BSC2011 Exam 3 Review SLIDE SET 12 Evolution species change over time and new species arise by the modification of earlier species Plato 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 Species Georges Cuvier early paleontologist and natural theologian Catastrophism Proponents accepted divine creation o o Believed in relatively young age for the earth o Sporadic catastrophes caused appearance and disappearance of organisms in the fossil record o No evolution James Hutton geologist Geologic gradualism of time Charles Lyell geologist Uniformitarianism Jean Baptiste Lamarck o Geological features were formed by slow gradual processes i e erosion over long periods o Mechanisms of geologic change are constant over time o o The same processes are operating today as in the past at same rate The earth is very old Species evolve by gradually changing to adapt to environment Use and disuse and inheritance of acquired characteristics both proven to be incorrect o Weisman disproved inheritance theory by cutting tails off of mice Thomas Malthus demographer political economist Said the fate of the poor is inescapable because their reproduction exceeds their means of sustenance First suggestion of natural selection and competition leading to survival of the fittest o Charles 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 evolve o Obs 1 organisms have great potential for fertility exponential growth o Obs 2 natural resources are limited o Obs 3 natural populations normally to not increase exponentially but remain fairly constant Inference struggle for existence occurs within a population o Obs 4 phenotypic variation occurs among individuals of a species o 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 species o Alfred Wallace had a similar view of evolution by NS Darwin s Model of Natural Selection 1 Within a population more offspring are produced than can survive leads to competition for resources struggle for existence Some of this variation affects fitness ability to survive and reproduce is not random 2 Random variation exists in all organisms and much of this variation is heritable 3 4 Better adapted individuals survive and produce more offspring pass on their adaptive genes 5 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 individuals Macroevolution the evolution of an entirely new species Adaptive radiation when populations of an ancestral species radiate into several new species each adapted by natural selection to a distinct environment or lifestyle Example finch species arising in different locations Convergent evolution when unrelated species evolve to look similar not because of common ancestry but because they adapted to similar environments in similar ways Comparative Anatomy G Buffon anatomist suggested that species could be similar because they descended from a common ancestor Homology similarity caused by shared ancestry o Homologous structures share common ancestry but not necessarily similar function o Example human arm whale fin cat leg bat wing Analogy similarity in function but not common ancestry o Example dragonfly wing bird wing Vestigial structures remnants of once functional ancestral structures Human appendix tail bone Evidence 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 humans o Dog breeds evidence of microevolution SLIDE SET 13 Hugo de Vries noted occasional spontaneous appearance of new heritable variants in true breeding flowers Called these mutations source of novel hereditary variation The Modern Neo Darwinian Synthesis reconciles Darwin s views of evolution with Mendel s genetic findings 1 Heredity is controlled by genes 2 Genes are subject to random mutations which generate genetic variation new alleles among individuals 3 NS chooses alleles that confer reproductive success o o The frequency of favorable alleles increases over generations in a population microevolution 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 species Hardy Weinberg Equilibrium No net change in allele frequency no evolution as long as 1 The population is large 2 There is no mutation 3 There is no immigration or emigration 4 Mating is random 5 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 1 o o o o For three alleles p q r 1 p2 q 2 r 2 2 pq 2 pr 2qr 1 p2 probability of homozygous p genotype 2pq probability of heterozygous pq genotype q 2 probability of homozygous q genotype If expected frequencies are not observed population is not in H W equilibrium no evolving Forces 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 Founder effect when a small number of individuals break off from a main population to colonize a new habitat genetic drift comes in 2 stages o Colonizers are most likely a random sample of the original population the new colony has
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