The nineteenth and twentieth centuries in Europe were marked by deep changes in fertility behaviour in which couples began to deliberately limit their number of children. These changes led to an unparalleled and long-lasting decline in fertility levels – a process known as the fertility transition. Even though this transition affected every society in Europe, it did not happen everywhere at the same time. Instead, the transition unfolded in a specific pattern: it spread from pioneering spots towards laggard areas in particular geographies and varying rhythms.
In a new study, Rafael Costa (Netherlands Interdisciplinary Demographic Institute), Philippe Bocquier (Université catholique de Louvain) and Thierry Eggerickx (Université catholique de Louvain) explore the role of diffusion mechanisms in the historical process of fertility decline. To what extent do ideas, attitudes and information related to a new fertility behaviour spread through social interactions, leading to fewer babies per women? To answer this question, the authors explore a unique dataset from historical sources in Belgium containing yearly information on fertility at the municipality level and a range of structural and cultural indicators over half a century (1887–1934).
Overall, their findings support the diffusion hypothesis but only in the early stages of the fertility transition. Fertility decline unfolded following a strikingly contiguous pattern, gradually spreading among neighbouring places year after year (see GIF below). It spread more quickly through industrial and transportation axes, whereas it was stalled by the linguistic border separating French- and Flemish-speaking populations. Part of these patterns is explained by cultural and socioeconomic changes such as industrialisation and secularisation. Yet, a substantial part of this pattern remains unexplained by cultural and structural variables in the early stages of the transition, before the turn of the twentieth century.
Between 1888 and 1895, municipalities were between two and nine times more likely to initiate their fertility transition if a neighbouring municipality had initiated its transition in past few years. In other words, the onset of the transition in a given area seemed to trigger the transition in the adjacent areas, independently of other factors that influenced fertility (such as urbanisation, industrialisation, secularisation, etc.). Moreover, the authors found that these triggers accelerated the pace of transition during these periods: without them, the onset of the fertility transition would have been delayed by roughly five years. In sum, their results suggest that diffusion processes among neighbouring municipalities contributed both to the geography and the rhythm of the transition in Belgium but only before the turn of the twentieth century.
The authors argue that, in the early stages of the transition, the bulk of people’s interactions was confined to their own communities and neighbouring places and, as such, new ideas, attitudes, and information about fertility would spread among adjacent areas. Later on, since the turn of the twentieth century, the way people interacted in space was transformed by the growing urbanization, the development of transportation infrastructure and labour migration. In this new context, opportunities for social interactions were less constrained by space: if diffusion processes were still at play, they would have operated over longer distances.