Evidence for evolution shows that closely related organisms share a variety of characteristics, which can be observed in several ways:
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Homologous Structures: Many organisms have similar anatomical features that arise from a common ancestor, even if these structures have different functions. For example, the forelimbs of humans, whales, birds, and bats have similar bone structures, indicating a shared lineage.
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Genetic Similarities: DNA sequencing has revealed that closely related species have a high degree of genetic similarity. For instance, humans and chimpanzees share about 98-99% of their DNA, suggesting a recent common ancestor.
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Embryonic Development: Early stages of development in closely related organisms often show remarkable similarities. For example, the embryos of mammals, birds, and reptiles exhibit common features, such as pharyngeal pouches, which suggest a shared evolutionary origin.
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Biogeography: The geographical distribution of species provides evidence for evolution. For instance, similar species found on islands (like the Galápagos finches) reflect how different lineages adapt to varying environments while maintaining a connection to a common ancestor.
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Vestigial Structures: Organisms may possess structures that have lost their original function through evolution. Examples include the human appendix and the pelvis in whales, indicating shared ancestry with other species where these structures had specific functions.
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Fossil Record: Fossils demonstrate the gradual change of species over time and show transitional forms that link closely related groups. For example, the fossil record of horses illustrates a progression from smaller, forest-dwelling ancestors to modern horses, showcasing evolutionary changes driven by environmental factors.
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Molecular Evidence: Molecular biology provides insights into evolutionary relationships. Similarities in proteins, RNA, and other molecular markers across related species strengthen the case for a common ancestry.
These lines of evidence collectively support the theory of evolution, demonstrating that closely related organisms share many characteristics due to their descent from a common ancestor. This interconnectedness highlights the dynamic processes of evolution and adaptation over time.