Data also help explain the distribution of some canine genetic diseases
From the 80-kilogram Great Dane to the 1-kilogram tiny teacup poodle, there seems to be a dog for everyone. Now, the largest genetic analysis to date has figured out how those breeds came to be, which ones are really closely related, and what makes some dogs more susceptible to certain diseases.
“They show that by using genetics, you can really show what was going on as [breeders] were making these breeds,” says Elinor Karlsson, a computational biologist at the University of Massachusetts Medical Center in Worcester who was not involved with the work.
After dogs were initially domesticated—likely between 15,000 and 30,000 years ago—people picked the best hunters, house guards, and herding animals to be their best friends, depending on their needs. There were dogs for war and for cuddling, for fur and meat, and for being good companions. Today dogs come in 350 or so breeds, each with specific traits and behaviors. Many arose in the past 200 years. Some studies have defined the genetics of a relatively small number of breeds, but none has been comprehensive enough to show how and when most came into existence. “The whole period in between [domestication and today] has been a black box,” Karlsson says.
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 werent 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 dogs 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 couldnt 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.” Ostrander and Parker say they see this publication as a midpoint, not an endpoint. “We had reached a point where we could begin to do some of the things we wanted to do,” Ostrander explains. “By no means are we done.”
Liz Pennisi is a senior correspondent covering many aspects of biology for Science.
Don’t yet have access? Subscribe to News from Science for full access to breaking news and analysis on research and science policy.
We didn’t pick just any wolves for this project. We picked the ones that could help us and get along with us. Dogs are dumber than monkeys and other mammals in many ways, but they excel at one thing: interpreting human behavior. Three years ago, scientists tested this talent in wolves, adult dogs, puppies raised in households, and puppies raised in kennels. The wolves couldn’t read humans well, but the puppies could—even the puppies raised in kennels. Through selection, we’ve hardwired human compatibility into dogs. We’ve made a species in our . Advertisement Advertisement
Each need, each breed, called for special traits. We bred collies for vigilance, Rottweilers for aggression, retrievers for obedience. In a span of decades, we bred ferocity into Dobermans and then, with equal deliberateness, bred it out. We treated dogs like guns. We designed and bought them for protection, then complained when they hurt us. When cities banned pit bulls, we bought Rottweilers. It was as easy as replacing an illegal assault weapon with a legal one. Advertisement Advertisement Advertisement
In the course of engineering dogs to look, feel, and act as we wanted, we ruined millions of them. We gave them legs so short they couldn’t run, noses so flat they couldn’t breathe, tempers so hostile they couldn’t function in society. Even our best intentions backfired. Nature invented sexual reproduction to diversify gene pools and dilute bad variants. By forcing dogs into incest (which we ban among humans, in part for biological reasons), we defied nature. We concentrated each bad gene in a breed, magnifying its damage: epilepsy for springer spaniels, diabetes for Samoyeds, bone cancer for Rottweilers. That’s why the dog genome is so nifty: We can find disease genes just by comparing one breed’s DNA to another’s.
Have you heard the latest news? We’ve decoded the DNA of dogs. Here’s how the media-approved version of the story goes: We’re showing our love for “man’s best friend” by discovering and treating the genetic causes of his ailments. In return, we’ll learn to treat the same ailments in ourselves.
It’s a heartwarming story, but it’s a fraud. The reason we targeted the dog genome for decoding is that it’s useful for genetic research. The reason it’s useful for genetic research is that dogs are neatly divided into breeds, each of which is plagued by specific diseases. And the reason dogs are divided into diseased breeds is that we made them that way. Dogs are the world’s longest self-serving, ecologically reckless genetic experiment, perpetrated by the world’s first genetically engineering species: us. Advertisement Advertisement Advertisement Advertisement
Researchers say with future studies, we’ll learn the origins of the diseases modern-day dogs’ experience. Their genomic data may offer clues to novel treatment options. And since the dog is a good model for diseases that affect humans, understanding what genes they have that fight disease will help us learn more about diseases that affect us too.
There are still a lot of unknowns when it comes to dogs, including how early humans came to domesticate gray wolves, why the first separate breed popped up, what it was, and why dogs continued to evolve into the wide variety we see today. Unraveling how dogs have evolved will help us learn our own history and give us clues into our evolution.
Later on, dogs were bred for really specific tasks. Golden Retrievers, Irish Setters, and other “gun dogs,” can be traced back to Victorian England. With developments in firearm technology came these breeds best suited as the huntsman’s retriever, helper, and companion.
If asked outright, most American dog owners would say their loving pooch is a part of the family. Perhaps it’s the long history of interaction between our two species that makes us so close. Dogs and humans have been living together for at least 15,000 years.
Now, a team of researchers has assembled the most comprehensive genomic map on dogs to date. The results were published in the journal Cell Reports. Researchers gathered blood samples or mouth scrapings from 1,346 dogs, of 161 breeds, over the course of 20 years. The dogs came from Europe, North America, Africa, and Asia.
