Palaeontologist Donald Prothero at the Natural History Museum of Los Angeles County, is delighted with the results. “This is more in line with what the fossil record has told us for a long time,” he says.
“We have no real idea” where it originated, or how its descendants spread around the world, O’Leary says. And although the reconstruction looks like a rodent, “its teeth were completely different”.
Resolving the dispute is likely to require the discovery of new fossils. Brusatte and others are currently looking for mammal fossils from the Palaeocene Period, hoping to catch the earliest stages of the evolution of our common ancestor.
Hypothetical ancestor still has teeth ( courtesy of Carl Buell)
Molecular biologists and palaeontologists have long argued over the origin of placental mammals. For a long time, the accepted theory, based on fossil evidence, was that mammals had diversified after the dinosaurs were wiped out, exploding into myriad different species once the world was no longer dominated by these giants.
To some extent, dog genetic patterns mirror human ones, because people took their animal companions with them when they moved. But there were also important differences.
Dr Skoglund said it was unclear when or where the initial domestication occurred. “Dog history has been so dynamic that you cant really count on it still being there to readily read in their DNA. We really dont know – thats the fascinating thing about it.”
“For dogs, it could almost have been anywhere: cold Siberia, the warm Near East, South-East Asia. All of these are possibilities in my mind,” Pontus Skoglund explained.
Despite the expansion of European dogs during the colonial era, traces of these ancient indigenous breeds survive today in the Americas, Asia, Africa and Oceania.
But at some point, perhaps after the onset of the Bronze Age, a single dog lineage spread widely and replaced all other dog populations on the continent. This pattern has no counterpart in the genetic patterns of people from Europe.
Instead of finding that different wolf species were related to different domesticated dog breeds, they found all the different dogs shared one common ancestor — a “single ancient, now-extinct wolf population.”
From this common ancestor, the researchers narrowed in on five distinct canine lineages found in different areas of the world:
“The dog is the oldest domesticated animal,” Bergström says. “It has a very long relationship with humans.”
The stomachs of the ancient dogs held more clues. In dogs who lived near agricultural human populations (as opposed to hunter-gatherers), researchers found raised levels of gene responsible for starch digestion. Humans likely developed this gene thousands of years before dogs, but the data sync up with older studies suggesting the gene is a sign of how dogs adapting their diet to human-cultivated food has influenced their evolution. Essentially, ancient humans may have been transforming these dogs from the inside out.
Pontus Skoglund is the lead researcher on the study and a geneticist at the Francis Crick Institute. In a video describing the research, he says that when he and his team uncovered the diversity among the ancient dog samples, it was a shock.
Are We All Related?
A study of dog DNA has shown that our “best friend” in the animal world may also be our oldest one.
The analysis reveals that dog domestication can be traced back 11,000 years, to the end of the last Ice Age.
Our canine companions were widespread across the northern hemisphere at this time, and had already split into five different types.
Despite the expansion of European dogs during the colonial era, traces of these ancient indigenous breeds survive today in the Americas, Asia, Africa and Oceania.
The research fills in some of the gaps in the natural history of our close animal companions.
Dr Pontus Skoglund, co-author of the study and group leader of the Ancient Genomics laboratory at Londons Crick Institute, told BBC News: “Dogs are really unique in being this quite strange thing if you think about it, when all people were still hunter gatherers, they domesticate what is really a wild carnivore – wolves are pretty frightening in many parts of the world.
“The question of why did people do that? How did that come about? Thats what were ultimately interested in.”
To some extent, dog genetic patterns mirror human ones, because people took their animal companions with them when they moved. But there were also important differences.
For example, early European dogs were initially diverse, appearing to originate from two very distinct populations, one related to Near Eastern dogs and another to Siberian dogs.
But at some point, perhaps after the onset of the Bronze Age, a single dog lineage spread widely and replaced all other dog populations on the continent. This pattern has no counterpart in the genetic patterns of people from Europe.
Anders Bergström, lead author and post-doctoral researcher at the Crick, said: “If we look back more than four or five thousand years ago, we can see that Europe was a very diverse place when it came to dogs. Although the European dogs we see today come in such an extraordinary array of shapes and forms, genetically they derive from only a very narrow subset of the diversity that used to exist.”
An international team analysed the whole genomes (the full complement of DNA in the nuclei of biological cells) of 27 ancient dog remains associated with a variety of archaeological cultures. They compared these to each other and to modern dogs.
The results reveal that breeds like the Rhodesian Ridgeback in southern Africa and the Chihuahua and Xoloitzcuintli in Mexico retain genetic traces of ancient indigenous dogs from the region.
The ancestry of dogs in East Asia is complex. Chinese breeds seem to derive some of their ancestry from animals like the Australian dingo and New Guinea singing dog, with the rest coming from Europe and dogs from the Russian steppe.
The New Guinea singing dog is so named because of its melodious howl, characterised by a sharp increase in pitch at the start.
Greger Larson, a co-author from the University of Oxford, said: “Dogs are our oldest and closest animal partner. Using DNA from ancient dogs is showing us just how far back our shared history goes and will ultimately help us understand when and where this deep relationship began.”
Dogs are thought to have evolved from wolves that ventured into human camps, perhaps sniffing around for food. As they were tamed, they could then have served humans as hunting companions or guards.
The results suggest all dogs derive from a single extinct wolf population – or perhaps a few very closely related ones. If there were multiple domestication events around the world, these other lineages did not contribute much DNA to later dogs.
Dr Skoglund said it was unclear when or where the initial domestication occurred. “Dog history has been so dynamic that you cant really count on it still being there to readily read in their DNA. We really dont know – thats the fascinating thing about it.”
Many animals, such as cats, probably became our pets when humans settled down to farm a little over 6,000 years ago. Cats were probably useful for controlling pests such as mice, that were attracted by the waste generated by dense settlements. This places their domestication in cradles of agriculture such as the Near East.
“For dogs, it could almost have been anywhere: cold Siberia, the warm Near East, South-East Asia. All of these are possibilities in my mind,” Pontus Skoglund explained.