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 stepsDepression forms under surface of eye spot.

Can distinguish basic direction and intensity of light. Indentation protects eye spot from damage.

538 stepsDimpling continues.

Increased awareness of direction of light.

Flatworm

808 stepsRim constricts.

Pit fills with clear jelly which helps maintain shape and protect. Jelly’s refractive index.

Refraction Vacuum: 1 (exactly)Air: 1.000293Water: 1.333Vitreous Humor: 1.336

1033 steps“Pinhole camera” eye.

Aperture decreases until reaching optimal size.Can distinguish shapes.

Nautilus

1225 stepsLens.

1533 stepsLens moves inward.

Can perceive detail with greater precision.

1829 stepsLens 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.

ScallopReflector eyes

DragonflyCompound eyes

Night Owl MonkeyThe only nocturnal Primate

Arctic Lion’s Mane JellyfishHas 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-lindsay-archive.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, 06-16-1995, 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-of-a>• “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>