How Are New Dog Breeds Created?
There are more than 400 pure breeds of dogs in the world and many other mixed breed dogs. They share many common behaviors and habits, but they also look very different from each other. That raises an interesting question: “Do the Chihuahua and Great Dane come from the same ancestry?” The answer is YES! All the pure breed dogs and mutts come from one common ancestry, gray wolf, which first appeared about 1 million years ago in Eurasia. Dogs were domesticated from gray wolf around 15,000 years ago. The fossilized remains of a 33,000-year-old dog-like animal, found in the 1970s in southern Siberia’s Altay Mountains, is the earliest well-preserved dog-like animal. Dog-like fossils dating from 12,000-11,000 years BP have been found buried alongside humans in Israel(Davis and Valla, 1978; Ovodov et al., 2011). However, the problem of the fossil study is that we can hardly know whether the fossil belongs to a dog or wolf based on their skulls and shapes. These evidences can only suggest a roughly timeline of this evolution process, we need more evidence to make the conclusion. Genomic information indicates that dog domestication started at least 10,000 years ago in southern East Asia or the Middle East. It is unclear that where, why and how dogs were first domesticated. A famous argument is that wolves have scavenged around human settlements and domesticated themselves. This process could occurred in any area where both wolves and human lived, and from hundreds of thousands of years ago to the present(Clutton-Brock et al., 2017).
There are many differences between modern dogs and gray wolf ancestors. These include reduced aggressiveness and altered social cognition capabilities. Dogs also differ physically from wolves, showing floppy ears, various coat colors, and curled tails(Clutton-Brock et al., 2017). A study published in Nature, a scientific journal, in 2013 compared the genome between wolves and domesticated dogs, and found 36 genomic regions differ between them. These parts of the genome contain many genes involved in brain function and the nervous system. Interestly, the regions also contain many genes involved in starch digestion and fat metabolism(Axelsson et al., 2013). It’s possible that increased starch digestion function provides ancient domesticated dogs with a better chance to survive. An increased capacity for digesting starches, which are found in grains and other foods from plants, would certainly help dogs to make good use of foods shared by humans. Even we are able to find the genomic difference, we still don’t know what genes drove the evolution from wolf to dogs, what genes are the most crucial causes.
During the past 200 years, selective breeding by humans has resulted in the artificial “evolution” of the dog into many different types. There are now over 400 dog breeds all over the world, and they drastically vary in shapes and sizes. Some dogs are bred for their abilities to help humans. For example, Border Collies are selected to protect flocks because of their sagacity, intelligence, and trainability. In addition, the Labrador Retriever was bred to be both a friendly companion and a useful working dog breed. Some dogs are bred just for their physical characteristics. Like the Chihuahua, who’s adorable big head and small body size is favored by many pet owners. Dogs have large range of body sizes, the Great Dane is one of the largest breeds, and it usually weighs around 100-120 pounds. Chihuahua, the smallest breed of dogs, only weighs around 4-6 pounds. In 2010, the Bustamante group at Stanford University found that variation in just six places of the dog genome can explain about 80 of the variation in height and weight among dog breeds(Boyko et al., 2010). With so many studies have been done and so many controversies have been come up, we still have a long way to go to find out those ‘hidden’ truth. With the development of sequencing technology, we are able to sequence every dog and wolf to find out what their DNA looks like. However, the problem is we don’t really know what the difference stands for, one single gene with large effect made the evolution happen or many genes with minor effect worked together to drive this evolution from wolf to dog? We don’t know the answer yet, but with all the advanced technology and all the help from people who are interested in science, we will get there one day!
Axelsson, E., Ratnakumar, A., Arendt, M.L., and Maqbool, K. (2013). The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature.
Boyko, A.R., Quignon, P., Li, L., Schoenebeck, J.J., Degenhardt, J.D., Lohmueller, K.E., Zhao, K., Brisbin, A., Parker, H.G., vonHoldt, B.M., et al. (2010). A Simple Genetic Architecture Underlies Morphological Variation in Dogs. PLoS Biol. 8, e1000451.
Clutton-Brock, J., vonHoldt, B.M., Lord, K., and van den Berg, L, et al. (2017). The Domestic Dog.
Davis, S.J.M., and Valla, F.R. (1978). Evidence for domestication of the dog 12,000 years ago in the Natufian of Israel. Nature.
Ovodov, N.D., Crockford, S.J., Kuzmin, Y.V., Higham, T.F.G., Hodgins, G.W.L., and van der Plicht, J. (2011). A 33,000-Year-Old Incipient Dog from the Altai Mountains of Siberia: Evidence of the Earliest Domestication Disrupted by the Last Glacial Maximum. PLoS One 6, e22821.