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EVOLUTION NOTES Evolution o Change in gene frequency / species over time o Unifying theory of biology based on scientific observation o Occurs in populations – not individuals. Microevolution Change in a population’s alleles over a period of time (small scale) still the same species. Macroevolution Large changes recorded in the fossil record (large scale) and gives rise to new species. Associated Theories and Concepts: Catastrophism – successive changes in species was caused by major catastrophes Gradualism – Evolution in slow gradual steps Punctuated equilibrium – short periods of rapid species formation followed by long periods of little evolution Lemarck’s theory o Organisms develop new organs or change their structures to meet changes in their environment (use it or lose it) o Inheritance of acquired traits – traits acquired during a lifetime could be passed on to next generation Darwin’s theory o all species reproduce in excess of the numbers that can survive o all organisms compete for limited resources o variations exist within a species o environment selects for the more advantageous variations Needed for evolution to occur 1. Means of increasing Variation Mutations – changes in nucleotide sequence of DNA Recombination – reshuffling of genetic material during meiosis Gene flow – gene frequency changes due to immigration from other populations 2. Means of decreasing variation o Natural selection – organisms with more advantageous traits (genes) will survive more often to produce off-spring. Those without those traits will be naturally selected not to survive. This process drives evolution. o Genetic drift – random events cause change in gene frequency (small Populations) o Gene flow – gene frequency changes due to emigration Speciation: When a group of one species is cut off from the rest of the population and gene flow is stopped. Each group is acted on by local selective conditions. Observations that led to, and support evolution Fossils Any preserved remnant or impression left by organisms that lived in the past. o Relative dating – superimposition of sedimentary rocks tells the relative age of fossils o Absolute dating – dating using radioactive isotopes (Potassium 40, Rubidium 87, Uranium 238, Carbon 14) o Transitional forms – Archeoptryx and similar bird-like reptiles. Absence of some forms can also be used as an argument against evolution. Homologous structures Structures that share a common ancestry. Modified versions of the same structure. Vestigial structures Remnants of an organism’s evolutionary past. The structure serves no purpose at this time. DNA comparison Protein comparison