Name________________________________Date____________Per_____ Darwin: Natural Selection & Evolution Charles Darwin 1831 – set sail for __5__ years on HMS _Beagle as a Naturalist 22 year old English Medical student Questioned the belief that organisms never Change Natural Selection In 1859, Darwin offered an explanation – evolution occurs by Natural Selection. He published his idea in The Origin of Species. Darwin’s Observations Diversity – each area of the world has very different organisms. Fossils - preserved remains of an organism that lived in the past. The fossils Darwin saw looked different than organisms living at that time. Characteristics of Galapagos Islands organisms – organisms were different from organisms elsewhere and from organisms on other Galapagos Islands Adaptations Adaptation - trait that helps an organism survive & reproduce Examples: the finches’ beaks; the iguanas’ claws; poison & bad taste; bright colors of flowers; animal coloring Evolution Darwin studied his observations for 20 years after returning to England. Reasoned that organisms arriving on Galapagos faced conditions different from on the mainland of South America He hypothesized the species gradually changed over many generations & became better adapted to the new conditions This gradual change is called Evolution. However Darwin could NOT explain how the changes happened Natural Selection Natural selection – process by which individuals that are better adapted to their environment are more likely to survive & reproduce than other members of the same species Factors that affect natural selection o Overproduction – produce more offspring than can survive o Variation – any variation between individuals of the same species o Competition – members of a species will compete for resources Organisms with a helpful variation will survive & reproduce. Poor variations will die out. Over a long time, natural selection will lead to change. Reasons for Species Variation (speciation): Climate: example is snowshoe rabbit Geographic Isolation: example is Kaibab squirrel and Abert squirrel Interaction Between Species: Mutualism – relationship in which Both species Benefit Commensalism – relationship in which one species benefits and the other is neither helped nor harmed Parasitism – 1 organism lives in or on another organism and harms it Genetic Mutation: - chromosomal changes Darwin knew that changes happened, but couldn't explain how. At the same time, Mendel was explaining how change happens through genetics.