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Evolution Just a “Theory?” Evolution • Genetic change in species through time • Microevolution: a change in a population’s allele frequencies • Macroevolution: large scale patterns, trends among larger groups Is God Involved? • • • • • It depends on who you ask! Atheistic evolution: does not believe in God Nontheistic evolution: divorce the two ideas; believe in God, but believe that God has nothing to do with evolution; scientific approach is separate. Theistic evolution (gradual creation): creator was responsible for the initial creation event, but then “hands off.” Progressive evolution: creator is playing a role in directing evolution; guides it (implies a goal) Quick creation (Scientific Creationism”): believe in the biblical account of creation. (Genesis) Craig Nelson, Indiana University Darwin’s Theory • Variation already exists within a species • Scarcity of resources leads to competition • Only the “fittest” survive to reproduce • Natural selection: organisms with favorable variations survive and reproduce Darwin’s Theory • Natural selection can lead to the formation of new species • Implies that many species once shared a common ancestor • Adaptive radiation: where many species evolve from one Change in gene frequency • A population contains variation: same traits, but different alleles. • A given allele may become more common, less frequent, or stay the same. • So differences from point A to B on a time line can occur Change over time • Populations can evolve— individuals cannot evolve! How do Gene Frequencies Change? • • • • Mutation Gene flow Genetic Drift Natural selection • There is not a goal, as some cartoons depict Evidence of Evolution • Fossil • Comparative anatomy • Homologous structures analogous structures vestigial structures • Comparative embryology • Biogeography • Comp biochemistry Fossil evidence • Deepest layers of rock are the oldest • Can trace the changes that occurred in some species over time • Not all species are fossilized Comparative Anatomy • Homologous structures: similar in skeletal structure • May look different on the outside • May vary in function Comparative Anatomy Suggest a common ancestor Homologous Structures Homologous Structures Whale metacarpals are similar to our knuckle bones Whale phalanges are similar W to our finger bones h a Vestigial Structures • Structures or organs that appear to serve no purpose • Examples: human tailbone, appendix • Often homologous to structures that are useful in other species • Suggest common ancestry Comparative Embryology • Embryos of certain species develop almost identically, especially in the early stages • Similar genetic instructions • Suggests that organisms descended from common ancestor Biogeography • Same environments in different parts of the world yield different organisms • Ostrich, rhea, emu Biogeography Comparative Biochemistry • Complex biochemical compounds such as cytochrome c, antibodies, and blood proteins are almost identical in many species • Suggests high degree of relatedness and common ancestry Microevolution Changes occur in a population’s allele frequencies over time. Microevolution • Individuals in a population have same number and kinds of genes • But forms of the gene may vary (alleles) • Each individual is unique because of his combination of alleles Microevolution • One allele may be more or less common than others. • One or more alleles may disappear • One or more alleles may become more or less common Causes of allele frequency changes • • • • • Recombination Mutation Gene flow Genetic drift Natural selection • All these shuffle the alleles Recombination • Creates new genetic varieties • Sperm and ovum both bring 23 chromosomes • Resulting in a zygote with a new combination of chromosomes distinct from either parent Mutation • Heritable change in the DNA • Can be helpful, harmful, lethal, or neutral • Can cause changes in the individual’s ability to survive and reproduce Gene Flow • Genes are transferred from one population to another. • Migration • People travel to another area and successfully mate with the population there. Genetic Drift • In small, reproductively isolated populations, chance can change the gene frequency. • The smaller the population, the more dramatic the change Genetic Drift • Very pronounced after a bottleneck • A severe reduction in population results in only a small population surviving • Gene frequencies are altered • Page 288-289 Natural Selection • Usually the most important mechanism of evolution • Environment selects the individuals with the best suited genotypes for survival and reproduction Natural Selection • For natural selection to cause evolution, it must select for or against one or more genotypes for a trait • AA Aa aa • AA and aa • AA or aa… and so on Frequency drops, but not to 0. • The a will never completely disappear as long as there are heterozygotes (Aa) • It is not a disadvantage to the heterozygote Selection against one of the homozygotes (aa) Expected offspring genotypes Possible parent mating patterns AA AA X AA 4 AA X Aa 2 2 Aa X AA 2 2 Aa X Aa 1 2 1 6 ( 38% ) 1 ( 6% Total 9 ( 56% ) Aa aa Selection against aa Directional Selection • Allele frequencies tend to shift in a consistent direction • In response to the environment, or a new mutation gets it started • One end of the range becomes more common than the midrange Peppered moth example; page 282 Stabilizing Selection • Intermediate forms are favored. • Tends to counter mutation, gene flow, and genetic drift • Could favor the heterozygote • Page 284 Disruptive Selection • Forms at both ends of the range are favored; the intermediate forms are selected against • Page 285 Speciation An example of microevolution What is a species? • A species consists of organisms that can interbreed and produce fertile offspring • A horse and a donkey can interbreed to produce a mule, but the mule is not fertile New species emerge… • As a result of reproductive isolation • As a result of geographic isolation • Populations become cut off from each other, and evolve separately Reproductive isolation • Any heritable feature of body form, function, or behavior prevents interbreeding • Not necessary to have a physical separation • Prezygotic or Postzygotic • Pages 294-295 Geographical isolation • Physically separated • Could by mountains, river, body of water separating islands, etc. Geographical isolation • Allopatric speciation: a physical barrier intervenes between populations and prevents gene flow among them • Hawaii, Galapagos Islands, Florida Keys Sympatric Speciation • A species may form within the home range of an existing species • No physical barrier Parapatric Speciation • Neighboring populations become distinct species, while maintaining a hybrid zone Bullock’s oriole range Baltimore oriole range Adaptive Radiation • A burst of different species from a single lineage • May be due to physical access to a new habitat or • Key innovations may permit better survival Classification Five or six kingdoms? The Old 5 Kingdom System The Old 5 Kingdom System • All the bacteria were grouped into Kingdom Monera • Monera included eubacteria and archaebacteria New relationships discovered • In the 1970’s, with better methods to analyze biochemical makeup and sequence DNA, huge differences emerged between eubacteria and archaebacteria Differences emerge • Archaebacteria live in harsh environments • Subdivided into three groups bases on habitat: methanogens, thermoacidophiles, and extreme halophiles Archeabacteria • Methanogens are anaerobic, and are found in swamps, marshes, sewage treatment plants, digestive tracts • Produce methane Archeabacteria • Extreme halophiles live in very salty water • Use salt to generate ATP • Found in Dead Sea, Great Salt Lake Archaebacteria • Thermoacidophiles live in extremely hot and acidic water • Temp of 110 C, and pH of 2 • Hot springs, volcanic vents, cracks on ocean floor that leak scalding water The New 6 Kingdom System Higher organisms are more closely related to the archaebacteria than to the eubacteria. Showing relationships • Phylogeny: evolutionary relationships between species, starting with ancestral forms and showing branches leading to descendants Showing relationships • Phylogeny can be shown in an evolutionary tree or a cladogram Showing relationships Showing relationships Taxonomy • Identifies, names and classifies species • Binomial system • Scientific name is Genus species • Homo sapiens