This image, from San Francisco, courtesy of Flickr user Ken Walton under a Creative Commons license.

Americans are pulling apart. We're pulling apart from each other in general. And, in particular, we're pulling apart from people who differ from us.

The evidence on this idea is varied, broad and often weird.

We are, as Robert Putnam famously put it, less likely to join community bowling leagues.

We're more likely, as I mentioned yesterday after a police confrontation with a group of black teens at a private swimming pool, to swim in seclusion, in gated community clubs and backyard pools that have taken the place of public pools.

We're more likely to spend time isolated in our cars, making what was historically a communal experience — the commute to work — a private one. In 1960, 63 percent of American commuters got to work in a private car.

Now, 85 percent of us do. And three-quarters of us are riding in that car alone.

Within large metropolitan areas, we live more spread out, more distant, from each other than we once did. The population density in central cities plummeted by half after the 1950s, as many residents left for the suburbs.

As a result, writes economist Joseph Cortright in a new City Observatory report, in metropolitan America we now have fewer neighbors, on average, and we live farther from them than we did five decades ago.

It's little wonder, then, that we now socialize with them less often, too.