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  • To us humans, aging seems inevitable - probably because no human has ever not aged. But getting

  • older isn’t as universal a fact of life as we might think.

  • Take the naked mole rat. Unlike their less-naked brethren, they don’t appear to age after

  • reaching adulthood - years pass, but the rats don’t get weaker, more susceptible to disease,

  • or wrinkly...at least not any more wrinkly...and they keep on making as many babies as ever.

  • Surprisingly, they aren’t any more likely to die in old age than when theyre young

  • adults. It’s as if theyve found the fountain of youth, though perhaps not the fountain

  • of beauty. And naked mole rats aren’t alone in not aging: rockfish, lobsters, and bristlecone

  • pines also seem to stay forever young...or at least forever middle-aged.

  • Were not exactly sure how these species do it, but their anti-aging secret may have

  • to do with their ability to rebuild the DNA caps on their chromosomes. These caps, called

  • telomeres, are one line of defense against aging in many species. That’s because cells

  • need to divide to replace old or dysfunctional cells, but each time they replicate, they

  • lose a little bit of DNA from the end of each chromosome. Normally that doesn’t matter,

  • since these lost bits come from the telomere end caps that don’t encode important information.

  • But after many replications, the telomeres get trimmed so short that the cells can’t

  • afford to lose any more DNA, and they stop replicating.

  • Age-defying species like naked mole rats, however, pump out high levels of a telomere-rebuilding

  • enzyme that enables them to keep on replacing old and dysfunctional cells indefinitely.

  • A few kinds of human cells make this enzyme, but the vast majority don’t. And even if

  • we could trick the rest into producing it, then we’d have another problem: more replications

  • means more chances for mutations that could turn a cell cancerous unlimited replication

  • increases a cell’s chances of becoming cancerous. Naked mole rats don’t care because they

  • seem to be immune to cancer; but we humans certainly aren’t.

  • However, as amazing as naked mole rats are, they can only pause their agingthe tiny

  • jellyfish Turritopsis dohrnii can age in reverse. Like butterflies, Turritopsis morph through

  • multiple stages during their life cycle. But unlike butterflies, if Turritopsis get wounded

  • or if times get tough, they can morph backwards, reverting to their immature polyp form until

  • conditions improve. Theyre like, real life phoenixes.

  • However if humans could somehow imitate Turritopsistrick, it might not give us the kind of eternal

  • youth we’d be looking forfor one thing, melting into an amorphous blob where our cells

  • are reorganized and reprogrammed with new functions would not only be a mess; it would

  • likely turn our brain cells into skin or muscle cells - and vice versa - erasing our memories

  • and our sense of self. And no matter what, eternal youth wouldn’t

  • make us invincible - in fact, the longer a creature lives, the more time it has to get

  • chomped, starved, or smooshed. So eventually, every naked mole rat, pine tree, and jellyfish

  • will ultimately meet its end - because it’s possible to be immune to aging, but not to death.

To us humans, aging seems inevitable - probably because no human has ever not aged. But getting

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B2 中上級

年を取って死ななければならないのか? (Do We Have to Get Old and Die?)

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    Charlene Tai に公開 2021 年 01 月 14 日
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