Dogs And Wolves Do NOT Have A Common Ancestor, Claims New Study; Genetic Similarities Due To Interbreeding
A recent analysis of modern dog and wolf genomes reveals that they evolved from a common ancestor between 9,000 and 34,000 years ago — long before human transitioned to agricultural societies. The study, published in PLoS Genetics on January 16, 2014, contradicts many studies that came before it, which claimed that domestication of dogs was linked to the agrarian phase in human history.
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This study also differs from the previous studies in showing that dogs are more closely related to each other than wolves. According to the researchers, the genetic overlap between dogs and wolves can be attributed to interbreeding after dogs were domesticated, and not from a common ancestor as was previously thought. In other words, dog domestication is more complex than thought up until now, said John Novembre, associate professor in the Department of Human Genetics at the University of Chicago and a senior author on the study.
According to the current understanding on dogs, they evolved from friendly docile wolves that were first domesticated by the early farmers. The current study on the contrary claims that the earliest dogs may have lived in the hunter-gatherer societies that later adapted to the agricultural life.
"In this analysis we didn't see clear evidence in favor of a multiregional model, or a single origin from one of the living wolves that we sampled. It makes the field of dog domestication very intriguing going forward," Novembre said in a press release.
Three gray wolves, one each from China, Croatia, and Israel were chosen for the highest quality genome sequences (dogs are believed to have originated in these three regions). The researchers also obtained genomes for a basenji, a breed from central Africa and a dingo from Australia. These areas have been historically isolated from modern wolf populations. The scientists also sequenced the genome of a golden jackal representing earlier divergence and to sever as an "out group."
The researchers found that basenji and dingo genomes (as well as the genome from a boxer dog from Europe) were the most closely related to each other. In addition, the three wolves from different geographical regions were more closely related to each other than they were to any of the dogs.
According to Novembre, the research team had anticipated all three dogs to be closely related to one of the wolf lineages or to their closest geographic counterpart. Instead, they all seemed to descend from an older wolf-like ancestor common to both species. "There may have been other wolf lineages that these dogs diverged from that then went extinct," Novembre said, explaining that modern dogs are not really related to any modern wolves.
A crucial step in the study, according to Adam Freedman, a UCLA post doctoral fellow and the lead author of the study, was accounting for gene flows between dogs and wolves after domestication, which in his opinion is more pervasive across canid species than thought before. "If you don't explicitly consider such exchanges, these admixture events get confounded with shared ancestry," he said. "We also found evidence for genetic exchange between wolves and jackals. The picture emerging from our analyses is that these exchanges may play an important role in shaping the diversification of canid species."
Freedman and his colleagues could also discern a significant correlation between domestication and a severe drop in the population sizes of both dogs and wolves. Dogs suffered a 16 fold reduction in their population size as they diverged from wolves. So did the wolves. The researchers figured out these population size changes from analysis of genome-wide patterns of variation.
An important indicator of domestication is the presence of the amylase (AMY2B) genes, which help the animals digest starch, thereby enabling them adapt to an agricultural diet. The researchers found that most dog breeds had a high number of amylase genes - except Siberian husky and dingo, who we know never lived within agrarian societies. Surprisingly, however, he AMY2B gene was also found in wolves, meaning it didn't develop exclusively in dogs after diverging from wolves.
This new research doesn't do much to clear up why dogs love humans - in fact, it just muddies the picture. The good news is that, knowing humans, we'll keep looking for the answer.
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