A genetic switch allowed dogs to adapt to a starch-rich diet and evolve from meat-munching wolves into Man's leftover-loving best friend, scientists said.
Comparing the genetic code of the domestic dog to that of its wolf cousins, a team of researchers from Sweden, Norway and the United States found several telling differences.
"Our findings show that the digestive system of dogs have adapted to be able to live on a diet similar to ours," co-author Erik Axelsson from Uppsala University in Sweden told AFP of the study published in the journal Nature.
Previous research had suggested that dog domestication started when ancient wolves started scavenging on waste dumps near human settlements.
The dog is estimated to have split from the wolf anything from 7,000 to 30,000 years ago.
"A completely new piece to the puzzle is our finding of a more efficient starch digestion in dogs," Axelsson said by email.
This could mean that only wolves who learnt to better digest the leftovers survived to become dog ancestors.
"In addition, it suggests that the domestication process took off when agriculture developed."
The team had compared the sequenced genomes of 12 wolves from different areas in the world with those of 60 dogs from 14 breeds, and found 36 genomic regions that had probably been modified through domestication.
More than half of these regions were related to brain function, including central nervous system development, which may explain behavioural differences such as a dog's reduced aggression compared with the wolf.
Three genes with a role in starch digestion also showed evidence of evolutionary "selection", the scientists said.
The dog was most likely the first animal to be domesticated by Man -- a key development in the development of modern human civilisation.
The new study demonstrated "a striking case of parallel evolution" between humans and dogs, its authors wrote, with similar evolutionary changes allowing two species to cope with a diet ever richer in starch.
"This emphasises how insights from dog domestication may benefit our understanding of human recent evolution and disease," said the study.