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Evolution by means of Natural Selection Evolution by Natural Selection: 5 KEYS 1. VARIATION • • Variation is inherent in populations of organisms (members of a population are not all the same). This Variation is Heritable – able to be passed from generation to generation. Elaphe obsoleta Evolution by Natural Selection: 5 KEYS 2. More offspring are born than survive. • • Differential reproduction and survival. “Survive” = Live long enough to reproduce. Evolution by Natural Selection: 5 KEYS 3. Differences occur between surviving offspring and those not surviving. • • Advantageous Varations = Certain characteristics found in surviving offspring that afford them a survival advantage. Sometimes called “Adaptations” (but this implies a goal, and Natural selection is NOT goaloriented). Evolution by Natural Selection: 5 KEYS 4. More individuals with advantageous adaptations occur in succeeding generations of organisms. • • • Their variations are beneficial, therefore they survive & reproduce. Individuals without beneficial variation do not survive to reproductive age. Individuals Evolution by Natural Selection: 5 KEYS 5. Results in a population that is welladapted to its environment. • Population as a whole is becomes fitted to its particular environment. NATURAL SELECTION • This takes a long time – many generations. – Earth is old (We now know the Earth is roughly 4.5 Billion Years Old!). NATURAL SELECTION • Variation is essential – Previously viewed as imperfection… – Now viewed as the raw material on which evolution occurs. – We now know that GENES (Alleles) are responsible for variation: • • • • • Crossing Over (Meiosis) Independent Assortment (Meiosis) Oogenesis Fertilization Mutation NATURAL SELECTION • “Struggle for Existence” – Limited Resources are available for a population, leading to Competition. • Some survive, some don’t • Sometimes this is random – The “Struggle” is for the resources, not as much direct competition between individuals. NATURAL SELECTION • “Survival of the Fittest” – The most FIT organisms survive & reproduce. – Fitness = how well an organism fits into its environment • Securing resources • Avoiding predators • Finding food – What determines Fitness? • Varies with organism, but ultimately….ENVIRONMENT • This is always changing – what is most fit one month, may not be the next. NATURAL SELECTION • Environment is important! – In Artificial Selection, humans select for survival & reproduction. – In Natural Selection, “nature” selects for survival & reproduction. • • • • Habitat Climate Food & Shelter Availability Etc. NATURAL SELECTION • Not goal-oriented, no particular goal. – Environmental conditions are always changing. – Organisms’ needs are always changing. – Genotype is heritable, not phenotype. NATURAL SELECTION • Populations Evolve, NOT individuals. – Populations: Groups of individuals belonging to the same species and occupying the same given area, and being similar in form, behavior, and physiology. – Inheritance of acquired characteristics by Individuals (Lamarck) does NOT occur. NATURAL SELECTION • “Adaptation” – Traits are sometimes referred to as either “Adaptive” or not. – “Adaptive” traits are those that accumulate in each succeeding generation (due to differential reproduction). – This is somewhat arguable …why? EVIDENCE for Common Descent 1. Direct observation. Bacterial Capsules Evidence for Evolution (Common Descent) 2. Fossil Record – History of life recorded in fossils. • Bones, plants, shells, insects, etc. – Many fossils offer evidence for transitions. (Transition of the Ancient Reptilian Pelvis to Early Modern Birds) (Sequential evolution of the lower foreleg of horses) – Special Creation predicts no historical pattern of change -- the same organisms today as before. Evidence for Evolution (Common Descent) 3. Biogeography – – Different organisms with similar adaptations found in similar environments, but in very distant locations. Adaptive Radiation • Slight adaptations to slightly different environments in the same basic geographic area. Emu Rhea Ostrich – Special Creation predicts perfectly-adapted organisms occupying suitable habitats, despite geography. Evidence for Evolution (Common Descent) 4. Comparative Anatomy – Similarities in organisms’ internal structures, despite their functions. – Homologous Structures – Vestigial Structures – Special Creation predicts no similarity in structure if used for different functions & no such thing as a structure with no function. Evidence for Evolution (Common Descent) 5. Comparative Embryology – Similarity of different organisms during early (neo-natal, pre-birth) development. Evidence for Evolution (Common Descent) 6. Comparative Biochemistry – Similarities and differences in chemicals: • Nucleotide Sequences (DNA, RNA) • Amino Acid Sequences (Proteins) The Theory of Evolution • Populations of organisms have the capacity to change over time, generally in response to changes in their supporting environment.