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INTRO TO EVOLUTION AND NATURAL SELECTION Evolution:changes over time Populations and species can change Population: group of members of the same species living in the same place at the same time (first level of evolution, micro), change over time to adapt to environment Species: group of individuals that can mate and make fertile offspring → biological species concept (second level of evolution, macro) change over time makes new species, speciation Individuals cannot evolve only populations can Evolution is a change in proportions of genes Curvier and Fossils: Catastrophism Curvier was one of the first paleontologists Species used to exist that don’t anymore and species that exist now may have not existed in the past Catastrophism: the reason you saw different fossils in different strata of rock because all of the species in certain times went extinct Gradualism (Hutton): earth is gradually changing over time Uniformitarianism (Lyell): earth changing at a uniform rate Darwin thought that if earth is changing, then species must be too Lamarck: early theories on evolution Use and disuse: only correct idea Use it or lose it, parts of the body that are used heavily will be accentuated, but parts that are reduced will not be maintained (won’t waste energy) Inheritance of acquired characteristics: Characteristics created over an individual’s lifetime would be passed on Bonzai trees would not reproduce as small trees Natural Transformation of Species: each species naturally goes from simple to complex, no speciation and no extinction CHARLES DARWIN: traveled to Galapagos Islands and other places Came up with the idea of Natural Selection NOT the idea of evolution → On the Origin of Species on the Basis of Natural Selection “Descent with modification” Generation to generation change for a particular trait that takes place in a population, constantly changing to become better adapted to the environment → Natural Selection Environment is the driving force of natural selection Selection Pressures: control which traits are the most beneficial E.g. food source, temperature, avoid predation Theory of Natural Selection: differential reproductive success, different ability to pass on genes I. Organisms overproduce offspring Based on Charles Malthus’ idea that human pop will exceed resources II. Offspring are variation in appearance and function and some of those variations are heritable → variation is the fuel for selection Variation is created through genetic recombination (random fertilization, independent assortment, crossing over) originally from mutation III. Environmental resources are limited and those varied offspring must compete for their share → struggle for existence IV. Individuals best able to survive in the environment will survive and reproduce → differential inheritance of genes Adaptation to an environment causes changes within a population and the forming of new species, if changes build up and can no longer mate must be two new species Unity of Life: all organisms are similar (common ancestor) Diversity of Life: better adapted to unique environments Match between organisms and environment History of Life:phylogenetic tree tree with branches showing life’s diversity, and where the come from Alfred Russel Wallace: sent his ideas of natural selection to Darwin, Darwin’s ideas were more developed so only Darwin published Natural Selection in Action: Beak depth in a finch changes as an environment changes Drier years mean nuts they eat are harder → thick deep beaks survive Wetter years means nuts are easy to eat → beak depth decreases Drug and antibiotic resistance from bacteria and viruses Peppered moths got polluted, trees became darker as covered by soot and other material, peppered moths became darker for camouflage Artificial Selection: nature does not determine selected traits, but humans select them Wild mustard creates brussel sprouts, cabbage and broccoli, by selecting for various traits E.g. select for leaves, breed those to make kale Biogeography: geographical distribution of species Modern species are found where they are because they come from ancestors in the hose regions Fossil Record (palaeontology): deeper the rock fossil, older it is, can look progression of species over time Comparative Embryology: different stages in embryonic dev. Most animals look extreme similar in the womb, closer species are more similar embryonic development Comparative Anatomy: anatomical similarities between species, to determine common ancestry → evidences evolution Focuses on homology (w/ bones often), similarity from common ancestry Homologous structures: same structure but different function in different species, only different because of adaptation Analogous structures: structures that look similar, adapted to the same environment, but do not share a common ancestor, or similar structures Vestigial Structures: leftover pieces of from ancestors that used to serve a function when it was necessary Coccyx (tailbone) when humans had tails Molecular Biology: study molecules amino acids and DNA that are shared in common between species, distant species have less DNA base pairs in common Change in ratios (in phenotypes/genotypes, change in proportion of alleles, one of those alleles is being selected for) in a population over time Individuals cannot evolve, only populations can, generation after generation, it adapts better to the environment Population Genetics: combines evo with genetics to measure change taking place in a population Gene Pool: all alleles in a populations Genetic Variation: crucial for natural selection and evolution Measured by average heterozygosity, contains both alleles for a particular gene Natural Selection: selects for advantageous alleles within a population Evolution: when a population’s gene structure changes Gene structure: ratio of dominant alleles to ratio of recessive alleles AA:Aa:aa Hardy-Weinberg Theorem: measure the ratio of alleles and genotypes in a population Genetic structure of a non evolving population remains constant, in Hardy-Weinberg equilibrium p^2+2pq+q^2=1(100% of alleles, p + q =1) equation can measure ratio of genes in equilibrium If frequencies change over time then evolution has occurred, always begin by finding q^2, easy because only recessive expressing people have aa Measure frequency at time A and then at time B, if you find a difference in the ratios, then quantified evolution must be occurring Equilibrium Requirements: pop will not evolve in equilibrium can only use the equation in this theoretical state Genetic Drift: when a small random change has a large effect on a small population frequencies, doesn’t affect large pops Bottlenecking: when an event drastically reduces population size (disaster, disease event), will not reflect same frequencies of same population → microevolution, chance creates new frequencies Founder Effect: small subgroup moves away from large pop. will have a different ratio of genotypes of alleles than original → also microevolution, random events will change this pop. drastically NOT adaptive (doesn’t make population better) Isolation from other populations Gene Flow: when two different populations begin mating, reduce the differences between the populations (become similar) → microevolution, still evolving, movement of alleles betwee pops Mutations are the raw source where new variation is created (not the major source of variation though, that would be recombination) Nonrandom mating/Sexual Selection: just as important to drive evolution as natural selection, not adaptive, just about mating
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