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Transcript
Chapters 22-25 Evolution Evolution The definition of Evolution is: change over time Biological Evolution is: genetic change in population over time process by which modern organisms have descended from ancient organisms (slow change over long time) • Even relatively quick evolution takes hundreds of thousands of years History of Evolutionary Theories Plato (427-347 B.C.) 2 worlds – 1 perfect, 1 imperfect. No change in organisms Aristotle (384-322 B.C.) Organisms placed on “ladder of complexity / perfection” (scala naturae) No change Judeo-Christian culture tried to explain the Creator’s plan as observable, natural phenomena – Natural Theology History of Evolutionary Theories Carolus Linnaeus (1707-1832) Designed modern taxonomic system (binomial nomenclature) From this system, we can (he didn’t) now infer evolutionary relationships between different groups Geologists: Georges Cuvier James Hutton Charles Lyell History of Evolutionary Theories Georges Cuvier (1769-1832) helped develop Paleontology – study of fossils Discovery of fossils (extinct species, similarities to modern species) put some doubt into Earth’s age and the origin of species Cuvier explained differences in strata with “catastrophism” – floods, droughts, volcanoes, etc. changed local areas drastically over short periods of time • Organisms did not change, just migrate History of Evolutionary Theories James Hutton (1726-1797) proposed that rocks, mountains, and valleys have been changed by water, wind, temperature, volcanoes, and other natural forces He described the slow processes that shape Earth as “gradualism” History of Evolutionary Theories Charles Lyell (1797-1875) – agreed with Hutton and said that scientists must always explain past events in terms of observable, PRESENT events and processes (“uniformitarianism” – what happens today happened yesterday) They theorized Earth was much older than a few thousand (6,000) years, which didn’t set well in the traditional timeframe of Creationism Age of the Earth We now know Earth is approximately 4.5 billion years old Darwin used the work of Hutton and Lyell as a basis for his theories of slow change over time. Darwin’s work was a biological duplicate of Hutton and Lyell’s works in geology. Geologists study Earth’s rocks Fossils are preserved remains of ancient organisms As fossils are found that don’t resemble organisms today, evidence increases that Earth has changed and that organisms have changed with it Biologists and geologists date Earth’s past with the help of rocks Geological Time Scale RELATIVE DATING Technique used to determine age of fossils relative to other fossils in different strata This technique is VERY approximate Geological Time Scale ABSOLUTE (RADIOMETRIC) DATING Using radioactive elements in rock that decay at a steady rate to determine age Decay measured in terms of HALFLIFE • Half-life – time required for half the radioactive atoms in a sample to decay Radioactive Decay During radioactive decay, the atoms of one element break down to form something else Lose a proton 6 protons 4 neutrons 5 protons 4 neutrons Rocks contain radioactive elements, each having a different half-life EXAMPLES: Uranium-238 Lead-206 HL = 4.5 B yrs Potassium-40 Argon-40 HL = 1.3 B yrs Carbon-14 Nitrogen-14 HL = 5770 yrs Scientists often date rocks using Potassium-40, which decays to form the stable element Argon-40 It has a half life of 1.3 billion years This is used to date the oldest rocks on earth K-40 Formed K-40 Ar-40 Ar-40 1.3 B yrs 2.6 B yrs Uranium and Potassium are useful for dating rocks Carbon-14 is useful for dating things that were once alive such as wood, natural fiber, or cloth C-14 is in the atmosphere; living things take it in their cells. After the organism dies, it doesn’t take in any more C-14. We can then compare the amounts of C-14 to N-14, knowing its half-life, to determine the age of the sample Fossil Evidence Found in Sedimentary rock: layers of sand, silt, and clay in streams, lakes, rivers, and seas form rock that may have trapped living organisms Fossil records – Show change over time. Some time frames are missing, but will show change of climate and geography. Ex: Shark teeth in Utah How can this be? Jean Baptiste de Lamarck (1744-1829) He also recognized that organisms were adapted to their environments and that they change He relied on three ideas: 1. A desire to change (innate drive for perfection) 2. Use and disuse (Giraffe’s necks and vestigial organs) 3. Inheritance of acquired characteristics Darwin’s Dilemma Set sail around the world in 1831 on HMS