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Charles Darwin’s Theory of Evolution
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Introduction Charles Darwin was a biologist who lived during the 1800s – Scientific thinking was shifting (biology & geology) Evolution = the process of change over time Darwin developed a theory that explains how modern organisms evolved over long periods of time through descent from common ancestors.
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Darwin’s Observations Darwin was invited to sail aboard the HMS Beagle’s 5-year journey – The captain and crew were mapping the coastline of South America – Darwin was collecting animal and plant specimens and making notes about the biological diversity (species) he observed – They visited South America, remote islands, New Zealand, Australia, and the southern tip of Africa
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Examples Birds: – Rheas are similar to ostriches but live on separate continents – Finches on the Galapagos Islands were similar but each species had a differently-shaped beak Marsupials are found only on Australia Fossils – Many fossils that Darwin collected resembled living species.
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Other Scientists’ Ideas James Hutton and Charles Lyell (Geologists) – Concluded that the Earth is extremely old – The processes that changed Earth in the past were still operating in the present. Jean-Baptiste Lamarck (Biologist) – Suggested that organisms could change by using or not using parts of their bodies Thomas Malthus (Economist) – Studied factors that limited population growth
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Artificial Selection Plants and animals are bred for certain characteristics – Cows that produce more milk – Horses that run faster – Plants that produce better fruit – Dogs that possess certain skills (dog breeds) Artificial selection = nature provides the variations in a species, but humans select those that they find useful. (Darwin had NO idea how heredity worked)
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Darwin’s Conclusions Organisms struggle to survive – They compete for limited resources Some variations are more beneficial than others (adaptations) – Individuals with these variations were more likely to reproduce and pass them on to offspring. “Survival of the fittest” – An organism’s fitness describes how well it is able to survive and reproduce in its environment
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Natural Selection The process by which organisms with certain variations are more likely to survive and produce more offspring. – The natural environment determines fitness Natural selection exists when organisms compete for resources, possess variations, and there are different levels of fitness among individuals in a population.
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Evidence for Evolution 1. Biogeography – Patterns of species distribution – Closely related but different = variations among populations that resulted in the development of different species – Distantly related but similar = species that are similar and live in similar environments but in different locations 2. Fossils – The geologic record of organisms that have lived in the past – Some extinct organisms are similar to living species.
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3. Anatomy and Embryology – Homologous structures = structures that are anatomically similar but have different uses Ex: arm bones of amphibians, reptiles, bird wings, and mammals – Vestigial structures = traces of structures Ex: hip bones in marine mammals, tailbones – Embryos of different species show similar development patterns 4. Genetics and Molecular Biology – All organisms share the same basic genetic code
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