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

相對而言，烏龜可以活超過一百年。

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

中、小型鼠的壽命則大約為四年，

while for the bowhead whale, Earth's longest-lived mammal, death can come after 200.

而地球上最長壽的哺乳類是弓頭鯨，壽命超過 200 歲。

Like most living things, the vast majority of animals gradually degenerate after reaching sexual maturity in the process known as aging.

大多數動物和大部分生物一樣，在性成熟後身體便開始退化，這個過程稱為老化。

But what does it really mean to age?

但老化到底是什麼？

The drivers behind this process are varied and complicated, but aging is ultimately caused by cell death and dysfunction.

這過程的成因十分繁雜，簡單來說，細胞死亡和功能失常最終會導致老化。

When we're young, we constantly regenerate cells in order to replace dead and dying ones.

年輕時，我們的細胞會不斷再生，取代已死亡及凋零的細胞。

But as we age, this process slows down.

隨著年紀增長，再生速度會愈來愈慢。

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，

That makes our bodies go into a decline, which eventually results in disease and death.

這使得我們的身體開始衰退，最終導致疾病與死亡。

But if that's consistently true, why the huge variance in aging patterns and lifespan within the animal kingdom?

若這現象是所有生物的共通點，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, including environment and body size.

有幾種因素，像是環境和體型。

These can place powerful evolutionary pressures on animals to adapt, which in turn makes the aging process different across species.

在演化上都會大幅影響動物適應狀況，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, where Greenland sharks can live to over 400 years,

在大西洋和北極海的深處，格陵蘭鯊可以活超過四百年，

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

而北極貝（又稱蚌礪）的壽命長達五百年。

Perhaps the most impressive of these ocean-dwelling ancients is the Antarctic glass sponge, which can survive over 10,000 years in frigid waters.

在這些海洋古生物中，最令人印象深刻的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。

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。

When it comes to size, it's often, but not always, the case that larger species have a longer lifespan than smaller ones.

而當談到體型時，大部分的狀況是，體型較大的生物壽命也比較長。

For instance, an elephant or whale will live much longer than a mouse, rat, or vole, which in turn have years on flies and worms.

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，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, are also limited by the mechanics of their cell division.

像小蟲和蒼蠅這類的小動物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, so their bodies expire more quickly.

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。

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, like an evolutionary defense mechanism against its shorter lifespan.

因此，老鼠得加快成長與繁殖的速度，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 and reproduce multiple times during their lives.

所以牠們有充分時間可以長大，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 that allow them to escape predators.

不過這些動物都有各自的方式可以逃過掠食者的捕捉。

But there are still cases where animals with similar defining features, like size and habitat, age at completely different rates.

有些動物在體型、棲地等特性上都很相似，但老化速度卻完全不同。

In these cases, genetic differences, like how each organism's cells respond to threats, often account for the discrepancies in longevity.

在這些狀況下，基因差異，例如細胞因應威脅方式的不同才能夠解釋壽命長短的差異。

So it's the combination of all these factors playing out to differing degrees in different animals that explains the variability we see in the animal kingdom.

綜合所有因素的作用造成動物之間的差異，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, meaning that we're not even close to being the longest living inhabitants on Earth.

人類目前平均壽命為 71 歲，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。

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

20 世紀初期，人類平均只能活到 50 歲。

Since then, we've learned to adapt by managing many of the factors that cause deaths, like environmental exposure and nutrition.

從那時起，我們漸漸學會控制一些會導致死亡的因素，例如環境和營養。

This, and other increases in life expectancy make us possibly the only species on Earth to take control over our natural fate.

種種延長壽命的方式也許能讓我們成為地球上唯一一種 可以主宰自己命運的生物。