There are few breeds today that have been kept since pre-industrial revolution era. The bloodhound and the greyhound were mentioned above. To the common person, breed type and standard for breed was not a thought until mid 1800's and was predominantly exclusive to the upperclass (like the greyhound and their coursing clubs). Common class people who mainly kept these type of working terriers and bulldogs had a type more than a breed. If it was the type to do the job then it was the type to be bred as a lot of these folks had to make due with what they had locally. The american pitbull terrier would come to fruition as these commoners would come to the new world and bring their local working type dogs with them. Who's to say what these folks had in their dogs some generations back... the folks from Ireland probably didn't have the same background as the folks from England and the Blend of the two would create the dogs we have today.