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Natural Selection • Natural Selection- Individuals best suited to their environment survive and reproduce most successfully. • Adaptations- inherited traits that increase an organism’s chance of survival. • Because of these adaptations, a species changes over time- Evolution. Evolution evidence • Fossil Record • Geographic Distribution of living species Fossils • Paleontologist- scientist that study fossils • Fossil record provides evidence about the history of life on earth. • Relative dating- estimate age by fossil position in the sediment. Top layers are the youngest, bottom layers the oldest. • Absolute dating- age calculated from amount of radioactive atoms remaining in fossil. This is most accurate Fossil Dating • Fossil record- • Order of fossils in sedimentary rocks. Relative dating. Absolute Dating or Radiometric dating of fossils Geologic Time Scale • Precambian- Life begins 4.6 billion years ago • Paleozoic- greatest diversity of marine life • Mesozoic- flowering plants and Dinosaurs • Cenozoic- Age of the Mammals- Humans appeared. More definitions • Extinction- Disappearance, or dying out, of a • • • • • species Speciation- formation of a new species Gene pool- all of the genes in a population Adaptive radiation- process in which one species evolves into diverse species according to environment. Ex- Darwin’s finches Biogenesis- Life arises from life Spontaneous generation- life can arise from nonliving matter . Scientists • Redi- 1st to try to prove biogenesis • Pasteur proved Biogenesis • Miller and Urey-explained how life could have arisen from primitive earth. Carbon dioxide, electricity, ultraviolet radiation and water. Figure 26.9 Louis Pasteur Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 3) Figure 26.10 The Miller-Urey experiment YouTube - Tree of Life video HD Darwin • Charles Darwin- 1809-1882 • HMS Beagle 1831 • Did not use the word evolution, but instead “Descent with modification” • Natural selection • Tree of life Natural Selection = Populations + Environment Populations Environment • Exhibit Variations • Limited Resources • Possess enormous • Competition reproductive potential Natural Selection on a population • In most populations, a trait that has the highest • • • fitness, leads to a greater numbers of organisms with this phenotype. Stabilizing Selection- the populations tends to exhibit the middle of the curve- average Directional Selection- populations tend to exhibit one trait. Disruptive Selection-The extremes of the population are favored. The normal is not favored. Speciation- formation of a new species • • • • • Founding of a new population Geographic isolation Reproductive isolation Competition Resources and environment PEPPERED MOTH Darwin’s Finches Small Tree Finch Photo courtesy of Dr. Bob Rothman. http://www.rit.edu/~rhrsbi/HomePage/homepage.html Large Cactus Finch Finches Photo courtesy of Dr. Bob Rothman. http://www.rit.edu/~rhrsbi/HomePage/homepage.html