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Evolution Intro change over time. descent with modification. populations evolve, not individuals. It is not the strongest of the species that survives,

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Presentation on theme: "Evolution Intro change over time. descent with modification. populations evolve, not individuals. It is not the strongest of the species that survives,"— Presentation transcript:

1 Evolution Intro change over time. descent with modification. populations evolve, not individuals. It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is most adaptable to change.

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 Good Morning!! Have out your case study from yesterday. I will give you time to discuss with your group the answers you have. Behavior Labs should be done for tomorrow. See me if you have questions. We will prep our Natural Selection Lab tomorrow!

9 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?

10 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

11 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

12 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

13 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)

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