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