“The single most important factor behind human progress is the dramatic reduction in child mortality.” — Vaclav Smil
Eight billion people now live on Earth. A century ago, there were fewer than two billion. The planet’s human population quadrupled in a hundred years — an event without precedent in the entire history of our species. Understanding what drove that growth, and where it’s headed, is one of the most important intellectual tasks of our time.
The growth story is not what most people imagine. The global population growth rate actually peaked in the late 1960s at about 2.1% per year and has been slowing ever since. Today it is approximately 1% per year and falling. Most demographers expect global population to peak somewhere between 10 and 11 billion — probably in the 2080s — and then begin to decline. The population bomb, it turns out, has a slow fuse.
The key to understanding population change is the demographic transition — the well-documented pattern by which societies move from high birth rates and high death rates (pre-modern) to low birth rates and low death rates (modern). Every country that has undergone economic development has followed this pattern.
In 1900, a woman in a developing country might expect to have six or seven children, and two or three would survive to adulthood. Today, the global average is about 2.3 children per woman, and nearly all survive. This is not a coincidence or a policy choice — it is the almost inevitable consequence of lower child mortality. When parents can be reasonably confident their children will survive, they choose to have fewer of them.
In 1900, global average life expectancy at birth was approximately 31 years. Today it is approximately 73 years — more than doubled in a century. This is arguably the greatest achievement in human history, dwarfing any economic statistic.
The dominant narrative attributes this to modern medicine — antibiotics, vaccines, surgical advances. This is partly true, but Smil insists on the numbers: the largest single contributor to increased life expectancy was the dramatic reduction in infant and child mortality, which in turn was driven primarily by:
In 1900, approximately 200 out of every 1,000 children died before their fifth birthday in most countries. Today, the global rate is below 40 per 1,000, and in wealthy countries it is below 5 per 1,000. This single change, multiplied across billions of lives, explains most of the life expectancy gain.
In 1800, approximately 3% of humanity lived in cities. In 1900, it was roughly 15%. Today it is over 55% — and in wealthy countries, it exceeds 80%. Humanity has undergone the most dramatic transformation in how it organizes itself since the invention of agriculture.
Urbanization is strongly correlated with economic development, reduced fertility, improved education, and better health outcomes. Cities, for all their problems, are extraordinarily efficient at delivering economic opportunity, social mobility, and access to services.
But urbanization also concentrates poverty, creates enormous infrastructure demands, and — in developing countries — often produces massive informal settlements rather than well-planned urban environments. The next billion urban dwellers will mostly live in Africa and Asia, in cities that are growing faster than their governments can build roads, pipes, and schools.
As fertility rates fall and life expectancy rises, the world’s population is aging rapidly. Japan’s median age is now 49 years. Germany’s is 46. By 2050, Europe and East Asia will have more people over 65 than under 30.
What does it mean for a society when there are more retirees than workers? How do you fund pensions, healthcare, and elder care in a world where the dependency ratio has inverted? These are not abstract future problems — they are present crises in Japan, Italy, and South Korea today.