Philip Cohen takes a fascinating look at how America's population has changed since 1972 -- broken down by religion, race, marital status, and age of first marriage. Lots of changes and increasing diversity on all fronts.
There are various ways of constructing a diversity index, but I use the one sometimes called the Blau index, which is easy to calculate and has a nice interpretation: the probability that two randomly selected individuals are from different groups...Read the whole thing. Lots of interesting graphs.
I have complained before that using the 1950s or thereabouts as a benchmark is misleading because it was an unusual period, marked by high conformity, especially with regard to family matters. But it is still the case that since then diversity on a number of important measures has increased. Over the period of several generations, in important ways the people we randomly encounter are more likely to be different from ourselves (and each other).