Humans would have noticed those tendencies in puppies, suitable dogs would have been kept, fearful or aggressive dogs would not. The differing opinion on the timescale of the domesticated dog suggests two alternative theories. If we are to consider that the dog became domesticated some 135,000 years ago, it is suggested that dogs exploited a niche for humans to care for them. If we consider the more recent time line, it is argued that humans fueled the domestication to serve as guards or companions. Either way, what we do know, even modern day dogs share similar genes to the ancient wolf.
