At some point over the past generation, people around the world entered what you might call the age of possibility. They became intolerant of any arrangement that might close off their personal options.

The transformation has been liberating, and it’s leading to some pretty astounding changes. For example, for centuries, most human societies forcefully guided people into two-parent families. Today that sort of family is increasingly seen as just one option among many.

The number of Americans who are living alone has shot up from 9 percent in 1950 to 28 percent today. In 1990, 65 percent of Americans said that children are very important to a successful marriage. Now, only 41 percent of Americans say they believe that. There are now more American houses with dogs than with children.

This is not a phenomenon particular to the United States. In Scandinavia, 40 percent to 45 percent of the people live alone. The number of marriages in Spain has declined from 270,000 in 1975 to 170,000 today, and the number of total Spanish births per year is now lower than it was in the 18th century.

Thirty percent of German women say they do not intend to have children. In a 2011 survey, a majority of Taiwanese women under 50 said they did not want children. Fertility rates in Brazil have dropped from 4.3 babies per woman 35 years ago to 1.9 babies today.

These are all stunningly fast cultural and demographic shifts. The world is moving in the same basic direction, from societies oriented around the two-parent family to cafeteria societies with many options.

This global phenomenon has been expertly analyzed in a report called “The Rise of Post-Familialism: Humanity’s Future?” written by a team of scholars including Joel Kotkin, Anuradha Shroff, Ali Modarres and Wendell Cox.

Why is this happening? The report offers many explanations. People are less religious. People in many parts of the world are more pessimistic and feeling greater economic stress. Global capitalism also seems to be playing a role, especially, it seems, in Asia.

Many people are committed to their professional development and fear that if they don’t put in many hours at work they will fall behind or close off lifestyle options.

Toru Suzuki, a researcher at the National Institute of Population and Society Security Research in Japan, gave Kotkin’s team this explanation in its baldest form: “Under the social and economic systems of developed countries, the cost of a child outweighs the child’s usefulness.”

Singapore is one of the most interesting cases. Like most Asian societies, it used to be incredibly family-centered. But, as the economy boomed, the marriage rate plummeted. Singapore now has one of the lowest fertility rates in the world. “The focus in Singapore is not to enjoy life, but to keep score: in school, in jobs, in income,” one 30-year-old Singaporean demographer told the researchers. “Many see getting attached as an impediment to this.”

This cultural shift is bound to have huge consequences. Globally, countries that remain fertile, like the U.S., will do fine while countries that don’t, like Japan, will decline. Geographically, singles will dominate city life while two-parent families will be out in suburbia. Politically, married people in America are more likely to vote Republican; Mitt Romney easily won among married voters, including married women. Democrats, meanwhile, have done a much better job relating to single people. President Obama crushed Romney among singles, 62 percent to 35 percent.

The 2012 election results illustrate the gradual transition we are making from one sort of demography (the current Republican coalition) toward another sort of demography (the Democratic coalition). The rise of post-familialism is a piece of that shift.

My view is that the age of possibility is based on a misconception. People are not better off when they are given maximum personal freedom to do what they want. They’re better off when they are enshrouded in commitments that transcend personal choice — commitments to family, God, craft and country.

The surest way people bind themselves is through the family. As a practical matter, the traditional family is an effective way to induce people to care about others, become active in their communities and devote themselves to the long-term future of their nation and their kind. Therefore, our laws and attitudes should be biased toward family formation and fertility, including child tax credits, generous family leave policies and the like.

But the two-parent family is obviously not the only way people bind themselves. We are inevitably entering a world in which more people search for different ways to attach. Before jumping to the conclusion that the world is going to hell, it’s probably a good idea to investigate these emerging commitment devices.

The problem is not necessarily a changing family structure. It’s people who go through adulthood perpetually trying to keep their options open.