[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:09.34,0:00:12.02,Default,,0000,0000,0000,,The human eye is an amazing mechanism,
Dialogue: 0,0:00:12.02,0:00:16.46,Default,,0000,0000,0000,,able to detect anywhere \Nfrom a few photons to direct sunlight,
Dialogue: 0,0:00:16.46,0:00:19.08,Default,,0000,0000,0000,,or switch focus from \Nthe screen in front of you
Dialogue: 0,0:00:19.08,0:00:22.63,Default,,0000,0000,0000,,to the distant horizon \Nin a third of a second.
Dialogue: 0,0:00:22.63,0:00:26.36,Default,,0000,0000,0000,,In fact, the structures required\Nfor such incredible flexibility
Dialogue: 0,0:00:26.36,0:00:28.37,Default,,0000,0000,0000,,were once considered so complex
Dialogue: 0,0:00:28.37,0:00:33.50,Default,,0000,0000,0000,,that Charles Darwin himself acknowledged\Nthat the idea of their having evolved
Dialogue: 0,0:00:33.50,0:00:37.46,Default,,0000,0000,0000,,seemed absurd in the highest\Npossible degree.
Dialogue: 0,0:00:37.46,0:00:42.98,Default,,0000,0000,0000,,And yet, that is exactly what happened,\Nstarting more than 500 million years ago.
Dialogue: 0,0:00:42.98,0:00:46.76,Default,,0000,0000,0000,,The story of the human eye begins\Nwith a simple light spot,
Dialogue: 0,0:00:46.76,0:00:49.82,Default,,0000,0000,0000,,such as the one found \Nin single-celled organisms,
Dialogue: 0,0:00:49.82,0:00:51.62,Default,,0000,0000,0000,,like euglena.
Dialogue: 0,0:00:51.62,0:00:53.84,Default,,0000,0000,0000,,This is a cluster \Nof light-sensitive proteins
Dialogue: 0,0:00:53.84,0:00:56.41,Default,,0000,0000,0000,,linked to the organism's flagellum,
Dialogue: 0,0:00:56.41,0:01:00.02,Default,,0000,0000,0000,,activating when it finds light,\Nand therefore food.
Dialogue: 0,0:01:00.02,0:01:05.04,Default,,0000,0000,0000,,A more complex version of this light spot\Ncan be found in the flat worm, planaria.
Dialogue: 0,0:01:05.04,0:01:07.51,Default,,0000,0000,0000,,Being cupped, rather than flat,
Dialogue: 0,0:01:07.51,0:01:12.04,Default,,0000,0000,0000,,enables it to better sense\Nthe direction of the incoming light.
Dialogue: 0,0:01:12.04,0:01:13.77,Default,,0000,0000,0000,,Among its other uses,
Dialogue: 0,0:01:13.77,0:01:19.49,Default,,0000,0000,0000,,this ability allows an organism\Nto seek out shade and hide from predators.
Dialogue: 0,0:01:19.49,0:01:20.60,Default,,0000,0000,0000,,Over the millenia,
Dialogue: 0,0:01:20.60,0:01:23.43,Default,,0000,0000,0000,,as such light cups grew \Ndeeper in some organisms,
Dialogue: 0,0:01:23.43,0:01:26.45,Default,,0000,0000,0000,,the opening at the front grew smaller.
Dialogue: 0,0:01:26.45,0:01:31.19,Default,,0000,0000,0000,,The result was a pinhole effect,\Nwhich increased resolution dramatically,
Dialogue: 0,0:01:31.19,0:01:36.46,Default,,0000,0000,0000,,reducing distortion by only allowing\Na thin beam of light into the eye.
Dialogue: 0,0:01:36.46,0:01:39.08,Default,,0000,0000,0000,,The nautilus, \Nan ancestor of the octopus,
Dialogue: 0,0:01:39.08,0:01:45.15,Default,,0000,0000,0000,,uses this pinhole eye for improved \Nresolution and directional sensing.
Dialogue: 0,0:01:45.15,0:01:48.56,Default,,0000,0000,0000,,Although the pinhole eye allows\Nfor simple images,
Dialogue: 0,0:01:48.56,0:01:52.49,Default,,0000,0000,0000,,the key step towards the eye \Nas we know it is a lens.
Dialogue: 0,0:01:52.49,0:01:54.11,Default,,0000,0000,0000,,This is thought to have evolved
Dialogue: 0,0:01:54.11,0:01:58.56,Default,,0000,0000,0000,,through transparent cells covering \Nthe opening to prevent infection,
Dialogue: 0,0:01:58.56,0:02:01.62,Default,,0000,0000,0000,,allowing the inside of the eye\Nto fill with fluid
Dialogue: 0,0:02:01.62,0:02:05.24,Default,,0000,0000,0000,,that optimizes light sensitivity\Nand processing.
Dialogue: 0,0:02:05.24,0:02:07.44,Default,,0000,0000,0000,,Crystalline proteins \Nforming at the surface
Dialogue: 0,0:02:07.44,0:02:09.90,Default,,0000,0000,0000,,created a structure that proved useful
Dialogue: 0,0:02:09.90,0:02:13.14,Default,,0000,0000,0000,,in focusing light \Nat a single point on the retina.
