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Evolution of Life How Organisms Survive What Is Necessary To Survive? • Variation is an appearance of an inherited trait or behavior that makes one organism different from others in the same species. • Adaptations are variations that make an organism better able to survive. Variations vs. Adaptations How Does Evolution Work? • Natural selection is the process where the organisms that are better adapted to their environment are more likely to survive and reproduce. Charles Darwin Theory of Natural Selection • Charles Darwin is credited as discovering the mechanism, or tool, for evolution to occur. He called this the theory of natural selection. • His theory can be summarized as “survival of the fittest”. Theory of Natural Selection 1. Organisms produce more offspring than can survive. Ex. Tree seeds, salmon eggs. 2. Variations exist within populations. 3. Some variations are more advantageous for survival. The struggle to survive results in competition. 4. Over time only those individuals with advantageous variations will survive and reproduce. Natural Selection Species Are Always Changing • Evolution is the change in the hereditary features of a population of organisms over time. • When a species changes it is said to have evolved. How Do Species Change? • A mutation is a permanent change in a gene or chromosome that changes the organism in some way. – Ex. Size, shape, color, behavior, etc. • Some mutations are harmful. • Some mutations are beneficial. Mutations Mutation vs. Adaptation • Only beneficial mutations are adaptations because these provide an advantage to survival. Mutation vs. Adaptation What Evidence Is There Of Evolution? • • • • • • • Evolution of species is evident in: Fossils Cell Structures DNA Homologous Structures Embryos Shared Characteristics Fossil Evidence of Evolution • Fossils are remains of life from earlier times. • Fossils are usually found in rock layers that provide a time reference: – Youngest (most recent) layers are on top. – Oldest layers are on the bottom. • Fossils provide evidence about the past climates and/or landscapes. Fossil Evidence Cell Structure Evidence of Evolution • Studying cell structures shows similarities between organisms. • A comparison of ancient and modern cells shows similarities in cell membranes and cytoplasms. Cell Structure Evidence DNA as Evidence of Evolution • Studying DNA shows more similarities between organisms. • The more similar the DNA, the more closely related the species are. • Ex. The DNA of Gorillas and Humans are ~92% similar whereas the DNA of any two humans is 99.9% similar. DNA Evidence Homologous Structures as Evidence of Evolution • Homologous structures are body parts of different organisms that are similar in origin and structure. • Ex: human arm, bird wing, bat wing, and dolphin flipper all have similar bone structure and function and show the relatedness of the species. Homologous Structures Homologous Structures Embryo Evidence of Evolution • Studying the similarity seen in the embryos of vertebrates shows that they share a common ancestor. Embryo Evidence Shared Characteristics as Evidence of Evolution • Primates are a group of mammals, including monkeys, apes and humans, that share many characteristics. • For example, they share: – Opposable thumbs – Flexible shoulders – Binocular vision Opposable Thumbs