A Pew survey late last week found that 44% of Americans between 18 and 49 who aren't parents say it is not too likely or not at all likely that they will have children — an increase of 7 percentage points from 2018.

Why it matters: The shift could lead to smaller family Thanksgiving dinners and major social and economic changes, as children become rarer in many parts of the country and more American adults reach old age with little to no family to support them.

By the numbers: The effect of greater childlessness is being felt in U.S. fertility numbers, which were already at a record low before 2020 and have continued to drop during the pandemic.

• "[T]he main cause of declining fertility in America is increasing childlessness at all ages" rather than declining second or third births, writes Lyman Stone, a research fellow at the Institute for Family Studies (IFS).
• More adults are reaching retirement age without children, and increasingly without a partner. Data released by the Census Bureau this year found that 19.6% of Americans between 55 and 64 reported being childless, compared to 15.9% of those 65–74 and 10.9% of those over 75.
• In San Francisco — where there are more dogs than children — kids make up just 13% of the population, down from 13.4% in 2010 and dead last among the 100 most populous U.S. cities.

The big picture: Most of those in the Pew survey who report they're unlikely to have kids say the reason is that they just don't want to have children. But Americans, in general, have also become more interested in smaller families.

• Data from Gallup polls find that Americans' ideal number of kids has fallen from around 3.5 in the 1930s to 2.5 today. And that's still well above the current actual level of 1.7 lifetime births per woman.
• Fears about the environment, supposed overpopulation and the general state of the world have been getting a lot of press. Morgan Stanley analysts this summer noted that the concerns are "impacting fertility rates quicker than any preceding trend in the field of fertility decline."
• Yes, but: Just 5% of expected non-parents in the Pew survey cited environmental reasons, a figure that is largely unchanged from earlier surveys.

What they're saying: Much of the increase in childlessness is a result of what Stone calls "stage of life reasons," including declining rates of marriage and coupling.

• Another factor is the perception among many Americans that modern parenting is particularly time- and labor-intensive, which means that choosing to have children means forgoing leisure and work.
• "People who say they are worried about how good a parent they'll be and who think parenting is really important for the child, tend to have lower fertility rates," says Stone.

Details: Such parental anxiety is an example of one of the most powerful forces behind changing fertility norms: social contagion.

• A 2012 study found that in Brazil, where TV soap operas portrayed smaller families than the norm, increased access to television was associated with significantly lower fertility.

What's next: Increased financial support for families does tend to boost fertility, but largely at the margins.

• Scandinavian countries with generous family leave policies have higher fertility rates than southern European countries without them. But births there are still below the "replacement rate" of 2.1 children per woman — the number of births needed to maintain the population — and roughly equivalent to the U.S.
• The Democrats' Build Back Better plan includes significant subsidies for child care, but a number of commentators have made the case that it will actually raise the cost of child care significantly for much of the middle class.

What to watch: There's a growing political and cultural division in the U.S. over family size.

• While religious Americans have long tended to get married earlier and have more children than secular Americans, the differences were much smaller in the 1970s and '80s than since 2000.
• A report last month co-authored by Stone about the pandemic's effect on family formation found that religious Americans were three times more likely than secular Americans to say they plan to have a baby in 2021 or 2022.
• At the same time, religiosity is largely declining in the U.S. — less than half of adults say they belong to a house of worship — leaving fewer Americans exposed to pro-childbearing norms.

The bottom line: Whether it's right to bring a child into the world is an individual decision, but one that is highly influenced by changing social attitudes — in either direction.