(Coincidentally, this is the approximation of Dunbar's number. Dunbar is a scientist who studies humans. Based on research on primates like other apes, Dunbar hypothesized that there was a maximum number of individuals that a given primate could interact with on a regular basis while maintaining a close workable relationship. He thought this number would be based on the size and structure of the primate's brain. Based on the size and structure of human brains, he calculated that the average number of humans that a human could know and get along with would be around 150. It seems that archaeological and anthropological data would support this. If you get too far above this number, it becomes difficult to maintain stable relationships. Heck, it becomes difficult to remember everyone's names!)
So, what does this have to do with names? Well, in the original human settings, first names were probably enough to tell everyone apart in conversations. These days there are thousands of unique first names, although most parents use only a selection from the top hundred or so. If everyone you know has a unique name, there is no need for a "last name". Indeed, when we look at naming conventions in societies with small groups, last names are relatively rare. Instead, names are descriptive. Let's divert and talk about that for a moment.
Names aren't just sounds. They are usually words that have meaning. Societies in general follow a number of naming conventions. A few of these are:
- Names are not permanent. In societies that have some sort of passage into adulthood (usually around the time of puberty,) there can be the concept of earning or being given an adult name. In these cases, the name assigned as a baby can be descriptive. "Huh. Our newborn looks kinda like a little turtle, cause of how she purses her lips. Makes 'em look like a beak." "Let's call her Little Turtle!"
- Names are not permanent. New names can be assigned based on events or characteristics. "Little Turtle fell off a horse when she was thirteen! Haw! Let's all call her Falls Off Horses!"
- Names are permanent. In these cases, for religious or traditional reasons, the name given at birth is the name you have for life. It is worth pointing out, the names chosen by the parents or family usually fit into one of four categories: Descriptive, Inherited, Aspirational, and Sound. Descriptive is just that. The name is chosen because it "fits." This is subject to a lot of interpretation, of course. Inherited is where a family name is used, usually out of tradition, or as a compliment to the family member. (We named our baby after you!) Aspirational is where the name implies something good for the kid's future. (We named him Rich, because we want him to get rich!) To name based on Sound just means the parents like the sound of the name. (We named her Infiniti, because the name sounds pretty and the cars are expensive!) Yes, people have named little girls Infiniti.
As another brief aside, parts of modern society do have adult naming ceremonies. In some native groups, a boy or girl could earn an adult name by going through a ceremony, or by completing an important or difficult task, like going hunting overnight while alone. In some versions of Christianity, children can go through a confirmation process, which can include selecting a Saint name to add to their own. Much like in other such ceremonies, the name chosen has significance, and can indicate something about the person.
Anyhow, back to "Last names." Once agriculture got invented, humans started settling into larger communities. This is all well and good, but now we start having the modern problem of "Uh-oh. Two sets of parents named their kid the same thing. Now what?" In this case, the group needs a way to distinguish the individuals for economic, political and social reasons. The easiest way to do this is to make the name longer. By combining names, they become more specific. These new names are not always "Last." Sometimes they are called Family Names, or Patronymics. Sometimes a society will place them first, sometimes last. In any case, most of these are general names: they identify the individual with a group, and then the individual's specific name identifies them within that group. For example, I'm a member of the (a) Stevenson Family, and I'm the one named Seth Michael. So, where do these names come from?
- Descriptive. How do we tell James and James apart? Well, one of them has Brown hair. He will be James Brown. The other one has green eyes. He'll be James Green. What about Tom and Tom? Well, old Tom will be Tom Oldman. Young Tom will be Tom Youngman.
- Profession. How can we tell tell Lanie and Lanie apart? Well, one is a butcher, and one is a dancer. So we get Lanie Butcher and Lanie Dancer. Common modern names based on this in English are Smith, Miller, Butcher, etc.
- Location. In societies where people begin traveling, it can be helpful to give them a name based on their origin. It describes where they are from, and it acts as a more unique identifier. Names that end in -ton, -ville, -berg or -burg, or that include De/Du/Von can all indicate a location. Alan Livingston would be someone who had an ancestor from the town of Livingston. (Livingston would then be a Town that was originally begun or ruled by someone name Living or Livings. Hence, Living's-Town. Livingston.)
- Patronymics or Matronymics. In these cases, the person takes on the name of one of their parents, or a ruler or master. Slaves in the American South sometimes took the names of their masters as an identifiers. In Medieval England, people could be identified with their local lord. Timothy is a soldier for Duke John? Well, then, he's Tim Johnsman. More commonly, people would be identified based on their parent(s). That guy over there? He's Seth, son of Steven. He's Seth Stevenson.
- Clan or Tribe. In this case, the individual is identified with a larger group, sometimes a tribe with Military or Political significance. Jamie MacDonald is one of the Jamies who belongs to the Clan of Donald.
Now, these days, we usually just inherit our names from our parents. This makes sense, given that the family (whatever its particular structure) is the basic economic unit of society. Depending on the society, the name you get can be inherited from your father or your mother. Our society is still fairly patriarchal. When people marry, the wife still usually takes the name of the man, and the children will all share that name as well. In this case, family names trace the fathers in a person's ancestry. The reverse is true in some societies, but not many. (And yes, I'm leaving out a bunch of alternative family structures. That said, the average family is still male/female/kids, so that's what we'll talk about for now.)
It is worth noticing that, much like first names no longer are really identified with their meaning in modern Western Society, neither are last names. Having the family name of Miller doesn't mean you or your family owns a Mill to grind wheat...but it does imply that somewhere in your ancestors you have a great-great-great(times however many greats)-grandfather who did. Similarly, my father's name isn't Steven. In fact, there are NO Stevens in my immediate family (probably because Steven Stevenson is a terrible name,) but there must have been a Steven waaaay back when.
It is also worth pointing out that in nations with hundreds if not thousands of millions of people, names aren't actually unique. This is why governments use other identifiers such as social security numbers, and drivers license numbers, and addresses. It is why Facebook includes information about the locations where people live, or the schools they've attended. In the end it all comes down to identifying people, and the bigger the society, the more information is needed to create a unique identifier.
Ta!