[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.00,0:00:09.80,Default,,0000,0000,0000,,Symmetry is everywhere in nature,
Dialogue: 0,0:00:09.80,0:00:12.18,Default,,0000,0000,0000,,and we usually associate it with beauty:
Dialogue: 0,0:00:12.18,0:00:13.83,Default,,0000,0000,0000,,a perfectly shaped leaf,
Dialogue: 0,0:00:13.83,0:00:17.57,Default,,0000,0000,0000,,or a butterfly with intricate patterns\Nmirrored on each wing.
Dialogue: 0,0:00:17.57,0:00:21.20,Default,,0000,0000,0000,,But it turns out that asymmetry\Nis pretty important, too,
Dialogue: 0,0:00:21.20,0:00:23.13,Default,,0000,0000,0000,,and more common than you might think,
Dialogue: 0,0:00:23.13,0:00:25.71,Default,,0000,0000,0000,,from crabs with one giant pincer claw,
Dialogue: 0,0:00:25.71,0:00:30.63,Default,,0000,0000,0000,,to snail species whose shells'\Nalways coil in the same direction.
Dialogue: 0,0:00:30.63,0:00:34.94,Default,,0000,0000,0000,,Some species of beans only climb up\Ntheir trellises clockwise,
Dialogue: 0,0:00:34.94,0:00:37.20,Default,,0000,0000,0000,,others, only counterclockwise,
Dialogue: 0,0:00:37.20,0:00:41.06,Default,,0000,0000,0000,,and even though the human body\Nlooks pretty symmetrical on the outside,
Dialogue: 0,0:00:41.06,0:00:43.74,Default,,0000,0000,0000,,it's a different story on the inside.
Dialogue: 0,0:00:43.74,0:00:47.40,Default,,0000,0000,0000,,Most of your vital organs \Nare arranged asymmetrically.
Dialogue: 0,0:00:47.40,0:00:51.94,Default,,0000,0000,0000,,The heart, stomach, spleen, and pancreas\Nlie towards the left.
Dialogue: 0,0:00:51.94,0:00:55.68,Default,,0000,0000,0000,,The gallbladder and most of your liver\Nare on the right.
Dialogue: 0,0:00:55.68,0:00:57.57,Default,,0000,0000,0000,,Even your lungs are different.
Dialogue: 0,0:00:57.57,0:01:00.53,Default,,0000,0000,0000,,The left one has two lobes,\Nand the right one has three.
Dialogue: 0,0:01:00.53,0:01:05.30,Default,,0000,0000,0000,,The two sides of your brain look similar,\Nbut function differently.
Dialogue: 0,0:01:05.30,0:01:10.16,Default,,0000,0000,0000,,Making sure this asymmetry is distributed\Nthe right way is critical.
Dialogue: 0,0:01:10.16,0:01:15.15,Default,,0000,0000,0000,,If all your internal organs are flipped,\Na condition called situs inversus,
Dialogue: 0,0:01:15.15,0:01:16.69,Default,,0000,0000,0000,,it's often harmless.
Dialogue: 0,0:01:16.69,0:01:19.04,Default,,0000,0000,0000,,But incomplete reversals can be fatal,
Dialogue: 0,0:01:19.04,0:01:22.10,Default,,0000,0000,0000,,especially if the heart is involved.
Dialogue: 0,0:01:22.10,0:01:24.03,Default,,0000,0000,0000,,But where does this asymmetry come from,
Dialogue: 0,0:01:24.03,0:01:28.56,Default,,0000,0000,0000,,since a brand-new embryo looks identical\Non the right and left.
Dialogue: 0,0:01:28.56,0:01:31.75,Default,,0000,0000,0000,,One theory focuses \Non a small pit on the embryo
Dialogue: 0,0:01:31.75,0:01:33.04,Default,,0000,0000,0000,,called a node.
Dialogue: 0,0:01:33.04,0:01:36.00,Default,,0000,0000,0000,,The node is lined with tiny hairs\Ncalled cilia,
Dialogue: 0,0:01:36.00,0:01:40.19,Default,,0000,0000,0000,,while tilt away from the head\Nand whirl around rapidly,
Dialogue: 0,0:01:40.19,0:01:42.44,Default,,0000,0000,0000,,all in the same direction.
Dialogue: 0,0:01:42.44,0:01:46.75,Default,,0000,0000,0000,,This synchronized rotation pushes fluid\Nfrom the right side of the embryo
Dialogue: 0,0:01:46.75,0:01:48.30,Default,,0000,0000,0000,,to the left.
Dialogue: 0,0:01:48.30,0:01:50.20,Default,,0000,0000,0000,,On the node's left-hand rim,
Dialogue: 0,0:01:50.20,0:01:52.61,Default,,0000,0000,0000,,other cilia sense this fluid flow
Dialogue: 0,0:01:52.61,0:01:56.96,Default,,0000,0000,0000,,and activate specific genes\Non the embryo's left side.
Dialogue: 0,0:01:56.96,0:02:00.72,Default,,0000,0000,0000,,These genes direct the cells\Nto make certain proteins,
Dialogue: 0,0:02:00.72,0:02:02.08,Default,,0000,0000,0000,,and in just a few hours,
Dialogue: 0,0:02:02.08,0:02:06.34,Default,,0000,0000,0000,,the right and left sides of the embryo\Nare chemically different.
