1.3 Population challenges and opportunities

In high-income countries (HICs), average family size has fallen sharply over the past half-century. Many HICs now have a total fertility rate (TFR) — the average number of children a woman would have during her reproductive years — below the replacement level of approximately 2.1 children per woman. This is a defining feature of the later stages of the demographic transition model, where both birth rates and death rates are low.

Three interlinked social and economic drivers explain this shrinkage:

• Education: As access to secondary and tertiary education expands, especially for women, the average age of marriage and first childbirth rises. Years spent studying are years not spent starting a family, directly compressing the reproductive window.
• Career priorities: Greater female participation in the workforce means many women weigh the financial and personal benefits of career progression against the demands of child-rearing. Delaying or limiting births is often a rational response to maximizing lifetime earnings and professional advancement.
• Rising cost of raising children: In HICs, childcare, housing, education, and healthcare costs have all risen relative to income. Children in HICs are typically net financial dependants for two decades or more, rather than contributors to household income or old-age support, as they might be in lower-income agrarian societies.

This trend has significant downstream consequences: sustained sub-replacement fertility contributes directly to the aging population structures common in HICs, which in turn creates pressure on pension systems, healthcare provision, and the working-age support ratio — issues addressed by pro-natalist policies such as France's childcare incentives and financial support schemes.

While total fertility rates (TFR) have fallen below replacement level (2.1 children per woman) in most high-income countries (HICs), many low-income countries (LICs) - particularly across Sub-Saharan Africa and parts of South Asia - continue to record TFRs of 4, 5, or more children per woman. This persistence is not accidental or random; it reflects a combination of deep-rooted cultural values, structural barriers to fertility control, and rational economic decision-making by households responding to their circumstances.

Cultural and social values. In many LIC societies, large families carry strong social prestige and are linked to religious or traditional beliefs that regard children as a blessing. High status may be attached to motherhood and fatherhood, and extended family or communal living structures mean the costs of raising children are shared across households. Early marriage and limited female autonomy in decision-making about reproduction also contribute to sustained high fertility, since women often have less power to space or limit births.

Lack of access to contraception. Family planning services, reliable contraception, and reproductive health education are frequently scarce, expensive, or culturally stigmatized in LICs. Rural and remote populations especially may lack clinics, trained health workers, or the transport needed to reach services. Where governments have not invested in national family planning programmes (unlike China's historical anti-natalist approach or India's ongoing initiatives), unintended and closely spaced births remain common.

Children as economic assets. In agrarian, low-income economies, children - particularly from a young age - contribute labour to farming, herding, water collection, and informal trading, effectively lowering household production costs. High rates of infant and child mortality in LICs also encourage families to have more children as a form of insurance, anticipating that not all will survive to adulthood. Additionally, in contexts without state pensions or comprehensive social security, children (especially sons in many patriarchal societies) are relied upon to support parents in old age, making a larger family a rational long-term economic and welfare strategy rather than simply a cultural preference.

The sex ratio of a population is the balance between males and females, usually expressed as the number of males per 100 (or per 1,000) females. In most human populations, biology alone produces a slightly male-skewed ratio at birth (roughly 105 boys per 100 girls), which evens out over the life course because male infant and child mortality tends to be marginally higher. When the sex ratio deviates sharply from this natural baseline, it is described as skewed, and this is almost always a sign of human intervention rather than a biological pattern.

$\text{Sex ratio at birth}=\frac{\text{Number of male births}}{\text{Number of female births}}\times 100$

In countries such as China and India, sex ratios have become significantly skewed toward males. Two interlinked drivers explain this:

• Cultural son preference: in patriarchal and patrilineal societies, sons are traditionally valued more highly than daughters. Sons are expected to carry on the family name, inherit land or property, work in agriculture, and support parents in old age, since daughters in many traditions leave their birth family upon marriage and support their husband's family instead. Daughters can also be perceived as an economic burden because of dowry customs.
• Government population policy: China's one-child policy (in force from 1979 to 2015) restricted most urban families to a single child. Combined with strong son preference, this created intense pressure to ensure that the one permitted child was male, especially once affordable ultrasound technology made prenatal sex determination widely accessible from the 1980s onward.

The combination of a strict fertility limit with a strong cultural preference for sons is what converted an existing cultural attitude into a measurable demographic distortion, through practices such as sex-selective abortion, and in more extreme historical cases, female infanticide or neglect of infant girls' healthcare and nutrition.

India shows a related but distinct pattern: there is no historical national one-child policy, but sex-selective abortion still occurs in some states because of persistent son preference linked to dowry costs and inheritance customs, despite the practice of prenatal sex determination for the purpose of sex selection being legally banned. This shows that policy is not the only trigger — cultural preference alone, combined with access to medical technology, can skew ratios even without a fertility-limiting law.

The social and economic consequences of a sustained male surplus include:

• A marriage squeeze, where a growing cohort of men cannot find spouses within their own country, sometimes fuelling cross-border marriage migration or human trafficking of women.
• Potential rises in social instability, as some research links large surplus male populations to increased crime rates and social tension.
• Long-term shifts in the population pyramid, where the imbalance is visible as a wider male bar than female bar in the age cohorts born during the peak of policy enforcement or strongest son preference.