Presentation on theme: "Evolution of the Eye Katharine Hamilton. The First Eye on Earth Trilobite, 543 million years ago."— Presentation transcript:
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.
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.
808 steps Rim constricts. Pit fills with clear jelly which helps maintain shape and protect. Jelly’s refractive index.
1033 steps “Pinhole camera” eye. Aperture decreases until reaching optimal size. Can distinguish shapes.
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.
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, Chapter 6. Andrew Parker. In the Blink of an Eye. Perseus Publishing, Pages “Richard Dawkins on the Evolution of the Eye.” [Online] October 27, “Dawkins Makes an Eye.” [Online] October 27, “How Could an Eye Evolve?” [Online] October 27, 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, “Evolution of the Eye.” [Online] October 27, Michael Shermer. How We Believe, Second Edition. Holt Paperbacks, Page 110 Richard Dawkins. “Where d’you get those Peepers?” Vol. 8, New Statesman & Society, , pp 29. Gert Korthof. “The Cambrian Explosion and Eye Evolution Solved at One Stroke.” [Online] November 22, “Compound Eye: Dragonfly.” [Online] November 23, a “Giant Jellyfish.” [Online] November 23, Christopher Hitchens. “Losing Sight of Progress.” Slate, Posted Monday, July 21, 2008, at 11:34 AM ET. “Fresh Fossil Evidence of Eye Forerunner Uncovered.” ScienceDaily. November 24, 2008.