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The Evidence for Evolution
Darwin’s Voyage – BBC 2009
• http://www.sciencechannel.com/tv-shows/greatest-discoveries/videos/evolution.htm
Evidence for Evolution
• Types of evidence Darwin used to support his theory:– 1. Biogeography– 2. Homologous and Analogous features– 3. Vestigial features– 4. Competition within populations
1. Biogeography + Darwin’s Observations
Reptiles, Birds, but No Mammals or Amphibians?
Key Observation from Galapagos Islands
Testing Darwin’s Hypotheses:Hawaiian Islands
Testing Darwin’s Hypotheses
• When non-native mammals and amphibians introduced to islands, they have been able to thrive. This eliminates the possibility that they can’t survive on remote islands. Dodo Bird Extinction within 175
years – Mauritius Islands (Indian Ocean)
2. Homologous Features• Structures with common evolutionary features
which serve different functions in modern species . Example of Divergent Evolution
• Video on homology: http://www.youtube.com/watch?v=XgXT9sU6y18&feature=related
http://www.xspore.com/community/drama/6876-evolution-vs-religion-4.html
Homology: Similar structures for different functions
How many bones in the Human Neck?
How many bones in a Giraffe’s neck?
Embryological Homology
2. Analogous Features
• Structures that perform same function in two species but are not similar in origin or anatomy
Convergent Evolution
Analogous: Same function, different structure
3. Vestigial Features
• Features that no longer serve the function they do in similar species
http://rebeccamcc.blogspot.com/
http://paxarcana.wordpress.com/2009/08/25/your-appendix-may-actually-do-something/
http://www.youtube.com/watch?v=lBkiT0zyYm0
4. Competition Within Populations• Thomas Malthus (Principle of Population)
showed that all population are limited in size by the environment (food supply)
Darwin’s thoughts:• All species produce more offspring than can
survive to reproduce• This results in competition for resources
between members of the same species• Environment might be favouring certain
individuals
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• J.W. Tutt hypothesized that light-colored moths declined because of predation
• Light moths were easily seen by birds on darkened (sooty) trees
Evidence of Natural Selection
• http://www.techapps.net/interactives/peppermoths.htm
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Evidence of Natural Selection
• Bernard Kettlewell tested the hypothesis– Dark tree trunks = more dark-colored
moths survived– Light tree trunks = more light-colored
moths survived• When environmental conditions reverse, so
does selection pressure
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• Industrial melanism: phenomenon in which darker individuals come to predominate over lighter ones
• Pollution control resulted in lichen growing on trees and bark color being lighter again
• Light-colored peppered moths now are dominant in the population
Evidence of Natural Selection
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• The agent of selection may be difficult to pin down
• Could poisoning by pollution be the agent of natural selection?
Selection against melanism
Evidence of Natural Selection
Homework
• Page 303 # 1,2,4-7