Thread by @stevenbjohnson

Is the doubling of global life expectancy just a statistical sleight-of-hand? I get this a lot. Adults aren’t *really* living longer, the argument goes; it’s just that infant mortality has dropped.

But that argument is misguided, for a number of reasons. Let me count the ways.

(Some of what follows is briefly referenced in my @NytMag essay from this weekend, and it’s covered more extensively in my book Extra Life: A Short History of Living Longer, which comes out next week.)

nytimes.com/2021/04/27/mag…

Let’s time travel back to England a little more than a century and a half ago, in the middle of industrialization. Life expectancy at birth averaged about 40 years nationwide, but was as low as 25 in cities like Liverpool.

Was that shockingly low average lifespan simply the result a huge number of 3-month-old babies dying? If you made it out of infancy, were you likely to live into your 80s the way residents of the UK do today?

No.

Demographers distinguish between life expectancy at different ages. In 1850, the average British person who lived to 20 would go on to live to 60. Today, the average 20-year-old can expect to live into their mid-80s.

ourworldindata.org/life-expectanc…

That extra 20+ years of life is a massive change: the difference between living long enough to meet your grandkids and living long enough to meet your *great* grandkids. It helped create the whole idea of a "retirement" phase of your life.

You can measure the change at the extremes of old age as well. As @ferrisjabr writes in this excellent piece from the @nytmag Longevity issue, the population of centenarians (people living over 100) has increased almost 5x in the last few decades.

nytimes.com/2021/04/28/mag…

Now, it is true that infant/childhood mortality has dropped precipitously. That’s why I think overall life expectancy at birth is such a powerful trend to follow, because it reflects improvements across the age spectrum. And reductions in child mortality are a huge deal….

One of things that jumps out at you if you study the history—or read novels from the 19th-century—is that childhood was just incredibly dangerous. In NYC during the 1850s, SIXTY PERCENT of all deaths recorded were of children.

For most of human history, childhood mortality was somewhere close to 40 percent. If you’re a parent, think about what that would have meant: if you had five kids, odds were that two of them would die before reaching adulthood. (We've reduced those odds 10X globally.)

And this wasn’t just kids dying in their first days of life—as tragic as that is—it was kids dying at 5 and 10 and 15. Take a look at this amazing “life table” that William Farr created in the 1840s of deaths by age group in London.

Many children die before the age of 5, but 10% of overall deaths are between the ages of 5-20. Think about the 200 or so people of your age-group that you knew growing up. Did 20 of them die during that time? That would have been the norm a little more than a century or so ago.

The story of our extended life is not just about keeping babies alive, as wonderful as that achievement has been. It’s much more sweeping and consequential than that.

But the more important question is *how* we we managed to extend our lives‚ and how we can reduce the inequalities that remain. That’s the main focus of the Extra Life book, and the PBS/BBC series coming out next week…

pbs.org/show/extra-lif…