BSC2011 Exam 3 ReviewSLIDE SET 12Evolution: species change over time and new species arise by the modification of earlier speciesPlato: “essentialism”, believed that God created all things with a constant and perfect essence/ideal form- Variation is an imperfect reflection of inner essence- Species don’t change! No new species!Aristotle: scala naturae (scale of nature), all living things are fixed in a hierarchy - Species don’t/can’t/shouldn’t change!Carolus Linnaeus- Organized life into nested classification system based on similar appearance- Each type has binomial scientific name (genus & species)o Kingdom, Phylum, Class, Order, Family, Genus, SpeciesGeorges Cuvier: early paleontologist and natural theologian- Catastrophism:o Proponents accepted divine creationo Believed in relatively young age for the eartho Sporadic catastrophes caused appearance and disappearance of organisms in the fossil recordo No evolution!James Hutton: geologist- Geologic gradualism:o Geological features were formed by slow gradual processes (i.e. erosion) over long periods of timeCharles Lyell: geologist- Uniformitarianismo Mechanisms of geologic change are constant over timeo The same processes are operating today as in the past, at same rateo The earth is very oldJean Baptiste Lamarck- Species evolve by gradually changing to adapt to environment- “Use and disuse” and “inheritance of acquired characteristics” both proven to be incorrecto Weisman disproved inheritance theory by cutting tails off of miceThomas Malthus: demographer & political economist- Said the fate of the poor is inescapable because their reproduction exceeds their means of sustenanceo First suggestion of natural selection and competition leading to survival of the fittestCharles Darwin- 1831, unpaid naturalist on 5-year voyage of HMS Beagle- Expanded on Malthus’ idea by applying concept to animals and plants- Natural selection: Darwin’s proposed hypothesis to explain why/how species evolveo Obs. 1: organisms have great potential for fertility (exponential growth)o Obs. 2: natural resources are limitedo Obs. 3: natural populations normally to not increase exponentially, but remain fairly constant Inference: struggle for existence occurs within a populationo Obs. 4: phenotypic variation occurs among individuals of a specieso Obs. 5: variation is heritable Inference: there is differential survival and reproduction among individuals in a population favoring advantageous trait Inference: NS gradually results in individuals with new adaptations, perhaps new specieso Alfred Wallace had a similar view of evolution by NS- Darwin’s Model of Natural Selection1. Within a population, more offspring are produced than can survive; leads to competition for resources, struggle for existence2. Random variation exists in all organisms, and much of this variation is heritable3. Some of this variation affects fitness; ability to survive and reproduce is not random4. Better adapted individuals survive and produce more offspring, pass on their adaptive genes5. Results in a change in gene composition from one generation to the next; basic definition of evolution!Microevolution: the gradual evolution of traits within a population of a species over time; populations evolve, not individualsMacroevolution: the evolution of an entirely new speciesAdaptive radiation: when populations of an ancestral species “radiate” into several new species, each adaptedby natural selection to a distinct environment or lifestyle. - Example: finch species arising in different locationsConvergent evolution: when unrelated species evolve to look similar, not because of common ancestry but because they adapted to similar environments in similar waysComparative Anatomy- G. Buffon (anatomist) suggested that species could be similar because they descended from a common ancestor- Homology: similarity caused by shared ancestryo Homologous structures share common ancestry, but not necessarily similar functiono Example: human arm, whale fin, cat leg, bat wing- Analogy: similarity in function, but not common ancestryo Example: dragonfly wing, bird wingVestigial structures: “remnants” of once-functional ancestral structures- Human appendix, tail boneEvidence for Evolution- Comparative embryology; von Baer’s Law- Molecular biology: the more closely two species share a common ancestor, the more similar their proteins & DNA- Artificial selection: new species created from common ancestor via selective breeding by humanso Dog breeds: evidence of microevolutionSLIDE SET 13Hugo de Vries: noted occasional spontaneous appearance of new heritable variants in true-breeding flowers- Called these “mutations”; source of novel hereditary variationThe Modern (“Neo-Darwinian”) Synthesis: reconciles Darwin’s views of evolution with Mendel’s genetic findings1. Heredity is controlled by genes2. Genes are subject to random mutations which generate genetic variation (new alleles) among individuals3. NS chooses alleles that confer reproductive successo The frequency of favorable alleles increases over generations in a population (microevolution)o Perhaps over time new species may arise (macroevolution)The study of evolution, in its most simple form, is the study of changes in allele frequencies and allele combinations in a population- Population: a group of interbreeding individuals of the same speciesHardy-Weinberg Equilibrium: -No net change in allele frequency, no evolution as long as:1. The population is large2. There is no mutation3. There is no immigration or emigration4. Mating is random5. All individuals survive and reproduce with equal success; no NS- Fixed: when only one allele is present in a population; all individuals are homozygous for a trait- p + q = 1-p2+2 pq+ q2=1op2 = probability of homozygous p genotypeo 2pq = probability of heterozygous pq genotypeoq2 = probability of homozygous q genotypeo If expected frequencies are not observed, population is not in H-W equilibrium; no evolving!- For three alleles: p + q + r = 1; p2+q2+r2+2 pq+2 pr+ 2qr =1Forces that disrupt H-W Equilibrium:1. Genetic drift in small population (reduces genetic variation over time; eventual fixation of one allele)o Genetic drift: random/unpredictable changes in allele frequencies due to chance sampling events that have a big effect in small populations (i.e. moose stepping on a population of flowers); two major types:o Founder effect: when a small number of
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