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Evolution History of Evolution Aristotle- all living forms arranged on a scale of increasing complexity, species are perfect and do not evolve Natural theology: species are individually designed and perfect Linnaeus- founder of taxonomy, developed 2 part naming system (binomial nomenclature) Cuvier- founder of paleontology; advocated catastrophism Hutton- gradualism, change happens over time Lyell- uniformitarianism; geological processes have not changed over time Lamarck- use and disuse, “felt needs”, adaptation to the environment Darwin Origin of new species and adaptation to the environment are intertwined (Alfred Wallace) Descent with modification Natural selection Darwin’s Inferences Natural selection is the unequal success of individuals when surviving and reproducing Natural selection comes out of the relationship with the environment Product of natural selection= adaptation Tenets of Natural selection Populations evolve Can only exaggerate or diminish traits that can be inherited Situational Support of Evolution Fossil record Comparative anatomy Comparative embryology Molecular biology Population Genetics Before Population Genetics Before population genetics the science of genetics was contradictory to evolution. Geneticists recognized “either-or” traits. They hadn’t yet learned that most physical characteristics are controlled by more than one gene so having a continuum in a trait was counterintuitive to their findings. There was no genetic basis to support Darwin’s findings. Population Genetics Recognizes the continuum and large variation of traits Modern Synthesis First main comprehensive theory involving population genetics Integrated discoveries from different disciplines Tenets of Modern Synthesis theory Populations are the units of evolution Natural selection= primary mode of evolution Importance of gradualism The effect of location on evolution Effect of location on evolution Species vs. populations Populations that are isolated from others of the same species by geographic boundaries exchange genetic material with others outside of their population occasionally, if at all. This may cause a divergence in populations of the same species that have been separated by a geographic barrier. The gene pool All of the genes in a population at any one time Fixed alleles Allelic frequency 300 dogs in population. Brown (B) is dominant to white (b). 50 white dogs, 250 brown dogs (150 homozygous, 100 heterozygous) Allelic frequency Example: 300 dogs in population. Brown (B) is dominant to white (b). 50 white dogs, 250 brown dogs (150 homozygous, 100 heterozygous) Total of 600 copies of allele for fur color Copies of dominant allele (B): 150*2 (BB)+100= 400 Frequency of B allele= 400/600= 0.667=66.7% So b allele frequency= 100%-66.6%= 33.3% Genotype frequency: BB= 150/300=0.5 Bb= 100/300=0.33 bb= 50/300=.166 Hardy Weinberg Equilibrium Describes a non evolving population Allelic and genotypic frequencies remain constant over generations unless acted on by something other than sex Equation: (p + q) x (p + q)= p2 + 2pq + q2 (allelic frequency of male x allelic frequency of female) Hardy-Weinberg Equilibrium Assumptions Very large population (smaller populations mean more chance for changes in allelic frequency) No gene flow No mutations Random mating No natural selection Microevolution Generation-to-generation change in population’s allele or genotype frequencies If populations deviate from the baseline provided by H-W equilibrium then population is evolving Practice Hardy-Weinberg Equilibrium problems What causes microevolution? Genetic drift Gene flow Mutation Nonrandom mating Natural selection *only natural selection adapts population to nature Genetic Drift Changes in the gene pool of a small population from chance Can be caused by: Bottleneck effect and founder effect Bottleneck Effect Unselective event that greatly diminishes the population Resulting population frequencies will not be indicative of the original population Bottleneck effect combined with genetic drift reduce genetic variability Founder Effect Genetic drift caused by a small number of individuals colonizing a new area May account for higher populations of inherited disorders in certain places (islands) Gene flow Due to migration (immigration, emigration) Introduction of new genes or just alteration of gene frequencies Mutations Changes in organism’s DNA Can alter phenotypic frequencies Nonrandom mating In reality mate with closer neighbors more often. This eventually creates inbreeding which alters allelic frequencies. Assortive mating: like selects like Natural Selection Differential success in reproduction The organisms better adapted to their environment will live longer, produce more offspring and those offspring will have a better chance of survival than others who are not as well adapted Accumulates and maintains favorable traits in the environment Not all variation is heritable Phenotype= genotype + environmental influence Only the genetic component of this has evolutionary consequences (remember Lamarck) Variation within Populations Polymorphism: 2 or more forms of a discrete (either-or) trait are present in the population ex: freckles, blood type (4 morphs) non examples: height, weight, hair color (no characteristics that vary continuously) Variation between Populations Geographical variation Natural selection Genetic drift clines Genetic variation from other factors Mutation Sexual recombination The fact that most organisms are diploid hides many genetic variations (recessives even harmful ones can continue on for generations even if they don’t physiologically manifest) Heterozygote advantage Frequency dependent selection Types of selection Disruptive/diversifying Directional Stabilizing Disruptive selection Directional Selection Stabilizing selection Sexual selection Females choose males with certain traits Those traits are perpetuated with greater intensity