Bella DePaulo, a visiting professor of psychology at the University of California, Santa Barbara, is the author of "Singled Out." She writes the “Living Single” blog for Psychology Today.

There are so many ways to live and love. The sentimentalized image of Mom, Dad and the kids gathered around the hearth has had its day. A new American experiment has begun. We’re not all going nuclear anymore.

Among the innovators are people of all ages who are single at heart. They are not single because they have issues or because they have not yet found a partner. They are not looking. Single is who they really are. Many are in the market for places of their own. So, too, are plenty of divorced and widowed people and single parents whose children have grown.

We’re not all going nuclear anymore. The results can be far more fulfilling than the same old boxes.

An unlikely demographic has also joined the quest for solo living – committed couples. In a trend dubbed “living apart together,” the two people maintain homes of their own not because far-flung jobs demand that but because they want it. A study of married couples at two different points in time showed that even living together under the same roof is not what it used to be. In 2000, the couples were less likely to eat together or work on projects together than they were in 1980. They also had fewer friends in common.

Are we all just crying out for more solitude and separation?

I think not. What we are really seeking is the optimum balance of time alone and time together. It is the social and personal quest that transcends marriage, family status, age, race and just about every other demographic characteristic.

Walk outside the door of the people living solo and you may just find a sibling or lifelong friend in the neighborhood or even in the same building. That’s not happenstance. In a variation on the same theme, people live in the same home with some private spaces and some shared.

Adults approaching the end of their working years are opting out of “retirement homes” and instead creating their own communities. Singles and couples, friends and family members, plan years in advance where and how they want to live. Rather than stepping into someone else’s vision of how to age, they are inventing their own, complete with roommates or neighbors of their own choosing.

Sometimes people are jolted into shared living by economic challenges or natural disasters. Young adults or parents with small children move in with their own parents. Friends welcome friends into their homes to ride out the rough patch. The new doubled-up arrangements can be experienced as little more than a hardship. Occasionally, though, the sailing is so smooth and warm that all agree to continue. When people organically develop their own experiments in living, the results can be far more fulfilling than the solutions unpacked from the same old boxes from the past.

Alongside all of the imaginative designs for living generated in free-wheeling conversations by a pair of friends here or a group of baby boomers there, are options that are becoming systematized. Co-housing, co-ops, pocket neighborhoods, co-parenting and condos with dual master bedrooms are just a few examples. Sometimes the community members share an identity – perhaps as artists or single parents or home-schoolers; other times, the main connection is affection. These living arrangements are the communes of the 21st century.