Here’s something to ponder: From an evolutionary biology point of view, is aging just one big accident?
The answer, surprisingly for those of us who assume that falling apart over time is the natural order of things, is Yes. Evolution didn’t “plan” for us to deteriorate in later life for the simple reason that evolution doesn’t “plan” anything. Rather, as bio-demographer S. Jay Olshansky at the University of Illinois puts it, aging “is an accidental byproduct of surviving beyond our biological warranty period, beyond fixed genetic programs that exist for growth, development, and reproduction.”
So what, then, does boost our chances for longer, healthier life? The main thing that is under our control, as I argue in my new book, Exercise is Medicine, is, of course, exercise. But other things help determine longer life, too, chiefly our genes and our environment. Let’s pause a moment to consider that. If you are born into an environment full of hazards, your chances for long-term survival are obviously poor, no matter how good your genes. If you’re born into a safe environment, your chances for long life improve.
And this feeds into the genetics. Over generations, if you grow up in a safe environment, you can afford to postpone the age at which you reproduce. This is key, because delayed age of reproduction helps select for genes that indirectly allow for or encourage longer life. In other words, if you’re healthy and safe enough to think about having babies – whether you’re a human or an opossum – in later life, you’ve probably already got good genes.
Think about what’s been going on with humans for decades now. All over the comparatively safe developed world, women are having children later. In the United States, the average age for the birth of a first child is now 26.3, up from 24.9 just a few years ago. Women whose biological clocks are ticking slowly enough that they are still capable of having a baby beyond age 33 are twice as likely to reach very old age as women who have their last baby at 29.
Worldwide, life expectancy has been steadily rising. Life expectancy at birth is now 68.6 around the world and is projected to rise to 76.2 by 2050. In the United States, life expectancy at birth for women in 2016 was 81.1, and for men, 76.1.
In other words, most of the increase in human longevity in recent times has to do with the fact that, in the developed world at least, we have made our environment safer, not that the process of aging itself has changed.
So what is that process of aging?
Not long ago, it wouldn’t have been possible to give a satisfying answer to that question. But in 2013, European scientists boiled down the most important changes to nine “hallmarks” of aging. This gets into some serious cell biology, but don’t panic. In future posts, we’ll make it accessible. For now, the take-home message is this: At least in the view of some researchers, the beneficial effects of aging affect all nine hallmarks of aging, in a positive direction.
Contrarily, our Westernized lifestyle – too much food and too little exercise – accelerates things in the wrong direction.
To be continued….