Transcript Notes 7-1
Notes 7-1 Charles Darwin Changes Over Time Darwin’s Voyage • Charles Darwin was an English Naturalist who sailed on the Beagle, from England to the Galápagos Islands. Darwin’s Vogage • Saw Diversity in organisms (scientists have now identified over 1.7 million species!!) • A species is a group of similar organisms that can mate to produce fertile offspring • fossils Compared Galapagos organisms with South American organisms • Found many similarities and differences • Galapagos iguanas had sharp claws to grip slippery rocks and eat seaweed • South American iguanas had small claws to climb trees and eat leaves • Thought iguanas came from South America to Galapagos islands and evolved (changed over time) Compared Organisms among the different Galapagos Islands • Different shells on turtles of different islands • Variations in birds beaks (Darwins Finches) due to what they ate • Adaptations are traits that help organisms survive and reproduce in its environment • Example: Beaks of finches • CAN YOU THINK OF OTHER EXAMPLES OF ADAPTATIONS? Who was Charles Darwin Video Clip: • http://www.pbs.org/wgbh/evolution/educato rs/teachstuds/svideos.html Natural Selection • Individuals best adapted to environment will survive to reproduce, therefore pass on its traits • Nature is selecting for certain traits • Overproduction, variation, and competition affect the natural selection process Changes Over Time Overproduction and Variation Changes Over Time Competition and Selection • Variations among turtles make some of them better able to survive. Turtles that survive to become adults will be able to reproduce. How does evolution really work? Video clip: • http://www.pbs.org/wgbh/evolution/educato rs/teachstuds/svideos.html • Darwin thought that over long periods of time, natural selection would lead to change (evolution). Helpful variations would become more common, and unfavorable variations would slowly disappear. • Environmental factors and genes affect natural selection The Story of the Peppered Moth: Natural Selection at Work Let’s begin by looking at some real data! Table "A" represents data from a ten-year study of two varieties of the same species of peppered moth. The numbers represent moths captured in traps for ten consecutive years. The traps were located in the same area each year. Table A: YEAR NUMBER OF LIGHT MOTHS CAPTURED NUMBER OF DARK MOTHS CAPTURED 1 556 64 2 537 112 3 484 198 4 392 210 5 246 281 6 225 357 7 193 412 8 147 503 9 84 594 10 56 638 The Story of the Peppered Moth The English peppered moth, can be found throughout the English countryside. There are two varieties that exist in the population that differ in coloration: 1. Light gray with splotches 2. All Dark These moths feed at night and rest during the daytime. Sometimes they rest on the trunks of trees or rocks both of which are covered with a light gray colored lichen (an algae and a fungus that live together). The light variety of moth is camouflaged, but the dark moths, are easy prey for birds. Why? They stand out like a sore thumb. Before the Industrial Revolution, the darker variety was considered rare. Why? Because presumably they were eaten by birds before they could reproduce and pass the gene for darkness onto their offspring. In the late 1800’s, pollution killed the lichen that was found on the trees and rocks. With a lack of lichen, the tree trunks were now darker (no longer a gray color). The light moths now stood out among the dark bark of the tree and the dark variety were concealed from birds. As a result, the frequency of dark individuals in the population began to increase (they were more fit). They successfully reproduced and passed the gene for darkness on to their offspring. By the turn of the century, the population consisted almost entirely of dark moths. PreIndustrial Revolution After Industrial Revolution (Pollution killed the lichen) Summary: After 1800, dark moths were reproductively favored (more fit) because the light variety were now more commonly eaten by birds and therefore left fewer offspring. The gene for light color was therefore reduced in the population. Let’s look at that data table one more time! Table A: YEAR NUMBER OF LIGHT MOTHS CAPTURED NUMBER OF DARK MOTHS CAPTURED 1 556 64 2 537 112 3 484 198 4 392 210 5 246 281 6 225 357 7 193 412 8 147 503 9 84 594 10 56 638 BACTERIA Why does evolution matter now? Video clip: • http://www.pbs.org/wgbh/evolution/educato rs/teachstuds/svideos.html