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Transcript
8-5 Notes: Natural Selection SO HOW DID ORGANISMS BECOME SO WELL ADAPTED TO THEIR ENVIRONMENT? DARWIN’S EXPLANATION Darwin proposed that animals evolved to fit their environments. EVOLUTION The change in a population of organisms over time DARWIN’S EXPLANATION • Darwin realized that animals have many offspring and some don’t survive. • The survivors are better suited to their environment. HE CALLED THIS PROCESS…. NATURAL SELECTION • Mechanism by which EVOLUTION occurs • The environment is the selective agent Darwin said that in nature, the environment creates selective pressure STEPS OF NATURAL SELECTION 1. Overproduction -organisms have many offspring, but not all will survive. STEPS OF NATURAL SELECTION 2. Genetic Variation • Individuals vary within a population STEPS OF NATURAL SELECTION 2. Genetic Variation • Individuals vary within a population • New traits appear due to genetic mutations STEPS OF NATURAL SELECTION 3. Struggle to Survive • Organisms compete for resources (food, water, shelter, and mates) • Organisms have to get away from predators STEPS OF NATURAL SELECTION 3. Struggle to Survive • Some adaptations allow organisms to survive at a higher rate and individuals are “naturally selected” to survive and produce offspring STEPS OF NATURAL SELECTION 4. Descent with Modification • Organisms with the best adaptations will survive and reproduce passing these beneficial traits down to their offspring NATURAL SELECTION • Natural Selection acts on PHENOTYPES (traits) not genotypes NATURAL SELECTION • Natural Selection acts on PHENOTYPES (traits) not genotypes • As environment changes, different traits will become beneficial. EXAMPLES OF NATURAL SELECTION INSECTS BECOME RESISTANT TO INSECTICIDES. 1. Insecticide kills off most insects. 2. Those insects that survive have a gene that makes them resistant. 3. Resistant insects reproduce with other resistant insects. 4. Their offspring have the resistant gene. Insecticides don’t work very well over time! OTHER EXAMPLES OF EVOLUTION: • Bacteria become resistant to antibiotics • Don’t take antibiotics unless you have a bacteria infection! OTHER EXAMPLES OF NATURAL SELECTION: • Peppered Moths in England • There were more light moths (on light trees) before 1850. OTHER EXAMPLES OF NATURAL SELECTION: • Peppered Moths in England • There were more dark moths (on dark trees) after 1850. ARTIFICIAL SELECTION Humans breed for specific traits causing differences in species (i.e. dog breeding)