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Evolution Introduction Science vs. non-science Common Misconceptions Definition of evolution Let’s eliminate the Non-Science Evolution & Science vs. Non-Science • • • • • • Who? What? When? Where? Why? How? • Is there a force (God) governing evolutionary processes? • What is evolution?…factual (evidence) • When has evolution occurred? …factual (evidence) • Where has evolution occurred? …factual (evidence) • What is the motivation behind evolution (if it is governed by God)? • How can biodiversity be explained by evolution? ...evolutionary theory The differences between the two can be accounted for in the approach; life’s diversity is one topic viewed from two different perspectives. What is evolution? Evolution is NOT: • the idea that people are descended from monkeys • “EVILution” / science vs. religion • an idea created by Charles Darwin – Darwin contributed the theory of natural selection as a model for HOW evolution takes place • an organism gaining a trait and passing it on to its offspring – Logic and genetics refute this position Evolution IS: • any change in traits • within a group of organisms • over multiple generations • which has been confirmed by biological studies Science is not asking IF evolution happened, or IF it is happening. Science is searching for evidence to support an evolutionary picture of biodiversity. Evolution Unit Overview I. History of Evolutionary Theory II. Evidence Supporting Evolutionary Theory III. History of Life IV. Patterns in Evolution I. History of Evolutionary Theory Ch 10.1-10.3, Ch. 12 A. Earlier published scientists (all in 1700s): − Linnaeus: grouped organisms according to similarities − Georges Louis Leclerc de Buffon: species shared ancestors; rejected idea of 6000 yr-old Earth − Erasmus Darwin: all from common ancestor; more complex arises from less complex B. Hutton (mid-late 1700s) & Lyell (early 1800s): − An ancient, slowly changing Earth − Earth is millions of years old − the processes that changed Earth in the past are the same processes that operate in the present Darwin’s conclusion from Hutton/Lyell: : (mid 1800s) If the earth could change, then so could the life which depends on the earth. Life changes in response to a changing environment. Such a change, however, would take many years (that’s why the earth’s age is significant). C. Lamarck’s (1809)Theory of Evolution: – By selective use or disuse of organs, organisms either acquired or lost certain traits during their lifetime. – Acquired traits would then be passed on to the next generation – e.g.—fiddler crab, giraffe, duck Lamarck’s Theory of Evolution: Inheritance of Acquired Characteristics Darwin’s conclusion from Lamarck: (mid 1800s) Organisms can pass only inherited traits. For example, in artificial selection, humans can select the most beneficial traits (selective breeding) There are differences in populations across time and even across geographic regions. …but how? D. Malthus (early 1800) Population Growth: If the human population continued to grow unchecked, sooner or later there would be insufficient space and food for all Darwin’s conclusion: (mid 1800s) Other animals and plants reproduce in greater numbers than humans; their populations were not overrunning the world There must be factors that determine whether or not organisms survive and or reproduce Hutton & Lyell: Lamarck: Early scientists: Malthus: Darwin Hutton & Lyell: ancient earth Lamarck: acquired traits Early scientists: past vs. present organisms Malthus: population growth Darwin Natural Selection E. Darwin’s Case Ideas in Darwin’s book, On the Origin of Species: 1. Variation in populations is a major feature of life − new traits are the result of spontaneous mutations − the variation must already be present before the population experiences a challenge − natural selection acts on existing variation 2. Large numbers in a population are trimmed by competition for resources (overproduction) −there is a struggle for existence based on the natural competition within a population −as in artificial selection, “good” traits are passed to the next generation −difference: nature selects the survivors… survival of the fittest 3. Variations that favor reproductive potential will be passed to future (adaptation) generations − Reproducing or Surviving = passing on the traits that made the survivors successful − Fitness: how well-suited an organism is to compete in its environment • Birds select beetles animation 4. Favorable variations can be inherited (descent with modification) – over time, the characteristics in a population change in response to a changing environment – species today have different traits than past organisms (…because they lived under different circumstances) – Implication: living things are related to each other (a single ‘family tree’ of life) Peppered Moth Example of an organism affected by Natural Selection Prior to 1848, was the dominant species of moth Typica species By 1895, 98% of the moths were this species Carbonaria species An example of natural selection Evolution in Resistance Explanation of how resistance happens: http://www.sumanasinc.com/scienceinfocus/sif_antibiotic s.html Explanation of how bacteria transmit resistance: http://survivalrivals.org/the-x-bacteria/animation Video about antibiotic resistance: http://www.youtube.com/watch?v=W-WumllRPLI Evolution in Resistance Summary • Bacteria possess a natural immunity to some antibiotics. • The immune ones survive and reproduce. • The successive generations possess increasing percentages of the immunity. • New drugs push the selective pressure toward more resistant