The United Nations is currently forecasting that India will overtake China as the worlds most populous country by 2027. India and Nigeria are estimated to add 470 million people over the next three decades – nearly a quarter of the worlds population will grow by 2050. However, a new study from the University of Washington found that so-called demographic dividends could be much less of a blessing than expected. The UW study published in the Lancet improved the UN model by modeling fertility differently and making its decline more sensitive to the availability of contraceptives and the spread of education. In many parts of India, for example, the total fertility rate – the expected average number of children born by each woman – is already well below the replacement rate of 2.1 and is falling faster than expected. The study, which is also trying to take into account the feedback loops between education, mortality and migration, concludes that the population around the world will shrink earlier and faster than planned. In South Asia, for example, 2100 600 million people would live fewer than previously predicted because fertility is below expectations. Instead of growing steadily, Indias population would peak in 2050 and then decrease to 70% of that number by the end of the century. At that time, Chinas population would be about half the size it is today. On the other hand, sub-Saharan Africa would continue to grow, and Nigeria would enter the 22nd century as the second largest country in the world after India and just before China and Pakistan. This is not good news for policy makers in India and several other developing countries. As the authors of the UW study emphasize, a shrinking world population has "positive effects on the environment, climate change and food production". But it also means that the time for the development clocks of these nations is running out – maybe even expired. China has really been lucky in its demography; it peaked at the right time. Chinese of working age, both in total and as part of the population, had peaked just when world trade was most open. This made it easier than for centuries to take advantage of the opportunities for growth-oriented growth. The next countries – especially India and Pakistan – will face a more closed world. And worse, they now know that it is people who are currently employed or children in school who have to make the country prosperous throughout their lives. For countries whose population will decrease in the 2040s, there are these and the next generation of workers: like their Chinese colleagues, they have had to drive their countries from farm to factory and beyond in the past two decades. Indias boosters are currently touting the fact that the working-age population is increasing by a million people per month and driving economic growth. If this demographic surge comes earlier than expected, growth will depend on individual productivity, not mere numbers. This means that education and healthcare and a similar “soft” infrastructure no longer look like luxury from rich countries. Countries like India, Indonesia, and Brazil may never get rich if they are not introduced within the next decade, or even years. There are other dangers that the Lancet article points out in passing. It is the proliferation of womens education and womens reproductive rights that is causing this drop in fertility. If women do not gain the right political clout, they may be held responsible for the loss of national power caused by a graying population. These hard-won rights could be restricted. In places with particularly patriarchal societies, such as in large parts of South and West Asia, this is even more dangerous than elsewhere. Even the happiest countries have to be careful. China is expected to be the worlds largest economy by 2050. However, the studys authors predict that immigration should theoretically further strengthen the American workforce given the shrinking Chinese population. The United States could become the worlds largest economy again in 2098 if the country lived up to its ideals and continued to welcome the worlds migrants. Theres no better way to make sure America gets great again. Bloomberg