Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Topic 3: Evidence for evolution Fossil record • The sequence that fossils appear within layers (strata) of sedimentary rocks • Three types of fossils: – Mineralized bones and shells – Trace fossils – Preserved remains • Aging of fossils – C-14 – U-235 Fossil record • Earliest fossils= stromatolites • 3.5 billion years old • Mineralized layered mats of ancient cyanobacteria (we can thank them for early oxygen) Proterozoic rocks (~2 billion years old) Fossil Record “Descent with modification” Biogeography Homologous Structures • Similar or different function • Similar structure • Indicates common ancestors Homologies can be used to infer evolutionary history Vestigial organs • Remnants or whole structures that once served a function in an ancestor but are useless now • Examples: human ear muscles, hind-leg and foot bones in whales Embryonic development • Many organisms share traits as embryos that are not kept as adults. • For example, at one stage of development in the womb, reptile, bird, and mammal fetuses have structures resembling gills and they all have tails. Biochemical experiments • Stanley Miller (1953): Miller-Urey experiments – Simulated the conditions of primeval earth (~4 billion years ago) – Ocean + atmosphere (water vapor, methane, ammonia) + electrical charge (lightning) amino acids and other organic compounds that are today found in living things – Proved that organic molecules can be synthesized from inorganic molecules – These experiments have been repeated independently many times, with similar results • Since then, many meteorites have been analyzed and found to contain amino acids! Biochemical evidence • How did we get living organisms from organic compounds? – Remember the properties of cell membranes (phospholipid bilayer)? – Protobionts (lab experiments confirm) – Self-replicating RNA (lab experiments) Prokaryotes and endosymbiosis • Chloroplasts and mitochondria are probably remnants of those smaller prokaryotes – Evidence: both have their own DNA, replicate themselves like bacteria (binary fission) Molecular evidence • Universal code of life (DNA) • Conserved sequences of DNA – Example: gene for cytochrome c • Protein synthesis – RNA – Ribosomes – 20 amino acids Primate family tree If we scaled time to 24 hours… Modern humans (Homo sapiens) appear about 2 seconds before midnight Age of reptiles Insects and amphibians invade the land Plants invade the land Age of mammals Recorded human history begins 1/4 second before midnight Origin of life (3.6–3.8 billion years ago) Fossils become abundant Fossils present but rare Evolution and expansion of life