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Why do organisms ‘match’ their environment? fitness Natural selection: differential survival and reproduction of individuals based on genetic differences in some trait(s) adaptation • The ‘match’ is genetic and induced by environment. Charles Darwin figured out how natural selection could lead to adaptive evolution. • offspring resemble parents • variation in traits can be inherited • life is full of challenges! • variation in traits variation in fitness Fitness: - ability to survive and reproduce - depends on the environment How natural selection works Resistance to antibacterial soap Generation 1: 100% not resistant 0.00% resistant How natural selection works Resistance to antibacterial soap Generation 1: 100% not resistant 0.00% resistant How natural selection works Resistance to antibacterial soap Generation 1: 100% not resistant 0.00% resistant Generation 2: 96% not resistant 4% resistant mutation! How natural selection works Resistance to antibacterial soap Generation 1: 100% not resistant 0.00% resistant Generation 2: 96% not resistant 4% resistant Generation 3: 76% not resistant 24% resistant How natural selection works Resistance to antibacterial soap Generation 1: 100% not resistant 0.00% resistant Generation 2: 96% not resistant 4% resistant Generation 3: 76% not resistant 24% resistant Generation 4: 12% not resistant 88% resistant Natural selection – key points differential survival and reproduction of individuals based on genetic differences in some trait(s) For adaptations to evolve: - differences in the trait must cause differences in fitness - differences in the trait must be heritable Fitness depends on the environment. local adaptation Natural Selection • Directional Selection: natural selection removes organisms at one extreme and in the middle, favoring one extreme: – The peppered moth – Bacterial resistance to antibiotics – Insect resistance to pesticides Natural Selection • Stabilizing Selection: natural selection removes organisms at the extremes of a population: – Birth weight in humans (heaviest and lightest babies have the highest mortality) Natural Selection • Disruptive selection: natural selection that favors two extremes of a characteristic – Grass plants in Welsh copper mines – Sickle cell heterozygotes in Africa Why do organisms ‘match’ their environment? fitness Natural selection: differential survival and reproduction of individuals based on genetic differences in some trait(s) adaptation • The ‘match’ is genetic and induced by environment.
