In the 1990s a British anthropologist, Robin Dunbar, postulated something that many business leaders had viscerally intuited: once a group grows larger than around 150 people, social constructs dilute to the point where dysfunctions begin to occur.

Several businesses have used this so-called 'Dunbar Number' as a limit for the size of individual operating units. Gore-Tex, for example, constructed company buildings with room for only 150 people.

The Dunbar Number is something we see companies bumping up against all the time - in fact, it's one of the major contributing factors to pushing a business into Whitewater. Broaching the Dunbar Number amplifies silo-ization, contributes to the breakdown of cross-functionality and dilutes alignment - three of the clearest symptoms that you've left Fun and have indeed fallen into Whitewater.

Here's the kicker: Unlike in the field of anthropology (Professor Dunbar's area of study), an organization's Dunbar Number isn't so easily narrowed to 150. A virtual company's Dunbar Number, for example, will be much lower (it can be as low as 20 people) than say, a manufacturing company (where 150 is typically pretty accurate). A highly Synergistic business will have a higher Dunbar number than say an Operator-dominant company.

So how can you tell you're reaching your Dunbar number, and what should you do about it when you do? Here's my personal Predictable Success finger-in-the-air test: The first time you see someone walking down the corridor and you can't remember their name, you've entered the Dunbar Zone...and the first time you see someone and can't recall even hiring them - you've hit your number.

What should you do? Obviously not everyone can simply go find another office building, like Gore-Tex, so here are some other tools you can use:

1. Amp up the communication.

Start water cooler sessions, increase the frequency of all-company meetings, start an internal company blog - anything to force non-siloed interactions.

2. Carve out a 'commons'.

Create a place or places where your people can mix in a relaxed, non-work environment. (The classic ping-pong table is a great start.)

3. Start walking around.

Don't just meet with your peers and direct reports - get out into the corridors, offices, cubicle farms, factory floors and talk. Talk. Talk. Engage with your people as people, be open and accessible.

One thing is guaranteed: unless you want a dysfunctional, siloed, increasingly ineffective business, once you're in the Dunbar Zone, inaction is not an option.

Learn How to Succeed in the Dunbar Zone here.