1. Natural Selection, Speciation, and Evolution
Textbook Reference
Chapter 14 & 15

2. Lamarck’s Early Theory on Evolution
Based on 3 ideas
1. Desire (will) to change
2. Use and Disuse
3. Passing on acquired traits (weight lifting)
Brought idea of evolution to forefront
Knew nothing of genes or genetics

3. Charles Darwin Observations aboard Beagle
Led to his theory of evolution
- change in species over time
- modern organisms descend from ancient
- change in allele frequency in gene pool
Darwin’s mechanism: NATURAL SELECTION
Wrote On the Origin of Species

4. Influences that Shaped Darwin’s Theory
Charles Lyell, geologist
- Earth very old, changed over time
Farmers, artificial selection
- choose organisms with desireable traits to produce offspring
Thomas Malthus, economist
- Malthusian Doctrine

5. Evidence for Evolution
Contrasting theories over mechanism for evolution, typically not evolution itself
Evidence of Change:
1. Fossil Record
2. Embryonic Development
3. Anatomical Structures
4. Biochemical Similarities
All pieces support Darwin’s idea of descent from a common ancestor

6. Evolution by Natural Selection
Darwin’s observations:
1 - wild species show variations
2 - high birthrates & shortage of necessities, causes competition
3 - individuals whose characteristics are well-suited to their environment survive and reproduce, survival of the fittest
4- larger portion of each new generation will have favorable variation
5 – over long periods of time, small changes accumulate, population has adapted and natural selection took place
The environment selects which characteristics are advantageous
Video Clip

7. Peppered Moths: Natural Selection in Action
Two varieties, population mainly light colored prior to the Industrial Revolution
Soot from burning coal coated trunks
Dark moths now “fit” the best, better suited to survive, birds can’t spot the moths
Relative frequency of alleles for color changed in the gene pool for the population
H.B.D. Kettlewell tested the theory

8. How do Genes Fit In? Darwin did not know about genes and genetics
1. Responsible for variations
2. Genetic variations arise by mutations
3. Not controlled; no goal in mind
Phenotypic/Genotypic variation
1. Raw material for natural selection
2. One genotype proves to be advantageous example, sickle cell carrier

9. Modern Evolutionary Theory
Today we define evolutionary fitness as the success an organism has in passing on its genes to the next generation
An adaptation is any genetically controlled trait that increases an organism’s fitness
Think about the weight lifter- big muscles won’t be inherited but gene for the potential to develop large muscles could be

10. How do new species evolve?

11. Speciation
Species- individuals that can breed and produce fertile offspring.(share common gene pool)
Niche- habitat and role/job of organism, no 2 can occupy same niche, choices: adapt, move, or go extinct.
Speciation occurs when populations are separated by some barrier
Natural selection can work differently in each group
Groups cannot interbreed develop reproductive isolation
Each group will become fit to the environment they are in
Overtime, two populations cannot breed, new species
Example, Darwin’s finches underwent adaptive radiation

12. Adaptive Radiation

13. Darwin’s Finches on the Galapagos Islands
Islands isolated populations of finches; natural selection occurred independently in each group
Relative frequency for certain traits changed in isolated populations

14. Convergent vs. Divergent Evolution
One species gives rise to many species
Also known as adaptive radiation
Many species with common ancestor
Many homologous structures

15. Convergent vs. Divergent Evolution
Similar looking species that do not have a common ancestor
Similar behavior and appearance
Many analogous structures
Video Clip

16. Evolutionary Theory Continues to Evolve
Gene pools can change in absence of natural selection by:
1. Genetic Drift- allele becomes common by chance
2. Genetic drift implies not all characteristics contribute to fitness
Gene pools can remain unchanged for long periods of time ex. Horseshoe crab, living fossil
Gradual evolutionary change, theory of gradualism
Punctuated equilibrium, long stable periods with spurts of change