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Transcript
Evolution Evolution: The process by which modern organisms have descended from ancient organisms Change in a type of organism over time Favorable traits become more frequent in a population, while less favorable traits become less frequent Puzzle of Life’s Diversity Voyage of the Beagle ( 1831 - 1836 ) Charles Darwin Traveled to the Galapagos Islands and around the world from England Made numerous observations and collected evidence leading to his Theory of Natural Selection Darwin’s Observations Collected 68 different beetle species in one day in the Brazilian rainforest Observed different but similar species on different continents that had similar biomes Collected Fossils from different continents ( some resembled living organisms, some were like nothing he had ever seen before ) Shapes of tortoise shells varied from one Island to the next Beaks of finches varied on each Island Ideas that Shaped Darwin’s Thinking Most people believed that the Earth and its inhabitants were only a few thousand years old, and that they had not changed over that time Fossil evidence was being collected, and interpreted as the demise of creatures from some great catastophe Catastrophism Ancient and Changing Earth James Hutton (1795) Published a detailed hypothesis about the geological forces that shaped the Earth ( over millions of years ) -Charles Lyell (1830) - published “Principles of Geology” - proposed that the observable forces seen today are the same that acted in the past (uniformitarianism ) Jean-Baptiste Lamark (1809) - organisms acquired or lost certain traits during their lifetime, these traits could be passed to offspring, over time this could lead to new species Thomas Malthus ( 1798 ) Published that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone - War, famine and disease work against this growth Darwin reasoned that this would be true of all species - but not all offspring survive, and not all survivors reproduce - Why??? Darwin Presents His Case Began filling notebooks with his ideas about species diversity and the process that would later be called evolution. 1858 – he receives a short essay by Alfred Russel Wallace, summarizing thoughts on evolutionary change 1859 – publishes “On the Origin of Species” Proposed Natural Selection as the mechanism for evolution (descent with modification ) Inherited Variation and Artificial Selection Noted that members of each species vary from each other in important ways, and they could be inherited Current thought was that the variations were not important Artificial Selection Nature provides the variation, and humans selected the variations they found useful Evolution by natural Selection 1. the Struggle for existence Members of a species compete for survival 2. Survival of the Fittest ( natural selection ) Fitness : ability of an individual to survive and reproduce in its specific environment Adaptation: any inherited characteristic that increases an organism’s chance of survival Changes increase the specie’s fitness in its environment 3. Descent with Modification Common Descent: all species were derived from common ancestors ( single “tree of life” links all living things ) Evidence for Evolution 1. Fossil Record 2. Geographic Distribution of living species 3. homologous body structures 4. similarities in embryology 5. Analogous structures 6. Vestigial Structures 7. DNA evidence Fossil Record Geographic Distribution Homologous structures Analogous Structures Vestigial Structures DNA evidence Summary of Darwin’s Theory 1. individual organisms differ, and some of this variation is inheritable 2. organisms produce more offspring than survive, and some survivors do not reproduce 3. organisms compete for limited resources 4. successful organisms survive to reproduce and pass on characteristics to their offspring, this process causes speciation over time 5. Modern species are descendents from a common ancestor Microevolution Changes within individuals that lead to new species Macroevolution Changes in populations that lead to changes in species Biogeography How does the geographic distribution of species today relate to their evolutionary history? Patterns in the distribution of living and fossil species tell us how modern organisms evolved from their ancestors. Closely Related but Different Distantly Related but Similar Genetics and Molecular Biology How can molecular biology be used to trace the process of evolution? At the molecular level, the universal genetic code and homologous molecules provide evidence of common descent. Also, we now understand how mutation and the reshuffling of genes during sexual reproduction produce the heritable variation on which natural selection operates All living cells use information coded in DNA and RNA to carry information from one generation to the next and to direct protein synthesis. This genetic code is nearly identical in almost all organisms, including bacteria, yeasts, plants, fungi, and animals. This is powerful evidence that all organisms evolved from common ancestors that shared this code. Peter and Rosemary Grant of Princeton University spent more than 35 years studying Galápagos finches. They realized that Darwin’s hypothesis rested on two testable assumptions. First, for beak size and shape to evolve, there must be enough heritable variation in those traits to provide raw material for natural selection. Second, differences in beak size and shape must produce differences in fitness. The Grants have documented that natural selection takes place in wild finch populations frequently, and sometimes rapidly. Changes in food supply created selection pressure that caused finch populations to evolve within decades. This evolutionary change occurred much faster than many researchers thought possible. The Grants’ work shows that variation within a species increases the likelihood of the species’ adapting to and surviving environmental change Chapter Review P.476 # 1 – 13 P. 476-77 # 16 – 20, # 25 - 29