1. Evolution: How Change Occurs

2. Charles Darwin Proposed formal theory of evolution - change in species over time - modern organisms descend from ancient - change in allele frequency in gene pool NATURAL SELECTIONDarwin’s mechanism: NATURAL SELECTION Wrote On the Origin of Species Change occurs, controversy is often over how

3. 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

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

5. Evolution by Natural Selection Darwin’s observations: variations 1 - wild species show variations competition 2 - high birthrates & shortage of necessities, causes competition survival of the fittest 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 natural selection 5 – over long periods of time, small changes accumulate, population has adapted and natural selection took place The environment selects which characteristics are advantageous

6. 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 gene pool populationRelative frequency of alleles for color changed in the gene pool for the population H.B.D. Kettlewell tested the theory

7. Genes How do Genes Fit In? Darwin did not know about genes and genetics Genes: 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

8. Modern Evolutionary Theory evolutionary fitnessToday we define evolutionary fitness as the success an organism has in passing on its genes to the next generation adaptationAn 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

9. How do new species evolve? SpeciesSpecies- individuals that can breed and produce fertile offspring.(share common gene pool) NicheNiche- 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 reproductive isolationGroups 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

10. 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

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

12. Convergent vs. Divergent Evolution Convergent Similar looking species that do not have a common ancestor Similar behavior and appearance analogous structuresMany analogous structures

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

14. 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 descent from a common ancestorAll pieces support Darwin’s idea of descent from a common ancestor