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Darwin and Mechanisms of Evolution The theory and why it works Evidence of Evolution: The Fossil Record • Indicates life began 3 bya • Prokaryotes then Eukaryotes then multicellular Eukaryotes • Fossil record determines: • When species appeared • The type of environment • When/if species became extinct What does the theory of evolution say? • Theory b/c lots of evidence • Tested and re-tested by many scientists • States that: • Variations in individuals can lead to changes in whole species Natural Selection: The Idea Behind the Theory • Evolution controlled by NATURAL processes • THE PROCESS IS: LIVE + BREED + PASS ON GENETIC INFO = SURVIVAL OF SPECIES • “Survival of Fittest” • Those best ADAPTED will be able to DO THE PROCESS Results of Natural Selection • Short term result: • Best fit (adapted) will pass on GOOD genes to offspring • Long term result: • Change in frequency (number) of certain traits • Which do you think will increase in frequency GOOD OR BAD? GOOD OF COURSE! • As more individuals have good trait, species is evolving What drives evolution? Interactions btw individuals and the environment: 1. OVERPRODUCTION 2. STRUGGLE FOR SURVIVAL 3. GENETIC VARIATION 4. SELECTION BY THE ENVIRONMENT Evolution Cause #1: B. OVERPRODUCTION • POTENTIAL TO PRODUCE MORE OFFSPRING THAN WILL SURVIVE • This means the best “fit” individuals will survive, grow and reproduce. • EX: DEER, FISH Evolution Cause #2: C. STRUGGLE FOR SURVIVAL • Overproduction leads to STRUGGLE within species: 1. Only some live to reproduce 2. Competition for resources 3. Best competitors will live and breed • Must STRUGGLE with environment also (disease, predators, temp changes etc) • Those that withstand will survive! Evolution Cause #3: D. GENETIC VARIATION • Variation must exist within survivors • Ex: Longer legs, bigger claws, diff. fur color • Favored traits will stay in pop’n and lead to evolution • Adaptive Value: • Describes a trait that helps an individual survive in a particular environment • EX: polar bears have black skin; the black skin has adaptive value b/c it helps them survive Evolution Cause #4: E. SELECTION BY ENVIRONMENT • Traits w/ adaptive value benefit those individuals • If reproduce, offspring have traits too • Eventually, # of individuals with trait increases, and most all will have it! • Therefore, adapting to environment DRIVES EVOLUTION! Evolutionary Trees: Animals = COMMON ANCESTOR Comparison of Human and Chimp Chromosomes Actual Cartoons from Scope’s Trial, 1925