Last week I met four bright co-founders working on a new company together. Given that they were school-friends, it's not surprising that they had age, gender, ethnicity and many interests in common.This is a natural way for teams to form. It also tends to self-perpetuate: before we know it, those 4 co-founders expand to a team of 10 and then 20 from the same in-groups... at which point it gets hard to attract candidates who don't look and feel the same. I've previously written how this happened to me: our demographic mix at 1000 people was the same as it had been for the first 20.