How Old Am I, Really? A Biology Lesson

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     On the most recent November 27, at approximately 7:30 in the morning, I achieved the age of 86, a milestone I acknowledged broodingly. We see such announcements daily in the Village.

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     I don’t know about you, but as time has gathered these events, I have become increasingly uneasy. There are in fact only two future events in my recollected history that ever promoted a desire to be older: to be licensed to drive and to have the license to drink. Accumulating more birthdays now only sends negative signals.

 

     So, imagine my surprise when I recently discovered that my actual biological age has little bearing on the number of years since my birth. In fact, essentially every one of the organs, tissues, cells, and fluids in my body is a recent acquisition. I am a composite of replacement parts, like a computer upgraded regularly and downloaded with recent apps. I’m not 86—I’m way younger. A living example of the Ship of Theseus.

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Consider: I have about 25 trillion red blood cells coursing through my bloodstream at this moment. That’s about 80% of the total cells in my body. Not one of them existed five months ago! Five million are murdered every second, killed by giant macrophages!

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     The same youthfulness and mournfulness attach to the rest of me. The youngest parts are the millions of cells lining my intestines, not one of which is older than four days. Few will survive the coming weekend. My skin is about two weeks old, my liver a year and a half, my muscle cells are still teenagers at 15, and the bones they attach to have been around only a decade. When bone replacement cells are outnumbered by homicidal osteoclasts, the result is called osteoporosis. Most of our cells are actively and regularly killed off like this.

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     So I’m a pretty young guy, thank you very much. My oldest cells are in the brain. Most of them won’t die until I do. I’ve had twenty percent of them since birth. The cells holding my memory have stuck around since I was 3 or 4 (even though remembering hasn’t.)

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     This all leads me to two conclusions: 1) a significant part of me is not yet a toddler, and 2) a significant part of me is a crime scene.

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Ron Wetherington