TedTest

From the Ted Talk by Joshua Harvey: The evolution of the human eye

Unscramble the Blue Letters

The human eye is an amazing mechanism, able to detect anywhere from a few photons to direct sunlight, or stwich focus from the screen in front of you to the dasnitt hrozoin in a third of a second. In fact, the structures required for such irnlbiedce flexibility were once cieedsornd so complex that Charles Darwin himself acknowledged that the idea of there having evolved seemed absurd in the highest possible degree. And yet, that is exactly what happened, starting more than 500 million years ago. The story of the human eye begins with a simple light spot, such as the one found in single-celled omsaingrs, like euglena. This is a cluster of light-sensitive pntreios lknied to the organism's flagellum, activating when it finds light and, therefore, food. A more complex veoirsn of this lghit spot can be found in the flat worm, prianlaa. Being cupped, rather than flat, enables it to better snsee the direction of the iminocng light. Among its other uses, this aitbily allows an oragsnim to seek out shade and hide from predators. Over the milienla, as such light cups grew deeper in some organisms, the opening at the front grew smaller. The result was a pinhole effect, which increased ruesitolon dramatically, reducing distortion by only allowing a thin beam of light into the eye. The nautilus, an ancestor of the octopus, uses this pinhole eye for improved resolution and directional sensing. Although the pinhole eye allows for simple images, the key step towards the eye as we know it is a lens. This is thought to have evolved through transparent clles covering the opening to prevent infection, allowing the inside of the eye to fill with fluid that optimizes light sensitivity and processing. Crystalline proteins forming at the surface created a structure that proved useful in focusing light at a single piont on the retina. It is this lens that is the key to the eye's adaptability, changing its curvature to adapt to near and far vision. This structure of the pihnloe creama with a lens served as the basis for what would eventually evolve into the human eye. Further refinements would inludce a colored ring, called the iris, that colnorts the amount of light entering the eye, a tough white outer layer, known as the sclera, to maintain its structure, and tear glands that setrece a protective film. But equally important was the accompanying eotiovlun of the bairn, with its expansion of the visual cortex to process the sharper and more colorful images it was receiving. We now know that far from being an ideal masterpiece of design, our eye bares traces of its step by step evolution. For example, the human retina is inverted, with light-detecting cells facing away from the eye opening. This results in a blind spot, where the optic nvere must pierce the ritena to reach the pitonetvhsiose layer in the back. The similar looking eyes of clhaodepops, which evolved independently, have a front-facing retina, allowing them to see without a blind spot. Other creatures' eyes dpiasly different adaptations. Anableps, the so called four-eyed fish, have eyes divided in two sections for looking above and under water, perfect for spotting both pdaroerts and prey. Cats, clcasallisy ngihttime hunters, have evolved with a reflective layer maximizing the amount of light the eye can dcteet, granting them elcexelnt nghit vision, as well as their signature glow. These are just a few examples of the huge diversity of eyes in the animal kingdom. So if you could dgisen an eye, would you do it any differently? This question isn't as strange as it might sound. Today, doctors and scientists are looking at different eye structures to help design biomechanical implants for the vision impaired. And in the not so distant future, the machines built with the precision and ftbleiixly of the human eye may even ebnlae it to surpass its own evolution.

Open Cloze

The human eye is an amazing mechanism, able to detect anywhere from a few photons to direct sunlight, or ______ focus from the screen in front of you to the _______ _______ in a third of a second. In fact, the structures required for such __________ flexibility were once __________ so complex that Charles Darwin himself acknowledged that the idea of there having evolved seemed absurd in the highest possible degree. And yet, that is exactly what happened, starting more than 500 million years ago. The story of the human eye begins with a simple light spot, such as the one found in single-celled _________, like euglena. This is a cluster of light-sensitive ________ ______ to the organism's flagellum, activating when it finds light and, therefore, food. A more complex _______ of this _____ spot can be found in the flat worm, ________. Being cupped, rather than flat, enables it to better _____ the direction of the ________ light. Among its other uses, this _______ allows an ________ to seek out shade and hide from predators. Over the ________, as such light cups grew deeper in some organisms, the opening at the front grew smaller. The result was a pinhole effect, which increased __________ dramatically, reducing distortion by only allowing a thin beam of light into the eye. The nautilus, an ancestor of the octopus, uses this pinhole eye for improved resolution and directional sensing. Although the pinhole eye allows for simple images, the key step towards the eye as we know it is a lens. This is thought to have evolved through transparent _____ covering the opening to prevent infection, allowing the inside of the eye to fill with fluid that optimizes light sensitivity and processing. Crystalline proteins forming at the surface created a structure that proved useful in focusing light at a single _____ on the retina. It is this lens that is the key to the eye's adaptability, changing its curvature to adapt to near and far vision. This structure of the _______ ______ with a lens served as the basis for what would eventually evolve into the human eye. Further refinements would _______ a colored ring, called the iris, that ________ the amount of light entering the eye, a tough white outer layer, known as the sclera, to maintain its structure, and tear glands that _______ a protective film. But equally important was the accompanying _________ of the _____, with its expansion of the visual cortex to process the sharper and more colorful images it was receiving. We now know that far from being an ideal masterpiece of design, our eye bares traces of its step by step evolution. For example, the human retina is inverted, with light-detecting cells facing away from the eye opening. This results in a blind spot, where the optic _____ must pierce the ______ to reach the ______________ layer in the back. The similar looking eyes of ___________, which evolved independently, have a front-facing retina, allowing them to see without a blind spot. Other creatures' eyes _______ different adaptations. Anableps, the so called four-eyed fish, have eyes divided in two sections for looking above and under water, perfect for spotting both _________ and prey. Cats, ___________ _________ hunters, have evolved with a reflective layer maximizing the amount of light the eye can ______, granting them _________ _____ vision, as well as their signature glow. These are just a few examples of the huge diversity of eyes in the animal kingdom. So if you could ______ an eye, would you do it any differently? This question isn't as strange as it might sound. Today, doctors and scientists are looking at different eye structures to help design biomechanical implants for the vision impaired. And in the not so distant future, the machines built with the precision and __________ of the human eye may even ______ it to surpass its own evolution.

