The world's population ranking is deceptively stable at the top — the same countries have occupied the top 10 for decades — but the underlying dynamics are shifting dramatically. India's overtaking of China as #1 is the most significant demographic event of the century, reflecting China's fertility decline (now below 1.1 children per woman, well below replacement) and India's continued, if slowing, population growth.
The demographic divergence between regions has enormous economic implications. Sub-Saharan Africa's population is projected to roughly double by 2050, from about 1.2 billion to over 2 billion. This represents either a massive demographic dividend (a young, growing workforce driving economic growth) or a demographic time bomb (if job creation and institutional development can't keep pace). The outcome depends entirely on policy and investment decisions made in the next decade.
Among the population giants, the economic performance per capita varies wildly. The United States, with 335 million people, generates GDP per capita 30x higher than India with its 1.4 billion. This reflects vastly different levels of productivity, capital accumulation, institutional quality, and technological sophistication. Population is a necessary but far from sufficient condition for economic power.
The most concerning demographic trend is in countries where population growth substantially exceeds economic growth. Niger, with the world's highest fertility rate (roughly 7 children per woman), faces mathematical certainty that per-capita incomes will decline unless economic growth dramatically accelerates. Several Sahelian countries face similar arithmetic.