Why the Baby Bust Is Our Biggest Problem

All species must reproduce to continue their existence. Furthermore, they must raise enough offspring to replace individuals who die. If reproduction falls below replacement level, a population declines—and ultimately disappears.

While we are undergoing a contemporary population explosion, the tide is destined to turn. Reproduction is already declining sharply in developed countries and there are two key reasons for this: One is economics; specifically, changes in the work lives of women. The other is biological. Industrial pollutants are most likely responsible for the declining quality of human eggs and sperm. Pollution may also speed up reproductive senescence. The reproductive clock is now running faster for both women and men.

Changes in the Work Lives of Women

Greater participation in careers means that the phase of their lives during which women bear children is shorter (1). Marriage also occurs later than previously, as many women complete a college degree and get established in a career before having a family.

In some careers, such as academic life, the demands of work are so great that many women may not have children at all (2). But generally, women in developed countries today have small families compared to their grandmothers' generation. If the reproductive phase of women's lives is initially postponed by economics, it is curtailed at the end by faster reproductive senescence.

As countries develop, their fertility falls. This trend is so predictable that it is referred to as “the demographic shift,” with the suggestion that it will always occur. Apart from the demands of women's work, there are other explanations, including inflation's effects on the cost of raising children. Given the high costs of housing, food, third-level education, childcare, and many of the other expenses of raising children, most couples find it financially challenging to raise more than two.

Faster Reproductive Senescence

It used to be that women's fertility plateau extended from the ages of 20 to 40, but that is no longer true. If a woman marries at the age of 30, she often has only five years in which to conceive offspring without using in vitro techniques.

Indeed, a contemporary woman who is 35 years old is about as likely to conceive as her grandmother was at the age of 45 years (3). Biological fertility is also more limited in contemporary men. There are two main reasons for this: One is the steady decline in testosterone levels that produces erectile dysfunction for a quarter of men after the age of 40 years. At the current pace of decline, half of men may be incapable of regular sexual intercourse after four decades. Semen quality also declines over time. Sperm count is declining steadily and many male gametes are misshapen so that they cannot produce viable offspring.

Declining Gamete Quality

Female gametes (ova) are also declining in quality, which is one reason for earlier reproductive senescence (3). Animal experiments found that exposure to plastics—present in everyday products from cosmetics to food packaging—degrade the quality of both male and female gametes.

Much of the animal research has focused on phthalates widely used in body creams and food wrappings. These substances act as hormone mimics that interfere with sexual differentiation early in life and now affect wildlife just as much as they do humans.

When the impact of such chemical insults are added to the many socioeconomic influences that bring down contemporary fertility, we can conclude that the human population is under serious threat. We may be about to join the many extinct species affected by the current wave of human-caused mass extinctions.

The Impending Baby Bust Is the Biggest Challenge our Species Faces

A newly-published book argues that we are destined to fall below replacement fertility not just in developed countries but around the globe. This conclusion rests on the assumption that developing countries are converging with affluent ones in their fertility patterns as their average income increases. Indeed, the baby bust applies not just to affluent countries, like Japan, but most middle-income countries, like China, which may now also be well below replacement fertility. Japan's cities are expected to lose half their population this century, and life in China is already affected by graying of the population.

There is a certain inevitability to this process that defies other influences, including religion; the fertility rate in Islamic countries today is only half what it was four decades ago. Global urbanization of the population—another negative for fertility—recently crossed the halfway point and proceeds at a rate of around one percent per year. Of course, urbanization is a proxy for economic development.

When one combines the impact of development with that of industrial toxins and hormone mimics, it suggests that natural reproduction for humans may be virtually impossible within about 40 years (4). If so, it is lights out for the human species.