Yet as she and other experts note, single people often contribute more to the community — because once people marry, they tend to put their energy and focus into their partners and their own families at the expense of friendships, community ties and extended families.

In a report released this week by the Council on Contemporary Families, Dr. Gerstel notes that while 68 percent of married women offer practical or routine help to their parents, 84 percent of the never-married do. Just 38 percent of married men help their parents, compared with 67 percent of never-married men. Even singles who have children are more likely than married people to contribute outside their immediate family.

“It’s the unmarried, with or without kids, who are more likely to take care of other people,” Dr. Gerstel said. “It’s not having children that isolates people. It’s marriage.”

The unmarried also tend to be more connected with siblings, nieces and nephews.