why didn't anybody care about the eyes, nose, or anything else?

為什麼沒有人在乎眼睛、鼻子或是其他東西呢？

Hey digitals, Lissette here for Dnews. I am the proud owner of 10 fingers and 10 toes,

嗨， 我是DNews的Lissette。我可以很開心的說我有十根手指與腳指

I can prove half of this just right now. You’ll just have to trust me on the 10 toes thing. But,

我可以證明一半給你看，另一半腳趾的部分你只能選擇相信我了。但，

have you ever wondered why that is? Why don’t we have 12 fingers and 14 toes? Or 6 fingers

你有沒有想過為什麼是十根？為什麼不是12根手指與14根腳指？或者六根手指

and 1 toe? Well, this may not come as a shocker to you DNews fans out there, but no one really

與一根腳趾？各位 DNews 的忠實粉絲可能不會太意外：但是

knows. It might all come down to math.

從來沒有人知道切確原因。可能一切得回歸數學來探討

Mark Changizi, a theoretical neurobiologist, developed a hypothesis called the Limb Law,

Mark Changizi是個神經生物學家，研發了一套「四肢法則」的理論

first published in the Journal of Theoretical Biology in 2001. It’s a mathematical equation

首次於2001年在生物理論日報出刊，這個數學公式是

that tries to figure out the correct number of limbs an animal needs in order to connect

用以求出動物為了符合這世界的生活環境，所演化出的四肢切確數量，

to the world around it based on the length of its limbs relative to it’s body size.

以及與他們的軀幹大小的相對關係

Okay, wow. The equation looks like this. Confusing, I know. But he used this equation with 190

Okay，哇。這個公式是這樣的。我知道很難理解。這個公式是以190

different animal species from seven different animal Phyla, and the math seems to check

種動物，分別從七個不同的生物分類法演算出來的。而這數學公式似乎是

out. Mark thinks this same equation could be used to figure out why humans have five

可行的。Mark認為這個公式可以用來算出為什麼人類一隻手

fingers on each hand.

有五根手指頭

The calculation treats our palms as the animal and our fingers as limbs. Also it takes into

在運算中，他們把人類的手掌比擬做動物體，而人類的手指比擬做動物的四肢。也有另一

account that the whole reason behind having fingers is that they’re able to fold over

重點是，手指的存在是為了彎曲摺疊時能夠

our entire palm, in order to grasp things. So, first, fingers have to be at least as

覆蓋住整個手掌，以便於抓取東西。所以，手指必須至少跟我們的

long as our palms, also known as length need to connect to the outside world. When you crunch the

手掌一樣長，並與外界連接，計算出的

numbers, you'll get 9.42 digits per hand. But, he argues, since our hand is not a free

數字是，每隻手應該要有9.42根手指。但是，我們的手不單單是個

roaming creature, but is attached to our arm, it doesn't need limbs protruding from all

漂浮的物體。由於手與手臂相連接，因此不需要四面八方都有指頭，

sides. Hands only need half the total number of limbs. That gets us to 4.71 fingers per

只需要一半的數字就夠了。所以算出一隻手平均會有4.71根

hand. Just based on math. Pretty amazing.

手指頭。這只是光靠數學公式算出的，蠻讓人驚艷的

But other explanations are simpler than that. Evolutionary biologists say that we have 10

但有其他的解釋比這個簡單多了。生物演化學家指出我們的十根

fingers and 10 toes because that’s the best combination for us. If 8 fingers and 8 toes

手指、腳趾恰逢其所。如果八根手指、腳趾

would have given us an evolutionary advantage, humans would have 4 fingers on each hand.

有利於演化，則人類就會一手有四根手指

Cliff Tabin, a Harvard Medical school geneticist focusing on limb development in vertebrates,

哈佛遺傳學家Cliff Tabin則是著重在脊椎動物的四肢演化

pointed out that our motor skills come down to our thumb and index finger, and that another

他指出，我們之所以如此靈巧是由於大拇指與食指的存在，若是生長出

small, 6th finger wouldn’t really change anything. And if we ever did grow a 6th finger,

第六跟小指頭，則不會對人類有什麼改變。而若我們真的有第六根指頭

Tabin argues, it would probably grow out of our wrists, like panda’s . It gives

Tabin認為，第六根應該會長在我們的手腕內側，就像熊貓一樣。這讓

them extra support when gripping bamboo, which gives them an evolutionarily advantage. So,

熊貓們在抓竹子的時候有更多的支撐力量，這也有利於熊貓的演化。所以

basically, we'd have six if people with six fingers got an advantage.

基本來說如果人類有六根手指頭是有利於演化的話，我們就會有六根手指頭了

Then, there is this more complicated science answer to why we have the number of digits

除此之外，還有更複雜的科學解釋我們五根手指的原因

we do. James Sharpe from the Centre for Genomic Regulation in Barcelona discovered

位於巴賽隆納染色體編號規則中心的James Sharp發現

it all comes down to three molecules in our body. Bmp, Wnt and Sox9. They’re responsible

我們身體中的三個分子Bmp、Wnt 跟 Sox9 負責

for marking out in an embryo where fingers will go and how far apart they’ll grow.

胎兒生長時手指該長的方向與間隙

And for the most part it marks out space for five fingers on each hand and five toes on

還有最大的功用是那些分子決定了指頭的分隔

each foot. But of course sometimes things can go wrong, resulting in the gaps between

但當然有時候可能會出錯，造成手指間的空隙

fingers being bigger and only having room for four fingers. Or, sometimes it screws

太大而只容得下四根手指；或者有時候也會搞砸

up and you have room for an extra finger. Oh and fun fact, the basis for this discovery

而使你多長出一根指頭。有趣的是，首先提出這個理論的人是

was a theory first proposed by Alan Turing back in 1952 about how animals get their spots and

是Alan Turing，他在1952年研究動物為什麼有斑紋

stripes. Love you, Alan.

或者是線條。愛你，Alan

So why 10 fingers and 10 toes? Again, we’re still not entirely sure. But it all seems

所以為什麼有十根手指、腳趾？再一次說明，我們仍然不確定原因。但似乎

to come down to because that’s exactly the number of fingers and toes we need. Sometimes

結論是因為十根手指、腳恰恰符合需求。有時候，

it’s best to just trust evolution and be thankful we don’t have hoofs. Amirite?

直接信任演化的結果就好了呀！而且得心存感激我們有手指而非蹄，對吧？

So that’s hands. But what about feet?

這是講到手，那腳呢？

When did they evolve and why do they look

腳是什麼時候演化的？而且為什麼腳看起來

different from hands? Julia walked a mile in those shoes, here.

跟手差那麼多？Julia深入探討了一番

Toes likely evolved from the same bones that became fins, wings and hoofs in other species.

演化出腳趾的骨頭跟演化初鰭、翅膀、蹄的骨頭相同。

The dominating scientific theories are that fingers and toes are exclusive features of tetrapods.

較有說服力的科學理論是，手指根腳趾是四足類動物的身體特徵

Or vertebrates with limbs.

還有有四肢的脊椎動物

But according to one study toes may evolve even before our fishy ancestors left the ocean.

但一份研究顯示，腳趾的演化或許比魚類祖先離開海洋的時間還早

Why do you think we have 10 fingers and toes? Would you rather have more or less?

你覺得為什麼我們有十根手指、腳趾？你想要更多還是更少呢？

Let us know on the comments and remember to subscribe to DNews for more episodes everyday.

在下面留言處跟我們說你的想法，並且不要忘記訂閱DNews，可以看到更多的節目喔

Thanks for watching, guys.

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