What unites communities with historically high rates of discrimination against girls is a rigid patriarchal culture that makes having a son a financial and social necessity. When a daughter grows up and marries, she essentially becomes chattel in her husband’s parents’ home and has very limited contact with her natal family. Even if she earns a good living, it will be of no help to her own parents in their old age. So for parents, investing in a daughter is truly, in the Hindi expression, planting a seed in the neighbor’s garden. Sons, by contrast, provide a kind of social security. A family with only daughters will also likely lose its land when the father dies: although women can legally inherit property, in areas of north India and China, they risk ostracism or even murder if they claim what is theirs. And sons are particularly important to mothers, who acquire power and authority when they have married sons. Sons, according to Chinese custom, are also needed to care for the souls of dead ancestors.

What Das Gupta discovered is that wealthier and more educated women face this same imperative to have boys as uneducated poor women — but they have smaller families, thus increasing the felt urgency of each birth. In a family that expects to have seven children, the birth of a girl is a disappointment; in a family that anticipates only two or three children, it is a tragedy.

Thus development can worsen, not improve, traditional discrimination. This can happen in other ways too. With the access it brings to cutting-edge technology, development can also offer more sophisticated and easier options for exercising old-fashioned prejudice. In China and in the north and west of India, for instance, the spread of ultrasound technology, which can inform parents of the sex of their fetus, has turned a pool of missing girls into an ocean. The birth of girls has long been avoided through infanticide, which is still practiced often in China. But there are even more couples who would abort a pregnancy than would kill a newborn. Ultrasound has been advertised in India as “pay 5,000 rupees today and save 500,000 rupees tomorrow.” In both countries, it is illegal to inform parents of the sex of their fetus, and sex-selective abortion is banned. But it is practiced widely and rarely punished.

Finally, because higher education and income levels generate more resources, development offers new opportunities to discriminate against living girls. After all, if people are very poor, boys and girls are necessarily deprived equally — there is little to dole out to anyone. But as parents gain the tools to help their children survive and thrive (and indeed, all children do better as their parents’ education and income levels advance), they allocate advantages like doctor visits to boys and firstborn girls, leaving subsequent daughters behind.

To be sure, development can eventually lead to more equal treatment for girls: South Korea’s birth ratios are now approaching normality. But policymakers need to realize that this type of development works slowly and mainly indirectly, by softening a son-centered culture. The solution is not to abandon development or to stop providing, say, microcredit to women. But these efforts should be joined by an awareness of the unintended consequences of development and by efforts, aimed at parents, to weaken the cultural preference for sons.

The lesson here is subtle but critical: Development brings about immense and valuable cultural change — much of it swiftly — but it doesn’t necessarily change all aspects of a culture at the same rate. (India and China have myriad laws outlawing discrimination against girls that are widely ignored. And how to explain the persistence of missing girls among Asian immigrants in America?) In the short and medium terms, the resulting clashes between modern capabilities and old prejudices can make some aspects of life worse before they make them better.