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Mechanisms of Evolution a. Species: a group of organisms that can interbreed and produce fertile offspring b. Population: a group of interbreeding species occupying a particular area c. Evolution is simply a change in the frequency of genes in a population. Evolution occurs by Natural Selection. Natural selection states: 1. More organisms are born than can survive. 2. Resources are limited, so there is competition for those resources. 3. Organisms with favorable adaptations (characteristics) to a particular environment survive and leave more offspring than those without favorable adaptations. *variations exist within a species; some adaptations are advantageous to survival so those with the variation can survive & reproduce What results is a change in the frequency of genes in a populationEvolution. Conceptually, there are two types of evolution. Microevolution- change in gene frequencies within a population over time Macroevolution- tells us how species of higher levels of classification are related to one another Changes in the frequency of genes in a population can be characterized by three types of selection: What kind of selection favors medium sized spiders? What kind of selection favors large spiders? What kind favors large and small spiders? What kind of selection favors small spiders? Changes in the frequency of genes may result from a number of different scenarios. How could migration change the frequency of genes in a population? How could isolation change the frequency of genes in a population? How could mutation change the frequency of genes in a population? Patterns of evolution Divergent evolution: individuals become more and more different from the common ancestor as they adapt to different environments Convergent evolution: different species adapt to similar environments and develop similar characteristics Mimicry: a species may develop a favorable adaptation by “mimicking” another type of species Choose the term which best fits each example. 1. Polar bears evolved from a group of brown bears that became geographically isolated in the north. A polar bear’s white coat helps it to blend in on the ice as it hunts sea mammals. 2. The orangutan line split off first. The gorilla and chimpanzee lines split later. 3. The swordfish is a fish, the beaked whale is a mammal, and the ichthyosaur is an extinct reptile. All three show adaptations to an aquatic life. 4. The climate of an area becomes colder, and most of the thin coated rabbits die. 5. A species of nonpoisonous snake has evolved to look almost exactly like the brilliantly colored poisonous coral snake. 6. A river changes course, dividing a population of ground squirrels and forming a barrier that keeps the two groups from mating. 7. A species of sparrow becomes established on a newly formed volcanic island. After 50,000 years this one species had evolved into several different species.