At the time Tobus is referring to surnames, as we use them today, were just beginning to take hold in Scotland.

Everyone had a first name, and everyone was referred to as the "son of" or "daughter of" their parent. Example: Tom, son of Edward.

As society evolved it became the norm for a person to be known by the name of their parent as well as by their trade, occupation, or a physical characteristic. Example: Tom, son of Edward the Farmer.

Now if Tom had big ears, he might be called Tom Luggs, son of Edward the Farmer to clearly differentiate him from Tom, son of Edward the Blacksmith.

As land ownership shifted from a tribal concept to a feudal concept, two distinct strata of society developed: those who owned the land and those who were tenants on the land. Because land ownership was transferable by sale or inheritance there had to be some way to identify the owner in written documents as well as in everyday conversation. Since land has been named from the dawn of time (The Black Glen, for example) the easiest way to keep track of the owner was to attach the name of the land to his Christian name. Example: Tom, son of Edward the Farmer is given ownership of all the land in the Black Glen. He now becomes Tom of Black Glen.

Now if Tom of Black Glen has four boys (Manny, Moe, Jack, and Ralph) they are each known as the "the son of Tom of Black Glen". Now the oldest boy, Manny, will inherit the land, so during his father's life time he is called "Manny, young Black Glen". As his brothers move out, and get married and have children, they will still be known as Moe, Jack, and Ralph son of Tom. But because they don't own the land, they will be known as simply "at" or "being" in Black Glen. Example: Ralph, son of Tom at Black Glen.

As you move forward couple of centuries Ralph's descendants could end up with either of two last names: Tomsson, or Blackglen. Example: William Tomsson, Lucas Blackglen.

What about Tom, who originally owned the Black Glen? Well, he could have moved on, married well and became the owner of another property (which we will call Fair Meadow). He would then become Tom son of Edward of Fair Meadow. In time his descendants would become either Tomssons, Edwards, or Fairmeadows.

So how does this relate to Kilpatrick and Colquhoun? Here is an imaginary genealogy:

Odo de Brissac arrives in Scotland (remember "de" = "of" in English)

His son Humphry fitzOdo (remember fitz=son) obtains the charter of the lands known as the Church of Patrick (Kilpatrick) and becomes Humphry de Kilpatrick.

Later, Humphry marries the daughter of the owner of the lands of Colquhoun. In order to build a castle for his bride he sells the lands of Kilpatrick to his cousin Rolo fitzWalter, who leaves Flanders, moves to Scotland and becomes Rolo de Kilpatrick. Humphry, meanwhile, builds his castle and buys the lands of Colquhoun, and becomes Humphry de Colquhoun.

But what about the people "at" Kilpatrick and Colquhoun? Their last names evolve in much the same way, with some adopting as their last name the first name of their father or grandfather; for others their occupation becomes their last name; and finally there are those who use as their last name the place where they were born and, in all likelihood will die and be buried, hence there will be Kilpatricks and Colquhouns abounding who may or may not be a blood relation to the first "owner" of the land.

What you have to remembers is that this was a very gradual process, and in Scotland last names were still in a state of flux into the 19th century. Some names are a fusion of languages and cultures with Norman French, English, Norse, and Gaelic all jumbled together in the creation of family names. Example: the son of Thomas==fitzThomas==MacThomas==Thomson.

For a more detailed (and scholarly) explanation of how names evolved check out the Encyclopedia Americana or Encyclopedia Britannica at your local library, and ask the reference librarian for assistance in locating other books on the subject. (The foregoing plug was to remind those who constantly refer to wikipedia that there are more and better sources available AT THE LIBRARY.)