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Introduction to Biology (Biol 1020) Chapter Summaries- Ch 13-27

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University of Guelph
BIOL 1020
Andreas Heyland

Introduction to Biology Chapter Summaries Chapter 13 How Populations Evolve Darwins Theory of Evolution 131 A Sea Voyage Helped Darwin Frame his Theory of EvolutionEvolution the idea that Earths many species are descendants of ancestral species that were different from those living today Darwins Cultural and Scientific ContextThe study of fossils the imprints or remains of organisms that lived in the pastJean Baptiste Lamarck suggested that the best explanation for the relationship of fossils to current organisms is that life evolves o He proposed that by using or not using its body parts an individual may change its traits and then pass those changes on to its offspring Darwins Sea VoyageDarwin realized that natural forces gradually changed Earths surface and that these forces are still operating in modern times o He had come to realize that the Earth was very old and constantly changing Darwins WritingsAlfred Wallace asked Darwin to evaluate the manuscript he had written to see if it merited publication which was presented together with Darwins ideasIn 1859 Darwin published his book titled On the Origin of Species by Means of Natural Selection in which he wrote that presentday species arose from a succession of ancestors o This is known as descent with modification or as we know it adaptation 132 Darwin proposed natural selection as the mechanism of evolutionArtificial selection humans choose the desirable traits and breed only organisms with those traits over many generationsDarwin deduced that the production of more individuals than the limited resources can support leads to a struggle for existence with only some offspring surviving in each generationThe essence of Natural selection is this unequal reproduction o Individuals whose traits better enable them to obtain food or escape predators or tolerate physical conditions will survive and reproduce more successfully passing these adaptive traits to their offspringo Natural selection the environment does the choose individuals with traits best suited to the environment survive and reproduce most successfully passing those adaptive traits3 key points about evolution by natural selection 1 Natural selection occurs through interactions between individual organisms and the environmentIndividuals do not evolve rather populations evolve 2 Natural selection can amplify or diminish only heritable traitsAn organism may be modified through its interactions with the environment during its lifetime but unless coded for in the genes of the organisms gametes such acquired characteristics cannot be passed on to offspring 3 Evolution is not goaldirected it does not lead to perfectly adapted organismsNatural selection is the result of the environmental factors that vary from place to place over time 133 Scientists can observe natural selection in actionAn example of natural selection in action is the evolution of pesticide resistance in hundreds of insect speciesA relatively small amount of poison dusted onto the crops may kill 999 of the insects but subsequent sprayings are less and less effective o The few survivors of the first pesticide wave are insects that are genetically resistant carrying an allele that somehow enables them to resist chemical attacks o The resistant individuals left reproduce and pass the alleles for pesticide resistance to their offspring o The proportion of pesticideresistant individuals thus increases in each generationThis example of evolutionary adaptation highlights 2 important points about natural selection 1 Natural selection is more an editing process than a creative mechanism 2 Natural selection is contingent on time and place it favours those heritable traits in a varying population that fit the current local environment 134 The Study of Fossils provides strong evidence for evolutionFossils result when a dead organism captured in sediment decays and leaves an empty mold that is later filled by minerals dissolved in water o The casts that form when minerals harden are replicas of the organismThe fossil record the sequence in which fossils appear within layers of sedimentary rock o Provides some of the strongest evidence for evolution o The rock forms in strata also known as layers o The fossil record reveals the historical sequence in which organisms evolved and radiometric dating helps determine the age of rocks and fossilsThe oldest known fossils dating from 35 billion years are prokaryotes which were the ancestors of all life 135 Many Types of Scientific Evidence Supports the Evolutionary View of Life BiogeographyIt was the geographic distribution of species known as biogeography that first suggested to Darwin that organisms evolve from ancestral species Comparative AnatomyAnatomical similarities between species give signs of common descantSimilarity in characteristics that results from common ancestry is known as homology o For examples the same skeletal elements make up the forelimbs for many animals but the functions of these forelimbs differ o If these structures were uniquely engineered we would expect that their basic designs would be very different o The logical explanation is that the arms forelegs flippers and wings of these different mammals are variations on an anatomical structure of an ancestral organism that over millions of years has become adapted to different functions o Anatomical similarities in different organism is called homologous structures features that often have different functions but are structurally similar because of common ancestryFor example at some point in animal developed all vertebrate embryos have a tail posterior to the anus as well as structures called pharyngeal throat pouches o These homologous pouches ultimately develop into structures with very different functions o Such as gills in fish and parts of ears and throat in humansInteresting homologies are leftover structures that are marginal or perhaps no importance to the organism o These vestigial structures are remnants of features that served important functions in the organisms ancestors Molecular BiologyAnatomical homology is not helpful in linking very distinctly related organisms such as plants and animals and microorganismsAdvances in molecular biology have enabled biologists to read a molecular history of evolution in the DNA sequence of organisms o If 2 species have homologous genes with sequences that match closely biologists conclude that these sequences mist have been inherited from a relatively recent common ancestor o The greater the number of sequences differences between species the more distant is their last common ancestorDarwins boldest hypothesis was that all lifeforms are related o Molecular biology provides strong evidence for this claim all forms of life use the same genetic language of DNA and RNA and the genetic code 136 Homologies indicate patterns of descent that can be shown on an evolutionary treeHomologous structures both anatomical and molecular can be used to determine the branching sequences of the evolutionary tree The Evolution of Populations 137 Evolution Occurs within PopulationsA population is a group of individuals of the same species that live in the same area and interbreed
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