Beagle on a 5 year voyage He had prior knowledge of geology (Lyell was a good friend) and agriculture that helped influence the development of his theory Anchored all along the way and took samples from each place Darwin’s Dilemma He collected and studied beetles from Brazil, birds from Chile, and iguanas, tortoises, and finches from the Galápagos Islands He noticed similarities between mainland (Ecuador) and Galapagos finches Later, he noticed differences in beak size among finches from different islands in the Galapagos Darwin’s Dilemma Thomas Malthus – wrote paper on population growth in Great Britain Population grows exponentially Limiting factors on growth (carrying capacity) • Food • Area • Resources Darwin’s Dilemma Darwin applied Malthus’, Hutton’s, and Lyell’s work to species’ ability to change, and called the mechanism Natural Selection Nat.Sel.: Process by which organisms with favorable variations survive and produce more offspring than less welladapted organisms He was sure Nat.Sel. was true, but he feared public ridicule. So, he kept his ideas to himself Darwin’s Dilemma Alfred Russel Wallace (1823-1913), working independently, came to the same conclusions as Darwin He sent a manuscript to Darwin, basically for proofreading “I never saw a more striking coincidence… so all my originality, whatever it may amount to, will be smashed.” – Charles Darwin Letter to Charles Lyell, June 18, 1858 Darwin quickly abridged and published his work “On the Origin of Species” Darwin’s Natural Selection Ernst Mayr, an evolutionary biologist, has dissected the logic of Darwin’s theory into three inferences based on five observations (Pg. 435) Observations: Tremendous fecundity Stable populations sizes Limited environmental resources Variation among individuals Heritability of some of this variation. Darwin’s Natural Selection Observation #1: All species have such great potential fertility that their population size would increase exponentially if all individuals that are born reproduced successfully. Darwin’s Natural Selection Observation #2: Populations tend to remain stable in size,except for seasonal fluctuations. Observation #3: Environmental resources are limited. Darwin’s Natural Selection Inference #1: Production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population, with only a fraction of the offspring surviving each generation. Darwin’s Natural Selection Observation #4: Individuals of a population vary extensively in their characteristics; no two individuals are exactly alike. Observation #5: Much of this variation is heritable. Darwin’s Natural Selection Inference #2: Survival in the struggle for existence is not random, but depends in part on the hereditary constitution of the individuals. Those individuals whose inherited characteristics best fit them to their environment are likely to leave more offspring than less fit individuals. Darwin’s Natural Selection Inference #3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over the generations. Evidence in Living Organisms Comparative embryology: All vertebrate embryos look similar to one another in early development, with the development of a tail and gill arches • Ernst Haeckel made early drawings – later exposed as frauds. • Gave fuel to anti-evolutionists Evidence in Living Organisms Comparative embryology: These anatomical similarities indicate similar genetics are at work Become more dissimilar as they grow • Cell specialization and differentiation Common ancestor? Evidence in Living Organisms Evidence in Living Organisms Comparative anatomy: Homologous Structures Analogous Structures Vestigial Organs Evidence in Living Organisms Homologous Structures – structures that are similar in anatomy, but may serve very different functions Ex: cat, whale, and human forearm Homologous Structures Flying Swimming Running Grasping Evidence in Living Organisms Analogous Structures – structures that serve similar functions, but have evolved independently of each other Not homologous; analogous Not homologous; not analogous Homologous; not analogous Homologous; analogous Evidence in Living Organisms. Vestigial organs – organs that have little or no purpose in the organism; may become smaller or even disappear Ex: Tailbone or appendix in humans Ex: Tiny leg bones in snakes (boas and pythons) thought to come from 4 legged ancestor Evidence in Living Organisms Comparative biochemistry and molecular biology: All cells have DNA, RNA, ribosomes, the same 20 amino acids and use ATP to do work Similarities in biochemistry indicate relationship Evidence in Living Organisms Cytochrome c is a highly conserved respiratory