the searing pain of a stubbed toe,

踢到腳趾頭的劇痛感

and the throbbing of a toothache.

還有牙痛的抽痛感

We can identify many types of pain and have multiple ways of treating it.

我們可以辨認出許多種類的疼痛，也有很多的處理方式

But what about other species?

但是其他種生物呢？

How do the animals all around us experience pain?

我們周遭的動物是怎麼感受到疼痛的？

It's important that we find out.

找出答案對我們來說很重要

We keep animals as pets,

我們把動物當成寵物

they enrich our environment,

牠們豐富了我們的環境

we farm many species for food,

我們為了食物而畜養很多種生物

and we use them in experiments to advance science and human health.

我們也拿牠們作實驗，以增進科技與人類健康

Animals are clearly important to us,

動物顯然對我們很重要

so it's equally important that we avoid causing them unnecessary pain.

因此，讓牠們免受不必要的疼痛也同樣很重要

For animals that are similar to us, like mammals,

哺乳類等跟我們很相似的動物

it's often obvious when they're hurting.

牠們受傷時常常顯而易見

But there's a lot that isn't obvious,

但很多時候卻不這麼明顯

like whether pain relievers that work on us also help them.

像是對我們有用的止痛藥，是否也能幫助牠們？

And the more different an animal is from us,

動物與我們愈不相同

the harder it is to understand their experience.

就愈難了解牠們的感受

How do you tell whether a shrimp is in pain?

你怎麼知道蝦子有沒有疼痛？

A snake?

蛇？

A snail?

蝸牛？

In vertebrates, including humans,

脊椎動物，包含人類在內

pain can be split into two distinct processes.

感受疼痛可分為兩種不同的過程

In first, nerves and the skin sense something harmful

在第一種過程，神經與皮膚感知到受傷了

and communicate that information to the spinal cord.

接著傳遞受傷的訊息到脊椎神經

There, motor neurons activate movements

脊椎神經中的運動神經元會使器官活動

that make us rapidly jerk away from the threat.

讓我們能迅速遠離威脅

This is the physical recognition of harm called nociception,

這種對傷害的身體認知就稱為痛覺

and nearly all animals,

幾乎所有動物

even those with very simple nervous systems,

即便是那些神經系統非常簡單的動物

experience it.

都會感受到痛覺

Without this ability, animals would be unable to avoid harm

若沒有了這項能力，動物就不能避開傷害

and their survival would be threatened.

生存就會因此受威脅

The second part is the conscious recognition of harm.

第二種過程是對於傷害的意識認知

In humans, this occurs when the sensory neurons in our skin

以人類來說，這發生於皮膚內的認知神經

make a second round of connections via the spinal cord to the brain.

進行第二次聯繫，透過脊椎神經傳到大腦

There, millions of neurons in multiple regions create the sensations of pain.

大腦中不同區域的神經元產生疼痛的感覺

For us, this is a very complex experience associated with emotions like fear,

對我們來說，這是非常複雜的感覺，與恐懼

panic,

驚慌

and stress,

緊張的情緒有關

which we can communicate to others.

而我們可以傳達這些情緒給其他人

But it's harder to know exactly how animals experience

但是我們難以知道動物如何感覺

this part of the process

這個過程

because most them can't show us what they feel.

因為牠們大部分都無法表露出牠們感受到什麼

However, we get clues from observing how animals behave.

然而，我們可以從觀察動物的行為中獲得線索

Wild, hurt animals are known to nurse their wounds,

野生、受傷的動物會照料傷口

make noises to show their distress,

製造噪音來表示焦慮

and become reclusive.

甚至把自己藏匿起來

In the lab, scientists have discovered that animals like chickens and rats

科學家在實驗室裡發現，像是雞、老鼠等動物

will self-administer pain-reducing drugs if they're hurting.

如果受傷了會自己服用減緩疼痛的藥物

Animals also avoid situations where they've been hurt before,

動物也會避開曾經受傷過的情況

which suggests awareness of threats.

這意味著他們有危險意識

We've reached the point that research has made us so sure

研究已經讓我們非常肯定

that vertebrates recognize pain

脊椎動物認知得到疼痛

that it's illegal in many countries to needlessly harm these animals.

因此，無謂地傷害動物在許多國家是非法的

But what about other types of animals like invertebrates?

那麼像是無脊椎動物等其他種類的生物呢？

These animals aren't legally protected,

這些動物沒有受法律保護

partly because their behaviors are harder to read.

部份原因是因為牠們的行為更難以解讀

We can make good guesses about some of them,

我們可以猜出哪些是無脊椎動物

like oysters,

像是牡蠣

worms,

蟲

and jellyfish.

還有水母

These are examples of animals that either lack a brain

這些例子中的動物不是缺少大腦

or have a very simple one.

就是大腦構造非常簡單

So an oyster may recoil when squirted with lemon juice, for instance,

因此，比方說，牡蠣會因為痛覺

because of nociception.

被噴到檸檬汁時會畏縮

But with such a simple nervous system,

但是牠們的神經系統因為太過簡單

it's unlikely to experience the conscious part of pain.

所以不可能感受到疼痛的意識認知過程

Other invertebrate animals are more complicated, though,

不過其他的無脊椎動物較為複雜

like the octopus,

例如章魚

which has a sophisticated brain

有著複雜的大腦

and is thought to be one of the most intelligent invertebrate animals.

被認為是無脊椎動物中最聰明的動物之一

Yet, in many countries, people continue the practice of eating live octopus.

不過，許多國家的人們還是有生吃章魚的習慣

We also boil live crawfish, shrimp, and crabs

即便我們不知道牠們有沒有感覺

even though we don't really know how they're affected either.

我們也還是會烹煮活生生的小龍蝦、蝦子，以及螃蟹

This poses an ethical problem

這就產生了道德上的問題

because we may be causing these animals unnecessary suffering.

因為我們可能讓這些動物受到不必要的折磨

Scientific experimentation, though controversial, gives us some clues.

科學實驗雖然有爭議，卻能給我們一些線索

Tests on hermit crabs show that they'll leave an undesirable shell

對寄居蟹的實驗顯示，牠們遭到電擊時

if they're zapped with electricity

會離開不好的殼

but stay if it's a good shell.

但如果是好的殼就會留在殼內

And octopi that may originally curl up an injured arm to protect it

章魚原本會將受傷的手臂彎曲以保護手臂

will risk using it to catch prey.

卻會冒險用那隻手臂來獵捕獵物

That suggests that these animals make value judgements around sensory input

這表示這些動物會在感受到感覺時衡量、判斷

instead of just reacting reflexively to harm.

而非只是反射性地對傷害作出反應

Meanwhile, crabs have been known to repeatedly rub a spot on their bodies

同樣地，螃蟹在遭到電擊時

where they've received an electric shock.

會反覆的摩擦被電擊的身體部位

And even sea slugs flinch

甚至連海參

when they know they're about to receive a noxious stimulus.

在知道自己要中毒時會退縮

That means they have some memory of physical sensations.

這意味著牠們有身體感覺的記憶

We still have a lot to learn about animal pain.

動物疼痛的知識我們還有很多可以學習

As our knowledge grows,

隨著知識增長

it may one day allow us to live in a world where we don't cause pain needlessly.

也許有一天，世界上就不會再有不必要的疼痛