10.4 Demographic Influences

In recent years, the media started bemoaning the declining fertility rate in the United States and other countries. This is a global phenomenon, begun largely in the mid-1950s and early 1960s, as major political and environmental shifts began to take place. This is known as a demographic transition.

So far, there have been four major demographic stages in human fertility rates. For millennia, humans have lived in small scale, foraging societies in which natural fertility was the norm. In a natural fertility society, women reach menarche later in life, marry earlier, and have an average of 5-7 children. The interbirth interval, time between births, is approximately 3 years, and menopause begins around 40 years of age.

The emergence of agriculture and changes in religious practice resulted in a significant increase of births per woman. This resulted in significantly reduced interbirth intervals, averaging just 1.5 years between births. Menarche began around 14 years of age, women married slightly later (usually around 18 years of age), and menopause began to set in later due to continued pregnancies and lactation. Some women had as many as 12-14 children in major agricultural settlements – including colonial America – though the average is 10 children. In addition to having children for future help with the land, it was not uncommon for women to lose some of these children to illness before they reached maturity. This second stage is known as the rural/pre-modern era.

The first demographic transition occurred during the Industrial Revolution. As cities grew, and manufacturing promised more stable income, children became an economic cost. As such, the first major drop in fertility occurred. By post-World War II, women were experiencing menarche as early as 12-13 years of age, marrying as late as 24 years of age, and having an average of two children – four years apart. Extended lengths of lactation gave way to bottle feeding, and women found themselves freed to consider personal fulfillment beyond motherhood.

Many cultures are now experiencing the second demographic transition, marked by subreplacement fertility rates, increased educational attainment, postponement of marriage and parenthood, alternative partnerships, and a new life orientation. For the first time, humans find themselves able to consider life options beyond marriage and parenting, and many are doing so.

The table below summarizes how demographic changes influences the fertility and life history of females. To view trends for total, global fertility rates or by country, visit the World Bank’s Fertility rate, total online database.