After long slide, fertility rates rising in richer nations, study hints

From 1975 to 2005, fertility dipped in countries as economic development rose, then began to rise in places that reached the highest levels of development, according to a study in the journal Nature.

The bounce-back of fertility suggests that advanced development doesn’t have to mean a vanishing population as some had feared, the research found.

Countries such as Japan, South Korea, Germany, and Italy have such low levels of fertility that not enough children are being born to replace their parents as they die.

Absent immigration, a smaller workforce may leave countries burdened with the costs of maintaining infrastructure, causing national economic declines, said study author Hans-Peter Kohler.

“This challenges the notion that as we become more developed, fertility only falls downward, which would produce rapid population aging,’’ said Kohler, a sociologist at the University of Pennsylvania’s Population Studies Center.

“In advanced societies, children are very desired and couples are willing to sacrifice to have them.’’

The finding amounts to a partial reversal of the fertility declines seen in the late 20th century fueled by a combination of factors, including birth control, the increased costs of childrearing, the entry of women into the workforce, and more years spent becoming educated, Kohler said.

The decrease began before the advent of readily available contraception, although that probably helped the process, he said.

“In the moderate stages of development, there are strong tradeoffs, and children are given up,’’ he said. “As societies advance, the tradeoffs become less severe.’’

Replacement-level fertility is the level at which a couple has enough children to replace themselves.

A replacement rate in countries with a long life expectancy is about 2.1, because some people die before having children.

The fertility rate in the United States rose to 2.05 in 2005, a comeback from the low of 1.74 in 1976.

Of the countries measured, only Israel has a higher fertility level in 2005, with a rate of 2.82.

The researchers found that some countries reaching advanced development were an exception to the fertility trend. South Korea’s fertility rate was the lowest at 1.08; Japan’s was slightly higher, at 1.26.

Most countries except Canada, Japan, and South Korea experienced a rising fertility rate when they achieved a measure of higher education, income, and longer lifespan.

These countries may not be facilitating work-family balances and gender equality, the study authors suggested.

For countries that limit immigration, today’s data predict a slower population decline than previously projected.