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Evolution: Change Over Time Origin of Life • Abiogenesis (spontaneous generation) –Life comes from nonliving material Francesco Redi (1668) • Disproved spontaneous generation of larger organisms – Nonliving material cannot produce life – Did an experiment involving meat and maggots Louis Pasteur (mid-1880’s) • Disproved spontaneous generation of microorganisms – Completely isolated a culture medium with no outside influence like spores or eggs • Boiled culture several times • Observed no living organisms appeared • Biogenesis: living organisms come only from other living organisms Scientific theory of the origin of cells • Scientists believe the first cells probably prokaryotes (anaerobic): 2 billion years ago • Unicellular • Heterotrophs • Archaebacteria – Live in harsh environments (deep sea vents and hot springs) • Development of photosynthesizing bacteria –Released oxygen from water –Oxygen turned into ozone by sun’s rays made ozone layer Endosymbiotic Theory • Proposed by Lynn Margulis in the 1960’s • Eukaryotic cells evolved from prokaryotic cells through a symbiotic relationship • Chloroplasts and mitochondria contain DNA similar to DNA in prokaryotes – Prokaryote ingested aerobic bacteria (produced energy for the cell) – Over time the aerobes became mitochondria – Some prokaryotes also ingested cyanobacteria (blue/green algae) that contain photosynthetic pigments – Cyanobacteria became chloroplasts when ingested • Theory of Evolution: proposed by Charles Darwin –Observed plant and animal life on the Galapagos Islands (ex: finches, tortoises) –Wrote On the Origin of Species • Species evolve, not individual organisms • Occurs by Natural Selection: “Survival of the Fittest” – Process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species 3 Factors that Affect Natural Selection • Overproduction • Species produce far more offspring than can survive • May not be enough resources (food, water, living space) • Competition • Members of a species must compete with each other to survive • Does not usually involve direct physical fighting (usually indirect) • Lack of finding food • Predation • Genetic Variations – Differences between individuals of the same species – Can make individuals better adapted to their environment (more likely to survive and reproduce) – Offspring may inherit helpful characteristics – Environmental changes • Can lead to selection – Genetic variation • Can result from the shuffling of alleles during meiosis or mutations • Over time natural selection can lead to change in populations – some individuals have differences that permit them to adapt and increase their chances for survival – Organisms with favorable variations survive, reproduce, and pass their variations to the next generation – Organisms lacking favorable variations less likely to survive and reproduce – The ability to survive and reproduce in an environment is an organism’s fitness. Evidence for Evolution Adaptations • any variation that aids an organism’s chances of survival in its environment – Develop over many generations – Can be structural or behavioral Mimicry Stop at 2:00 • one species can resemble another species • Can provide protection from predators • Can look harmful or look like another harmful species Camouflage • Allows species to blend in with their surroundings • Used to avoid predators survive to reproduce Physiological Adaptations • Changes in an organism’s metabolic processes – Bacterial antibiotic resistance – Resistance to pesticides • Used to kill harmful insects • Some insects have traits that protect them from the pesticide and can survive • Surviving offspring inherit the pesticide protection • Pesticide becomes ineffective over several generations Fossils • studied by paleontologists – Used to learn the history of life – Evidence of an organism that lived a long time ago – 99% of species have become extinct • Can analyze structures of ancient organisms • Can also be used to find out about ancient climate and geography Fossil Formation • Can form in many ways – Organisms die and become buried in sediments (particles of soil and rock, mud, sand, or clay) – Become compressed over time which hardens into rock • Many found in sedimentary rock – Oldest fossils in the deepest layers – Can show a gradual series of changes in form of a species through layers of sediment Types of Fossils • Petrified fossils: minerals replace hard parts of an organism • Trace fossils: footprints, trials, burrows • Molds: decayed organism leaving an empty space • Casts: minerals fill spaces • Preserved remains • Hard parts: bones, teeth, shells, leaves • Imprints • Amber: resin from trees • Tar pits Relative Dating • Used to determine age of fossils in layers of rock • Compares a fossil’s location relative to other fossils in nearby rock layers • Cannot tell actual age • Look at rock layers oldest closer to the bottom The Law of Superposition is that sedimentary rock layer is older than the layers above it and younger than the layers below it. Radiometric Dating • Used to determine specific age of rocks and fossils • Radioactive isotopes in rocks (decay