but we have phones that can store our frequently used numbers, so
we don’t have to keep longer strings of numbers in our head. Some
of us can keep in mind only five categories or, say, tasks on a to-do
list at the same time. Some of us can keep track of nine categories
simultaneously, but for most of us, seven is the benchmark, hence
Miller’s seven plus or minus two.
Until publication of Malcolm Gladwell’s book The Tipping
Point,most of us were probably not familiar with the “Rule of 150,”
although the documentation supporting the importance of this rule
had been around for a long time.^10 Gladwell highlighted the rule as
one of his many examples of “tipping points.” The book’s title is
based on the phenomenon of how an activity can exist for quite
some time without change or growth and then all of a sudden “take
off.” For example, a virus can for some period of time be limited to
only a few organisms or human beings, and then suddenly a tipping
point is reached and an epidemic occurs. A fashion trend can
appear and for a while no one seems to notice or join in; then a tip-
ping point of people joining in is reached and a raging fad ensues.
Gladwell explains the significant and quick drop in the crime rate
in New York City during the 1990s the same way.
The Rule of 150 is another example of a tipping point. When
the number of people who interact with one another—at work, in
a community, in a social club or society, or a commune—reaches
150, a tipping point occurs. Now let’s look to the documentation
and what the Rule of 150 means.
Gladwell points us to the work of British anthropologist Robin
Dunbar, who has studied the relationship of brain size in primates
and their social behavior.^11 He found that the larger the neocortex
in the brain, the larger the average size of the groups the primates
live with. One needs a sizable neocortex and overall brain to deal
with the complexities of large social groups. For us humans, if we
belong to a group of five people, we have to keep track of ten sepa-
rate relationships—our own relationship with the four others in
the group plus the six additional two-way relationships between the
others. “That’s what it means to know everyone in the circle,”^12
276 LEADINGORGANIZATIONALLEARNING