How the Human Life Span Doubled in 100 Years

Between 1920 and 2020, the average human life span doubled. "There are few measures of human progress more astonishing than this..." argues author Steven Johnson. In a recent 10,000-word excerpt from his new book Extra Life: A Short History of Living Longer (now also a four-part PBS/BBC series that's streaming online), Johnson tries to convey the magnitude of humanity's accomplishment: [I]t manifests in countless achievements, often quickly forgotten, sometimes literally invisible: the drinking water that's free of microorganisms, or the vaccine received in early childhood and never thought about again... The decade following the initial mass production of antibiotics marked the most extreme moment of life-span inequality globally. In 1950, when life expectancy in India and most of Africa had barely budged from the long ceiling of around 35 years, the average American could expect to live 68 years, while Scandinavians had already crossed the 70-year threshold. But the post-colonial era that followed would be characterized by an extraordinary rate of improvement across most of the developing world... The forces behind these trends are complex and multivariate. Some of them involve increasing standards of living and the decrease in famine, driven by the invention of artificial fertilizer and the "green revolution"; some of them involve imported medicines and infrastructure — antibiotics, chlorinated drinking water — that were developed earlier. But some of the most meaningful interventions came from within the Global South itself, including a remarkably simple but powerful technique called oral rehydration therapy... the treatment is almost maddeningly simple: give people lots of boiled water to drink, supplemented with sugar and salts.... The Lancet called it "potentially the most important medical advance of the 20th century." As many as 50 million people are said to have died of cholera in the 19th century. In the first decades of the 21st century, fewer than 66,000 people were reported to have succumbed to the disease, on a planet with eight times the population... Of all the achievements that brought the great escape to the entire world, though, one stands out: the vanquishing of smallpox... One key factor was a scientific understanding about the virus itself... Scientific innovations also played a crucial role in the eradication projects... But another key breakthrough was the development of institutions like the W.H.O. and the C.D.C. themselves. Starting in the mid-1960s, the W.H.O. — led by a C.D.C. official, D.A. Henderson — worked in concert with hundreds of thousands of health workers, who oversaw surveillance and vaccinations in the more than 40 countries still suffering from smallpox outbreaks. The idea of an international body that could organize the activity of so many people over such a vast geography, and over so many separate jurisdictions, would have been unthinkable at the dawn of the 19th century... The list of new ideas that propelled the great escape is long and varied. Some of them took the form of tangible objects: X-ray machines, antiretroviral drugs. Some of them were legal or institutional in nature: the creation of the Food and Drug Administration, seatbelt laws. Some of them were statistical breakthroughs: new ways of tracking data, like the invention of randomized controlled trials, which finally allowed us to determine empirically if new treatments worked as promised, or proved a causal link between cigarettes and cancer. Some of them were meta-innovations in the way that new treatments are discovered, like the development of "rational drug design," which finally moved drug development from the Fleming model of serendipitous discovery to a process built on the foundations of chemistry... The truth is the spike in global population has not been caused by some worldwide surge in fertility. What changed is people stopped dying... All those brilliant solutions we engineered to reduce or eliminate threats like smallpox created a new, higher-level threat: ourselves. Many of the key problems we now face as a species are second-order effects of reduced mortality.

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