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Natural Selection 4.1.2 OUTLINE THE MECHANISM OF NATURAL SELECTION AS A POSSIBLE DRIVING FORCE FOR SPECIATION. What is evolution? What does it mean to you? Do you think it happens? Evidence? (for or against) http://evolution.berkeley.edu/evolibrary/article/evo_25 DEFINITIONS: Evolution are the changes in the gene pool of a population over time. Natural selection process by which individuals that are better suited to their environment survive and reproduce most successfully. Adaptation is an inherited characteristic that increases an organism’s chance of survival. Darwin and Evolution Darwin Wolf Pinta Marchena Genovesa Santiago Bartolomé Fernandia Råbida Pin zon Seymour Baltra Santa Cruz EQUATOR Santa Fe Tortuga Isabela San Cristobal Española Floreana Galåpagos Islands Marine Iguana Land Iguana Darwin’s Postulates Variation within populations. Overproduction of offspring. Struggle for existence. Unequal survival and reproduction rates. (Those with traits more likely to help them survive will pass traits to their offspring) What is a species? A group of individual organisms that are capable of reproducing and produce viable offspring. When organisms can no longer reproduce or do not produce viable offspring then they are no longer the same species. KONA FINCH extinct KAUAI AKIALAOA AMAKIHI LAYSAN FINCH IIWI AKIAPOLAAU APAPANE MAUI PARROTBILL fruit and seed eaters insect and nectar eaters FOUNDER SPECIES Based on his observations, Darwin proposed that EVOLUTION occurs by NATURAL SELECTION. Population of organisms Overproduction of offspring Limited resources leads to a struggle for survival between offspring. Population changes over time. Mutations & Sexual reproduction produces variations among offspring. Survivors reproduce more successfully. The Genetic Makeup of a Population Can Change • Populations evolve by becoming genetically different • Genetic variations • First step in biological evolution • Occurs through mutations in reproductive cells • Mutations in other cells can happen , but only reproductive cell mutations are passed on • Sometimes a mutation can result in a new genetic trait that gives it a better chance to survive, sometimes not. Can a fish species willfully grow limbs and fingers if they are needed to crawl out of the water onto dry land? Individuals in Populations with Beneficial Genetic Traits Can Leave More Offspring • Natural selection: acts on individuals • Second step in biological evolution • Adaptation may lead to differential reproduction • Genetic resistance in bacteria, cockroaches • When environmental conditions change, populations • Adapt • Migrate • Become extinct A group of bacteria, including genetically resistant ones, are exposed to an antibiotic Normal bacterium Resistant bacterium Most of the normal bacteria die The genetically resistant bacteria start multiplying Eventually the resistant strain replaces the strain affected by the antibiotic Evidence Supporting Evolution Fossil Record Evidence Supporting Evolution Homologous Structures Evidence Supporting Evolution Vestigial Structures Evidence Supporting Evolution Embryo Development Activity: • Choose an online natural selection simulation. • Work through the simulation and discuss the strengths and weaknesses of the simulation with regard to modeling natural selection. • In your own words, explain how a new species forms. http://www.techapps.net/interactives/pepperMoths.swf (requires flash) http://www.sciencechannel.com/games-andinteractives/charles-darwin-game.htm http://phet.colorado.edu/en/simulation/natural-selection (requires shockwave)