Domestication of Dogs: The Complex History of Man’s Best Friend
by Dr. Marty Pets Team | Jun 26, 2018 | 0 comments
You probably haven’t given a lot of thought to the domestication of dogs. You just want your fur baby to be as healthy and happy as possible. But haven’t you ever wondered how your sweet dog got that way when his ancestors were definitely not?
A lot of brilliant scientists have devoted years to investigating the history of dogs. This is a complex area of study, and researchers haven’t yet agreed just how the domestic dog came to be.
In a nutshell, it’s complicated. There are a lot of different theories regarding the history of dogs. That just goes to show how very hard it is to determine exactly when and where dogs became domesticated.
Difficult to Pin Down
Researchers believe that the domestication of dogs occurred in two places – western Eurasia and eastern Eurasia – sometime between about 6,000 and 14,000 years ago. “Eurasia,” FYI, is the term given to a massive area of land that encompasses the continents of Europe and Asia.
According to the researchers, humans in both the eastern and western portions of Eurasia first domesticated grey wolves.
Over time, some of the dogs in the east went west with humans. More than 90 percent of today’s breeds, the researchers say, evolved from the eastern Eurasian dogs. Fewer than 10 percent come from the western dogs, which eventually became extinct.
One of the driving forces behind the researchers’ hypothesis was the finding of a canine bone located near a 4,800-year-old monument in Ireland. This specific bone was a fossilized petrous bone, located just behind the ear.
The Eurasian wolf
What made this find so important is that the petrous bone is an especially good source of DNA. The DNA of most fossilized bones is filled with contaminated microbes. Only a small portion comes from the original “owner.” The petrous bone, however, is filled with as much as 80 percent original DNA.
The researchers were able to compare the DNA of the Irish bone with that of nearly 700 present-day dogs. They were able to build a connection between the ancient and modern dogs. It was through this connection that they determined there were two main groups of ancient, domesticated dogs.1
Differing Point of View on Domestication of Dogs
Another study, however, paints a distinctly different picture of how dogs became domesticated. The scientists who produced this 2017 study believe that the domestication of dogs only occurred once, anywhere from 20,000 to 40,000 years ago.
They studied dog fossils found in Germany that were between 4,700 – 7,000 years old. They also analyzed the same bone found in Ireland used in the 2016 study. They compared their findings with genetic data from nearly 6,000 modern-day wolves and dogs.
Based on these findings, the researchers believe there was some sort of genetic split which occurred between dogs and wolves.
This split, they say, occurred between about 37,000 – 41,500 years ago. They agree there was an eastern and western Eurasian divergence among ancient canines, but that it happened anywhere from about 18,000 to 24,000 years ago – far earlier than the researchers in the 2016 study believe. They say domestication happened once – in one area of Eurasia – and then, the ancient dogs went their separate ways as they followed the migration of the humans they bonded with.2
But What About the How?
While the studies are interesting in that they address where and when the dog that eventually became a beloved pet come from, they don’t explore just how man and dog became so closely intertwined.
This is another case where there is no set-in-stone answer. Rather, there are only theories.
· The Prey Model
There are three general ways in which humans domesticate an animal.3 The first is known as the “prey” model. This is where humans will typically hunt an animal, yet, in some cases will keep it instead of killing it. Some people, for instance, will keep pigs, chickens, and cows on a farm for purposes other than eating them.
· Directed Domestication
The second form of domestication is known as “directed” domestication. This is when an animal is used for a certain purpose. The perfect example is the horse, which was first taken from the wild for transportation and then bred.
· Commensal Domestication
The last type is “commensal” domestication. In commensal domestication, humans unintentionally provide an environment that first attracts an animal and then benefits it.
Over time, humans, in turn, also receive a benefit. The animal gradually becomes separated completely from the wild. Cats, for example, were believed to start bonding with humans when agriculture first began. Humans would store grain, which would attract rodents. The cats were then attracted to the rodents.
The relationship between dogs and humans, some researchers believe, grew from something that wolves and man had in common – a taste for reindeer meat. There is evidence that suggests that both hunted reindeer in Siberia during the Neanderthal Era (estimated to be from 40,000 – 400,000 years ago).4
Wolf packs and humans alike would follow herds, with the humans viewing the wolves as being a type of ‘food source scout’, so to speak. The wolves would kill the weaker reindeer, such as those that were sick, or old. This, as a result, helped strengthen the reindeer herds. And eliminating the weak and sick reindeer would also help keep away animals from harming humans, such as bears and hyenas.5
It’s ironic that sheepherders today will often use dogs to guard their herds against wolf attacks.
