Why did we tame dogs?

Canine evolution : The wolf was tamed only once

"Analyzing prehistoric DNA that has been damaged by centuries of storage in the ground is really very difficult and takes weeks and months," sighs Amelie Scheu from the University of Mainz. Nevertheless, the paleogeneticist managed to elicit information about the evolution of the four-legged friend from around 7000 and 5000 year old canine genes. Their results now speak against the previous assumption that humans tamed the wolf several times.

The oldest dog bones come from Germany

The oldest, clearly identified remains of a prehistoric dog can be found in Germany: 14700 years as if the jawbone of a Canis lupus familiaris, the domestic dog that was excavated near Bonn-Oberkassel. Scheu examined a dog's skull that came from the cherry tree cave in the Franconian Alb. “It probably belonged to a peat dog, a prehistoric breed that resembles today's Spitz,” says Scheu. What the dog looked like, for which the bone remains from an excavation site near Herxheim, is unknown: “We only have a tiny piece and at first thought it was a sheep or a goat.” Only DNA analysis showed that the splinter was belonged to a dog. A stroke of luck, because the researchers were able to shed light on an important epoch in the development of the pet dog with the 7,000-year-old, early Stone Age Herxheim dog and the late Stone Age, 4700-year-old skull from the cherry tree cave.

So far, researchers have assumed that there was an exchange of dog populations in Europe between the Neolithic and today. Before this event, there were mainly dogs with a type C genome in the mitochondria, the energy-supplying cell organelles. However, these animals have been displaced by type A dogs, so that today there are only ten percent of type C dogs. That spoke in favor of domestication of the dog at least twice - the A-dogs must have come from somewhere.

Wild animals can rarely be tamed

"We find no evidence of a large population exchange," contradict the Mainz researchers, who among others worked with colleagues from Stony Brook University in New York, now in the journal "Nature Communications". “Rather, our results are in line with a scenario in which the modern European dogs emerged from a Neolithic population.” Both the Early Stone Age Herxheim dog and the Late Stone Age from the Kirschbaumhöhle belonged to genetic type C. No trace of a population exchange. "But our study is certainly not the ultimate answer," admits Scheu. More recent finds could change the picture of the evolution of the dog if, for example, remains of old, hitherto unknown dog breeds are found. “Domestication is a complex process that doesn't just happen all the time.” Getting a wild animal used to humans is rather rare. The most economical explanation is that there was only one domestication event. "Our data speak for it."

Shy cannot say where the wolf became a pet. "The 5000 to 7000 year old dogs that we analyzed are very similar to modern Europeans and are probably their direct ancestors," says Scheu. Whether the original domestication event also took place in Europe or even in Germany is uncertain as it was much further back - between 20,000 and 40,000 years ago. "We don't name a place for a good reason: we don't know it."

Strays occasionally mated with wolves

How difficult it is to reconstruct the evolution of dogs was shown by the analysis of 18 genome regions that differ particularly between wolf and dog and where the gene mutations that made the dog tamer are apparently. However, in the 7000 year old Herxheim dog, 17 of these 18 gene regions are typical for dogs. The "more modern" dog from the cherry tree cave, last barking 4700 years ago, had wolf-typical variants in six of these gene regions. That is not a contradiction in terms, says Scheu. “Perhaps this dog has more wolf-like gene variants, because shortly beforehand there has been a mixing with a wild wolf population in its ancestral line.” It is not unlikely that one or the other stray also hooked up with wolves.

Nevertheless - in the end dogs emerged that even adapted to the diet of humans. In the genome of today's dogs, those genes have been multiplied that enable a better digestion of starch - precisely the carbohydrate-rich diet that sedentary and agriculturally active humans relied on in the Neolithic Age. It was therefore assumed that gene replication in dogs took place during this time, as the animals were dependent on the more and more starchy food of humans. “But we cannot confirm that,” says Scheu. It could be a coincidence that the examined dogs were not genetically adjusted to the new diet. "But it is more likely that these gene duplications took place later."

And then the dog tamed the man

The knowledge about domestication of dogs could also be helpful for today's breeding programs, says the researcher: "If we collect information about dogs from this time, then we learn which genes were lost in the course of breeding or which genetic changes are disadvantageous."

There are many hereditary diseases that breeders have unwittingly dragged along over the centuries when choosing animals with certain traits. "If we know the genetic structure of the dogs of origin, we can see which variants are advantageous or which original genetic condition we have to restore in the interests of the dogs' health." The three examined dog genomes are just the beginning.

Is it then perhaps also possible to understand how the dog changed people and “tamed” them for their own purposes? “Yes, why not,” says Scheu and laughs. “It is entirely possible that humans - for example their immune systems due to living with dogs and other pets - have changed. Perhaps we should research that too in the future. "

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