How The Human Eye Evolved To Be So Complex

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eyes are really weird when you think
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about them they’re like little gel
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filled sack sticking out of our faces
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they take all those wavelengths of
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lightens somehow make pictures out of
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them but how did they evolve to be like
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that
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hey seers Julia here for dnews eyes are
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extraordinarily complex and the theory
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of evolution posits that such complexity
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arose from the process of natural
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selection over millions of years but
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extraordinary claims demand
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extraordinary evidence so how did eyes
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evolved well with each generation of
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offspring having slightly altered eyes
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with ever-increasing improvement that
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gave them a decisive advantage over
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predators and peers back when life was
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just a bunch of cells in a soup I
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probably got their start in bacteria
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over 600 million years ago a random
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mutation gave some bacteria a collection
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of light-sensitive cells these cells
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helped the bacteria know how bright
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sunlight was and some bacteria who could
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sense this light moved away from it
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which helped them since bright sunlight
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also carries harmful UV rays after a few
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more random mutations these little ice
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bolts as they’re called turned into a
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kind of early eye early eyes if you
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could even call them that with just a
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collection of cells with photoreceptors
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with photosensitive cells with proteins
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called opsins
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they lay on top of the photoreceptor and
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catch photons coming into the eye they
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trigger a series of chemical reactions
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that causes the photoreceptor to send an
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electrical signal toward the brain their
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appearance in the tree of life can be
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traced back more than 580 million years
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it can even be found in everything from
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jellyfish to insects to dogs and humans
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one study published in the journal
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National Review of neuroscience found
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that evidence like this strongly
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supports the notion that a common
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ancestor of sea squirts and vertebrates
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possessed many of the building blocks
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that are fundamental to light signaling
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in our own eyes and we could see some of
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this process happening in the fossil
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record we can find evidence in the
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fossils of trilobite a marine arthropod
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that lived around 543 million years ago
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as in most cases of evolution the
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delicate balancing act or should I say
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arms race between predators or prey
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drove the evolution of the eye so you’re
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probably wondering how could we tell
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what their eyes looked like since ice
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don’t fossil all that well and you’re
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mostly right except trilobite had a type
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of bacteria
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their eyes that laid down a thin layer
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of minerals and it’s these traces that
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we can see but only with super
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high-powered x-rays according to a study
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published in the journal Science Reports
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trilobite eyes looked like flowers under
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a lens their sensory cells are shaped
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like petals surrounding a photoreceptor
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while basic these I served well enough
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for these bottom of the ocean dwellers
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they worked so well in fact a relative
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of the trilobite the horseshoe crab
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still has them as time wore on the arms
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race drove the evolution of more and
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more complex eyes rather than looking
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for fossilized evidence we can examine
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the eyes of modern animals that haven’t
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changed all that much take a look at the
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two balerion worm their eyes are more
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like little cups lined with pigment
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cells these cells are opaque and don’t
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let light pass through so they act as a
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way to direct light towards the
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photoreceptor cells after a few more
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years of evolution the eye cup becomes
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more of a chamber in the opening narrows
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the shape allows greater ability to tell
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where the light is coming from and an
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early way to form images of shapes and
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things this is called a pinhole eye and
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can still be seen on primitive animals
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like the beautiful Nautilus along the
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evolutionary way animals evolved spines
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and skulls and with it their eyes got
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more advanced according to a study
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published in the journal Nature Reviews
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neuroscience researchers found we could
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trace our own complex eyes all the way
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back to early lamprey Lake vertebrates
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who lived over 500 million years ago
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their eyes start to look more how we
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think of eyes a lens forms from a thin
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layer of adapted epithelial cells
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covering the opening to keep out
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infection they even have a retina and
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ocular muscles that allow for eye
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movement these eyes would have been able
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to form a simple image over a broad
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range of wavelength but there was a
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problem
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these eyes evolved for living in water
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once our ancestors moved onto land our
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eyes needed to evolve again around 430
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million years ago according to a study
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published in the Journal of Experimental
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Biology tetrapod eyes took on a more
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elliptical shape to compensate for
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seeing in the air rather than the light
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distorted water and the development of
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evolution even decides where eyes are
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located Branston spray like deer tend to
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have eyes on either side of their heads
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so they can keep a watchful eye out over
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a nearly 360-degree area for a predator
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and predators like wolves tend to have
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eyes on the front of their head so they
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have depth perception all the better to
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hunt you with my dear
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so our eyes aren’t perfect an
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isn’t a perfect process but as Charles
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Darwin said from so simple a beginning
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endless forms most beautiful and most
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wonderful happen and are being evolved
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speaking of eyeball weirdness ever look
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up at the sky and see those strange
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floating bits what the heck are they
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should I be worried about them trace has
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the whole scoop in this episode right
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here so the floaters are pieces of
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protein or clusters of cells floating
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inside of your eye suspended in that
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vitreous gel what you’re seeing isn’t
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the piece itself but actually a shadow
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of that piece on your retina so eyeballs
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how cool are they thumbs up this video
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