Solution

linked
incredible
evolution
pinhole
horizon
detect
flexibilty
predators
distant
brain
ability
display
retina
sense
controls
version
switch
cephalopods
photosensitive
planaria
considered
secrete
cells
resolution
nerve
light
millenia
nighttime
design
night
excellent
camera
classically
proteins
incoming
organism
point
include
organisms
enable

Original Text

The human eye is an amazing mechanism, able to detect anywhere from a few photons to direct sunlight, or switch focus from the screen in front of you to the distant horizon in a third of a second. In fact, the structures required for such incredible flexibility were once considered so complex that Charles Darwin himself acknowledged that the idea of there having evolved seemed absurd in the highest possible degree. And yet, that is exactly what happened, starting more than 500 million years ago. The story of the human eye begins with a simple light spot, such as the one found in single-celled organisms, like euglena. This is a cluster of light-sensitive proteins linked to the organism's flagellum, activating when it finds light and, therefore, food. A more complex version of this light spot can be found in the flat worm, planaria. Being cupped, rather than flat, enables it to better sense the direction of the incoming light. Among its other uses, this ability allows an organism to seek out shade and hide from predators. Over the millenia, as such light cups grew deeper in some organisms, the opening at the front grew smaller. The result was a pinhole effect, which increased resolution dramatically, reducing distortion by only allowing a thin beam of light into the eye. The nautilus, an ancestor of the octopus, uses this pinhole eye for improved resolution and directional sensing. Although the pinhole eye allows for simple images, the key step towards the eye as we know it is a lens. This is thought to have evolved through transparent cells covering the opening to prevent infection, allowing the inside of the eye to fill with fluid that optimizes light sensitivity and processing. Crystalline proteins forming at the surface created a structure that proved useful in focusing light at a single point on the retina. It is this lens that is the key to the eye's adaptability, changing its curvature to adapt to near and far vision. This structure of the pinhole camera with a lens served as the basis for what would eventually evolve into the human eye. Further refinements would include a colored ring, called the iris, that controls the amount of light entering the eye, a tough white outer layer, known as the sclera, to maintain its structure, and tear glands that secrete a protective film. But equally important was the accompanying evolution of the brain, with its expansion of the visual cortex to process the sharper and more colorful images it was receiving. We now know that far from being an ideal masterpiece of design, our eye bares traces of its step by step evolution. For example, the human retina is inverted, with light-detecting cells facing away from the eye opening. This results in a blind spot, where the optic nerve must pierce the retina to reach the photosensitive layer in the back. The similar looking eyes of cephalopods, which evolved independently, have a front-facing retina, allowing them to see without a blind spot. Other creatures' eyes display different adaptations. Anableps, the so called four-eyed fish, have eyes divided in two sections for looking above and under water, perfect for spotting both predators and prey. Cats, classically nighttime hunters, have evolved with a reflective layer maximizing the amount of light the eye can detect, granting them excellent night vision, as well as their signature glow. These are just a few examples of the huge diversity of eyes in the animal kingdom. So if you could design an eye, would you do it any differently? This question isn't as strange as it might sound. Today, doctors and scientists are looking at different eye structures to help design biomechanical implants for the vision impaired. And in the not so distant future, the machines built with the precision and flexibilty of the human eye may even enable it to surpass its own evolution.

Frequently Occurring Word Combinations

ngrams of length 2

collocation	frequency
human eye	4
pinhole eye	2

Important Words

ability
absurd
accompanying
acknowledged
activating
adapt
adaptability
adaptations
allowing
amazing
amount
anableps
ancestor
animal
bares
basis
beam
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biomechanical
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brain
built
called
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changing
charles
classically
cluster
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colorful
complex
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controls
cortex
covering
created
crystalline
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curvature
darwin
deeper
degree
design
detect
differently
direct
direction
directional
display
distant
distortion
diversity
divided
doctors
dramatically
effect
enable
enables
entering
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euglena
eventually
evolution
evolve
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examples
excellent
expansion
eye
eyes
facing
fact
fill
film
finds
fish
flagellum
flat
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flexibilty
fluid
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focusing
food
forming
front
future
glands
glow
granting
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hide
highest
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huge
human
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idea
ideal
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implants
important
improved
include
incoming
increased
incredible
independently
infection
inverted
iris
key
kingdom
layer
lens
light
linked
machines
maintain
masterpiece
maximizing
mechanism
millenia
million
nautilus
nerve
night
nighttime
octopus
opening
optic
optimizes
organism
organisms
outer
perfect
photons
photosensitive
pierce
pinhole
planaria
point
precision
predators
prevent
prey
process
processing
protective
proteins
proved
question
reach
receiving
reducing
refinements
reflective
required
resolution
result
results
retina
ring
scientists
sclera
screen
secrete
sections
seek
sense
sensing
sensitivity
served
shade
sharper
signature
similar
simple
single
smaller
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spotting
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