Robin Dunbar is an anthropologist/primatologist who discovered a correlation between the size of a primate’s brain (or really its neocortex) and the size of that animal’s social network. For example, clever chimpanzees tend to live in groups of 60 or so individuals, who maintain complex intimate social relations (yet chimpanzees don’t really care about outsiders without elaborate introductions). Howler monkeys tend to live in groups of 6 or 7. Dunbar studied primate brains until he believed he found the correlation index… then he applied it to human beings based on our own neocortices (is that the right word?). The number he arrived at was around 150. He posited that this is the average number of stable meaningful social relationships we can have at once. Here is a humorous (yet oddly serious) article which explains the concept elegantly (albeit with some fairly salty language and preachy talk).
When one starts looking for the number 150, it crops up all over the place. Hunter gatherer tribes were (and still are) limited to about that number. Military companies of all sorts of different armies throughout history have been that size. Business consultants say that this is an ideal size for companies (come to think of it there are 150 people at the company where I work) or for departments of companies.
But of course the 150 people I work with are not the entirety of my social interactions. I have 500 or so Facebook friends and not a one of them is from work….and the people I am closest to are not always on Facebook. And there are people I know about but have never (and will never) meet (like Susanna Hoffs, the emir of Qatar, and…Robin Dunbar). High functioning individuals like Presidents, CEOs, and world famous artists probably know many thousands of people—or at least know the one or two key pieces of information which makes each contact useful.
So there are lots of troubles and quibbles with Dunbar’s number…yet if you really write out everyone you have a true worthwhile meaningful relationship with you will probably come up with about 150 (if you are a gregarious adult with a full life in a big city—you can have many fewer close relations and there is nothing wrong with that…it doesn’t mean you are a capuchin monkey or something).
(Not that there is anything wrong with that either)
There is a line we draw around our tribe. Within this line are people we care about and need, outside it are… others—people we may care about in the abstract, or because they share a language, or a characteristic, or a nationality with us…but who are not dear to our heart in the same way as our intimate associates. The writer I linked to in the first paragraph up there asks us to imagine having a beloved pet…or two beloved pets…or six, or 23. How long would it be before our love and our attention were so diluted that we only cared about them in the most general abstract terms (or just outright despised them as a furry horde)? Whether you accept the premise of Dunbar’s number or not, it is a worthwhile question. If our brains are built by evolution in such a way as to make an “us” and a “them” what does it mean for all of us?