Week 6- Natural Selection
Week 6- Natural Selection Biology 152
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This 4 page Class Notes was uploaded by BettyAnn Mead on Friday March 6, 2015. The Class Notes belongs to Biology 152 at University of Massachusetts taught by Peteh in Winter2015. Since its upload, it has received 49 views.
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Date Created: 03/06/15
What is the evidence for evolution Critiques of Natural Selection 0 Some traits are too complex 0 Counterargument 1 Cumulative selection Cumulative Selection For a population to evolve complex traits Each step of the evolution of the traits must confer an advantage on those that have it o Counterargument 2 Imperfections in nature 0 Nature of the evidence 0 Counterargument 3 Fossil record Gaps Every time you nd a new fossil that lls a gap it created two new gaps Paleontologists keep digging and nding new fossHs No surprise there are gaps since the creation of fossils is a rare event Fossil Genes Genes that have mutated into non functioning sequences that are still identi able Genetic Code Four different letter base pairs of DNA Arranged into three letter words that spell out names of amino acids Words arranged into sentences genes that describe a string of amino acid that form a protein Proteins are building blocks and regulators Changing a letter in a word can describe a different protein Change can have no a positive or a negative effect What happens to mutations Proteins determine traits If a trait is adaptive a change making it non adaptive will be selected against and it won t be passes on to the next generation If a mutation makes a trait that is adopted it will be selected for If a trait is no longer necessary then a mutation will be neutral and it ill be passed on o Counterargument 4 Homologous structures Homology A special type of similarity based on common evolutionary ancestry Immortal Genes Genes that are shared by all forms of life Evolved early in the evolution of life Necessary for basic functions Convergent Evolution 0 Some similarities are analogies not homologies Due to common environmental pressures not common inher ance Super cially similar features evolve independent and do NOT indicate evolutionary relatedness o Counterargument 1 Arti cial selection 0 Counterargument 2 Actual observations Evidence for Evolution 1 Different species are related homologies 2 Species change over time Fossils of extinct organisms Fossil quotseriesquot showing replacement of one type of organism with a similar but different one o Vestigial traits 3 Observations of Natural Selection Evolution Pattern and Process Pattern Descent with modi cation Process Natural selection 0 The mechanism of evolution Natural Selection Darwin s approach Observation and Inference lnference The process of deriving logical conclusions from premises known or assumed to be true Observations 1amp2 Over production 0 Reproductive rates are high 0 But population sizes are relatively constant 0 Inference More individual are born then survive 0 Conclusion Individuals compete to survive and reproduce Observation 3 Variability o The individuals in a population are not identical 0 Inference Some individuals have traits that help them survive 0 Conclusion The subset of the population that survives long enough to reproduce is not a random sample Differential Reproduction Observation 4 Inheritance Some of the traits that vary among individuals can be passed to offspring o Inference Favorable traits will be more common in the next generation 0 Conclusions Individuals whose traits allow them to best survive are reproduce will leave the most offspring Those offspring will inherit the favorable traits Summary of Natural Selection 0 Competition Variation 0 Differential representation of favored phenotypes in succeeding generations 0 Over periods of time changes accumulate Darwinian Fitness The ability of an individual to survive and reproduce Measured in terms of relative reproductive success Adaptation Inheritable traits help an individual to survive and reproduce ie That increases the tness of an individual relative to other individuals Selection Pressure or Agent of Selection The neutral or anthropogenic force that affects an individual s survival and reproduction Examples include predators soil moisture plant toxins and parasites Evidence of Natural Selection 0 Arti cial selection experiments 0 Observations of rapid evolution 0 Experiments in the eld A Few Points About Natural Selection 0 Individuals are selected but populations evolve 0 Even small differences in tness can be signi cant 0 The best phenotype depends on the environment which can change 0 Selection does not cause variation it edits variation Evolution Pattern and Process Darwin s and Wallace s contribution Complied copious evidence to document the pattern Recognize and described the process mechanism
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