Recent research published in scientific report It suggests that political beliefs are increasingly tied to the number of children Americans choose to have. The findings show that conservative people tend to keep fertility rates close to historical averages, while left-leaning people have significantly fewer children. This demographic trend provides evidence that differences in fertility rates are a major factor in the recent decline in fertility rates in the United States.
Political attitudes are often thought of as simple opinions. However, research suggests that they are relatively stable traits shaped by both social upbringing and genetics. Because parents tend to transmit their political orientation to their children, differences in family size between political groups can influence the ideological balance of a population over time.
Martin Feeder and Suzanne Huber wanted to understand how this relationship developed. “As evolutionary biologists, we are interested in why left-wing and right-wing political orientations have evolved and whether they are influenced by natural selection due to differences in reproductive capacity,” explained Feeder, associate professor of evolutionary demography at the University of Vienna. “Early research shows that political orientation is heritable and that birth patterns vary across the political spectrum.”
Demographers study how societies transition to lower birth rates as they become wealthier. This shift is accompanied by cultural shifts, including a greater emphasis on individual achievement and non-traditional family structures. The authors aimed to investigate whether this general fertility decline is occurring evenly across the political spectrum.
“Globally, countries at both political extremes often have high birth rates, but the patterns in the United States and Europe are different,” Feeder said. “People with more conservative political views tend to have more children than people on the political left.”
These new findings build on previous work conducted by the researchers. In a 2018 study published in frontiers of psychologyresearchers analyzed global survey data. They found that in many regions, both far-left and far-right individuals had higher birth rates than political moderates.
However, analysis of US data in the same paper suggests that a unique advantage for conservatives began to emerge in the 1990s. More recently, a 2024 study by the same authors found that Biodemography and sociobiology He pointed out that conservatives in Europe tend to have more children and grandchildren than liberals.
“Previous research has demonstrated that these fertility differences are likely to contribute to Europe’s gradual demographic changes toward more conservative societies,” Feeder said. “In this study, we wanted to find out when this difference in fertility first appeared.”
To explore these trends, scientists analyzed data from the U.S. General Social Survey collected between 1970 and 2022. The sample included 22,975 adults, 10,681 men and 12,294 women. All participants were over the age of 40, meaning they had almost reached the end of their childbearing years.
Participants were grouped into 16 birth cohorts based on 5-year intervals. The study began with people born between 1903 and 1907 and ended with people born between 1978 and 1982. The researchers measured political orientation using a seven-point scale ranging from far left to far right, and grouped these responses into three broader categories representing left, center, and right.
To assess how fertility affects the spread of political traits over time, the researchers used statistical tools commonly applied in evolutionary biology to measure phenotypic selection. This method allows scientists to measure how strongly certain observable traits influence reproductive success.
The data revealed significant changes in the relationship between political beliefs and family size. For people born in the early 1900s, political orientation had little to do with the number of children they had. However, significant differences emerged from the population born between 1943 and 1947.
“We expected these results, but they weren’t that dramatic,” Feeder told SciPost. Since mid-century, people with right-wing political views have maintained birth rates at or slightly above replacement levels. The replacement level, usually considered to be 2.1 children per woman, is the rate required for the population to replace one generation to the next without immigration.
In contrast, birth rates on the left have fallen sharply and are well below replacement levels for recent groups. The authors found that this decline is consistent with historical changes in family planning. “We found that this gap started with the introduction of modern contraceptive methods,” Feeder said.
“Those on the political left of the political center had a marked decline in fertility, while those on the right of center generally maintained fertility near or above replacement levels,” Feeder added. Individuals with centrist political views fall somewhere in between. Their birthrate remained slightly below replacement level, but consistently higher than that of those on the left.
“These findings provide new insights into the demographic drivers of fertility decline and suggest that differences in fertility may contribute to long-term changes in the political composition of the population, given that political orientation shows substantial similarity between parents and offspring,” Feeder said. The study suggests that “much of the ‘shift to the right’ currently observed in many countries is related to underlying demographic changes.”
The authors also looked at how race interacts with these demographic trends. Analyzing white and black Americans separately, they found that the widening birth gap between the left and the right was driven primarily by white Americans. Among white participants, the conservative reproductive advantage increased significantly in more recently born cohorts.
For black Americans, researchers did not find similar political differences. The overall birth rate for Black Americans also declined over time, although birth rates remained relatively similar across the political spectrum. The authors suggest that this may occur because ideological labels such as liberal and conservative are often understood differently across different racial and cultural groups.
In addition to political views, the study found that other lifestyle factors strongly predicted family size. Education is consistently associated with lower fertility rates, meaning that people with more years of schooling tend to have fewer children. This negative association is particularly strong for women, and this pattern is consistent with broader demographic studies.
Religious attendance was positively associated with having more children. Interestingly, the data showed that frequent religious attendance promoted reproduction more strongly for men than for women. Still, as the reproductive advantage of right-wing politics has increased in recent generations, the independent effect of religious attendance on family size has weakened somewhat.
The authors suggest that different views on family planning and lifestyle autonomy may be contributing to these differences in fertility. “The main lesson is that political change is not only caused by persuasion, elections, or short-term social trends, but also by demographic processes,” Feeder said.
“Our findings suggest that differences in fertility across the political spectrum can gradually change the political composition of the U.S. population over time,” Feeder said. “In particular, the decline in overall fertility seems to be driven primarily by a sharp decline in the number of births among people outside the political center, perhaps since the widespread use of modern contraceptives, but our data cannot directly prove this mechanism.”
This represents an important limitation of the study. Because the study relied on observational data, it cannot prove that holding leftist attitudes directly causes fewer children to be born. Survey data do not track individuals’ fertility intentions or contraceptive use.
“We hypothesize that differences in the use of modern contraceptives may have contributed to the dramatic decline in birth rates among those far from the political center,” Feeder said. “However, our data do not allow us to directly test or confirm this hypothesis.”
Furthermore, measuring political orientation on a simple left-to-right scale oversimplifies the complex nature of human ideology. People often have a mix of socially conservative and economically liberal views, which can influence their life choices in many ways.
Future research could investigate how different types of conservatism, such as economic conservatism and social conservatism, affect family planning. The researchers also plan to examine how these patterns work outside of wealthy post-industrial countries.
“We also want to investigate whether similar trends are starting to emerge globally, particularly in developing countries. Our 2018 survey suggests that fertility rates across the political spectrum are still relatively balanced,” Feeder said.
The study, “Left-Left Fertility Decline as a Key Factor in U.S. Fertility Decline” was authored by Martin Feeder and Suzanne Huber.
