Name: 【Ted-Ed】為什麼人體不是對稱的? (Why are human bodies asymmetrical? - Leo Q. Wan)
Uploaded: 2021-07-25T21:01:20.000Z
Duration: 4 min 19 s

Symmetry is everywhere in nature, and we usually associate it with beauty: a perfectly shaped leaf, or a butterfly with intricate patterns mirrored on each wing.

大自然到處都看得到對稱，我們通常把它跟「美麗」這詞聯想在一塊： 一片完美形狀的葉子， 或是一隻蝴蝶翅膀上有著相對應的錯綜複雜圖案。

關係子句

But it turns out that asymmetry is pretty important, too, and more common than you might think, from crabs with one giant pincer claw to snail species whose shells' always coil in the same direction.

不過，結果發現，不對稱也是很重要，而且，不對稱的存在比你想的還要更普遍： 從有著一只大蟹蟄的螃蟹， 到蝸牛殼上的紋路總是朝同一個方向旋繞。

Some species of beans only climb up their trellises clockwise, others, only counterclockwise, and even though the human body looks pretty symmetrical on the outside, it's a different story on the inside.

有些豆類的藤蔓只會順時針繞著著支架攀爬，有的只會逆時針攀爬， 另外，即使人體外表看起來都很對稱， 但內部結構又是另一回事。

Most of your vital organs are arranged asymmetrically.

大部份的重要器官都是不對稱排列的。

The heart, stomach, spleen, and pancreas lie towards the left; the gallbladder and most of your liver are on the right.

心臟、胃、脾臟、以及胰臟都在身體左側；膽囊和大部份的肝臟都在身體右側。

Even your lungs are different; the left one has two lobes, and the right one has three.

甚至肺臟也不同：左邊的肺有兩葉，而右邊的肺有三葉。

The two sides of your brain look similar, but function differently.

大腦的兩邊看起來雖然相似，但功能不同。

Making sure this asymmetry is distributed the right way is critical.

確保不對稱器官的正確分配是非常重要的。

If all your internal organs are flipped, a condition called situs inversus, it's often harmless. But incomplete reversals can be fatal, especially if the heart is involved.

假如全部的內臟器官都翻轉過來，這情況稱之為「內臟逆位」，通常情況下是無害的，但不完整的內臟器官反轉則會致命，尤其如果心臟有包含在內的情況下 。

But where does this asymmetry come from, since a brand-new embryo looks identical on the right and left.

但這個不對稱是從哪兒來的呢？畢竟嶄新的胚胎左右兩邊看起來一模一樣。

One theory focuses  on a small pit on the embryo called a node.

有一個理論著重在胚胎裡一個小凹處，叫做「腹側結點」 。

The node is lined with tiny hairs called cilia, which tilt away from the head and whirl around rapidly, all in the same direction.

腹側結點表面有許多細細的纖毛，這些纖毛向遠離胚胎頭部的方向傾斜，並且全都按同一個方向快速轉動。

This synchronized rotation pushes fluid from the right side of the embryo to the left.

這同步的轉動，將液體從胚胎的右邊推至左邊。

On the node's left-hand rim, other cilia sense this fluid flow and activate specific genes on the embryo's left side.

在腹側結點的左手邊，其他的纖毛感應到了液體的流動， 而激活了胚胎左邊的特殊基因。

These genes direct the cells to make certain proteins, and in just a few hours, the right and left sides of the embryo are chemically different, even though they still look the same.

這些基因指示細胞製造出特定的蛋白質，在短短幾個小時內， 胚胎的左右邊有了不同的化學變化，即使它們外表看起來仍然相同。

These chemical differences are eventually translated into asymmetric organs.

這些不同的化學變化，最後演變成不對稱的器官。

It begins as a straight tube along the center of the embryo, but when the embryo is around three weeks old, the tube starts to bend into a c-shape and rotate towards the right side of the body.

它一開始在胚胎裡，是一條長條狀的管子，但當胚胎約三週大時， 管子開始彎曲成Ｃ字形狀， 並轉動靠近身體的右側。

It grows different  structures on each side, eventually turning into the familiar asymmetric heart.

它的每一邊長出不同的構造，最後變成我們熟悉的不對稱心臟。

Meanwhile, the other major organs emerge from a central tube and grow towards their ultimate positions.

同時，其他重要器官也從中心管子成長，慢慢靠向屬於它們的位置。

But some organisms, like pigs, don't have those embryonic cilia and still have asymmetric internal organs.

有些生物（有機體），像是豬，就沒有那些胚胎纖毛，但還是有不對稱的內臟器官。

Could all cells be intrinsically asymmetric? Probably.

有可能全部的細胞本質上就是不對稱的嗎？也許是。

Bacterial colonies grow lacy branches that all curl in the same direction, and human cells cultured inside a ring-shaped boundary tend to line up like the ridges on a cruller.

細菌菌落長出花邊狀的分支，全部都往相同方向捲曲，在環狀邊界裡培養出的人體細胞， 傾向排列成像突起的油條脊狀。

If we zoom in even more, we see that many of cells' basic building blocks, like nucleic acids, proteins, and sugars, are inherently asymmetric.

假如我們把它放大來看，可以看到許多細胞的基礎構造單元， 像是核酸、蛋白質、以及糖，都是天生不對稱。

Proteins have complex asymmetric shapes, and those proteins control which way cells migrate and which way embryonic cilia twirl.

蛋白質有複雜的不對稱形狀，而那些蛋白質控制細胞往哪個方向移動， 以及胚胎纖毛往哪個方向快速轉動。

These biomolecules have a property called chirality, which means that a molecule and its mirror image aren't identical.

這些生物分子有一個屬性，叫「手性」，意思是指一個分子和它的鏡面影像並沒有一模一樣。

Like your right and left hands, they look the same, but trying to put your right in your left glove proves they're not.

就像右手和左手，它們雖然看似相同，但試著用右手去戴左手手套，便會知道它們實際上不一樣。

This asymmetry at the molecular level is reflected in asymmetric cells, asymmetric embryos, and finally asymmetric organisms.

這個分子階段上的不對稱從不對稱細胞中表現出來，變成不對稱胚胎， 最後成了不對稱生物。

So, while symmetry may be beautiful, asymmetry holds an allure of its own, found in its graceful whirls, its organized complexity, and its striking imperfections.

因此，儘管對稱看起來很美麗，不對稱也有它自己的魅力所在——可以從它優雅的轉動、 組織的複雜性、 以及驚人的不完美中發現。