But is the rule true in today’s world of social media?

There are well-defined limits to the number of friends and acquaintances the average person can retain.

But are these limits the same in today’s digital world – one in which it’s common to have social media profiles, or online forums, with thousands of followers.

The Dunbar-Number Theory shows a ratio between brain sizes and group sizes. This ratio was mapped out using neuro-imaging and observation.

Dunbar applied this basic principle examining historical, anthropological and contemporary psychological data about group sizes, including how big groups get before they split off or collapse. They found remarkable consistency around the number 150.

It makes sense that there’s a finite number of friends most individuals can have.

Dunbar’s Number is 150

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According to Dunbar-Number Theory, the tightest circle has just five people – loved ones.

That’s followed by successive layers of 15 (good friends), 50 (friends), 150 (meaningful contacts), 500 (acquaintances) and 1500 (people you can recognize).

People migrate in and out of these layers, but the idea is that space has to be carved out for any new entrants.

– It turns out, as predicted, that there really is an inner-inner layer at 1.5

– Perhaps because girls can have two intimate relationships (a best girlfriend PLUS a boyfriend)

– But boys can only manage one (a girlfriend or nothing)?

These numbers really represent range. Extroverts tend to have a larger network and spread themselves more thinly across their friends, while introverts concentrate on a smaller pool. And women generally have slightly more contacts within the closest layers, than men.

More and more people are preaching the gospel of small being better when it comes to online social life. Scale may be one of the issues with the massive social networking sites that now dominate our lives.