Research Links Sex Ratios to Virus

Harvard economics graduate student Emily F. Oster ’02 has collected and analyzed data linking the gender disparity in China—where males are more prevalent than females—to the hepatitis B virus. In a paper that will be published in the Journal of Political Economy, she showed that mothers who carry hepatitis B are 1.5 times more likely to bear a boy instead of a girl.

“Countries with more hepatitis have higher sex ratios [male to female] at birth,” she wrote in an e-mail.

In most parts of the world, the number of newborn girls has roughly equaled the number of newborn boys. But historically there has been a pattern of gender imbalance in China—and over the past 20 years that gap has widened dramatically.

There are now 1.07 boys born for each girl in China, compared to a ratio of 1.05 in the West. Given the size of the world’s population, a 0.02 difference can translate into millions of people.

According to authors like Lamont University Professor Amartya Sen, as many as 100 million women have gone “missing” in Asia. Most authors have attributed the missing women to high levels of female mortality.

But in her paper, “Hepatitis B and the Case of the Missing Women,” Oster said that 45 percent of the missing women across Asia are the result of the hepatitis B virus. She attributed the 75 percent of missing women in China alone to hepatitis B.

Oster’s viral theory accounts only for the historical gender imbalance. She does not attempt to address the gender gap that has been increasing since the institution of China’s one-child policy.

Some publications have not made this distinction in their coverage of Oster’s research. A recent Newsday article used her research to explain the current gender imbalance in China, even though hepatitis B cannot be held exclusively accountable for the widening gap over the past 20 years—which has arisen due to a variety of social, economic, and cultural forces.

Dean of the Faculty of Arts and Sciences William C. Kirby, a Chinese historian by training, wrote in an e-mail that marked gender preferences in Asia are one reason that males are currently more prevalent than females.

“Historical reasons for prizing boys over girls in East Asian societies have to do with long-standing and intersecting belief systems and family structures,” he wrote. “In societies that lack any organized social security beyond the family, the best insurance for parents in their old age is a son with the responsibility of taking care of them.”

China’s adoption of the one-child policy in 1979 gave parents only one chance to bear that son. With the invention of ultrasound in the early ’80s, sex-selective abortions became possible for the first time, and many women pregnant with baby girls opted to abort them. Women who did not have access to abortions resorted to infanticide. This willingness to abort or kill a female, if necessary, prompted the gender gap to grow.

“In general, there is a lot of confusion in the world about whether the hepatitis B explanation [of the gender gap] is inconsistent with the sex-selective abortion explanation or with any explanations having to do with gender preference,” Oster said. “It is not inconsistent because the hepatitis B theory explains the naturally occurring, original gap, but preferences explain the increasing gap.”

Still, she said, her data is not irrelevant to understanding China’s current situation.

“Knowing the original gap helps us think about the current increases,” she said. “Understanding all the facets of what is going on may help us get a better sense of how to remedy these problems of gender inequity in this area of the world.”