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Transcript
Evolution Ms. Edwards Darwin’s Theory • Charles Darwin (English) set sail around the world on the Beagle in December 1831. • He was a naturalist and wanted to learn about the living things in the world. • The diverse animals and plants he saw lead him to create the Theory of Evolution by Natural Selection. Darwin’s Observations • He stopped in South America (S.A), and then went to the Galapagos Islands. • He observed: 1. The diversity of living things 2. Remains of ancient organisms 3. Characteristics of life on the Galapagos Islands. Diversity of Living Things • In South America, Darwin saw diverse insects, mammals, and plants. • Species- a group of organisms that can mate and produce fertile offspring. • To date, there are more than 1.7 million species of organisms on earth! Fossils • Fossil- the preserved remains of an organism that lived in the past. • The fossils Darwin saw made him wonder about life in the past. Galapagos Organisms • Darwin compared the organisms on the Galapagos to each other and to the organisms elsewhere in the world. Comparisons to S.A. Organisms • Many birds and plants on the islands were similar to those on the mainland. • Iguanas on the island had larger claws to grip rocks. Iguanas on mainland had smaller claws to climb trees. • Darwin hypothesized that a small number of animals were blown or drifted from the mainland to the islands. • Then those animals reproduced and slowly became different from their mainland relatives. Comparisons Among the Islands • Differences in tortoise shell shapes. • Differences in finches’ beaks. • Finches that ate worms had slender beaks. • Finches that ate seeds had strong, wide beaks. • Adaptation- a change that helps an organism survive and reproduce. Evolution • Darwin returned to England and spent 20 years analyzing his findings. • Darwin reasoned that organisms on the island faced conditions that were different from those on the mainland. • Therefore, the species gradually changed over time to adapt to their new environment. This is called evolution. Theory of Evolution • Scientific Theory- a well-tested concept that explains a wide variety of observations. • Darwin wasn’t sure how to explain his theory, so he studied selective breeding. • He studied how English sheep were bred to have fine wool. Natural Selection • Darwin published his findings in a book entitled The Origin of Species (1858). • Darwin explained that evolution occurred because of natural selection. Natural Selection- the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. Factors of Natural Selection • Overproduction- species produce more offspring than can survive. • Variation- differences between members of the same species. • Competition- food and resources are limited, so members of a species must compete to survive. - Darwin’s Theory Overproduction and Variation • Natural selection is the process by which individuals who are better adapted to their environment are more likely to survive and reproduce than other members of the same species. Natural Selection • Darwin proposed that over a long time, natural selection can lead to change. • Helpful variations accumulate in a species while unfavorable ones disappear. Genes and Natural Selection • Darwin did not know how these changes came about. • Scientists later discovered that changes occur because of mutations in genes. • Genes are then passed from parent to offspring. • Only traits that are inherited, or controlled by genes, can be affected by natural selection. Evidence of Evolution • Evidence tells us that evolution still occurs today. • Consider pesticides and insects: 1. Bugs are sprayed with pesticide 2. A few survive, reproduce, and pass their genes to offspring 3. Offspring now have resistance 4. After many generations, all bugs are resistant. Interpreting the Evidence • Fossils • Embryonic Development - Even though many adult organisms look different, they look similar while they are developing - This suggests that they have a common ancestor. Interpreting the Evidence • Some organisms have similar body structures. • Bird’s wing, dolphin’s flipper and dog’s leg all have similar bone structures, which suggest they share a common ancestor. • homologous structures- similar structures that organisms have inherited from a common ancestor. • Fossil evidence gives us clues about homologous structures. - Evidence of Evolution Homologous Structures The structure of the bones in a dolphin’s flipper, a bird’s wing, and a dog’s leg is similar. Homologous bones are shown in the same color. Inferring Species Relationships • Scientists have combined the evidence from DNA, protein structure, fossils, early development, and body structure to determine the evolutionary relationships among species. • Closely related species have similar DNA, which they inherited from a common ancestor. • Recent DNA evidence shows that dogs are more closely related to wolves than coyotes. Branching Trees • Branching Tree- a diagram that shows how scientists think organisms are related. How Do New Species Form? • A new species can form when a group of individuals becomes isolated from the rest of its species long enough to evolve different traits. How Do Fossils Form? • Most fossils form when organisms die and become buried in sediment. • Petrified fossils- Fossils that become buried and turn into rock. • Mold- a hollow space in sediment in the shape of an organism. • Cast- a copy of the shape of the organism that made the mold. - The Fossil Record How Do Fossils Form? Most fossils form when organisms that die become buried in sediments. Determining a Fossil’s Age • Two methods 1. Relative Dating- uses the position of the fossils. Can only be used when rock layers have been preserved in their original order. 2. Radioactive Dating- used to determine the exact age of fossils. Uses radioactive elements. • Half-life- the time it takes for half of the atoms in a sample to decay. - The Fossil Record Radioactive Decay The half life of potassium-40, a radioactive element, is 1.3 billion years. This means that half of the potassium-40 in a sample will break down into argon-40 every 1.3 billion years. The graph shows the breakdown of a 1-gram sample of potassium-40 into argon-40 over billions of years. What Do Fossils Reveal? • Fossil Record- the millions of fossils that scientists have collected. • Extinct- a species is extinct if no members of that species are alive. • Geologic Time Scale- the calendar of Earth’s history. - The Fossil Record Earth’s History as a Clock Fossils found in rock layers tell the history of life on Earth. The history of life can be compared to 12 hours on a clock. - The Fossil Record Precambrian Time and the Paleozoic Era - The Fossil Record Mesozoic and Cenozoic Eras Unanswered Questions • 2 questions about evolution: 1. What caused the mass extinctions? 2. How fast does evolution occur? Rate of Evolution • Gradualism- theory that says evolution occurs slowly but steadily. • Punctuated Equilibria- theory that accounts for the gaps in the fossil record. Says species evolve quickly during short periods of time and then have long periods of no change.