Dog DNA additionally reveals an early shift in brain function, likely tied to behavioral changes associated with living around humans. Since all dogs descend from one species, the grey wolf, (with some breeding with other closely related canines) it's possible that natural selection favored certain types of wolves.
"Being an efficient scavenger included being less shy so as to not waste energy on running away frequently," Axelsson said.
Natural selection therefore already started the process of separating wild wolves from their settlement-scavenging counterparts before direct human domestication of dogs began.
The precise moment when dogs first evolved from wolves remains in question, however.
Susan Crockford, a researcher at Pacific Identifications Inc. and author of the book "Rhythms of Life," believes that dogs were domesticated by at least 33,000 years ago, but these canines did not generate descendants that survived past the Ice Age.
She told Discovery News that the "right wolf/human conditions suitable for getting domestication started were present at least 33,000 years ago. However, such conditions would have had to be present continuously -- stable -- for many wolf generations, perhaps 20 over about 40 years for the domestication process to generate a true dog."