A peer-reviewed study published in Scientific Reports has found that the falling US birth rate is being driven overwhelmingly by left-leaning Americans, while right-leaning Americans continue to have enough children to sustain the population.

Using the US General Social Survey — one of the country's longest-running social-science datasets — Fieder and Huber examined birth records from 22,975 American adults across 16 five-year cohorts, spanning individuals born between 1903 and 1982.

For most of the twentieth century, the birth rates of Americans on the political left and the political right were roughly in line with each other. Beginning with the cohort born between 1943 and 1947, that changed.

From that point forward, the birth rates of left-leaning Americans dropped sharply and fell well below the level required to sustain the population. Right-leaning Americans, over the same span, maintained birth rates at or slightly above 2.1 children per woman — roughly the level needed to keep the population steady. Centrist Americans landed in the middle.

The divergence, the authors note, began with the introduction of modern contraception.

"We expected these results, but not to such a dramatic extent," the researchers told PsyPost.

The takeaway offered by the researchers themselves is not primarily electoral. It is demographic.

"The main takeaway is that political change is not driven only by persuasion, elections, or short-term social trends," they said, "but also by demographic processes."

In plain English: over generations, the American right is having more children than the American left. If the pattern holds, that gap compounds.

The authors are careful about the limits of their findings. The study is observational — it can identify a correlation between political orientation and birth rates, but cannot prove that holding a left-wing attitude directly causes a person to have fewer children. The General Social Survey did not collect information on fertility intentions or on contraceptive use, so the mechanism behind the divergence is not directly measured. And the study relies on a simple left-to-right political scale, which the researchers acknowledge oversimplifies a complex ideological landscape.

The findings do not depend on any single culture-war explanation. What the data show is the pattern. What the researchers say publicly is that political demography is real, that it has been running in one direction for eighty years, and that it is now large enough to matter.

America's overall fertility rate has been below the population-sustaining level of 2.1 for years. This study argues the national average is masking a split: one half of the country is at or above the sustaining level, the other half is well below it. It is not, in the researchers' framing, primarily an economic story. It is an ideological one.