Some researchers have tried to use the regular rate at which error patterns appear in dog DNA as a kind clock to time their rise, but this has produced contradictory results.

BBC: Dog evolved 'on the waste dump'

"Because mutations start occurring at regular intervals in these genes as soon as a new species evolves - like the ticking of a clock - we can use them to trace the evolutionary history of a species back to its time of origin, " said Dr Hedges.

BBC: Earth AP