Dialogue: 0,0:02:13.14,0:02:17.48,Default,,0000,0000,0000,,It is this lens that is the key\Nto the eye's adability,
Dialogue: 0,0:02:17.48,0:02:21.79,Default,,0000,0000,0000,,changing its curvature to adapt\Nto near and far vision.
Dialogue: 0,0:02:21.79,0:02:24.68,Default,,0000,0000,0000,,This structure of the pinhole \Ncamera with a lens
Dialogue: 0,0:02:24.68,0:02:29.78,Default,,0000,0000,0000,,served as the basis for what would \Neventually evolve into the human eye.
Dialogue: 0,0:02:29.78,0:02:33.19,Default,,0000,0000,0000,,Further refinements would include\Na colored ring, called the iris,
Dialogue: 0,0:02:33.19,0:02:36.38,Default,,0000,0000,0000,,that controls the amount \Nof light entering the eye,
Dialogue: 0,0:02:36.38,0:02:41.41,Default,,0000,0000,0000,,a tough white outer layer known \Nas the sclera to maintain its structure,
Dialogue: 0,0:02:41.41,0:02:45.47,Default,,0000,0000,0000,,and tear glands that secrete \Na protective film.
Dialogue: 0,0:02:45.47,0:02:49.48,Default,,0000,0000,0000,,But equally important was the accompanying\Nevolution of the brain,
Dialogue: 0,0:02:49.48,0:02:51.50,Default,,0000,0000,0000,,with its expansion of the visual cortex
Dialogue: 0,0:02:51.50,0:02:56.16,Default,,0000,0000,0000,,to process the sharper \Nand more colorful images it was receiving.
Dialogue: 0,0:02:56.16,0:03:00.24,Default,,0000,0000,0000,,We now know that far from being\Nan ideal masterpiece of design,
Dialogue: 0,0:03:00.24,0:03:04.34,Default,,0000,0000,0000,,our eye bares traces\Nof its step by step evolution.
Dialogue: 0,0:03:04.34,0:03:07.56,Default,,0000,0000,0000,,For example,\Nthe human retina is inverted,
Dialogue: 0,0:03:07.56,0:03:11.25,Default,,0000,0000,0000,,with light detecting cells facing away\Nfrom the eye opening.
Dialogue: 0,0:03:11.25,0:03:12.90,Default,,0000,0000,0000,,This results in a blind spot,
Dialogue: 0,0:03:12.90,0:03:15.63,Default,,0000,0000,0000,,where the optic nerve\Nmust pierce the retina
Dialogue: 0,0:03:15.63,0:03:18.38,Default,,0000,0000,0000,,to reach the photosensitive \Nlayer in the back.
Dialogue: 0,0:03:18.38,0:03:21.53,Default,,0000,0000,0000,,The similar looking eyes \Nof cephalopods,
Dialogue: 0,0:03:21.53,0:03:23.19,Default,,0000,0000,0000,,which evolved independently,
Dialogue: 0,0:03:23.19,0:03:27.97,Default,,0000,0000,0000,,have a front facing retina,\Nallowing them to see without a blind spot.
Dialogue: 0,0:03:27.97,0:03:30.79,Default,,0000,0000,0000,,Other creatures eyes display\Ndifferent adaptations.
Dialogue: 0,0:03:30.79,0:03:33.73,Default,,0000,0000,0000,,Anableps, the so called four-eyed fish,
Dialogue: 0,0:03:33.73,0:03:38.80,Default,,0000,0000,0000,,have eyes divided in two sections\Nfor looking above and under water,
Dialogue: 0,0:03:38.80,0:03:42.26,Default,,0000,0000,0000,,perfect for spotting \Nboth predators and prey.
Dialogue: 0,0:03:42.26,0:03:47.46,Default,,0000,0000,0000,,Cats, classically nighttime hunters,\Nhave evolved with a reflective layer
Dialogue: 0,0:03:47.46,0:03:51.18,Default,,0000,0000,0000,,maximizing the amount of light\Nthe eye can detect,
Dialogue: 0,0:03:51.18,0:03:55.72,Default,,0000,0000,0000,,granting them excellent night vision,\Nas well as their signature glow.
Dialogue: 0,0:03:55.72,0:04:00.47,Default,,0000,0000,0000,,These are just a few examples of the huge \Ndiversity of eyes in the animal kingdom.
Dialogue: 0,0:04:00.47,0:04:04.87,Default,,0000,0000,0000,,So if you could design an eye, \Nwould you do it any differently?
Dialogue: 0,0:04:04.87,0:04:07.63,Default,,0000,0000,0000,,This question isn't as strange \Nas it might sound.
Dialogue: 0,0:04:07.63,0:04:11.28,Default,,0000,0000,0000,,Today, doctors and scientists are looking\Nat different eye structures
Dialogue: 0,0:04:11.28,0:04:15.66,Default,,0000,0000,0000,,to help design biomechanical implants\Nfor the vision impaired.
Dialogue: 0,0:04:15.66,0:04:18.28,Default,,0000,0000,0000,,And in the not so distant future,
Dialogue: 0,0:04:18.28,0:04:22.20,Default,,0000,0000,0000,,the machines built with the precision\Nand flexibilty of the human eye
Dialogue: 0,0:04:22.20,0:04:26.28,Default,,0000,0000,0000,,may even enable it to surpass\Nits own evolution.