over time giving off radiation) • Half-life: decay rate of a radioactive isotope Homologous Structures • Structural features with a common evolutionary origin • Similarity in body parts of different organisms due to a common ancestor • May differ in function but are similar in structure • Ex: human hand, bat wing, amphibian leg, bird wing, whale forelimb Anatomical evidence Analogous Structures • Body parts that do not have a common evolutionary origin but are similar in function and appearance • Structures with different anatomy but similar function • Ex: flippers of dolphin, shark, and penguin, bird and insect wings Anatomical evidence Vestigial Structures • No current function presently but are similar to functional structures in related organisms • No longer serves its original purpose but was useful to an ancestor • Still inherited even though it is no longer needed • Ex: whale pelvic bone, snake leg bone, human appendix and tail bone Anatomical evidence Embryological evidence • Embryo: earliest stage of growth and development of plants and animals • All embryos have similar anatomy • Comparing early development of different organisms • Proceed through similar stages of development • Ex: fish, turtles, chickens, mice, humans all look the same • Gill arches and tails Molecular evidence (biochemistry) • DNA Similarities – Inherited similar genes from a common ancestor – Compare the sequence of nitrogen bases in DNA of different species to determine how closely related they are – Can compare the order of amino acids in a protein to compare relatedness • Cytochrome c – a protein in mitochondria – can compare the sequence of amino acids to determine relatedness Think about it: 1. A human’s appendix and snake legs are examples of ___. a. Vestigial organs b. Fitness c. Adaptation d. Struggle for existence 2. Another phrase for natural selection is “____”. 3. What conditions could force organisms to compete in a struggle for existence? Populations and Evolution • Evolution occurs as a population’s genes change over time – All genes together in a large gene pool: all of the alleles in a population’s genes – Evolution occurs when there is a change in the gene pool • Mutations –Environmental or by chance • Genetic drift: when chance events cause a change in allele variation – Ex. Overhunting, natural disasters cause decrease in population; or isolation of a small group in an area – Can affect small populations more than large • Gene flow is the movement of genes from one population to another population. Examples of this include a bee carrying pollen from one flower population to another, or a caribou from one herd mating with members of another herd. • 3 different types of natural selection that acts on variation – Stabilizing selection • Favors average individuals in a population • Diagram: • Directional selection – Favors one of the extreme variations of a trait – Diagram: • Disruptive selection – Individuals with either extreme of a traits variation are selected for – Tends to eliminate the intermediate phenotypes – Diagram: Evolution of Species • Species: group of organisms that live in the same area and can interbreed to produce fertile offspring • Speciation: the evolution of a new species – Members of similar populations can no longer interbreed to produce fertile offspring – Changes in allele frequencies that can result in the formation of a new species from a parent species – Ex: Darwin’s finches (another speciation video) • Creation of a new species – Form when a group of individuals remains isolated from the rest of its species long enough to evolve different traits – Isolation occurs when they are cut off from the rest of the species • Geographic Isolation: physical barrier divides a population – Bodies of water – Volcanoes – Mountain ranges – Island formation • Reproductive isolation: organisms can no longer mate and produce fertile offspring –Influenced by different genetic material and behavior patterns Patterns of Evolution • Charles Darwin observed different species of finches • Adaptive radiation (aka Divergent Evolution) – An ancestral species evolves into a variety of different species to fit a number of different habitats • Divergent evolution – Species that once were similar to an ancestral species become distinct or different – Populations change as they adapt to new/different environmental conditions – Results in new species • Convergent evolution –Distantly related organisms evolve similar traits –Occupy similar environments in different parts of the world Ch. 15-17 Bell Ringer #3: 1. The combined genetic information of all members of a particular population is called a (an) _____. 2. Genetic drift is more likely to occur in ___. a. Large populations b. Medium-sized populations c. Small populations d. One individual 3. What is the formation of a new species called? Pop Quiz! 1. All living things are ________________. 2. Name 3 types of evidence we can look at to determine relatedness. 3. What is the significance of the whale leg bones to evolution? 4. What is currently the closest related organism to whales? 5. Compare/Contrast whales and their closest relatives in a paragraph.