We have brought you views from different scientific sources and at the end of each segment we have added a link so that you can read refer to each source for indepth information.
Paleontologists and archaeologists have determined that about 60 million years ago a small mammal, called Miacis, the genus that became the ancestor of the animals known today as canids: dogs, jackals, wolves, and foxes.
Miacis did not leave direct descendants, but doglike canids evolved from it. By about 30 to 40 million years ago Miacis had evolved into the first true dog—namely, Cynodictis. This was a medium-size animal, longer than it was tall, with a long tail and a fairly brushy coat.
Over the millennia Cynodictis gave rise to two branches, one in Africa and the other in Eurasia. The Eurasian branch was called Tomarctus and is the progenitor of wolves, dogs, and foxes.
Genetic evidence suggests that dogs descended directly from wolves (Canis) and that the now-extinct wolf lineages that produced dogs branched off from the line that produced modern living wolves sometime between 27,000 and 40,000 years ago.
There is strong genetic evidence, however, that the first domestication happened in northern Eurasia between 14,000 and 29,000 years ago. In this region wolves likely facilitated their own domestication by trailing nomadic people in northern Eurasia and consuming the remains of game animals that hunters left behind.
Some genetic studies have documented evidence of early domestication events in specific regions. One study contends that wolves were domesticated 16,300 years ago to serve as livestock in China, whereas another reports that early dogs dating from about 12,000 to 14,000 years ago came from a small strain of gray wolf that inhabited India.
Genetic evidence also reveals that dogs did not accompany the first humans to the New World more than 15,000 years ago, suggesting instead that dogs came to the Americas only some 10,000 years ago.
One study even suggested that some dogs have descended not from the wolf but rather from the jackal. These dogs, found in Africa, might have given rise to some of the present native African breeds.
No matter what their origins, all canids have certain common characteristics. They are mammals that bear live young. The females have mammary glands, and they suckle their offspring. The early breeds had erect ears and pointed or wedge-shaped muzzles, similar to the northern breeds common today. Most of the carnivores have similar dental structures, which is one way paleontologists have been able to identify them. They develop two sets of teeth, deciduous (“baby”) teeth and permanent teeth.
Canids walk on their toes, in contrast to an animal like the bear, which is flat-footed and walks on its heels. Dogs, like most mammals, have body hair and are homeothermic—that is to say, they have an internal thermostat that permits them to maintain their body temperature at a constant level despite the outside temperature.
Fossil remains suggest that five distinct types of dogs existed by the beginning of the Bronze Age (about 4500 BCE). They were the mastiffs, wolf-type dogs, sight hounds (such as the Saluki or greyhound), pointing dogs, and herding dogs.
Pugs and poodles may not look the part, but if you trace their lineages far enough back in time all dogs are descended from wolves. Gray wolves and dogs diverged from an extinct wolf species some 15,000 to 40,000 years ago. There’s general scientific agreement on that point, and also with evolutionary anthropologist Brian Hare’s characterization of what happened next. ‘The domestication of dogs was one of the most extraordinary events in human history,” Hare says.
But controversies abound concerning where a long-feared animal first became our closest domestic partner. Genetic studies have pinpointed everywhere from southern China to Mongolia to Europe.
Scientists cannot agree on the timing, either. Last summer, research reported in Nature Communications pushed likely dates for domestication further back into the past, suggesting that dogs were domesticated just once at least 20,000 but likely closer to 40,000 years ago. Evolutionary ecologist Krishna R. Veeramah, of Stony Brook University, and colleagues sampled DNA from two Neolithic German dog fossils, 7,000 and 4,700 years old respectively. Tracing genetic mutation rates in these genomes yielded the new date estimates.
“We found that our ancient dogs from the same time period were very similar to modern European dogs, including the majority of breed dogs people keep as pets,” explained Dr. Veeramah in a release accompanying the study. This suggests, he adds, “that there was likely only a single domestication event for the dogs observed in the fossil record from the Stone Age and that we also see and live with today.”
End of story? Not even close.
In fact, at least one study has suggested that dogs could have been domesticated more than once. Researchers analyzed mitochondrial DNA sequences from remains of 59 European dogs (aged 3,000 to 14,000 years), and the full genome of a 4,800-year-old dog that was buried beneath the prehistoric mound monument at Newgrange, Ireland.
Comparing these genomes with many wolves and modern dog breeds suggested that dogs were domesticated in Asia, at least 14,000 years ago, and their lineages split some 14,000 to 6,400 years ago into East Asian and Western Eurasian dogs.
Elaine Ostrander and Heidi Parker, geneticists at the National Human Genome Research Institute in Bethesda, Maryland, and their colleagues spent 20 years going to dog shows, writing dog fanciers, and getting help from all corners of the world to collect DNA samples; in some cases they used already collected data.
They weren’t interested in determining how and when dogs were domesticated, but how all the breeds developed. Their sample now includes 1346 dogs representing 161 breeds, or not quite half of all kinds of dogs.
By comparing the differences at 150,000 spots on each dog’s genome, they built a family tree. “The scope of the analysis is very impressive, [a] tour-de-force on breed evolution,” says evolutionary biologist Robert Wayne of the University of California, Los Angeles, who was not involved with the work.
Almost all the breeds fell into 23 larger groupings called clades, the team details today in Cell Reports. Although genetically defined, the clades also tended to bring together dogs with similar traits: Thus boxers, bulldogs, and Boston terriers—all bred for strength—fall into one clade; whereas herders like sheepdogs, corgis, and collies fall into another; and hunters like retrievers, spaniels, and setters fall into a third.
The grouping of different breeds that share particular jobs suggests that ancient breeders likely bred dogs for specific purposes, choosing to care for those that were best at guarding or herding. Then, in the past 200 years, people subdivided those larger groups into breeds.
But the data also show how some breeds helped create others, as they share DNA with multiple clades. As one of the earliest small dogs, the pug, which hailed from China, was used in Europe from the 1500s onward to shrink other breeds. Thus, pug DNA is part of many other toy and small dog genomes, Parker explains.
“This is very exciting!” says Peter Savolainen, an evolutionary geneticist at the Royal Institute of Technology in Solna, Sweden, who was not involved with the work. “It shows how attractive traits from one breed [have] been bred into new breeds.”
Having these clades will help veterinarians spot potential genetic problems, Parker says.
For example, before vets couldn’t really understand why a genetic disease called collie eye anomaly, which can distort different parts of the eye, and shows up in collies, border collies, and Australian shepherds, also occurs in Nova Scotia duck tolling retrievers. But the genetic analysis shows that this retriever has either collie or Australian shepherd ancestors that may have passed on the defective gene. “Mixing has resulted in the sharing of specific genomic regions harboring mutations which cause disease in very different breeds,” Wayne says.
Wayne and Karlsson both stress that to provide more details, the researchers should work to compare whole genomes—the entire 2.5 billion bases. And as Savolainen points out, the work “is a very good first step into the origins of all dog breeds, but half of all breeds are still missing.”
This article is produced by SAVetshops, in the interest of informing people and sharing information. It is not considered a reference article or a definitive medical reference. Source references are listed below and any person wishing to know more should consult these references, their local vet, state health service or doctor.