There are two kinds of social capital: bonding and bridging. Bonding occurs when you are socializing with people who are like you. Bridging occurs with people who are not like you.
Robert Putnam, Bowling Alone (1995)
bonding
bridging
Self-destruction of diversity is caused by success, not by failure.
Jane Jacobs, The Death and Life of Great American Cities (1961)
building community:
who / how / why
The average scientist, so far as I can make out, spends almost all his time working on problems which he believes will not be important and he also doesn't believe that they will lead to important problems.