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WHAT CAUSES EVOLUTION TO OCCUR? DARWIN’S MECHANISM: THE THEORY OF NATURAL SELECTION NATURAL SELECTION • DEFINITION: – the process by which organisms that are better suited to an environment survive and reproduce in greater number than those less suited. • What is the KEY to natural selection? • The environment • “Survival of the Fittest” • (But what is fit????) • Categorized into 5 Steps STEP 1: Overproduction • All species over reproduce creating a population with variation in the gene pool. STEP 2: Inherited Variation Variation (varieties) within a species come from 2 places: MUTATIONS of the gene code RANDOM MATING- mixing of genes in the population (no inbreeding). Child looks similar to but not identical to parents. A change in the gene for feather color creates different looking variations of a birds population VARIATIONS IN BIRD COLOR: • Most birds are born with traits (genes) for being bluegreen in color. • Occasionally some birds are born with traits that make them more green. • Occasionally some birds are born with traits that make them more blue. STEP 3: Struggle to Survive Members of the same species compete for resources such as food, shelter, and mates. Those better suited to meeting these needs will survive. The birds face the challenge of blending in to survive. STEP 3: Struggle to Survive Ugh!, so full… Not all members of the species will survive this competition. Only some will survive and have the opportunity to pass on their successful genes. Since blue-green birds stand out more in the habitat than green birds, more blue-green birds are eaten EEP ! STEP 4: Successful Reproduction Favorable traits are passed to the next generation. Now, more members of the population are being born with the successful variation than those with the less suited trait. Now more green chicks than blue/ blue-green are being born. STEP 5: Adaptation of the Species ? (Not included in the textbook) Adaptation – process by which a species becomes better suited to its environment. Hee, hee… NATURAL SELECTION EXAMPLES • Giraffe’s long neck (see old textbook pg 187) • Peppered Moth • Ivory tusks of African elephant (textbook pg 122) NATURAL SELECTION EXAMPLES Antibiotics vs. Bacteria Salmonella (bacteria that causes food poisoning) vs Salmonycin antibiotic (fights against Salmonella bacteria) Darwin’s Finches Examples of Adaptations flounder lichen katydid Camouflage: Mimicry: monarch butterfly (left); viceroy butterfly (right) coral snakes "Red and yellow, kill a fellow; red and black, venom lack DEVELOPMENT OF NEW SPECIES? SPECIES: a group of organisms that can interbreed and produce fertile offspring. Steps to a NEW SPECIES 1. Separation: part of a population becomes isolated from the rest. 2. Adaptation: Natural selection constantly improves the fit between species & environment. Populations diverge. 3. Differences accumulate creating ecological races. 4. Division: Enough differences create a NEW SPECIES. DIVERGENCE: the accumulation of differences between populations or species ECOLOGICAL RACE: populations of the same species that differ genetically because they have adapted to different conditions At what pace does evolution occur? GRADUALISM: states that evolution occurs slowly over time and includes many transitions PUNCTUATED EQUILIBRIUM: states that evolution occurs in short bursts followed by long periods of stasis (no evolving) Discussion Questions • According to Natural Selection, explain why human overpopulation exists? • Are humans evolving?