Transcript Evolution Of The Eye

Evolution of the Eye
Katharine Hamilton
The First Eye on Earth
• Trilobite, 543 million years ago
The Cambrian Explosion
• Began 543 million years ago.
• Origin of 35 animal phyla in a duration of
only 5 million years.
Was the Eye a Catalyst?
• Australian zoologist Andrew Parker: In the
Blink of an Eye
– The first eye initiated an arms race among
predators and prey.
– New defenses, such as armor, spines, and
protective skeletons were a direct result of eyes
in predators.
Light Switch Theory
• The critical step of evolution was the
development of eyes.
– Expansion of the food chain.
– Predator-prey co-evolution.
– Demand for a complex nervous system and
brain to process visual information.
• Over 95 percent of all animal species have
eyes.
Doubts
• Darwin: “To suppose that the eye…could
have been formed by natural selection,
seems, I freely confess, absurd in the highest
possible degree.”
Nilsson and Pelger’s
Computer Model
Sheet of photoreceptive proteins.
Can distinguish between light and dark.
Daily synchronization of circadian rhythms.
Euglena
176 steps
Depression forms under surface of eye spot.
Can distinguish basic direction and intensity of light.
Indentation protects eye spot from damage.
538 steps
Dimpling continues.
Increased awareness of direction of light.
Flatworm
808 steps
Rim constricts.
Pit fills with clear jelly which helps maintain shape and protect.
Jelly’s refractive index.
Refraction
Vacuum: 1 (exactly)
Air: 1.000293
Water: 1.333
Vitreous Humor: 1.336
1033 steps
“Pinhole camera” eye.
Aperture decreases until reaching optimal size.
Can distinguish shapes.
Nautilus
1225 steps
Lens.
1533 steps
Lens moves inward.
Can perceive detail with greater precision.
1829 steps
Lens continues to move inward and thicken.
Graded index.
Fish!
Nilsson and Pelger’s Conclusion
• The entire process of 1829 steps could be
carried out in about 350,000 generations.
Easy Evolution
• Eyes have evolved between 40 and 65
different times in nature.
Scallop
Reflector eyes
Dragonfly
Compound eyes
Night Owl Monkey
The only nocturnal Primate
Arctic Lion’s Mane Jellyfish
Has eyes but no brain
Sources
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Charles Darwin. Origin of Species, Sixth Edition. Senate, London, 1872. Chapter 6.
Andrew Parker. In the Blink of an Eye. Perseus Publishing, 2003. Pages 172-174.
“Richard Dawkins on the Evolution of the Eye.” [Online] October 27, 2008.
<http://www.youtube.com/watch?v=rUOpaFVgKPw>
“Dawkins Makes an Eye.” [Online] October 27, 2008.
<http://www.youtube.com/watch?v=lEKyqIJkuDQ&feature=related>
“How Could an Eye Evolve?” [Online] October 27, 2008. <http://www.don-lindsayarchive.org/creation/eye.html>
Dan Nilsson and Susanne Pelger. “A Pessimistic Estimate of the Time Required for an Eye to
Evolve.” Proc Roy Soc London, 1994.
“Evolution of the Eye.” [Online] October 27, 2008.
<http://en.wikipedia.org/wiki/Evolution_of_the_eye>
Michael Shermer. How We Believe, Second Edition. Holt Paperbacks, 2003. Page 110
Richard Dawkins. “Where d’you get those Peepers?” Vol. 8, New Statesman & Society, 06-161995, pp 29.
Gert Korthof. “The Cambrian Explosion and Eye Evolution Solved at One Stroke.” [Online]
November 22, 2008. < http://home.planet.nl/~gkorthof/korthof60.htm >
“Compound Eye: Dragonfly.” [Online] November 23, 2008.
<http://student.britannica.com/eb/art-55462/Dew-covers-the-body-and-two-large-eyes-ofa>
“Giant Jellyfish.” [Online] November 23, 2008.
<http://www.extremescience.com/GiantJellyfish.htm>
Christopher Hitchens. “Losing Sight of Progress.” Slate, Posted Monday, July 21, 2008, at 11:34
AM ET. <http://www.slate.com/id/2195683/>
“Fresh Fossil Evidence of Eye Forerunner Uncovered.” ScienceDaily. November 24, 2008.
<http://www.sciencedaily.com /releases/2008/01/080101193317.htm>