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Transcript
Evolution . . . . What is evolution? The change of organisms over time. The mechanism is called natural selection. Evidence of Evolution The fossil record: signs of organisms from past times. We know that the Earth has been around for nearly 4.6 billion years! Started with no life Very little O2 No plants for photosynthesis Life evolved ~3.5 bya (billion years ago) This was most likely in the oceans because of the harsh atmosphere. First organisms were prokaryotic. The Fossil Record Types of fossils: Trace fossils- footprints, trails, burrows. Casts- minerals in rock fill in space left by organism. Imprints- objects leave an imprint in sediment that later hardens. Petrified- minerals replace the hard parts of an organism creating a copy. Amber- entire organisms found in tree sap. Molds- an organism is buried in sediment and decays, leaving an empty space. How old are these things??? Relative dating (not what it sounds like!) Older fossils are imbedded deeper in rock layers than new ones. Radiometric dating Using radioactive isotopes of elements that break down over time usually “Carbon 14”. Plate Tectonics The earth has plates of land that have been moving over the years. Single land-mass was called Pangea Continents are still moving. Humans Modern humans appeared about 200,000 years ago. Evolution now . . . Charles Darwin most famous for his theory of Natural Selection and his study of Galapagos finches. British biologist, traveled to the Galapagos Islands Researched animals there, especially the finches Darwin studied animals in the Galapagos Islands to help understand how species can change over time. Darwin collected evidence for 22 years. Published evidence in his book “Origin of Species” and introduced the idea of Natural Selection. Struggle to Survive Darwin proposed that organisms struggle to survive because they compete for: Food Space Mates They struggle to escape from predators Think of how organisms compete for food . . . . How do they compete for mates? What happens when an organisms loses these competitions???? Natural Selection Survival of the Fittest! What is fitness in this case? An organism’s ability to survive and pass on its genes to offspring. This does not necessarily mean the fastest and strongest . . . . . Sometimes it can mean the sneakiest is most fit. Natural Selection Natural selection acts on individuals. Natural Selection occurs when individuals with certain traits survive, reproduce, and pass on their genes to future generations. (Remember inheritable traits!) Organisms without these traits may be less likely to survive and reproduce. This results in the evolution of the species, or changes in that species over time. Natural Selection Requires 3 things! 1) Variation 2) Differential Reproduction 3) Heritability Adaptations Adaptations are structures or behaviors that give organisms a better chance of survival in their environment. Adaptations can arise as a mutation in one individual that allows it to survive better. That mutation will be passed on to offspring. Structural Adaptations These are physical characteristics that help an organism survive. Sharp teeth help to eat meat Long sticky tongue helps to catch insects Structural Adaptations Mimicry: Allows one organism to look like another (usually a nasty one!) Camouflage: allows organisms to blend in with their environment. Why do you think this is good? Peppered Moths http://www.ted.com/talks/david_gallo_shows_underwater_astonishments.html A structural adaptation . . . .the Aye Aye Darwin’s Finches Misconception :“Evolution is a theory about the origin of life.” Misconception : “Natural selection involves organisms ‘trying’ to adapt.” Either an organism has genes that enable its survival or it doesn’t. Misconception : “Natural selection gives organisms what they ‘need.’ ” A population either has the ‘right’ variation or it doesn’t. If it doesn’t, the population may die out. Misconception : “Evolution is like a climb up a ladder of progress; organisms are always getting better.” Mechanisms of Evolution Genetic Drift Gene Flow Artificial Selection Natural Selection Sexual Selection Genetic Drift Change in allele frequency by CHANCE Gene Flow Change in allele frequency as a result of MIGRATION Artificial Selection Humans choose desired traits and manipulate breeding Sexual Selection Special case of Natural Selection Variations selected for their ability to attract a mate May the best man/animal win The Lyre bird! Selective Pressures Environmental characteristics that favor the survival of certain organisms Examples: drought, lack of food, extreme temperatures, predation Sources of Variation GENE FLOW moves genes among populations SEXUAL REPRODUCTION introduces new gene combinations Random MUTATIONS in DNA lead to the formation of new alleles (sound familiar?) Natural selection affecting populations Three major types of natural selection are: Stabilizing Selection Directional Selection Disruptive Selection Stabilizing selection Average individual is selected for Directional selection One extreme trait is selected for Disruptive Selection Both extremes are selected for Average selected against. Can evolution produce new species? Of Course. Called “Speciation” This happens by two major methods 1. Geographic isolation 2. Reproductive isolation Geographic isolation Physical barrier divides a population New selective pressures Two different species Reproductive isolation No longer able to mate Different genetic information Mating behavior differences