For centuries, the Catholic Church upheld the biblical command to “be fruitful and multiply”, fostering large families. Yet today, Catholic-majority nations are experiencing a dramatic fertility collapse, raising the question: How did a religion once synonymous with high birth rates become linked to demographic decline?
Between 2014 and 2024, Argentina, Pope Francis’ home country, experienced a decline in its fertility rate, going from 2.33 children per woman to 1.16 children per woman. In that same period, the number of live births declined from 777 thousand to 420 thousand, a staggering 45% drop. A similar development occurred in Chile, Uruguay, and Colombia in the past decade.
Historically, Catholic countries in Europe that have undergone significant secularisation—such as Italy, Spain, Portugal, Malta, Poland, and Austria—now consistently face low fertility rates. In contrast, historically Protestant, though now largely secular countries—including the United Kingdom, the United States, Australia, New Zealand, Sweden, Norway, Finland, Canada, Iceland, and Denmark—have fared notably better. Between 1990 and 2020, the average fertility rate in the aforementioned Catholic grouping was 1.41 children per woman, compared to 1.85 in the Protestant-majority group of countries.
While the difference may seem minor at first glance, its impact is not. In a population with a fertility rate of 1.41, each generation will be about 33% smaller than the previous one. With a fertility rate of 1.85, the decline is slower, at around 12% per generation. Over multiple generations, these differences compound dramatically: in 100 years, the former population would shrink to less than a third of its original size, while the latter would retain roughly two-thirds of its former population. These figures might mean the difference between a managed decline (mitigated by immigration and social reforms) and outright societal collapse.
Significant differences in reproductive behaviour
As with every demographic trend, there are outliers. France or Ireland, both historically Catholic, resemble Protestant countries more than Catholic ones in their fertility patterns, while the opposite is true for German-speaking Protestant populations, whether in Germany or Switzerland. But the overall trends are strong enough to constitute a clear demographic cleavage between the two groups. While people often tend to ascribe higher fertility in certain countries, for example in France, UK or Sweden, to their large immigrant populations, data shows that it is caused by the native population's reproductive behaviour.
Even though it is indeed true that the migrant populations often have higher fertility than the natives, data shows that even among the latter, there are significant differences in reproductive behaviour from one country to another, i.e. without immigration.
In the past, that was not the case. Throughout the 20th century and up to the 1980s, Catholic countries usually had a fertility advantage. A similar story occurred on a micro-level between white Catholic and Protestant populations in the United States. During the baby boom era, Catholic families tended to have higher fertility rates compared to their Protestant counterparts. However, by the 1980s, this trend had reversed. Among non-Hispanic whites, Catholic total fertility rates were approximately one-quarter of a child lower than those of Protestants (1.64 vs. 1.91).
These demographic shifts raise a key question: Why has Catholic fertility collapsed so dramatically, while Protestant-majority countries have fared better? As with most demographic issues, it is a multifaceted problem that eludes clear and simple answers. Religion, or lack of it, is just one of numerous sociocultural factors determining fertility patterns.
While white American Catholics, often of Polish or Italian ancestry, may have lower fertility than white Protestants, their fertility is still closer to the American average than to the situation in Poland or Italy. Country-specific factors thus clearly play a significant role. An advanced French welfare state, similar to that of Sweden’s, contributes to France having a fertility rate similar to Sweden. Policy clearly matters.
The overall socio-economic development
One must also consider the overall socio-economic development of a country. High fertility rates among Catholic populations in sub-Saharan Africa, for example, do not disprove the overall trend of lower Catholic fertility, as these societies, with large rural and illiterate populations, are at a vastly different stage of development. Despite these factors, above all else Catholic fertility has been most affected by the wave of secularisation that swept the West in the second half of the 20th century.
Catholicism historically relied on strong communal enforcement of social norms—marriage, large families, and religious adherence were upheld through tight-knit family networks, local parishes, and social expectations. Protestantism, by contrast, has long emphasised personal faith and individual moral responsibility, meaning religious adherence was less dependent on external pressures.
Protestant countries secularised earlier and more gradually, allowing time for societal adaptation. When secularisation arrives in Catholic countries, it is swift and all-encompassing, rapidly eroding traditional norms. France, the earliest Catholic country to secularise, now mirrors Protestant fertility patterns.
In various attempts to rank cultures according to their promotion of individualism, such as in the Hofstede Model of Cultural Dimensions, Protestant countries always occupy the upper echelons. The rise of individualism, one of the major cultural revolutions post-WWII, came more easily to Protestant societies, to no small degree due to Protestantism's inherently decentralised character. While the Catholic Church is, true to its meaning, universal and all-embracing, Protestantism comprises thousands of denominations, large and small, worldwide.
Fertility advantage
This diversity also influences fertility. A study from the European Journal of Population shows that adherents of more conservative Protestant denominations in the Netherlands, such as the Dutch Reformed Church, have a fertility advantage of up to 0.5 children per woman over those who adhere to mainstream Protestant denominations. A similar trend is seen in the U.S., where Evangelicals, despite the fact that its white contingent is getting older, maintain a fertility advantage over mainstream Protestants.
There is an element of competition within Protestantism, and competition breeds dynamism. New denominations might pop up and grow, much like start-ups, with the Catholic Church resembling an ossified corporation unable to react to a fast-changing world. In Protestant-majority countries with a Catholic minority, such as the UK, Catholic fertility patterns are more favourable. Research by demographer Paul Morland showed that Catholic fertility in Northern Ireland during The Troubles was heightened by demographic competition with the local protestant majority. The fertility collapse is, on the contrary, most pronounced in countries where the Catholic church was the undisputed religious hegemon.
Swift secularisation
A process of swift secularisation is now unfolding in Latin America, home to 40% of the world’s Catholics. In Brazil, the Catholic population declined from 66% in 2010 to 55% in 2020, in Mexico from 83% in 2010 to 74% in 2020, and in Argentina from 76% in 2010 to 49% in 2020. Apart from an increase in the number of irreligious people, various Evangelical denominations are gaining traction in the region.
While certainly not the only factor contributing to Latin America’s fertility free-fall ,that of secularisation cannot be underestimated.
The Catholic Church, once linked to large families, now faces a demographic crisis in its traditional strongholds as secularisation reshapes fertility patterns. Meanwhile, Protestantism’s decentralised structure has allowed some denominations to sustain higher birth rates.
Yet Catholicism remains a global force, growing in Africa and parts of Asia. Its future position in its traditional strongholds might depend on its ability to harness the dynamism produced by competition, both with irreligiousness and protestantism.
Far from having a monopoly, it must make peace with the fact it is but one of the players on the ferocious marketplace of religious ideas.
Statement
Once synonymous with large families, Catholic-majority nations now face a demographic crisis, with fertility rates plummeting in both Europe and Latin America. In contrast, historically Protestant countries, though largely secular, maintain higher birth rates. The collapse of Catholic fertility aligns with rapid secularisation, eroding once-powerful communal and religious norms. Protestantism’s decentralised nature fosters competition and adaptability, with conservative denominations retaining a fertility edge. While Africa remains a stronghold for Catholic growth, the Church’s influence in the West is fading. Its future success will depend on its ability to compete with different belief systems.