We are also insulated from the consequences of aging when it happens to other people. The oldest and most unwell are tucked away in hospitals and nursing homes, hidden from view. When we are children, our grandparents are often kind, wrinkly souls whose health problems we aren't really aware of. Even as adults with fledgling careers and a young family, we rarely get involved caring for older friends and relatives. That responsibility usually falls either to our own parents stepping in to look after their mom and dad or to our grandparents themselves taking care of one another. All this means we usually don't get to see the full picture until our parents, or even our partners, need taking care of—by which time we're starting to age ourselves. While these are gross generalizations which will vary from family to family, they are borne out by statistics: a U.S. survey found that those caring for someone over 65 had an average age of 63 themselves. We can easily make it through the first four, five or even six decades of life without having to confront what aging means—which makes it all the easier to put from our minds.
If we do think about what our lives might be like in 10, 20, 50 years' time, we can allay our anxieties by telling ourselves that we are fortunate. Aging is a curse that we in the rich world are perversely lucky to have; we live long enough for it to be a problem. Better to live a long life and die from a heart attack than die in childhood of malaria, right? It is, of course—and the fact that deaths from diseases like malaria are in significant part preventable makes their continued death toll a moral indictment—but the bittersweet news is that age-related diseases outgun other causes of death in over three-quarters of countries around the world.
Global life expectancy was 72.6 years in 2019, and it's rising. If you already knew that, you're in the minority: in spite of our optimism about our own individual futures, surveys show that most people are pessimistic about the state of the world, and assume that life expectancy is 10 or even 20 years lower. Most of us imagine a large "developing world" where birth rates and death rates are high—this is, after all, what we were taught in school. The reality is that most countries are approaching the developed world, in life expectancy if not in wealth. This is astonishing progress, and well worth celebrating—we've beaten many deadly infectious diseases into submission, and improved quality and quantity of life worldwide. The flip side is that 70 is easily old enough to feel the effects of aging—this is another way to understand why age-related conditions are the greatest cause of death and suffering worldwide.
Aging is also a crisis which is snowballing as development continues and our global population gets older: even if it somehow fails to meet the definition of a global challenge now, it surely will do so in decades to come. The question is, what can we do?
The answer, thankfully, is biology. It all started in the 1930s, with a breakthrough that changed scientific history. There was a burgeoning interest in the new field of nutrition, and researchers were starting to wonder about the effects of food on growth and lifespan. Scientists took three groups of rats, one allowed to eat what they liked, and the other two on significantly more frugal diets, all while meticulously ensuring that they got all the nutrients they needed. The rats eating less were smaller than those in group one but, as the experiment progressed, it became obvious that their size wasn't the only thing being affected by their reduced rations. One by one, the rats eating what they liked got old and died, while the dieting rats kept going, and going. And these hungry rats didn't hobble along in ill health, gray-haired and cancer-ridden, somehow unable to muster the energy even to die after their better-fed counterparts had done so. The calorie-restricted animals were healthier and less frail for longer, too. It seemed almost as though eating less slowed down the aging process itself.
It turns out that this wasn't a fluke or experimental error. We've since tried dietary restriction in creatures from all over the tree of life, with astonishing generalizability: single-celled yeast (the fungus used in baking and brewing beer), worms, flies, fish, mice, dogs and many more all live longer and healthier if fed significantly less than normal. They are more active, and suffer less from the ailments of aging, from cancer to heart trouble (at least in those creatures that have hearts). Dietarily restricted rats even have better fur than animals with a normal food intake. It's possible to cut their food too far, which obviously leads to starvation—but get things just right and hungrier rats will significantly outlive members of their species who eat what they like, in significantly better health. These findings show us something remarkable: aging is not some rigid, immutable biological inevitability. A deceptively simple treatment can slow down almost everything about it, all at once, across the animal kingdom.
What seemed for the vast majority of human history to be a fixed fact of nature can in fact be altered by just eating less. What's more, aging seems to be, on some level, a coherent process: these extreme diets don't just prevent a single age-related disease, but all of them at once, at the same time as deferring frailty and death. That means it's not impossible to imagine that we could come up with medicines that could slow down or even reverse "aging" writ large, not just its individual components. Though it wouldn't be so christened for a few more decades, this was the birth of biogerontology: the study of the biology of aging.