Origin of Human's Best Friend

By Marlene Cimons, National Science Foundation

Man--and woman’s--best friend likely can trace its origins to Middle Eastern wolves,  not Asian or European wolves as previously thought, according to a genetic analysis by an international team of scientists led by UCLA biologists.

“Ours was a much more thorough analysis,’’ than earlier studies, said Robert Wayne, UCLA professor of ecology and evolutionary biology, and lead author of the paper, which appeared recently in the journal Nature.  “We looked across the entire dog genome, which allowed us to build a more realistic dog scenario of dogs’ origins from the wolf population.’’

The researchers studied genetic data from more than 900 dogs from 85 breeds, including all the major ones, and more than 200 wild gray wolves worldwide, including populations from North America, Europe, the Middle East and Asia.

They used molecular genetic techniques to analyze more than 48,000 genetic markers, vastly more than any earlier studies.  The process relied on a technology called a single nucleotide polymorphism, or SNP, genotyping chip, which integrates the nucleotides at 48,000 different locations, providing information on how breeds are related to one another, and to wolves. 

Earlier studies had suggested an East Asian origin based on the higher diversity of mitochondrial sequences in East Asia and China than from anywhere else in the world. Mitochondria are tiny cellular structures outside the nucleus that produce energy, and have their own genome. But that research was based only on one sequence, a small part of the mitochondrial genome, Wayne said.

“What we found is much more consistent with the archaeological record,’’ Wayne said. “We found strong kinship to Middle Eastern gray wolves and, to some extent, European gray wolves, but much less so to any wolves from East Asia,’’ he added.

Although 80 percent of dog breeds are modern ones, evolving only in the last few hundred years, some dog breeds have ancient histories that date back thousands of years. The first dogs that appeared in the Middle Eastern archaeological record date back 12,000 to 13,000 years, while wolves go back hundreds of thousands of years, he said.

The oldest dogs from the archaeological record come from Europe and Western Russia – a dog from Belgium dates back 31,000 years, while a group of dogs from Western Russia goes back about 15,000 years, he said.  “They already look domesticated, and they look more like Great Danes than they do wolves,’’ Wayne said.

“There are dogs closely associated with human culture in the Middle East,’’ he continued. “They are various sizes, and they are in close proximity to humans. They are buried with them, in various affectionate poses. In one case, a puppy is curled up in the arms of a buried human. We know this was occurring very early.’’

Some very old strains of dogs may be mixed with modern breeds, enhancing their diversity in certain areas, such as East Asia, according to the researchers. 

Moreover, one small set of East Asian breeds does not indicate a Middle East origin, and does show a high level of genetic sharing with Chinese wolves, suggesting that there was some intermixing between East Asian dog breeds and East Asian wolves, although it is unclear when this occurred, they said.

However, the vast majority of the dogs studied show significant levels of sharing with Middle Eastern wolves, the said.

It is possible that some populations of wolves, tens of thousands of years ago, began to follow humans – nomads, hunters – and developed a mutually beneficial relationship, he said. 

“Wolves may have provided some degree of protection, and helped with the hunt, whereas humans provided food,’’ Wayne said. “There was a kind of natural symbiosis that developed between wolves and people. Those early prototypes specialized in the human niche.’’

Today’s domesticated dogs, however, “are a far cry from these early prototypes,’’ he added. “Dogs genetically and to some extent behaviorally, share many attributes with wolves. If you raise a wolf from a puppy, you can sometimes develop bonds, but they would always have a certain wildness.’’

The researchers also developed the first evolutionary tree of dog breeds, showing a surprising structure that suggests the new breeds were developed from crosses within specific breed groups that share particular traits, Wayne said. 

For example, “if you want a new sight hound, they tend to cross sight hounds with each other, and the same with herding dogs and retrieving dogs,’’ he said.  “This may not seem so surprising, but we had no reason to think beforehand that these groups would be strongly genealogical.’’

Toy dogs proved to be one exception. “In this grouping, there are many different kinds of lineages represented, including traces of herding dogs and retrievers, ‘’ Wayne said. “When it comes to miniaturizing a dog, breeders start with a larger breed, and cross that with a miniature dog.’’

Toy breeds “have contributions from everywhere,’’ he added.  “That was a surprise, but in retrospect, it makes sense. When you want to create a dwarf breed, you cross a toy with an existing breed.’’

The tree “provides a mechanism of dog evolution,’’ Wayne said. “It tells us why there are so many different kinds of dogs, and something about how new dogs are created.’’

Other members of the research team included:  John Novembre, UCLA assistant professor of ecology and evolutionary biology; Bridgett vonHoldt, a UCLA graduate student in Wayne’s laboratory;   Eunjung Han, a UCLA graduate student of Novembre’s in biostatistics; John Pollinger, director of UCLA’s Conservation Genetics Resource Center and associate director of the Center for Tropical Research at UCLA’s Institute of the Environment; and James Knowles, a graduate student from Canada’s University of Alberta working in Wayne’s laboratory.

Also, researchers from the National Institutes of Health/National Human Genome Research Institute led by Elaine Ostrander; a group led by Carlos Bustamante, formerly of the Cornell University Department of Biological Statistics and Computational Biology and now a professor of genetics at the Stanford University School of Medicine; and scientists from China, Israel, Australia, Europe and Canada.

The work was funded by the National Science Foundation and the Searle Scholars Program.

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