Dialogue: 0,0:02:06.34,0:02:08.13,Default,,0000,0000,0000,,Even though they still look the same,
Dialogue: 0,0:02:08.13,0:02:14.05,Default,,0000,0000,0000,,these chemical differences are eventually\Ntranslated into asymmetric organs.
Dialogue: 0,0:02:14.05,0:02:17.81,Default,,0000,0000,0000,,Asymmetry shows up in the heart first.
Dialogue: 0,0:02:17.81,0:02:21.64,Default,,0000,0000,0000,,It begins as a straight tube\Nalong the certain of the embryo,
Dialogue: 0,0:02:21.64,0:02:24.22,Default,,0000,0000,0000,,but when the embryo \Nis around three weeks old,
Dialogue: 0,0:02:24.22,0:02:27.18,Default,,0000,0000,0000,,the tube starts to bend into a c-shape
Dialogue: 0,0:02:27.18,0:02:30.12,Default,,0000,0000,0000,,and rotate towards \Nthe right side of the body.
Dialogue: 0,0:02:30.12,0:02:32.94,Default,,0000,0000,0000,,It grows different \Nstructures on each side,
Dialogue: 0,0:02:32.94,0:02:36.46,Default,,0000,0000,0000,,eventually turning into the familiar\Nasymmetric heart.
Dialogue: 0,0:02:36.46,0:02:40.83,Default,,0000,0000,0000,,Meanwhile, the other major organs\Nemerge from a central tube
Dialogue: 0,0:02:40.83,0:02:43.66,Default,,0000,0000,0000,,and grow towards their ultimate positions.
Dialogue: 0,0:02:43.66,0:02:48.30,Default,,0000,0000,0000,,But some organisms, like pigs,\Ndon't have those embryonic cilia
Dialogue: 0,0:02:48.30,0:02:51.29,Default,,0000,0000,0000,,and still have asymmetric internal organs.
Dialogue: 0,0:02:51.29,0:02:54.57,Default,,0000,0000,0000,,Could all cells be \Nintrinsically asymmetric?
Dialogue: 0,0:02:54.57,0:02:55.70,Default,,0000,0000,0000,,Probably.
Dialogue: 0,0:02:55.70,0:03:00.95,Default,,0000,0000,0000,,Bacterial colonies grow lacy branches\Nthat all curl in the same direction,
Dialogue: 0,0:03:00.95,0:03:04.42,Default,,0000,0000,0000,,and human cells cultured \Ninside a ring-shaped boundary
Dialogue: 0,0:03:04.42,0:03:08.03,Default,,0000,0000,0000,,tend to line up \Nlike the ridges on a cruller.
Dialogue: 0,0:03:08.03,0:03:09.87,Default,,0000,0000,0000,,If we zoom in even more,
Dialogue: 0,0:03:09.87,0:03:12.56,Default,,0000,0000,0000,,we see that many \Nof cells' basic building blocks,
Dialogue: 0,0:03:12.56,0:03:17.90,Default,,0000,0000,0000,,like nucleic acids, proteins, and sugars,\Nare inherently asymmetric.
Dialogue: 0,0:03:17.90,0:03:20.68,Default,,0000,0000,0000,,Proteins have complex asymmetric shapes,
Dialogue: 0,0:03:20.68,0:03:23.86,Default,,0000,0000,0000,,and those proteins control \Nwhich way cells migrate
Dialogue: 0,0:03:23.86,0:03:26.73,Default,,0000,0000,0000,,and which way embryonic cilia twirl.
Dialogue: 0,0:03:26.73,0:03:30.40,Default,,0000,0000,0000,,These biomolecules \Nhave a property called chirality,
Dialogue: 0,0:03:30.40,0:03:34.65,Default,,0000,0000,0000,,which means that a molecule \Nand its mirror image aren't identical,
Dialogue: 0,0:03:34.65,0:03:37.65,Default,,0000,0000,0000,,like your right and left hands, \Nthey look the same,
Dialogue: 0,0:03:37.65,0:03:42.34,Default,,0000,0000,0000,,but trying to put your right\Nin your left glove proves they're not.
Dialogue: 0,0:03:42.34,0:03:47.62,Default,,0000,0000,0000,,This asymmetry at the molecular level\Nis reflected in asymmetric cells,
Dialogue: 0,0:03:47.62,0:03:49.07,Default,,0000,0000,0000,,asymmetric embryos,
Dialogue: 0,0:03:49.07,0:03:51.93,Default,,0000,0000,0000,,and finally asymmetric organisms.
Dialogue: 0,0:03:51.93,0:03:53.93,Default,,0000,0000,0000,,So while symmetry may be beautiful,
Dialogue: 0,0:03:53.93,0:03:57.08,Default,,0000,0000,0000,,asymmetry holds an allure of its own,
Dialogue: 0,0:03:57.08,0:03:58.73,Default,,0000,0000,0000,,found in its graceful whirls,
Dialogue: 0,0:03:58.73,0:04:00.66,Default,,0000,0000,0000,,its organized complexity,
Dialogue: 0,0:04:00.66,0:04:02.65,Default,,0000,0000,0000,,and its striking imperfections.