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- Darwin's Definition: Descent with modification
- -->The origin of species
- population of species changes over time
- ancesteral species differ from derived species
Importance of Fossile Record
- Shows life forms at different geologic times
- --forms of life change over time
- Sedementary rock layers form strata
- Older layers deeper, ancesteral life forms
- Newer layers near surface, derived life forms
- Characteristics that enhance survival and reproduction in specific environments
- Populations adapt to their environment
- --over generations
- Example: Galapagos Island Finches (Break morphology of species differs, based on food available on their home island.)
- Can view history of life as a tree
- Ancesteral organisms at the base
- Derived organisms at the tips of the branches
- Some branches become extinct, others extant
- Mimics natural selection
- Darwin saw this in farm animals and plants
- Breeders can influence nature of offspring
- Affect outcome of next generation
- Over generations, population change
- Agriculture plants and animals bear little resemblance to their wild ancestors.
Darwin's Observations on Natural Selection
- 1. Populations vary in their traits (individuals differ from one another).
- 2. Traits are heritable (Traits passed from parents to offspring).
- 3. Species can reproduce at high rates (more offspring than environment supports).
- 4. Not all offspring survive (due to a lack of resources).
Effect of Natural Selection
- 1. Individuals with favorable traits survive and reproduce at higher rates
- 2. Populations of the organisms become adapted to their environment
- Over generations
- Accumulation of favorable traits
Evidence for Natural Selection-- Direct observation
Not always easy due to time scale
Evidence of Natural Selection-- Fossil Record
- Past organisms often differ from present day organisms
- Gradual changes over short time periods (ex- Trilobite evol)
- Significant changes over long time periods
- Whale evolution from land mammal
- Whales retain vestigial hind lmbs (Lost most original function through evolution)
Evidence of Natural Selection-- Homology
- Similarity resulting from common ancestry
- Characters present in ancestors are often altered by natural selection. (adapted to different environments)
- Ex. Forelimbs of mammals (Homologous structures)
- Ex. DNA or protein similarity
- Molecular homology.
Evidence of Natural Selection-- Biogeography
- Where species are/were found
- Closely related species often evolved near to one another
- May have become separated over time by movement of continents, formation of islands, or mountain ranges
- Understanding past geography can help create an evolutionary tree.
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