South Korea’s gender imbalance is bad news for men with many facing bleak marriage prospects

South Korea’s bachelor time bomb is about to really go off. Following a historic 30-year-long imbalance in the male-to-female sex ratio at birth, young men far outnumber young women in the country. As a result, some 700,000 to 800,000 “extra” South Korean boys born since the mid-1980s may not be able to find South Korean girls to marry.

As a demographer who over the past four decades has conducted extensive research on East Asian populations, I know that this increased number of South Korean boys will have a huge impact on South Korean society. Coincidentally, similar trends are playing out in China, Taiwan and India.

In most countries, more boys are born than girls – around 105 to 107 boys per 100 girls. That sex ratio at birth (SRB) is a near constant. The gender imbalance is likely an evolutionary adaptation to the biological fact that females live longer than males. At every year of life, men have higher death rates than women. Hence an SRB of between 105 and 107 boys allows for there to be roughly equal numbers of men and women when the groups reach childbearing ages.

The SRB in the United States in 1950 was 105 and was still 105 in 2021; in fact, it has been stable in the U.S. for as long as SRB data has been gathered. In contrast, in South Korea the SRB was at the normal range from 1950 to around 1980, but increased to 110 in 1985 and to 115 in 1990.

After fluctuating a bit at elevated levels through the 1990s and early 2000s, it returned to the biologically normal range by 2010. In 2022, South Korea’s SRB was 105 – well within the normal level. But by then, the seeds for today’s imbalance of marriage-age South Koreans was set.

There are several reasons why South Korea’s SRB was out of balance for 30 years.

South Korea experienced a rapid fertility decline in a 20- to 30-year period beginning in the 1960s. From six children per woman in 1960, fertility fell to four children in 1972, then to two children in 1984. By 2022, South Korea’s fertility rate had dropped to 0.82 – the lowest fertility rate in the world and far below the rate of 2.1 needed to replace the population.

Yet, South Korea’s long-held cultural preference for sons did not shift as quickly as childbearing declined. Having at least one son was a strong desire influencing fertility preferences in South Korea, especially up through the early years of the 21st century.