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EVIDENCE FOR EVOLUTION Evidence from dead organisms Evidence from living organisms FOSSILS – REMAINS OF DEAD ORGANISM Recognizable evidence of ancient life •Fossilized hard parts (most common) ex. Bones, teeth, shells, spores, seeds etc •Traces of fossils (indirect evidence), footprints, leaf prints, tracks, burrows. Fossilization • Organism becomes buried in ash or sediments • Rapid burial and a lack of oxygen aid in preservation • The organic remains become infused with metal and mineral ions What Do Fossils Tell Us? • As a result of mutations, natural selection, and drift, each species is a mosaic of ancestral and novel traits • All species that ever evolved are related to one another by way of descent • Differences and similarities between fossils and living How old are the fossils? Radiometric Dating parent isotope in newly formed rock after one half-lives after two half-lives Continental Drift Evidence from Biogeography Continental Drift • Idea that the continents were once joined and have since “drifted” apart • Initially based on the shapes • Pangea: theoretical supercontinent: Explains the worldwide distribution of more ancient life 500-200MYA • Laurasia and Gondwanaland: Explains why certain life forms exist in the northern land and some only in the southern lands 180200MYA EVIDENCE FROM BIOGEOGRAPHY Evidence from Living things Comparative Morphology Comparing body forms and structures of major animals and plants • Morphological divergence • Morphological convergence • Vestigial structures Divergent evolution due to Adaptive Radiation 3 1 PTEROSARUR 4 1 2 CHICKEN 3 Seen in Homologous structures: evolved from a common ancestor (so similar in structure) but has changed (different environmental pressures) to serve different functions 2 2 STEM REPTILE 3 2 3 PENGUIN 1 4 1 5 2 3 4 5 PORPOISE 1 2 BAT 3 1 2 3 4 5 4 5 HUMAN MORPHOLOGICAL CONVERGENCE DUE TO CONVERGENT EVOLUTION Evidence in Analogous structures Evolved from different ancestors But serves the same purpose Different ancestry but similar function Q: Which structures here show convergent evolution and which show divergent? VESTIGIAL STRUCTURES Body parts that had a function in the ancestor but not anymore Evidence of descent from a ancestor that used those parts. Ex. Pelvic bones in snakes Human appendix etc. Comparative Development • During development, each animal or plant proceeds through a series of changes in form • Similarities in these stages may be clues to evolutionary relationships • Mutations that disrupt a key stage of development are selected against COMPARATIVE DEVELOPMENT Comparative Biochemistry • Kinds and numbers of biochemical traits that species share is a clue to how closely they are related • All life contains DNA, makes proteins using RNA and similar biochemical processes • More similarity means species are more closely related Comparing Proteins • Compare amino acid sequence of proteins produced by the same gene • Human cytochrome c (a protein) – Identical amino acids in chimpanzee protein – Chicken protein differs by 18 amino acids – Yeast protein differs by 56 Speciation & Natural Selection • Natural selection can lead to speciation • Speciation can also occur as a result of other microevolutionary processes – Genetic drift – Mutation “Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.” Ernst Mayr