APBEvo1 Evolution Intro modification.ppt
- 1. Evolution Intro change over time. descent with modification. populations evolve, not individuals.
- 2. Charles Darwin • (1809-1882) Englishman. Medical school dropout. Obsessed with nature. Aspiring clergyman. Married his cousin. • The 5 year trip that changed Darwin’s life: The Voyage of the HMS Beagle ▫ collected plants and animals. Noticed they were suited to diverse environments. ▫ Also found species resembled others around the world ▫ Influenced by geology (Lyell) Earth shaped by slow-acting forces that are still in work today ▫ The Galapagos. (finches)
- 3. • Alfred Russell Wallace. British naturalist that developed a theory very similar to Darwin’s. (His ideas were submitted for publication first) • Darwin publishes On the Origin of Species in 1859. His ideas convinced scientists of evolution to explain species diversity. ▫ Through time species accumulate differences; as a result, descendants differ from their ancestors. In this way new species arise from existing ones. ▫ Natural Selection is the mechanism for evolution ▫ Descent with modification: species share a common ancestor and diverged gradually over time
- 4. Darwin’s Ideas • Descent with Modification. ▫ organisms share similar characteristics suggesting common ancestry. ▫ accumulate adaptations as environment changes, leading to different species ▫ ‘gaps’ in record filled with fossil evidence • Natural Selection. ▫ Variation in a population certain traits will give a higher probability of surviving to reproduce ▫ Species produce more offspring than survive. lead to accumulation of favorable traits in the population over generations causes organisms to become suited specifically to their environment ▫ May result in new species forming
- 5. Evidence • Fossils ▫ evolutionary changes over time; “missing links” ▫ compare current (extant) organisms with extinct ones ▫ Use geologic information and carbon dating to estimate age of fossils • Homology (homologous structures) ▫ similar characteristics (but function differently) resulting from common ancestry forelimb of mammals vertebrate embryos ▫ vestigal structures: “leftover” structures from an earlier ancestor (was important once upon a time) pelvic bones in a whale, snake, appendix
- 6. Evidence • Biogeography ▫ geographic distribution of species ▫ influenced by continental drift (plate tectonics) ▫ Convergent evolution (similar environments yield similar anatomies) More evidence supporting organisms adapt to be best suited to their environment! • Molecular Evidence ▫ DNA sequences similar from shared genes ▫ relationships between groups of organisms
- 7. • microevolution: change in allele frequencies in a population over generations (small scale) ▫ Result from accumulation of mutations • Variation: differences among individuals in a population ▫ only genetically determined phenotypes (characteristics) will be subject to natural selection ▫ without variation there is no evolution
- 8. The White-Striped Clover… • Discuss with your group members your answers to this case study. Think specifically about the answers to the following…. ▫ How does this case study illustrate the process of natural selection? What is the evidence that it occurred?—Be able to justify your answers. ▫ What is “selection pressure”? How is it illustrated in each habitat? How does this affect the survival and reproduction of the clover? ▫ Thinking more broadly…what influences natural selection in all organisms?
- 9. • Selective pressures ▫ A phenotype (physical traits/behaviors) is selected for or against depending on the environment in which an organism lives ▫ Survival benefit or disadvantage ▫ Lead to differential survival and reproduction, driving natural selection Examples: climate, food, predators, diseases, humans
- 10. Influences on Variation • Geography (geographic variation) ▫ differences in the genetic composition of populations of the same species ▫ Affected by environmental differences • Mutations ▫ change in the nucleotide sequence of DNA ▫ only those present in gametes will be passed to offspring ▫ usually deleterious (harmful)…very few are beneficial • Chance/random events ▫ chromosomal shifts ▫ recombination during meiosis
- 11. Influences on Natural Selection • Competition = Differential Survival ▫ Individuals with more favorable phenotypes will survive and reproduce…passing on their traits to subsequent generations • Genetic Variation and Mutation ▫ Diverse genes allow for survival in changing environments ▫ Variation results from mutation • Environment ▫ Fluctuations in environment cause specific traits to be favored at certain times ▫ Human impacts • Chance and Random Events ▫ ie. Earthquake splits population in two
- 12. • Adaptation: inherited characteristics of organisms that enhance their survival and reproduction in specific environments • Natural Selection: a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than others because of those traits. ▫ acts on populations, not individuals ▫ only selects for heritable traits that exist within a population ▫ is specific to the environment in a particular time (flexible) ▫ consistently improves the match between organisms and their environment • Fitness: the number of surviving offspring in the next generation (measure of reproductive success) • Artificial Selection: human modified traits in a population due to selective breeding (agriculture, domestic animals) • Convergent Evolution: independent evolution of similar features in different lineages (analogous structures)