-study on the behavior and genetics of dog breeds, believes that the results of the study are limited by examining only a handful of genes to look for this correlation and not the entire genome: “There is always the possibility that the candidates are not the genes most relevant to the traits in question.

Many factors, many domestications

The CSIC researcher Carles Vilà believes that it would be very reasonable that these genes are involved in domestication, by facilitating coexistence due to this reduction in stress, but he assures that this study “is not conclusive” yet. “It is likely that there were some wolves that were genetically predisposed not to be so skittish, that approached human settlements. And surely these hormones are related, but work is needed.

Vilà, who has studied the genetics of those primitive dogs, does not believe that one can speak of a single genetic switch that would facilitate domestication. As he explains, it is not as simple as Mendel’s peas, which activated the green color or the rough texture: “We are too used to thinking of the gene that does this or that, but in general they are more complex characters”.

The CSIC researcher gives as an example another genetic adaptation of the first dogs: the ability to assimilate starch in their digestive systems, since they ate with humans or their leftovers. Another example: if puppies were born in the village, only those that showed greater docility when they reached adulthood could stay. One more: a study that found that a few cubs respond spontaneously when a person throws a ball at them; the gift to understand the intentions of humans is there, but only in some wolves. “I don’t think there is a single key, it’s a process that happened independently several times, in different ways, with a lot of mixing,” summarizes Vilà.

In any case, all these characters would imply that some Stone Age wolves had a natural inclination to make friends with those bipedal apes that spread over the world. As many specialists maintain, the dog was not domesticated, but rather some wolves domesticated themselves to become dogs. “Yes, it’s quite possible,” says Nagasawa, “self-domesticating may have made dogs more acceptable to humans.”

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