Robin Dunbar is a pretty cool dude. He’s an anthropologist (not a corporate anthropologist though, just a regular one), an evolutionary psychologist and a specialist in primate behaviour. But best of all, he has his own number.

Dunbar’s number – generally approximated to 150 – is a measurement of the "cognitive limit to the number of individuals with whom any one person can maintain stable relationships". I’ve just added “get my own number” to my bucket list … I think Pete’s number has a pretty good ring to it.

Turns out that with our neo-cortex the size it currently is, that’s about the limit to the number of genuinely social relationships we can have. And it turns out that number shows up everywhere when it comes to forming social groups.

Dunbar himself did a study of the Christmas-card-sending habits of the English (back in the pre-email days). Turns out the average Pom sent 153.5 Chrissy cards. Likewise anthropologists studying the world’s remaining hunter-gatherer societies have found that clans tend to have 150 members.

150 is also the basic unit size of the Roman army, and also the size of the modern Western military company.

Tom Peters wrote about W.L. Gore & Associates (the materials firm famous for innovative products such as Gore-Tex) who practice some pretty innovative management structures. When a branch exceeds 150 employees, the company breaks it in two and builds a new office.

How is this number relevant to us?

Firstly for any program you are offering or cluster you are taking to market, identify your top 150 prospects. Give them more love than you give to your whole list. If it’s a new cluster aim to get in front of 150 people over the first 12 months.

Secondly if you have a program that incorporates a community aspect, limit it to 150 people. That’s what we’ve done with Thought Leaders Business School. We are building fast to 150 students, but have capped the program at that number. Once we hit 150, there will be a waiting list.

And thirdly … I actually can’t think of the third thing, but I’m sure there is one. Love to hear your thoughts on what the third thing is, on what Pete’s number should be, or anything else. You can leave them below.