In the early 2000s, a “meme” about Dunbar’s Number was all the rage, helped along by Malcolm Gladwell’s book, “The Tipping Point.” The science of it is as complex as the whole “10,000 hours to becoming an expert” thing is. But it’s been helpful to me, particularly when thinking about limitations of time on what I can do.

Short Story: Dunbar was an anthropologist at the University College of London who, based in some part on evolution ideas, predicted that 147.8 was the ‘mean group size’ for humans, which matched census data on villages and tribe sizes in many cultures. (from LifeWithAlacrity.com, see whole article here).

I know, you heard evolution, but don’t throw the baby out with the bathwater, as my mother used to say.

Dunbar’s Number has been featured and analyzed in numerous books and studies. I’m not an evolutionist, but there’s been plenty of studies to show the number is about the average. Bigger groups via technology don’t disprove the theory: they are audiences, not communities.

However, it takes a lot of time and work to get to a community of 150 – the research suggests half the time you spend with a group has to be spent in “social grooming” (which some theorize is, for us, social communication). Most groups are far smaller than that. That LifeWithAlacrity article above looks at Dunbar’s Number in relation to online multiplayer groups and sees the vast majority of groups have sizes around the 30s, 60s, 80s, 100s, and 130s.

Dunbar’s Function from LessWrong builds on LifeWithAlacrity, together they look like:

• Group of 3 unstable, one person feeling left out; 4 develops into 2 pairs; 5 to 8, have a meeting where everyone can speak out and everyone feels empowered; 9 to 12 this begins to break down, not enough attention.
• Past 12, you start specializing, having departments and direct reports, but not quite large enough to be efficient; past 25, large enough for efficiencies to kick in.
• 30 to 50, typical size of cohesive hunter-gatherer band.
• Peak of most sizes is about 60, not 150.
• 150, size of a cultural lineage of related bands.
• Past 150, groups start to split (Hutterite farming communities split here), or companies start to need middle management.

Shorter: Peak is about 7 for simple groups, and about 60 for complex groups, and every community fractures in some way by the time it approaches 150.

Technology does not change this. Partly, it’s an aspect of the capacity of your brain to remember/recognize people (which tech can help with). Partly, in my book, it’s just this: you only have so many hours in the day. You can’t spend them with everyone. The more hours you spend with one person, the less with another. So if you’ve a tribe of 150, and you spend an hour with each, that’s a month’s work.

So, how do we apply this to our own work? Everyone needs a group of people they’re working with (mostly). How many people you choose determines how you spend your time.

• If you’re working on your own, you don’t need it. You can go fast. (But the African proverb suggests you might not get far).
• If you’re working with a small team, probably should limit it to 5 to 9 people. So, who are your 5? Since you have at maximum 5 to 10 slots, pick wisely for wisdom, influence and ability to execute. Define your objective and then identify 5 people who can work closely together to achieve the objective. You can spend a ton of time with the 5, which will bring you very close.
• If you’re working on a larger project, you’ll need between 10 and 80. Now, you need to pick for diversity of gifts, resources, etc., but you need to also think about your time commitments to each. They have to be able to work in small groups on their own. You’ll need some who can lead their own 5-10 groups, because you can’t spend 5-to-10 group time with all 80. And, if you pick all 80 to have that leadership ability, you’ve maximized your chances of getting a really large group together.
• Past 80, you’re starting to be very organizational. Expect that you’ll definitely have to institute organizational thinking at that point. At the very least, you’re going to need name badges.

Read more

• “The Dunbar Number as a limit to group sizes”
• “Dunbar’s Function”
• “Are humans hard wired for a limited social circle?”
• “Security, group size, and the human brain”