Another theory holds that ancient man trapped wolf pups and adopted, fed, and trained them, leading to dog domestication. But some researchers believe that as dogs gradually evolved from wolves, they just naturally had an attraction for man.
A characteristic known as “flight distance” was critical to our modern-day relationship with dogs. Flight distance is the distance that an animal will allow a human (or other perceived danger) to approach before fleeing. The shorter the flight distance, the longer an animal will linger. As the years went by, dogs became more and more comfortable with the presence of a human.6
Important Clues to Dog Evolution
So where did today’s modern dog breeds come from? How did we get collies, German shepherds, terriers, and the other wonderful breeds that became our beloved pets? There’s a theory for that as well.
Even though the history of dogs stretches back for thousands of years, most of the common dog breeds we’re familiar with today have only been around for about 250 years or so.7 One theory regarding how many of these breeds came about is fascinating.
Just about all dog breeds, according to one study, can be traced to 23 groups of dogs known as “clades.”8 A clade is a group of beings (dogs, humans, insects, etc.) that share a common ancestor, as well as the descendants of that ancestor.9
The majority of these clades first appeared in Europe and Asia, but there were a few that originated in what is known as North America.
These include the Peruvian hairless dog and Xoloitzcuintle (both hairless breeds), which came from what is known as the “New World Dog.” This breed, which eventually went extinct, is thought to have accompanied the ancestors of Native Americans as they crossed the Bering Land Bridge.10 This bridge, archaeologists believe, once connected North America with Asia.11
According to the study, each clade involved dogs that had similar characteristics.
One clade, for example, included dogs that were mainly bred for strength. These include the bulldog, boxer, and terrier. Collies, corgis, and sheepdogs fall into another clade, because they are herding dogs. Hunters, such as spaniels, setters, and retrievers, are grouped into another clade. These clades were then subdivided into more specific breeds, such as the Welsh corgi, English springer spaniel, or golden retriever.
The study also suggests that some breeds were used in order to create others. The pug, for example, which originally came from China, was used in Europe in the 16th century to make other dog breeds smaller.
Study Holds Important Health Ramifications for Dogs
But the results of the study aren’t just interesting. They may also help alert to certain genetic health issues so that veterinarians can warn pet owners.
It has been long known, for example, that certain herding breeds (such as Border Collies and Australian sheepdogs) are more prone to an eye disease known as collie eye anomaly (CEA). This condition leads to a weakened retina that can easily detach and lead to blindness.12
However, CEA also affects a breed known as the Nova Scotia Duck Tolling Retriever, a breed that had not been genetically associated with herders until the study. The study researchers found that the Nova Scotia breed’s genetic map includes a previously undocumented sheepdog or collie ancestor. This ancestor is the source of the CEA issue.
The results could also help researchers do a faster job of identifying which dog breeds could serve as models studying health problems in humans, such as kidney issues, diseases linked to high blood sugar levels, and more.
Wrapping it Up
The history of how dogs might’ve become domesticated is rich and complex. Even though there’s still not a consensus on what, exactly, led to the pet who’s very likely sleeping on your couch at this moment, the different theories paint an extremely interesting picture.
But whatever the actual answer may be regarding dog evolution and dog domestication, pet lovers are incredibly happy that it happened.
Sources:
1.https://www.ncbi.nlm.nih.gov/pubmed/27257259
2.https://www.nature.com/articles/ncomms16082
3.http://discovermagazine.com/2016/dec/the-origins-of-dogs
4.http://humanorigins.si.edu/evidence/human-fossils/species/homo-neanderthalensis
5.http://api.ning.com/files/6tMSoMz0FDA2xek2pzJH3bb2dUp-qGNa0Dw0Vk9xPj1pTllU8HED-kGChB*5z0h5dZs1HxPe0QuzI9vG91qfbr7SrUdxOkDn/2003_Coevolution_Wolfgang_Schleidt.pdf
6.http://www.pbs.org/wnet/nature/dogs-that-changed-the-world-what-caused-the-domestication-of-wolves/1276
7.http://www.sciencemag.org/news/2017/04/where-did-your-dog-come-new-tree-breeds-may-hold-answer
8.https://www.cell.com/cell-reports/fulltext/S2211-1247(17)30456-4
9.https://evolution.berkeley.edu/evolibrary/search/imagedetail.php?id=260
10.https://www.forbes.com/sites/grrlscientist/2017/04/25/old-dog-new-dog-genetic-map-tracks-the-evolution-of-mans-best-friend/#576a3f67ec77
11.https://www.nps.gov/bela/learn/historyculture/the-bering-land-bridge-theory.htm
12.https://www.petmd.com/dog/conditions/eyes/c_dg_collie_eye_anomaly
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