In 1997, a French woman named Jeanne Calment passed away after 122 years and 164 days on this Earth, making her the oldest known person in history. Her age was so astounding that a millionaire pledged $1 million to anyone who could break her record. But in reality, living to this age or beyond is a feat that very few, maybe even no humans, are likely to accomplish. Human bodies just aren't built for extreme aging. Our capacity is set at about 90 years. But what does aging really mean and how does it counteract the body's efforts to stay alive? We know intuitively what it means to age. For some, it means growing up, while for others, it's growing old. Yet finding a strict scientific definition of aging is a challenge. What we can say is that aging occurs when intrinsic processes and interactions with the environment, like sunlight, and toxins in the air, water, and our diets, cause changes in the structure and function of the body's molecules and cells. Those changes in turn drive their decline, and subsequently, the failure of the whole organism. The exact mechanisms of aging are poorly understood. But recently, scientists have identified nine physiological traits, ranging from genetic changes to alterations in a cell's regenerative ability that play a central role. Firstly, as the years pass, our bodies accumulate genetic damage in the form of DNA lesions. These occur naturally when the body's DNA replicates, but also in non-dividing cells. Organelles called mitochondria are especially prone to this damage. Mitochondria produce adenosine triphosphate, or ATP, the main energy source for all cellular processes, plus mitochondria regulate many different cell activities and play an important role in programmed cell death. If mitochondrial function declines, then cells and, later on, whole organs, deteriorate, too. Other changes are known to occur in the expression patterns of genes, also known as epigenetic alterations, that affect the body's tissues and cells. Genes silenced or expressed only at low levels in newborns become prominent in older people, leading to the development of degenerative diseases, like Alzheimer's, which accelerate aging. Even if we could avoid all these harmful genetic alterations, not even our own cells could save us. The fact remains that cellular regeneration, the very stuff of life, declines as we age. The DNA in our cells is packaged within chromosomes, each of which has two protective regions at the extremities called telomeres. Those shorten every time cells replicate. When telomeres become too short, cells stop replicating and die, slowing the body's ability to renew itself. With age, cells increasingly grow senescent, too, a process that halts the cell cycle in times of risk, like when cancer cells are proliferating. But the response also kicks in more as we age, halting cell growth and cutting short their ability to replicate. Aging also involves stem cells that reside in many tissues and have the property of dividing without limits to replenish other cells. As we get older, stem cells decrease in number and tend to lose their regenerative potential, affecting tissue renewal and maintenance of our organs original functions. Other changes revolve around cells' ability to function properly. As they age, they stop being able to do quality control on proteins, causing the accumulation of damaged and potentially toxic nutrients, leading to excessive metabolic activity that could be fatal for them. Intercellular communication also slows, ultimately undermining the body's functional ability. There's a lot we don't yet understand about aging. Ultimately, does longer life as we know it come down to diet, exercise, medicine, or something else? Will future technologies, like cell-repairing nanobots, or gene therapy, artificially extend our years? And do we want to live longer than we already do? Starting with 122 years as inspiration, there's no telling where our curiosity might take us.
在 1997 年,一位法國女士 雅娜・卡爾曼特 在世上活了 122 年 又 164 天後與世長辭 她是史上最長壽的人 由於她的年齡十分驚人 甚至有位百萬富翁願意付一百萬元 給打破她記錄的人 但事實上,活到那個歲數 或甚至更長壽 是十分少數人,甚至沒有人 可以達成的目標 人類的身體本來就不是 適合極度老化的 我們大約能活到 90 歲 但是衰老究竟代表什麼 還有這如何與身體 維持生命的力量抗衡 我們直覺上知道衰老是什麼意思 對於某些人來說,衰老就是成長 而其他人則認為衰老就是變老 但想找到衰老的 嚴謹科學定義是一個挑戰 我們能說的是衰老發生 在內在過程 以及與環境的互動,例如陽光 和空氣、水、我們日常膳食中的毒素 引致結構上的改變 以及體內分子和細胞功能的改變 這些改變進而導致它們的衰退 然後是整個生物的衰竭 我們對衰老的確實機制認識很淺 但近來,科學家辨識了九種生理特徴 範圍由基因變化 至細胞再生能力的變異 均扮演了重要角色 首先,隨年月過去, 我們的身體累積了基因損傷 以 DNA 損傷的形式出現 這些在身邊 DNA 複製時自然發生 但也會在非分裂細胞內發生 稱為「粒線體」的細胞器 特別容易因此受損 粒線體製造三磷酸腺苷 或簡稱為 ATP 是所有細胞過程的主要能量來源 而且調節很多不同的細胞活動 並在預設的細胞死亡中 扮演重要角色 如果粒線體的功能衰退 那麼細胞,繼而整個器官, 都會隨之惡化 其他變化已知是發生在 基因的表現模式 或稱為「表觀基因改變」 影響身體組織和細胞 新生嬰兒時,靜默 或只作低程度表現的基因 在較年長的人變得顯著 發展出退化性疾病 例如阿滋海默氏症,加速衰老 即使我們能夠避免 這些有害的基因變異 我們自己的細胞也不能拯救我們 事實仍是,細胞再生 這生命的基本 會隨我們年長而衰退 細胞內的 DNA 包裹於染色體內 每個染色體的兩個末端 各有保護性區域,稱為「端粒」 每次細胞複製時,那些區域會變短 當端粒變得太短 細胞便會停止複製並死亡 減慢身體更新自己的能力 細胞也會隨時間逐漸衰老 這過程是當有風險時 便停止細胞週期 例如當癌細胞增生時 但當我們年紀愈大 愈容易有這樣的反應 停止細胞生長,減低它們複製的能力 衰老也闗乎幹細胞 它們在很多身體組織內 並有無限分裂的特性 能補充其他細胞 當我們年歲漸長,幹細胞數目減少 並傾向失去它們再生的潛能 影響細胞組織的更新 和器官原有功能的維持 其他變化則圍繞細胞正常運作的能力 當它們老化,不能再有效控制蛋白質 導致受損並潛有毒素的營養堆積 進而引致過多的新陳代謝活動 這可讓細胞死亡 另外,細胞間的溝通減慢 最終削弱身體運作的能力 對於衰老,我們還有 很多不瞭解的地方 歸根究底,壽命較長是因為日常膳食 運動 藥物 抑或其他? 將來的科技 例如細胞修復奈米機械人 或基因療法 會否人為地延長我們的壽命? 而我們是否希望比現在更長壽? 以 122 歲作為想像起點 沒人能說準