A study by a team of American and Swedish researchers published on Jan. 23 in the Journal of Nature, shows that dogs have more genes involved in starch metabolism than wolves.
The finding suggests that this was a major factor in the evolution process of the wolf. No one knows exactly when or how our ancestors began to be so closely linked to dogs, but archaeological evidence indicates that it was thousands of years ago.
One theory suggests that modern behavior of the dogs came from the hunters that used wolves as guards or fellow hunters.
But another theory - that underpins the study - suggests that domestication began when the wolves began to approach the villages in search of food, stealing the remains left by people.
This practice became increasingly common and as a result, wolves began to live around humans. According to this second hypothesis, when we became sedentary and dependent on agriculture, waste dumps created around our settlements soon became the power source of many wolves, explains Erik Axelsson, of the University of Uppsala.
"I think that modern dogs derived from multiple wolf populations," said Axelsson. "So, we think our findings fit well with this theory that the dog evolved on the waste dump," he told the BBC .
Dr. Axelsson and colleagues examined the DNA of more than 50 modern breeds - from the Cocker Spaniel to the German Shepherd.
They then compared their genetic information with 12 wolves from around the world. They scanned DNA sequences of the two canids in areas with large differences. They assumed that these areas contained genes that could help explain the domestication of dogs. Axelsson's team identified 36 regions, with more than one hundred genes.
The analysis detected the presence of two major functional categories - genes involved in brain development and starch metabolism.
The latter suggests that dogs have many more genes encoding enzymes needed to break down starch, a feature that could have been advantageous to the ancestors who rummaged among the wheat and corn of the farmers.
"The wolves also have these genes, but not used as efficiently as dogs," said Dr. Axelsson.
"When we look at the wolf genome, we only see one copy of the gene [for the amylase enzyme] on each chromosome. When we look at the dog genome, we see a range from two to 15 copies; and on average a dog carries seven copies more than the wolf."
"That means the dog is a lot more efficient at making use of the nutrition in starch than the wolf."
As for the genes related to brain development, these probably reflect some of the behavioral differences we now see in the two canids.
The dog is an animal that is much more docile, which is probably due to the past humans preferring to work with animals that were easier to tame.
"Previous experiments have indicated that when you select for a reduction in aggressiveness, you obviously get a tamer animal but you also get an animal that retains juvenile characteristics much longer during development, sometimes into adulthood," said Dr. Axelsson.
This may help explain why it is said that dogs act like puppies throughout their lives.
The study of the origin of dogs is still, in many ways, a puzzle.
Fossil evidence suggests that some populations have been around for tens of thousands of years, long before the advent of agriculture. One reason why it is so difficult to determine the time of this change of behavior is that domestication may have occurred more than once.
Dr. Carles Vila, Conservation Group and Evolutionary Genetics at the Doñana Biological Station in Seville, Spain, said the debate was still open.
"I think that modern dogs derived from multiple wolf populations," he explains.
"It could be that dog domestication started once with some animals staying with humans which were then regularly back-crossed with wolves and that could have the same effect. But there could have been completely independent domestications. What is clear is that the number of bone remains is very rare more than 14,000 years ago."
After their adaptation to starch, wolf pups were adopted by early humans to watch the town at night and protect them from external threats, a relationship that was forged with the role of "man's best friend" 10,000 years ago.
Although the dog is presented as the faithful companion of man, the study suggests that this role might have been first used by cats. Their story is also related to agriculture, although they were not interested in the grain, but the animals that fed on it, like mice.
The similarities found in the digestive systems of humans and dogs, reinforced the possibility that this discovery could shed light on diseases such as diabetes, according to the Swedish expert.
Sources: BBC, Journal of Nature