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Transcript
Lamarck’s evidence and inference Comparisons between current species and fossils: lines of descendents Use and disuse Inheritance of acquired characteristics Darwin’s evidence and inferences 1. All species produce far more offspring than required just to replace parents. This would result in exponential growth if populations were not limited. ("Essays on Population" by Thomas Malthus) 2. Populations do not, however, increase exponentially. They generally remain stable in size. (Field observations at home and on the voyage of the Beagle) 3. The resources in the environment are limited. observations) (Field 1. Because of the limited resources in the environment, there is competition among individuals. Only a small fraction of the individuals born can survive. Darwin’s evidence and inferences 4. There is variation within species and populations. Some individuals possess characteristics that are better suited to the environment than others. (Field observations) 5. Most physical, and some behavioral characteristics are inherited. (Breeding experiments with pigeons. "Artificial selection") 2. Those individuals with the best characteristics for the particular environment will do a better job of producing and providing for offspring than will others with less "fit" characteristics. Darwin’s evidence and inferences 6. Geologic processes are very, very slow. (Principles of Geology by Charles Lyell, work by Hutton, as well as Darwin's own studies of geology) 3. The earth must be very, very old. Over very great periods of time, "good" characteristics have time to accumulate and less fit ones have diminished. Homologous vs. analogous structures vs. Vestigial structures Evolution Macroevolution: Changes ABOVE the species level Microevolution: Change in the genetic makeup of a population Gene pool Can remain constant (equilibrium) Can change Variation Within populations Polymorphisms Between populations Geographic variation (clines) Evolutionary fitness Darwinian vs. relative fitness Altering frequency of phenotypes Preservation of Genetic Variation Diploidy Balanced polymorphism Heterozygous advantage (sickle cell trait) Frequency dependent selection (fitness declines if a characteristic becomes too common) Common moths at a disadvantage since the jays recognized it quickly Neutral variation Mutations arising in noncoding regions, pseudogenes, or parts of a coding region may not be selected for or against Sexual selection Sexual dimorphism arises since they influence mating success (not REPRODUCTIVE success) Intrasexual vs. intersexual selection (mate choice) Advantage/disadvantages of sex? Preservation of allele frequencies Hardy-Weinburg Theorem Allele frequencies remain constant from generation to generation if only Mendelian inheritance is at work (segregation and recombination) H.W. equilibrium – Population state in which allele frequencies are not changing, so genotype frequencies can be predicted Conditions for PRESERVING HardyWeinberg equilibrium Large population size No gene flow No new mutations Random mating No natural selection The goal of natural selection? Evolution is limited by its ancestry Adaptations are often compromises Chance and natural selection interact (natural selection is not random) Selection can only edit existing alleles (new alleles do not arise ON DEMAND) Small genetic changes can result in large morphological changes Anagenesis vs. Cladogenesis Evolutionary theories must explain how new species form (macroevolution) in addition to evolution of adaptations in a population (microevolution) Adaptations ABOVE the species level can help define higher taxa What is a species? More importantly what evidence do we use to distinguish species Reproductive isolation Read through the following definitions of a species: biological, morphological, paleontological, ecological, phylogenetic Discuss as a group which one you think should be used when classifying species and why Allopatric speciation Sympatric speciation Adaptive radiation Punctuated equilibrium Small genetic changes can result in large morphological changes Small genetic changes can result in large morphological changes Species selection Phylogeny and Systematics Problem: Organism classification and evolutionary history Phylogeny: “tribe” “origin”: Evolutionary history of a species or group of species Evidence: Fossil record systematics (analytical approach using morphological or biochemical similarities) Molecular biology represents best method for VERY closely related species Sorting homology from analogy Example: Bat and birds have wings. Is this the result of divergent evolution (homologous structure) or convergent evolution (analogous structure)? We need to example the actual bone structure and complexity of it Homoplasies: analogous structures that evolved independently Molecular homologies and molecular clocks Sequences must first be aligned (problem with deletion mutations?) Problems with molecular systematics? Molecular homoplasy Molecular clocks Calibration: Graph number of nucleotide differences against known evolutionary branch points (fossil record) Neutral theory DNA coding for rRNA vs. mtDNA Classification Binomial: genus + specific epithet Homo sapiens Taxon (plural taxa): A taxonomic unit Phylogenetic trees A branched diagram that depicts the evolutionary hypothesis Cladograms Depicts pattern of shared characteristics but not evolutionary history If shared characteristics due to homology, then it is the basis of a phylogenetic tree Origin of Life Evidence supports this sequence of events that led to life on earth… 1. Abiotic synthesis of small organic molecules 2. Joining of monomers to form polymers 3. Packaging of polymers to form “protobionts” 4. Origin of self replicating molecules that made inheritance possible 1. Abiotic synthesis of organic molecules First conditions on earth Lot’s of water vapor (eventually condensed to form oceans) N2, nitric oxides, CO2, CH4, NH3, H2, H2S Reducing atmosphere with energy from UV rays and lightning (postulated by Oparin and Haldane in 1920’s Oceans were a “primitive soup” of organic molecules Current conditions on earth Mostly N2, CO2, and O2 O2 comes primarily from biological splitting of water in cyanobacteria Evidence: Stromatolites (3.5 billion years old) Oxidizing atmosphere 1. Abiotic synthesis of organic molecules Miller-Urey experiments 2. Abiotic synthesis of polymers 3. Formation of protobionts Chains of amino acids can form spontaneously on hot sand, clay, or rock Aggregates of abiotically produced molecules surrounded by a membrane “Laboratory” evidence: When lipids or other organic molecules are added to water liposomes form, which can do all the functions of a cell membrane (shrink and expand, transport materials, carry a voltage) 4. Origin of self replicating molecules Chech and Altman: RNA plays catalytic role in protein synthesis and can carry out enzymatic like reactions (ribozymes) Diversity and selection of RNA molecules Dyson: Possible scenario Other scenarios? Fossil and geology records Radiometric dating Index fossils (order in which fossils were laid down, but not age) Based on decay of radioactive isotopes Half-life: # of years it takes for 50% of material to decay A brief history of life Kingdom classification