Origin of Surnames
The relevance of surnames in genealogy (As quoted by Society of Genealogists Information)
Unfortunately only a very small number of pedigrees of British families can be traced to the person who first used the surnames they now bear. Many surnames have been corrupted to such an extent that their original forms may only be discovered after quite considerable research. This may involve tracing the pedigree step by step from the present backwards in time, not only to detect the changes but also to discover the area of the country from which the family came. Present day forms of a large number of surnames are due to the spelling of 16th or 17th century parsons, or even to the registrars of births in the 19th century. They had no guide to the spellings of names and attempted to reproduce phonetically the sounds they heard, as the great majority of the population were illiterate and had no notion that any one spelling of their name was more correct than any other.
All our original ancestors used a one-part name, whether they were Celts, Anglo-Saxons, Scandinavians or Normans. Certain people before the Norman conquest, and in growing numbers afterwards, had an additional 'by name', but these were not hereditary surnames in the modern sense as they did not pass from father to son. Such names may appear in Domesday Book, but they have no relevance here. It was not until the early 12th century that surnames became hereditary among the nobility. They spread gradually amongst the ordinary people in the next century, from the town to the country and from the south of England to the north. Most people in England did not, however, have anything approaching an hereditary surname until the end of the 14th century.