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Transcript
Ch. 15: Evolution I. Darwin’s Theory of Natural Selection Main Idea: Charles Darwin developed a theory of evolution based on natural selection A. Developing the Theory of Natural Selection 1. pre-Darwin: almost everyone believed the world was about 6000 years old and that animals and plants were unchanging 2. voyage of the HMS Beagle (1831-36): Darwin made observations on different species of plants and animals in South America and the Galapagos Islands. 3. Darwin hypothesized new species could appear gradually through small changes in an ancestral species a. artificial selection: humans promoting certain traits in organisms through selective breeding (ex: dogs, pigeons) b. Darwin thought if humans could change species, the same process could occur in nature given enough time 4. natural selection: Darwin thought that nature could produce new species if given enough time 4 basic principles individuals in a population show variations among others of the same species variations are inherited organisms have more offspring than can survive on available resources variations that increase reproductive success will be more common in the next generation 5. The Origin of Species (1859): Darwin’s published work on natural selection 6. evolution: cumulative changes in groups of organisms through time natural selection is a means of explaining how evolution works B. Evolution and The Origin of Life 1. Evolution of life is linked to the physical and chemical evolution of the Earth 2. Early Earth a. Big Bang Theory - particles scattered and condensed to form the Earth b. After the Big Bang, Earth had the elements needed to make biological molecules - carbon (methane), nitrogen (ammonia), water, and hydrogen c. Methane, ammonia, and water can combine (with energy in the form of lightning) to form amino acid 3. The first protein a. Remember - life is protein - "we're all just big bags of enzymes" b. How did the first amino acids assemble to make proteins? Hypothesis: Naturally occurring clay crystals served as templates for protein assembly; amino acids break apart too easily on their own Selection of specific assembled proteins came about from "survival of the fittest" Nucleotides (RNA) may also have been attracted to the clay particles and somehow participated in protein synthesis - replaced the clay particles 4. The first membrane a. Proteins, by themselves, form spheres called microspheres b. Microspheres tend to pick up lipids from water outcome is a lipid film around protein c. Membranes could have arisen through spontaneous, but inevitable chemical events 5. The first organisms - metabolism a. Probably anaerobic - produced ATP from anaerobic glycolysis b. Photosynthetic cells came along Photosynthesis changed the surface of the Earth by increasing the oxygen supply c. New organisms used oxygen to increase respiratory efficiency 6. The first cell and the first multicellular organisms (endosymbiont theory) a. eukaryotic cells appeared about 1.8 billion years ago b. may have lived closely with prokaryotic cells which became organelles. c. Chloroplasts and mitochondria may have been prokaryotes that became organelles (both contain their own DNA, ribosomes and divide independent from the cell) II. Population genetics - the study of inherited variation and its modulation in time and space A.Main concept: individuals do NOT evolve; populations do 1. Hardy-Weinberg principle: evolution will not occur in a population unless there are forces that cause change in the allele frequencies. B. Factors bringing about a change 1. Mutation - heritable change in kind, structure, sequence, or number of component parts of DNA; introduces new variation into population 2. Genetic drift - random fluctuation in allele frequencies as a result of random chance a. founder effect: extreme example of genetic drift when a small sample of a population settles in a location separated from the rest of the population (ex: Amish, Mennonites) b. bottlenecks: occur when a population declines to a low number then rebounds (ex: cheetahs in Africa) 3. Gene flow - change in allele frequencies: immigration (come) and emigration (go) 4. nonrandom mating: usually mating occurs bw individuals in close proximity; leads to inbreeding 4. Natural selection - differential survival and reproduction within a population; natural selection acts to select the individuals best adapted for survival and reproduction C. Evolution of a species - a GRADUAL process 1. Process by which species originate - speciation HOW?????? a) Reproductive isolating mechanisms 1) Mechanical - reproductive organs 2) Gamete isolation - external fertilization (sea urchin) 3) Time isolation - species "in heat," or time of emergence (cicadas) 4) Behavioral isolation - dancing or other reproductive ritual (ex: eastern and western meadowlark have different mating songs) 5) Hybrid inviability - incompatibility (abortion); ex: mules, ligers 2. Modes of speciation a) Allopatric (isolated location) - most common; no contact with original population (usually a physical barrier) b) Parapatric (transition location) - like mountains and desert; some contact with original population but offspring may not be successful or mating behavior discourages interbreeding c) Sympatric (ecological, behavioral, - barriers WITHIN boundaries); caused by polyploidy (plants and frogs) or when insects become dependent upon a specific plant III. Evolution - proceeds by modification of the genetic makeup of existing organisms Macroevolution - large-scale patterns, trends, and rates of change among groups of species A. Phenotype - morphological, physiological, and behavioral traits of an individual B. Phylogeny - evolutionary relationships among organisms C. Systems of classification (Remember KPCOFGS?) 1. Evolutionary taxonomy - based on a mixture of morphological and evolutionary relationships (reptiles, birds, and mammals grouped) 2. Cladistics - based on lines of decent (turtles, mammals, lizards & snakes, crocodiles, dinosaurs, and then birds) C. Patterns of evolution 1. adaptive radiation (divergent evolution)-one species gives rise to many species in response to a new habitat availability; often occurs after mass extinctions (ex: mass diversity of mammals following dinosaur extinction) D. 2. coevolution: evolution of one species affects the evolution of the other species in a close relationship (ex: comet orchids and moth mutualism) 3. convergent evolution: unrelated species evolve similar form, function and behavior due to inhabiting similar niches Rate of speciation 1. Gradualism - morphological changes occur slowly within a species 2. Punctuation - morphological changes take place rapidly during speciation E. Evidence of Evolution 1. fossil record: important source of information for determining the ancestry of organisms and the patterns of evolution. a. Transitional fossils: fossils that contain features shared by different species. i. Archaeopteryx: contains characteristics of a bird as well as dinosaur features b. derived traits: newly evolved features that do not appear in the fossils of common ancestors (ex: feathers) c. ancestral traits: primitive features that appear in ancestral forms (ex: teeth and tails) 2. Comparative anatomy: bones in vertebrates often have similar bones but different functions a. homologous structures: anatomically similar structures inherited from a common ancestor ex: bird wings and reptile forelimbs are similar in shape and construction indicating a common ancestor b. vestigial structures: reduced forms of functional structures in other organisms (ex: kiwi wings, snake pelvis, whale hindlimb bones, human appendix) c. analogous structures: structures used for the same purpose but are not inherited from a common ancestor (ex: eagle’s wings and a beetle’s wings) 3. Comparative embryology: studying evolutionary relationship through vertebrate embryos a. Vertebrate embryos exhibit homologous structures during development b. Ex: embryo tails and pharyngeal pouches (become gills in fish or ears, jaws, and throats in reptiles, birds and mammals) c. Shared embryo features suggests a shared ancestor 4. Comparative biochemistry: higher shared amino sequences in certain proteins (ex: cytochrome c) and in DNA and RNA mole indicate more recent common ancestors in organisms 5. Geographic distribution: organisms sharing the same location share closer ancestors F. Adaptation: a trait shaped by natural selection that increases an organism’s reproductive success. 1. fitness: measure of the relative contribution an individual trait makes to the next generation (often measured as number of viable offspring an organism produces) a. camouflage b. mimicry c. antimicrobial resistance 2. Consequences of adaptation: not all features of an organism are adaptive, but may arise as a consequence of other evolved characteristics (ex: spandrel example, human helplessness at birth)