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CHARLES DARWIN • Proposed Theory of Natural Selection; “Father of Evolution” • Naturalist who set out on a 5 year journey around the world on the ship HMS Beagle • Made many observations in South America and the Galapagos Islands • Wrote book “Origin of Species” Theory of Natural Selection •Organisms that are best adapted to an environment are able to survive and reproduce more than others SURVIVAL OF THE FITTEST • No agent acting on natural selection • Process of elimination • Individuals whose current traits are best adapted for the current environment are the ones that survive and pass on their genes to the next generation Includes some fundamental ideas: • Species change over time and space – representatives of a species today are not the same as the ones from recent past • Share common ancestor – as organisms divide and evolve they split from common ancestors which helps explain similarities between them; gives rise to new species • Evolutionary change is slow – supported by fossil record and lack of sudden appearance of new species ADAPTIVE RADIATION • Organisms diversify rapidly from ancestral species into many new forms in response to environmental changes (good or bad) Darwin’s Theory has four componets: •Variation •Inheritance •High Population Growth •Competition VARIATION • Each organism has a unique combination of inherited traits • These traits are expressed in color variation as well as behavior making no two individuals exactly alike • Higher species variation means higher chance of survival VARIATION INHERITANCE • Favorable traits are consistently passed down from parent to offspring • Best traits and adaptations will allow organisms to live/reproduce • Natural selection acts on the phenotype (physical appearance) not genotype (genetic makeup) of organism HIGH POPULATION GROWTH • Organisms will overproduce offspring • Each generation of offspring experiences high death rates COMPETITION • Organisms compete for limited resources such as food, shelter, mates • Those with favorable traits out-compete others and are able to reproduce SELECTION PRESSURES ON A POPULATION • Selection Pressure – agent that tends to cause a genetic change in a population: • Competition for food • Competition for shelter • Competition for mates • Changes in the environment • Predation • Parasitism MAIN TYPES OF SELECTIONAL PRESSURES • Stabilizing Selection – genetic diversity decreases and the population stabilizes on a particular trait value (average phenotype is favored) MAIN TYPES OF SELECTIONAL PRESSURES • Directional Selection – an extreme phenotype (physical characteristic) is favored, causing trait frequency to shift over time in the direction favoring that phenotype MAIN TYPES OF SELECTIONAL PRESSURES • Disruptive Selection – change in population genetics that favors extreme values for a trait causing the population to divide into two groups.