protein containing 104 amino acids in humans Evidence in Living Organisms Amino acid differences of hemoglobin between species What Homologies tell us… Similarities in structure and chemistry provide powerful evidence that all living things evolved from a common ancestor Darwin Concluded: Living organisms evolved through gradual modifications of earlier forms descent with modification What Similarities tell us… Two types of evolution can account for homologous AND analogous structures Convergent evolution Divergent evolution What Similarities tell us… Divergent evolution – two species evolve from a common ancestor (speciation) They share similarities in anatomy, biochemistry, and embryology due to common ancestry Explains homologous structures What Similarities tell us… Convergent – two species apparently becoming more similar Two species have adapted in similar ways to similar environmental conditions NOT due to common ancestry Explains analogous structures Convergent Evolution Ocotillo from California and allauidi from Madagascar have evolved similar mechanisms for protecting themselves Convergent Evolution Adaptive radiation of anoles has occurred on the islands of the Greater Antilles in a convergent fashion. On each island, different species of the lizards have adapted to living in different parts of trees, in strikingly similar ways. Convergent Evolution Convergent Evolution Diversity of Life Fitness: Physical traits and behaviors that enable organisms to survive and reproduce in their environment arises from adaptation. Adaptation allows species to be better suited to their environment and therefore can survive and reproduce. Evolution on Different Scales Microevolution – generation-togeneration change in a population’s allele frequencies Macroevolution – origin of new taxonomic groups; speciation 4 Driving Forces behind Evol. 1. Mutation Any change in the original DNA ONLY ultimate source of variation in a population 2. Gene Flow Movement of genes either into or out of a population Migration – Immigration (add alleles) and Emigration (subtract alleles) 4 Driving Forces behind Evol. 3. Genetic Drift Change in the allele frequency in a small population by chance alone • Bottleneck Effect • Founder Effect 4 Driving Forces behind Evol. 3. Genetic Drift Bottleneck Effect: population undergoes a high mortality rate; genetic variation decreases dramatically Ex: Cheetahs Genetic Drift: Bottleneck Effect 4 Driving Forces behind Evol. 3. Genetic Drift Founder Effect: few individuals leave a large population to start their own; gene pool is very limited Ex: polydactyly in PA Amish Genetic Drift: Founder Effect Genetic Drift: Founder Effect 4 Driving Forces behind Evol. 4. Selection Natural – differential success in the reproduction of different phenotypes resulting from the interaction of organisms with their environment • Nature does the selecting 4 Driving Forces behind Evol. 4. Selection (Natural) Resistance – overuse of insecticides and antibiotics have bred resistant species of bugs and germs 4 Driving Forces behind Evol. 4. Selection Artificial – breeding of domesticated plants and animals • Humans intentionally do the selecting • Cabbage, cauliflower, Brussels sprouts, kale, kohlrabi and broccoli have a common ancestor in one species of wild mustard 4 Driving Forces behind Evol. Problems with artificial selection – not enough genetic variation 4 Driving Forces behind Evol. 4. Selection (Sexual) Intrasexual selection – selection within the same sex (competition, usually between males Competition, usually between males Exaggerated anatomy Bighorn Sheep Rocky Mountain Elk Five-horned Rhinoceros Beetles Stagbeetles 4 Driving Forces behind Evol. 4. Selection (Sexual) Intersexual selection – one sex selects mate based on phenotypes Exaggerated anatomy Selection can influence populations in three major ways: Directional Sel. Stabilizing Sel. Disruptive (diversifying) Sel. Directional Selection Environment selects against one phenotypic extreme, allowing the other to become more prevalent Disruptive Selection Environment selects against intermediate phenotype, allowing both extremes to become more prevalent Stabilizing Selection Environment selects against two extreme phenotypes, allowing the intermediates to become more prevalent Key Points 1. Natural selection does not cause genetic changes in individuals. 2. Natural selection acts on individuals; evolution occurs in populations. 3. Evolution is a change in the allele frequencies of a population, owing to unequal success at reproduction among organisms bearing different alleles. 