Evolution

• Has become a unifying principle in Biology
• For >150 years, stimulated controversy - mostly nonscientists
• Initial theory sparked controversy within science and biology

Early History

• Preceded Darwin
• Ancient philosophers explained nature in terms of what they imagined to be true, not based on observation
• In 1500s, European philosophers began to exhibit discontent
• Discontent appeared relative to view on the diversity of life
• Charles Lyell (English geologist), 1830
• Proposed theory of Uniformitarianism
• Geologic changes take place slowly
• Biologists' perceptions began to change in 1700s
• Jean Baptiste Lamarck (French biologist), 1809
• Published theory of the inheritance of acquired characteristics
• Since replaced by Darwin & Mendel

Where Did The Idea Come From?

• Darwin's Voyage on "Beagle" shaped many ideas of Biology
• Purpose of voyage Sail around world & survey little known coastal areas

Darwin's Observations

1. 1. Populations have inherent potential to increase exponentially
2. 2. Populations are fairly constant in size over long periods of times
3. 3. Natural resources are limited
4. 4. Competition important in limiting survival
5. 5. There is variation within individuals of a population & variations are inherited

Darwin's Deductions

1. 1. Only some organisms survive
2. 2. There is a struggle for existence among individuals in population
3. 3. Individuals with favorable variations are more likely to survive and reproduce
4. 4. Accumulation of variation over many generations is evolution
5. 5. When great enough - a new species
6. 6. A gradual process

What Exactly are Species?

· Distinct if they do not interbreed in nature

· All have differences within them

· Traits in population change, eventually new species arise

How does Evolution Work?

· Indirect evidence

· Animal & plant husbandry - Farmers improve species by breeding

· Fossils/Modern horse

· Homologous structures

· All mammals evolved from common ancestor

· Analogous structures

· Structures have similar form & function, but are structurally quite different

· Convergent evolution; Unrelated organisms evolve similar adaptive characteristics

· Indirect evidence

· Life's chemicals - complex

· Proteins - long chains of amino acids

· More closely related organisms are, the more closely their proteins resemble each other

· Allopatric Speciation

· Speciation (species giving rise to new species)

· May occur when populations become isolated

· Sympatric speciation

· Species isolated by occupying different habitats in given range

Darwin's Finches

· Galapagos formed from volcanoes

· Finch ancestors came from South America

· Different islands, different environments

· Today - each island has own species

Patterns in Evolution?

· Unrelated organisms in similar environments sometimes

· Evolve similar characteristics; Convergent evolution

· Closely related organisms living in different territories

· Sometimes tend to drift apart; Divergent evolution

· Example: Wombat, Koala, & Kangaroo have common ancestors

· Evolution of one species may influence evolution of another

· · Co-evolution

· Parallel evolutionary changes occurring simultaneously

· Between interacting species

· Example: Cheetahs & their prey

· Different from original Darwin model

· Gradualism - Darwin described evolution as a slow & gradual process

· Evolution may occur more rapid than earlier thought: Punctuated equilibrium

· Evolution does not always occur

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