I can tell what projects David is working on by the things he notices. He came back from getting the Sunday paper and mentioned that everyone who drove past seemed to be on their cellphones. At first he saw this as a sign of the encroachment of urban life, but realized,he said, that until recently humans have spent almost all their time in close contact with lots of other people. Hunting and gathering in groups, farming and cooking and sewing together, and even sleeping in the same rooms. So the teenage compulsion to IM with a dozen people at once and talk to one friend after another is natural in terms of our cultural evolution. What’s unnatural is living in isolation.

It’s no surprise that one of our next big projects is the Berkshire Encyclopedia of World Cultures, “A roadmap to the cultural landscape of the contemporary world.” But we’ll still be trying to drag Rachel away from computer and phone to go for a walk. That’s natural, too.