4. Evolutionary changes are not “good” nor “progressive” in any absolute sense. Evolutionary Theory Foundation on which the rest of the biological science is built. Collection of carefully reasoned and tested hypotheses about how evolutionary change occurs. Speciation What is a species? Biological definition: a group of closely related organisms (population) that can interbreed to produce fertile, viable offspring Speciation Why can’t/don’t populations interbreed? Prezygotic barriers Postzygotic barriers Prezygotic Barriers Ecological (habitat) isolation – pops live in different habitats and do not meet Parasites generally don’t transfer hosts Temporal isolation – active or fertile at different times Flowering plants pollinate on different days or different times of the day Prezygotic Barriers Behavioral isolation – differences in activities Mating calls or actions are different Prezygotic Barriers Mechanical isolation – mating organs do not fit or match Enough said Gametic isolation – gametes cannot combine Sperm destroyed in “different” vaginal cavity Sperm and egg don’t fuse due to different membrane proteins Postzygotic Barriers Hybrid inviability – hybrid zygotes fail to develop or reach sexual maturity Hybrid infertility – hybrids fail to produce functional gametes Summary 2 or more mechanisms may occur at once Ex: Bufo americanus and Bufo fowleri are ecologically, temporally, and behaviorally isolated Bufo americanus breeds in early spring in small, shallow puddles or nearby dry creeks Bufo fowleri breeds in late spring in large pools and streams Their mating calls also differ Limitations of Biological Species Concept How do you classify organisms that: have the potential to interbreed, but do not do so in nature? do not reproduce sexually? exist only as fossils? Alternative species concepts (ecological, pluralistic, morphological, genealogical) help address limitations Modes of Speciation Allopatric (Greek, allos = other; Latin, patria = homeland) Speciation due to geographic separation Barrier stops gene flow between populations Evolutionary change acts independently on each pop to establish reproductive barriers Mitochondrial DNA analysis has shown that certain tamarin monkey pops (those separated by wide rivers) are diverging toward speciation Where the Amazon is very wide, tamarins on one side are brown, but on the other side are white. Where the Amazon is narrow, tamarins of both colors are found on either side Allopatric Speciation Birds can move freely across the gorge of the Grand Canyon; squirrels cannot A. leucurus A. harrisi Two species arose when their original pop was disrupted by the carving of the canyon A. harrisi A. leucurus Allopatric Speciation If not given enough time, speciation will not occur Also, even if they do come back together, they need to interbreed to be the same species Allopatric Speciation Figure 24.11 Adaptive Radiation: evolution of many diversely-adapted species from a common ancestor Ex: Hawaiian archipelago Sympatric Speciation Sympatric (Greek, sym = together; Latin, patria = homeland) Speciation occurs in populations that share a habitat Results from: Ecological isolation Polyploidy (number of sets of chromosomes increases) Sympatric Speciation Polyploidy (number of sets of chromosomes increases) A result of accidents in meiosis Will Speciation Occur? p+q=1 p2 + 2pq + q2 = 1 Will speciation occur? You tell me! Hardy-Weinberg PPT 1 Hardy-Weinberg PPT 2 Evolutionary Time Scales Evolution can take a long time or can occur relatively quickly Gradualism Punctuated Equilibrium Evolutionary Time Scales Gradualism – big evolutionary changes are the result of many small ones over a long period of time Evolutionary Time Scales Punctuated Equilibrium – speciation occurs fairly rapidly then remain constant Evolutionary Novelties Unique and highly specialized organs seem to complicated to have been naturally selected Ex: eyes are really just photoreceptors; some are more developed, but all do the basic function: receive light Evolutionary Novelties Evo-devo Evolutionary development A field of interdisciplinary research that examines how slight genetic divergences can become magnified into major morphological differences between species Evo-devo By blocking expression of one gene, researchers forced a chicken’s foot to develop to resemble a duck’s foot Two embryos from the same animal Evo-devo Left, a normal chicken leg will develop Right, a normal duck leg will develop… from a chicken embryo Chicken leg: scaled with 4 digits Duck leg: smooth and webbed Duck legs, due to one genetic evolutionary difference, help ducks do many things chickens cannot, like swim