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Darwin’s Theory of Evolution 15.3 Darwin Presents His Case Thursday, February 14, 2013 The Nora School Biology 955 Sligo Avenue Silver Spring, Maryland 20910 Period ________ On the Origin of Species • • Darwin filled notebooks with his ideas about species diversity and the evolution process. He shelved his manuscript for years and told his wife to publish it in case he died. The Nora School Biology 955 Sligo Avenue Silver Spring, Maryland 20910 Period ________ Darwin’s Publication • In 1858, Darwin received a short essay from naturalist Alfred Wallace. In 1859, Darwin published his book, On the Origin of Species. • • • The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Proposed a mechanism for evolution called natural selection. Presented evidence that evolution has been taking place for millions of years— and continues in all living things. Biology Period ________ 1 Artificial Selection • • • Variations were thought to be unimportant, minor defects. Darwin argued that this variation mattered. Artificial selection is the selection by humans for breeding of useful traits from the natural variation among different organisms. The Nora School Biology 955 Sligo Avenue Silver Spring, Maryland 20910 Period ________ Inherited Variation and Artificial Selection The Nora School Biology 955 Sligo Avenue Silver Spring, Maryland 20910 Period ________ Evolution by Natural Selection • The struggle for existence means that members of each species compete regularly to obtain: – Food – Living space – Other necessities of life. • The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 This was central to Darwin's theory of evolution. Biology Period ________ 2 Evolution by Natural Selection • • • Individuals not well suited to their environment either die or leave few offspring. Individuals better suited to their environment survive and reproduce most successfully. Because of its similarities to artificial selection, Darwin referred to the this phenomena (Survival of the Fittest) as Natural Selection. The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Biology Period ________ Evolution by Natural Selection • Natural selection results in changes in the inherited characteristics of a population. – – – • • Different structures Establish different niches Occupy different habitats. Each living species has descended, with changes, from other species over time (Descent with Modification) Implies Common Descent from one ancestor The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Biology Period ________ Evidence of Evolution • Darwin argued evolution has been going on for millions of years and that evidence could be found in several places. The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Biology Period ________ 3 The Fossil Record • By comparing fossils from older rock layers with fossils from younger layers, scientists could document that life on Earth has changed over time. The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Biology Period ________ Geographic Distribution • • Darwin decided that all Galápagos finches could have descended with modification from a common mainland ancestor. Similar species living on different continents could also descended from different ancestors. – – However, similar ecological conditions, resulted in exposure to similar pressures of natural selection. Therefore, different animals ended up evolving certain features in common. The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Biology Period ________ Homologous Structures • • Structures that have different mature forms but develop from the same embryonic tissues are called homologous structures. Similarities and differences in homologous structures help group animals according to how recently they last shared a common ancestor. The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Biology Period ________ 4 Vestigial Organs • The organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs in other species. The Nora School Biology 955 Sligo Avenue Silver Spring, Maryland 20910 Period ________ Similarities in Embryology • • The early stages, or embryos, of many animals with backbones are very similar. The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates. The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Biology Period ________ Summary of Darwin’s Theory 1. 2. 3. 4. 5. 6. 7. The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Organisms differ. Some of this variation is heritable. Organisms produce more offspring than can survive. They compete for limited resources. Individuals best suited to their environment survive and reproduce most successfully. Natural selection causes species to change over time. All living species are descended with modification from ancestral species. Biology Period ________ 5 Section 15.3 Assessment 1. How is Artificial Selection dependant on variation in nature? 2. The theory of evolution by natural selection explains, in scientific terms, how living things evolve over time. What is being selected in this process? 3. What types of evidence did Darwin use to support his theory of change over time? The Nora School 955 Sligo Avenue Silver Spring, Maryland 20910 Biology Period ________ 6