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• The evidence for evolution is compelling and extensive
• Looking at every level of organization in living systems, biologists see the signature of past and present evolution
• Darwin dedicated a large portion of his book, On the Origin of Species, to identifying patterns in nature that were consistent with evolution, and since Darwin, our understanding has become clearer and broader
• Fossil


  Any preserved remains, impression, or trace of any once-living thing from a past geological age

  
• Most fossils were commonly found in sedimentary rocks. They were from the hard parts of the organism like woody stem, bones, or teeth

  
• Paleontology


  The study of the history of life on Earth as based on fossils
• Body Fossils


  • Whole body fossils are the entire remains of prehistoric organisms including soft tissue, such as insects embalmed in tree sap that hardens to create amber

  
• Molds and Casts


  • An imprint left by the shell of a hard skeleton on surrounding rock, such as dinosaur bones buried beneath many layers of sediment

  
• Permineralization and Petrification Fossils


  • Petrification fossils form when the organic matter is entirely replaced by minerals and turns to stone. The original tissue is replicated in every detail
• Footprints and Trackways


  • Footprints, trackways, trails and burrows through mud sometimes harden and become fossils known as trace fossils
• Fossilized Feces


  • Coprolites (fossilized feces, also known as dung-stone) give clues to where certain animals lived and what they ate
• Comparative Anatomy


  The identification and description of the structures of living things
• Another type of evidence for evolution is the presence of structures in organisms that share the same basic form
• The bones in the appendages of a human, dog, bird, and whale all share the same overall construction resulting from their origin in the appendages of a common ancestor
• Homologous structures


  • Possess a similar underlying anatomy as a result of a shared evolutionary origin, but have evolved into a variety of distinct forms due to the presence of different selective pressures
• Example of homologous structure


  • Pentadactyl limb structure in vertebrates, whereby many animals show a common bone composition, despite the limb being used for different forms of locomotion (e.g. whale fin for swimming, bat wing for flying, human hand for manipulating tools, horse hoof for galloping, etc.)
• Analogous structures


  • Adaptations that possess similar features and functionality as a result of exposure to a common selective pressure, but have different underlying anatomies due to having unrelated evolutionary origins
• Example of analogous structure


  • Streamlined body shape in aquatic animals, regardless of ancestral origin (e.g. sharks are fish, dolphins are mammals, penguins are birds, etc.)
• Vestigial structures


  • Functionless and reduced remnants of organs that were once present and functional in their ancestors
• Example of vestigial structure


  • Pelvic bone in a whale - this bone serves no current purpose and is a remnant of a time when whales were terrestrial mammals

  
• Comparative Embryology


  The study of the formation and development of an embryo and fetus
• Studying the growing embryo in animals and plants shows that closely related organisms go through similar stages of development
• All terrestrial animals have non-functional gill slits (pharyngeal slits) as early embryos (indicating an aquatic origin)
• Many vertebrates (including humans) demonstrate a primitive tail at certain stages of embryonic development
• Molecular Biology


  Similarities and differences between the "same" gene in different organisms (that is, a pair of homologous genes) can help us determine how closely related the organisms are
• Evidence of a common ancestor for all of life is reflected in the universality of DNA as the genetic material and in the near universality of the genetic code and the machinery of DNA replication and expression
• DNA sequences have also shed light on some of the mechanisms of evolution, such as the evolution of new functions for proteins commonly occurring after gene duplication events
• Biogeography


  The geographic distribution of organisms on Earth follows patterns that are best explained by evolution, in combination with the movement of tectonic plates over geological time
• Broad groupings of organisms that had already evolved before the breakup of the supercontinent Pangaea