bacteria. Relate Adaptations to Changes in Organisms Apply the concept of natural selection to the following new terms (see adaptation tables). •Define the terms (first column) •Relate these traits to (a) increased survival OR (b) reproductive success (second column) II. Evidence Supporting Evolutionary Theory Ch. 10.4-10.5 A. Fossils • types of fossils found in certain rock layers but not others • fossil organisms in older layers of rock are more primitive B. Geography • Birds on Galapagos were similar—but not identical—to those on South American continent • Darwin hypothesized that island species originated from a common ancestor that migrated from the mainland C. Embryology D. Anatomy Homologous and Analogous Structures Analogous Structures - structures that can be explained by a shared way of life • functional requirement Ex. Wings – bats, birds, and insects Ex. Body shape of sharks, dolphins and whales Analogous structures: • Look similar on the OUTSIDE • Do not look similar on the inside • Are not evidence of common ancestry • Could be evidence of similar selective pressures in the environment Homologous Structures - structures that are similar in origin but not necessarily similar in function Ex. limbs of various animals Turtle Alligator Bird Typical primitive fish Mammals Ex. 5 digit limbs of various animals Homologous structures: • Do not necessarily look similar on the OUTSIDE • Do look similar on the inside • Are evidence of common ancestry • Could be evidence of DIFFERENT selective pressures in the environment Vestigial Structures • structures that are present but are not always used Ex: whales and snakes have pelvic girdles but have no hind limbs Ex. Human appendix What would it take for the appendix to evolve completely out of the human population? E. Molecular Data DNA sequence Analysis & Protein Comparisons III. History of Life Ch. 12 Spontaneous Generation: the idea that living things can spontaneously exist from non-living matter Redi’s Experiment on Spontaneous Generation OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat. HYPOTHESIS: Flies produce maggots. PROCEDURE Uncovered jars Controlled Variables: jars, type of meat, location, temperature, time Covered jars Several days pass Manipulated Variables: gauze covering that keeps flies away from meat Responding Variable: whether maggots Maggots appear No maggots appear appear CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur. Spallanzani’s Experiment Gravy is boiled. Flask is open. Gravy is teeming with microorganisms. Gravy is boiled. Flask is sealed. Gravy is free of microorganisms. Pasteur’s Experiment Broth is boiled. Broth is free of microorganisms for a year. Curved neck is removed. Broth is teeming with microorganisms. Conclusions from the experiments of Redi, Spallanzani, and Pasteur: • Life gives rise to life • There are living things that cannot be readily seen, but are present • The theory of spontaneous generation is not supported with data Current Theories on the Origins of Life General Theory of Progression 1.Nothing -> presence of matter 2.Non-Living matter-> Living things 3.Simple Life-> More Complex Life 4.Radiation of Multicellular Life 2. Primordial Soup Model • developed by A. I. Oparian – Russian chemist in 1920 • a theory that states there was an ocean filled with primitive chemicals • these primitive chemicals were the ancestor of amino acids (which are the monomers of proteins) • chemist Stanley Miller and physicist Harold Urey did a famous experiment in 1950 to test this theory. They mixed gases thought to be present on primitive earth: Methane (CH4) Ammonia (NH3) Water (H2O) Hydrogen (H2) No Oxygen They then electrically sparked the mixture to signify lightning. The results were amino acids, the building blocks of proteins. • it was later discovered that other energies also can excite gases and produce all 20 amino acids • considered the classic experiment on the origin of life 3. Endosymbiosis - mutualistic relationship between one organism and other that lives within it Endosymbiotic Theory: • The presence of eukaryotes is because of a primitive relationship between aerobic and anaerobic prokaryotes Endosymbiotic Theory • Lynn Margulis Explains Endosymbiotic Theory • the aerobic prokaryote (inside) evolved into what is now the mitochondrion • This combined cell would have been the ancestor to the modern eukaryotic cell • the chloroplast followed a similar evolutionary route to yield in time a primitive plant-like cell Mitochondrial DNA as evidence: • could have been independent organisms at one time • DNA replicates independently from the cell cycle • DNA is circular in shape (as in prokaryotes) • contains some of its own, unique genes –different than the rest of the cell’s genes 4. Radiation of Multicellular Life Multicellular life appeared in the Paleozoic Era (544 mya) First part: Cambrian Explosion— a huge diversity of animals species evolved Life moved from water to land Mass extinctions were followed by booms in numbers and varieties of plants and animals Appearance of the Hominid Species Members of the family of humans Lucy • Australopithecus afarensis • found in 1971 in Africa • 40% complete skeleton • 3.5 feet tall • between 3 - 3.6 million years old • many propose that she is the “missing link” • puzzle has not yet been solved • First appearance of genus Homo was 100,000 yrs ago Phylogeny Phylogenetic tree – family tree that shows evolutionary relationships that are thought to exist among organisms —provides a snapshot of evolutionary history • based on embryological development, chromosomal similarity and biochemical similarities Cladistics – type of phylogenetic