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Evolution Part II Microevolution – change in a population over time Lamarck – a French naturalist who worked in Paris at the Natural History Museum. Lamarck’s Hypothesis 1. Organisms constantly strive to improve themselves 2. The effort to improve causes the most used structures to improve and the others to waste away 3. Once a structure is advanced, the trait is passed to the offspring. Lamarck Disproven August Weismann – 1889 – disproved Lamarck Experimented with mice – cut the tails off, but offspring still were born with tails. Darwin’s Voyage 1831 traveled aboard the HMS Beagle to make maps Read a book by Charles Lyell – Lyell reasoned that the Earth was very old. Darwin also studied economist, Thomas Malthus. Malthus reasoned that without disease, starvation, and disasters, the human population would outgrow its resources. Darwin thought this of all species. Natural Selection There is variation in populations (mutations) Some mutations are favorable More young are produced each generation than can survive Those that survive and reproduce have favorable mutations Over a long, long time small changes accumulate and populations change Wallace Alfred Russel Wallace – Presented the same theory as Darwin, but papers and journals were lost in fire Mechanisms of Natural Selection Variations occur by mutation, recombination during sexual reproduction, and random fertilization Niche – an organism’s way of life and its use of the environment The niche includes whether or not the animal is a predator and things the animal needs to survive – light, temp., moisture When the niche changes, the organisms with the most favorable characteristics will survive and reproduce Peppered Moths English peppered moths live in the forests. Before the industrial revolution, the trees in the forest were covered with gray lichen. The moths were speckled light gray. Occasionally there were black moths born in the population because of mutations During the industrial rev., the lichen died and the trees became darker in color The black moths thrived and reproduced because they were better suited to the niche. Charles Darwin Voyage of the Beagle Types of Selection Types of Selection 1. Directional – when one extreme is selected for (Ex. Moths) 2. Disruptive – when both extremes are selected for (ex. Weeds) 3. Stabilizing – when the average is selected for (human height) 4. Sexual – male competition and female choice Genetic Equilibrium Gene pool is the combined genetic makeup of a population Genetic equilibrium occurs when a population is NOT evolving and the allele frequency is constant 1. No natural selection, random mating, no mutations, no migration Hardy-Weinberg equilibrium Genetic Drift Genetic drift – an accidental change in gene pool. Can cause drastic changes in small populations. Can be caused by reproductive isolation or catastrophe. Genetic Drift Bottleneck effect • Drastic reduction in population size • Ex. Population of cheetahs • Inbreeding occurs when population size drops • This decreases genetic variability • Makes them less “fit” Founder Effect Type of genetic drift When a few individuals colonize an island, lake, or other new habitat What Darwin observed with finches on the Galapagos Founder effect on humans Ex. In 1814, 15 people founded a British colony on a group of islands in the Atlantic One colonist carried the recessive allele for retinitis pigmentosa blindness Of the 240 residents in 1960, 4 had the disorder, and 9 were carriers That is a higher frequency than in Britain Gene Flow Gene flow is the loss or gain of alleles in a population USA is an example Mutations A mutation is a change in someone’s DNA Single mutations don’t have much of an effect on a gene pool, but those with mutations that make them more successful will be selected for and pass the mutation on to offspring Mutations are the raw material for evolution Survival of the fittest The individuals who work best in the habitat leave the most offspring Their alleles have the most impact on the gene pool Evolution of Cardiovascular Disease Rare among small populations of humans whose diets resemble that of early humans Early humans who had the tendency to eat fatty foods were more likely to survive famine Maybe that is why we have the taste for fatty, sweet foods Antibiotic resistance Some mutated bacteria can survive antibiotics Tuberculosis-causing bacteria Just like the pesticide-resistant plants in the web activity Speciation Species – an interbreeding population of organisms that produce healthy, fertile offspring Speciation usually begins by reproductive isolation Allopatric and Sympatric Allopatric Speciation Patterns of Evolution Divergent evolution – when two isolated population evolve independently (Ex. Brown and polar bears) Adaptive radiation – rapid evolution of a variety of species from a single ancestor (ex. Darwin’s finches) Convergent Evolution – when two organisms without a common ancestor occupy the same niche, so they have the same characteristics. (ex. Porpoise and penguin) Adaptive Radiation