Why do animals have such different lifespans? - Joao Pedro de Magalhaes

譯者: Phyllis Huang 審譯者: Yi-Leng Su

對於顯微鏡下的秀麗隱桿腺蟲而言

For the microscopic lab worm, C. elegans

一生不過短短幾週的時間

life equates to just a few short weeks on Earth.

相對而言，烏龜可以活超過100年

Compare that with the tortoise, which can age to more than 100 years.

中、小型鼠的壽命則大約為4年

Mice and rats reach the end of their lives after just four years,

while for the bowhead whale, Earth's longest-lived mammal,

而地球上最長壽的哺乳類是弓頭鯨

death can come after 200.

壽命超過200歲

Like most living things,

大多數動物和大部分生物一樣

the vast majority of animals gradually degenerate after reaching sexual maturity

在性成熟後身體便開始退化

in the process known as aging.

這個過程稱為老化

But what does it really mean to age?

但老化到底是什麼？

這過程的成因十分繁雜

The drivers behind this process are varied and complicated,

簡單來說，細胞死亡和功能失常 最終會導致老化

but aging is ultimately caused by cell death and dysfunction.

When we're young, we constantly regenerate cells

年輕時，我們的細胞會不斷再生

in order to replace dead and dying ones.

取代已死亡及凋零的細胞

隨著年紀增長，再生速度會愈來愈慢

But as we age, this process slows down.

In addition, older cells don't perform their functions as well as young ones.

而且老舊細胞的功能不如新細胞好

這使得我們的身體開始衰退

That makes our bodies go into a decline,

which eventually results in disease and death.

最終導致疾病與死亡

But if that's consistently true,

若這現象是所有生物的共通點

why the huge variance in aging patterns and lifespan within the animal kingdom?

為何不同動物的老化機制 和壽命會差這麼多？

The answer lies in several factors,

有幾種因素

including environment

像是環境

and body size.

和體型

These can place powerful evolutionary pressures on animals to adapt,

在演化上都會大幅影響動物適應狀況

which in turn makes the aging process different across species.

進一步使不同動物有不同的老化過程

Consider the cold depths of the Atlantic and Arctic Seas,

在大西洋和北極海的深處

where Greenland sharks can live to over 400 years,

格陵蘭鯊可以活超過400年

and the Arctic clam known as the quahog can live up to 500.

而北極貝(又稱蚌礪)的壽命長達500年

Perhaps the most impressive of these ocean-dwelling ancients

在這些海洋古生物中，最令人印象深刻的

is the Antarctic glass sponge,

或許是南極玻璃海綿

牠們可以在嚴寒的水中生存超過一萬年

which can survive over 10,000 years in frigid waters.

In cold environments like these, heartbeats and metabolic rates slow down.

在如此寒冷的環境， 心跳和代謝率都會下降

Researchers theorize that this also causes a slowing of the aging process.

研究員推論這會導致老化過程趨緩

In this way, the environment shapes longevity.

這麼看來，環境的確會影響壽命長短

而當談到體型時，大部分的狀況是

When it comes to size, it's often, but not always,

the case that larger species have a longer lifespan than smaller ones.

體型較大的生物壽命也比較長

For instance, an elephant or whale will live much longer

例如大象或鯨魚的壽命

就比小老鼠、中型鼠或田鼠的壽命長很多

than a mouse, rat, or vole,

which in turn have years on flies and worms.

而老鼠的壽命同樣也比蒼蠅和小蟲長很多

Some small animals, like worms and flies,

像小蟲和蒼蠅這類的小動物

are also limited by the mechanics of their cell division.

也受限於細胞分裂的機制

They're mostly made up of cells that can't divide and be replaced when damaged,

牠們的細胞無法分裂， 遭破壞時也無可替換

所以生命很快就會終止

so their bodies expire more quickly.

And size is a powerful evolutionary driver in animals.

對動物而言，體型是強大的演化驅動力

Smaller creatures are more prone to predators.

體型較小的生物容易受到掠食者攻擊

A mouse, for instance, can hardly expect to survive more than a year in the wild.

例如小老鼠就很難在荒野活過一年

So, it has evolved to grow and reproduce more rapidly,

因此，老鼠得加快成長與繁殖的速度

like an evolutionary defense mechanism against its shorter lifespan.

這就是演化的防衛機制 與短壽命相抗衡後的結果

Larger animals, by contrast, are better at fending off predators,

相對地，大型動物較擅於防禦掠食者

and so they have the luxury of time to grow to large sizes

所以牠們有充分時間可以長大

and reproduce multiple times during their lives.

而且一生可以繁殖很多次

Exceptions to the size rule include bats, birds, moles, and turtles,

但還是有例外，像蝙蝠、 鳥類、鼴鼠和海龜

but in each case, these animals have other adaptations

不過這些動物都有各自的方式

that allow them to escape predators.

可以逃過掠食者的捕捉

But there are still cases where animals with similar defining features,

有些動物在體型、棲地等特性上

like size and habitat,

都很相似

age at completely different rates.

但老化速度卻完全不同

In these cases, genetic differences,

在這些狀況下，基因差異

like how each organism's cells respond to threats,

例如細胞因應威脅方式的不同

often account for the discrepancies in longevity.

才能夠解釋壽命長短的差異

So it's the combination of all these factors

綜合所有因素的作用

playing out to differing degrees in different animals

造成動物之間的差異

that explains the variability we see in the animal kingdom.

這也解釋了動物王國裡的變異性

So what about us?

那我們人類呢

Humans currently have an average life expectancy of 71 years,

人類目前平均壽命為71歲

meaning that we're not even close to being the longest living inhabitants on Earth.

這表示我們和地球最長壽的居民 還差一大截！

But we are very good at increasing our life expectancy.

但我們擅於延長壽命

20世紀初期，人類平均只能活到50歲

In the early 1900s, humans only lived an average of 50 years.

Since then, we've learned to adapt by managing many of the factors

從那時起，我們漸漸學會控制

一些會導致死亡的因素

that cause deaths,

例如環境和營養

like environmental exposure and nutrition.

This, and other increases in life expectancy

種種延長壽命的方式

make us possibly the only species on Earth

也許能讓我們成為地球上唯一一種

to take control over our natural fate.

可以主宰自己命運的生物