classification that establishes evolutionary relationships by looking at derived characters derived characters – features that evolved only within the group being examined Ex: feathers on birds • the more features in common, the closer the organisms are in evolutionary history Cladogram IV. Patterns in Evolution Ch. 11 How Quickly Do Organisms Evolve? Rate of evolution – statistical measurement of the changes of an evolutionary lineage over time Gradualism Punctuated equilibrium High number of transitional species Low number of transitional species Two types of Evolution: 1. Microevolution – small-scale changes in gene frequencies in a population over a few generations • microevolution could be caused by: a. mutation, b. natural selection, c. artificial selection, d. gene flow, and/or e. genetic drift • microevolution results in changes in the phenotypic ratios within a population over time a. Mutation – a change in DNA Causes: random error, radiation, etc. b. Natural selection – the process by which organisms with favorable variations reproduce at higher rates than those without such variations c. Artificial selection – breeding of individuals by humans to produce certain phenotypic characteristics Ex. all domestic dogs are Canis familiaris d. Gene flow – the movement of genes into or out of a population e. Genetic drift – a shift in allele frequencies in a population due to chance; Usually an environmental change Generic Bell Curve for Polygenic Trait Frequency of Phenotype For a polygenic trait in a population, characteristics are exhibited with a bellshaped curve: few members on the extremes and a bulk of individuals with the intermediate trait. Phenotype (height) e. Genetic Drift In isolated samples of an original population… Sample of Original Population Founding Population A Founding Population B Descendants e. Genetic Drift …individuals that carry a certain allele may have more descendants. Over time, thisFounding can resultDescendants in… Sample of Original Population Population A Founding Population B e. Genetic Drift …the divergence of phenotypes in the future generations. Sample of Original Population Founding Population A Founding Population B Descendants This resulted from chance isolation of individuals from the original population. Summary: Genetic drift—there is a “random” change in the frequency of alleles in a population Example of microevolution: bacteria that are resistant to antibiotics • observable, so accepted • does not give rise to new species 2. Macroevolution – major evolutionary changes over very long periods of time The creation of new types of organisms from previously existing, but different, ancestral types • eventually gives rise to new species • not as accepted as microevolution because not easily observed during the typical life span of humans Patterns of Evolution Organism populations must adapt to changing environment in order to survive 1. Coevolution – the change of two or more species in close association with each other a. predators and prey b. parasites and hosts c. Plants and the animals that pollinate them Ex. fruit bats are able to detect light colored flowers and fruity smells at night and pollinate the fruit in return 2. Convergent Evolution – occurs when the environment selects similar phenotypes, even when the ancestral types are not similar Ex. Porpoises are mammals and sharks are fishes, but both have streamlined bodies and similar fin structure 3. Divergent Evolution – when two or more populations or species become more and more dissimilar • usually a response to differing habitats • may result in new species Red fox (farmlands and forests) Kit fox (desert) 4. Adaptive radiation – many related species evolve from a single ancestral species, producing a variety of characteristics Ex. finches of the Galapagos Generic Bell Curve for Polygenic Trait Frequency of Phenotype Remember the graph…? Phenotype (height) 5. Other patterns of selection a. Stabilizing Selection Stabilizing Selection Key Low mortality, high fitness High mortality, low fitness Selection against both extremes keep curve narrow and in same place. What good reasons can you come up with for this trend? Human babies that have a really low birth weight… Human babies that have a really high birth weight… Birth Weight –In stabilizing selection, the bulk portion of the bell-shaped curve is favored; –The average phenotype is favored b. Directional Selection Key Directional Selection Food becomes scarce. Low mortality, high fitness High mortality, low fitness –In directional selection, the one side of the bell-shaped curve is favored; –The one extreme phenotype is favored over the other, over the average c. Disruptive Selection Disruptive Selection Low mortality, high fitness High mortality, low fitness Population splits into two subgroups specializing in different seeds. Beak Size Number of Birds in Population Key Number of Birds in Population Largest and smallest seeds become more common. Beak Size –In disruptive selection, both end portions of the bell-shaped curve are favored; –Both extreme phenotypes are favored over the average Another example to demonstrate these selection patterns: http://bcs.whfreeman.com/thelifewire/ content/chp23/2302001.html d. sexual selection –In sexual selection, an ‘attractive’ mate is favored Evolution vs. Genetic Equilibrium • These are opposites! • Maintaining genetic equilibrium requires: – Random mating – Population must be very large – No movement of individuals in or out of a population – No mutations – No natural selection • Is it possible to meet all of these criteria at once? • If you can’t maintain g.e., then what is happening?