106Chap18a-Evolution - Earth History GEOL 106 Organic...

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Unformatted text preview: Earth History GEOL 106 Organic Evolution • Present-day organisms are descendents of past-life forms Chapter 18 • Evolution: change through time • Small-scale changes observable • Large-scale changes imperceptibly slow – Insects, bacteria, plants – Evolution of birds from reptiles – Fossil record needs to be considered – Biology (genetics, embryology, biochemistry) EVOLUTION - theory and supporting evidence Organic Evolution • Early research and theories – Jean-Baptiste de Lamarck (1744-1829) • Inheritance of acquired characteristics • Effects of the environment can be inherited by offspring Organic Evolution • Early research and theories – Charles Darwin (1809-1882) • 1831-1836 HMS Beagle • Observed geographic distribution • Marine species differ on Atlantic & Pacific sides of Isthmus of Panama • Galapagos Islands’ diversity 1 Charles Darwin • Published On the Origin of the Species, 1859 • Mechanism: Natural Selection • Artificial selection – Plant and animal breeders (e.g., dogs, cows, grains) Gregor Mendel • Austrian monk (1860s) • “Father of Genetics” • Pea experiments Gregor Mendel • Pea experiments • Traits controlled by a pair of factors, or genes • Recessive or Dominant Genes and Chromosomes • Chromosomes: doublestranded molecules of deoxyribonucleic acid (DNA) are found in all cells • Ribonucleic acid (RNA) in bacteria • Segments of DNA are hereditary units, the genes – Alleles : genes of different form controlling same trait • Traits usually controlled by many genes 2 The Modern View of Evolution • In the 1930s and 1940s the ideas of many scientists were merged to form a modern synthesis, incorporating the chromosome theory of inheritance and recognizing mutations • Emphasized that evolution is a slow, gradual process - phyletic gradualism- this idea has been challenged recently The Modern View of Evolution • Sources of variation: – reshuffling of genes during sexual reproduction, but still it is only variation that is already present in a population – Mutations are changes in the chromosome or gene and are inheritable if they take place in a sex cell – The benefit or harm of a mutation can only be judged with respect to the reproductive success of the organism Speciation and Rate of Evolution • Speciation: The rise of a new species from an ancestral one • Species: population of similar individuals that can interbreed and produce fertile offspring • reproductive barriers not complete – zebra - horse; goats - sheep; lions - tigers; donkey - horse Speciation and Rate of Evolution • Speciation: – Change in the genetic makeup of population • Allopatric speciation – New species arise when some individuals are geographically isolated • Varying degrees of change from ancestral species 3 Speciation and Rate of Evolution • Rate of evolution: two models – Gradualism: slow, continuous changes – Punctuated Equilibrium: New Species evolve rapidly with long periods of stability A. Punctuated Equilibrium B. Gradualism Divergent, convergent, and parallel evolution • Divergent evolution – Ancestor gives rise to diverse descendants each adapted to different lifestyles Divergent, convergent, and parallel evolution • Convergent evolution – Similar adaptations arise in distantly related groups – Marsupials (S-America) and placental mammals (N-America) adapted to similar environments 4 Placental mammals Australian marsupials Ecological parallelism Divergent, convergent, and parallel evolution • Parallel evolution – Similar adaptations arise in closely related groups – Kangaroo rat and jerboa, closely related, developed similar features independently Extinctions • Extinctions – – – – 99% of all species ever existed are extinct Some extinct groups have living relatives (birds, dinosaurs) Background extinction Mass extinction 5 ...
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