For many people, dogs are like family members. But it hasn't always been that way.
Before they were cuddly pooches, they were wild animals. Dogs are thought to have evolved from wolves to become the domestic animals they are today.
How, when, where, and why that happened has long puzzled scientists. But one research team says they have some clues, which they report in a paper published Tuesday in the journal Cell Research.
These scientists describe the scenario of Fido's origins something like this: Some 33,000 years ago, a population of wolves living in Southeast Asia diverged into two separate lineages. The domestic dog appeared along one of those lineages.
"Nobody knows exactly what happened, but the favorite theory for many in the field is that this domestication was a collaboration between humans and wolves," study co-author and evolutionary geneticist Peter Savolainen tells The Christian Science Monitor in an interview.
"It might have started with the wolves coming closer to humans, living from the debris of food leftovers around human camps," he says. "And then those wolves that were least aggressive or that were best accepted by humans to come near, they got the best food and therefore a selective advantage compared to other wolves."
Through this process, those friendly wolves would have become our furry friends over time.
Around 15,000 years ago, some of these dogs migrated across continents into the Middle East and Africa, reaching Europe about 10,000 years ago.
Along the way, dogs also occasionally cross-bred back with wolves, leaving a small bit of DNA evidence in some modern dogs' genomes.
"It's a little bit like the origins of humans," Dr. Savolainen says. "We all came out of Africa and coming to Eurasia, we mixed with Neanderthals and the Denisovans a little bit, giving a few percent of the whole diversity," he explains of our own migrations and genetic diversity.
Many questions swirl around the origins of the beloved domestic dog, but there is little archeological evidence to reveal answers. So scientists look elsewhere for clues. For this study, they dug into the genomes of dogs and wolves alive today. The researchers sequenced the entire genome of these animals, looking for evolutionary markers.
In the canine DNA, the scientists found evidence that the ancestral population of dogs is most likely from Southeast Asia, and that subsequent populations spread across the world. Mutations in the genome helped them map the dogs' origins.
The scientists also found clues into the way wolves adapted to become dogs.
Some genes had to do with behavior. Savolainen says that change made sense, because the aggression and hostility of wild wolves wouldn't have made them successful as domestic animals.
Other genes probably evolved later to help the animals better eat human food. "We see that dogs are much better than wolves to digest the starch-rich foods, like rice or wheat," Savolainen says. Wolves are carnivores, eating only meat. But as humans became agriculturalists some 12,000 years ago and began eating starches, dogs living with them would've needed to survive on that different diet too.
Savolainen says the first dogs may have appeared as early as 33,000 years ago or as late as 15,000 years ago. The genetic clues the scientists found suggest a divergence in the wolf population at 33,000 years ago, but, "was it also the origin of the dogs then or possibly later?" says Savolainen.
That split could represent the beginning of dog domestication, or it could just be the beginning of the lineage that yielded domestic dogs later. Perhaps the last step in dog domestication was the migrations described in this paper, Savolainen suggests.
Domestication could have been happening that whole time. "It might have been a very gradual thing that wolves got more and more used to humans and we got more and more, tighter and tighter dogs," Savolainen says.
When dogs spread out of Asia, they might have been stretching their legs across a newly revealed land mass after the last Ice Age, the scientists suggest in their paper. But it's likely they were following their new human friends, says Savolainen.
The question of where dogs were domesticated has been the subject of much research. Previous studies suggested canine domestication happened in regions such as the Middle East, Europe or Central Asia.
"I think the first thing you need to answer is where it happened," geneticist Adam Boyko, who authored a study published in October naming Central Asia as the location, told the Monitor in an interview then.
"Narrowing it down to where is the first step in coming up with a comprehensive theory of what was going on," Dr. Boyko said.
Boyko isn't concerned that this new research seems to falsify his own. "We're both seeing a clear signature of more diversity in Asian dogs than we're seeing outside of Asia," a sign indicating an ancestral population, he tells the Monitor in a recent interview.
Both Boyko and Savolainen say the conflict lies in the data. Each claims the other team did not sample enough dogs from their own highlighted region.
"The reality is, sampling dogs is hard," Boyko says. He adds that as more research is done, more data sets allow for more discussion among the scientists. "As geneticists, we love to get new data sets like this to play with. Maybe at some point we'll all be on the same page," he says.
Why are scientists fascinated with the story of dog domestication?
"People love their dogs and so they want to know what the story of dogs is," Boyko says. "But also understanding the story of dogs is sort of understanding the story of us."
Dogs were the first animals domesticated by humans.
"When we started to domesticate animals and plants, that was the most important step in human history," Savolainen asserts. "That's when we went from hunter-gathers into farmers and that was what built today's civilization. It's a key step in history."