Fertility

by

S. Philip Morgan

• LAST REVIEWED: 08 April 2020
• LAST MODIFIED: 26 August 2013
• DOI: 10.1093/obo/9780199756384-0150

Introduction

Fertility refers to the actual production of offspring and not the biological potential to reproduce (fecundity). Fertility is rooted in a biological sequence of conception, gestation, and birth; social and environmental factors heavily influence each stage. Thus, the factors affecting fertility are diverse and are potentially interactive; as a result, understanding fertility change/variation requires a multidisciplinary approach. Sociologists emphasize social and environmental factors that have potential impacts at the population level, that is, sociologists focus on factors that can account for fertility changes over time or differences between populations. Rapid global population growth in the second half of the 20th century emerged as a central policy concern in both the United States and internationally. Differential fertility of national co-resident groups or adjacent population groups has also spawned concerns about future governance and security. Sociologists study the underlying reasons for these fertility changes/differences and their purported consequences. Sociologists also study variation in fertility across individuals because fertility number and timing can affect the life courses of individuals (of parents and children) and the families they form.

General Overviews

Overviews are of three types: (1) those that describe or project the long-term trends and/or differences in fertility (and/or population growth more generally) (e.g., Cohen 2003, Lutz and Samir 2010), (2) overviews of the possible factors affecting fertility, either focusing on proximate causes (e.g., Davis and Blake 1956, Bongaarts 1978, Bongaarts and Potter 1983) or more distal/fundamental causes (Livi Bacci 2012), and (3) overviews of available data and measurement strategies (Preston, et al. 2001). Global population increased dramatically during the past few centuries (roughly tenfold from 1700 to 2000) and doubled in the last four decades (Cohen 2003). This population increase is the result of more rapid declines in mortality than in fertility. The 2010 global population of 7 billion is projected to peak at 8 to 10 billion in the later part of the 21st century (Bongaarts and Bulatao 2000) as global fertility approximates replacement levels. Populations experience fertility transitions from high to low levels. Prior to the transition, fertility was necessarily high to offset high mortality. Pre-transition levels were determined primarily by the “proximate determinants” of age of entry into sexual unions and the length of breastfeeding (Bongaarts and Potter 1983). By the beginning of the 21st century, many countries had completed a transition to low fertility. Most others countries were in the process of transitioning to low fertility. The fertility transition is driven by the proximate determinants of greater acceptability/use of birth control. General processes of social and economic development (including the decline of infant and child mortality) accompany the fertility declines although these changes can be asynchronous on a decadal time scale. Fertility levels show important variation post-transition, with fertility in some counties at very low levels. Past fertility levels/trends are well described, although the detail and accuracy are reduced as one reaches backward in time. Fertility research benefits from standardization of measurement and widely available data, much of it collected for administrative purposes.

• Bongaarts, J. 1978. A framework for analysing the proximate determinants of fertility. Population and Development Review 4:105–132.

  DOI: 10.2307/1972149

  Bongaarts describes a model of proximate determinants in which four factors are primarily responsible for fertility variation: the proportion of the population in a reproductive union, the length of breastfeeding, the use and effectiveness of contraception, and the use of abortion. Bongaarts describes how each of these factors can be operationalized with widely available data.

• Bongaarts, J., and R. A. Bulatao, eds. 2000. Beyond six billion: Forecasting the world’s population. Washington, DC: NAS Press.

  Written by members of a National Academy of Sciences panel, chapters in this book discuss past trends in fertility and their contribution to population growth. The accuracy of past projections is assessed and the most likely course for future fertility and population growth is forecast.

• Bongaarts, J., and R. G. Potter. 1983. Fertility, biology and behavior. New York: Academic Press.

  The authors develop in more detail the proximate determinants model described in Bongaarts 1978 and develop additional models and applications. The book contains a very useful chapter on sex preference and its effects on fertility levels.

• Cohen, J. E. 2003. Human population: The next half century. Science 302.5648: 1172–1175.

  DOI: 10.1126/science.1088665

  Cohen offers a brief, authoritative description of past trends in population growth and a balanced discussion of possible future scenarios.

• Davis, K., and J. Blake. 1956. Social structure and fertility: An analytical framework. Economic Development and Cultural Change 4:211–235.

  DOI: 10.1086/449714

  The authors developed a conceptual model of fertility’s proximate determinants, the precursor to Bongaarts 1978. They identified three classes of variables: those that influenced the likelihood of sexual intercourse, conception, and successful gestation. Thus, social, economic, and other variables can influence fertility only by influencing one of these proximate factors (intercourse, conception, or gestation).

• Livi Bacci, M. 2012. A concise history of world population. Malden, MA: Wiley-Blackwell.

  This book offers a broad, concise, accessible, authoritative history of population change.

• Lutz, W., and K. C. Samir. 2010. Dimensions of global population projections: What do we know about future population trends and structures?. Philosophical Transactions of the Royal Society B: Biological Sciences 365.1554: 2779–2791.

  DOI: 10.1098/rstb.2010.0133

  A recent, brief, balanced description of past global trends in fertility and population and forecasts of future fertility and population. Population stabilization and the onset of a slow population decline are forecast for the second half of the 21st century.

• Preston, S. H., P. Heuveline, and M. Guillot. 2001. Demography: Measuring and modeling population processes. Malden, MA: Blackwell.

  The book is the current standard reference on measurement and modeling demographic processes. See especially chapter 5, “Fertility and Reproduction,” which provides a straightforward description of the full range of fertility measures used by demographers.