Dunbar Numbers & Human Units of Time

I can't remember when I started having my hair cut by Dick at Razor's Edge...4? 5? I did need to use the board used as a booster seat to fit into the barber's chair.

While getting my haircut before Christmas I was talking with Dick; I'm one of his longest running customers -- having gone to him either 36 or 37 of the 38 years he's been in the business.

It will be traumatic for me when he's no longer cutting hair, I believe in those 36+ years I've had my hair cut by someone else once, when he was on a vacation and his partner cut my hair for a wedding or some such thing.

Dick then mentioned with a sense of pride and awe he had just passed another milestone in recent weeks -- he had cut the hair for the fifth generation of the same family; and while the oldest members had long since passed away he's now cut the hair of a Father, Son, Grandson, Great Grandson, and the grandson had just brought in the Great Great Grandson for his first haircut.

There's two interesting concepts with how humans interact with each other and across time which that reminded me of. The first is the somewhat better known Dunbar Number. Most people maintain an extended social circle of around 150 people; much above 150 and groups tend to break up into smaller units. Or since we tend to live as individuals instead of tribes today, once you hit 150 you'll drop someone out of your social circles as you add a new person.

Now as anyone whose played Seven Degrees of Kevin Bacon know a person may fit into more then one group especially over time...but the group each person assembles around themselves will max out around 150 (from close friends to friendly acquaintances).

The second is the Human Unit of Time. Things like millions of years, or even a couple millenium; even going all the way back 250 years are fairly abstract concepts that people have a hard time understanding. But the Human Unit of Time is Five Generations, just like Dick's career milestone with that family.

The Human Unit of Time that people can reasonably understand how things have changed and how they will change, and what they most care about, because it's in terms of people you care deeply about stretch two generations on either side of you -- from your oldest Grandparent, to your youngest Grandchild. There isn't a precise definition of this in years; it's more then a century, less then two. 160 years -- 80 years back and 80 years forward -- is a good guess.

These define two dimensions -- a quantity (150 people) and place in time (80 years in the past to 80 years in the future). There's got to be a third dimension, something about quality...but I'm not sure quite what it is or would be.