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Evolution – genetic change over time Oldest multicellular fossil Oldest fossil prokaryotic cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 13-1b Great Britain Europe Asia North America PACIFIC OCEAN The Galápagos Islands PACIFIC OCEAN Pinta Marchena Pinzón Isabela 0 0 40 km Equator Daphne Islands Santa Santa Cruz Fe Florenza 40 miles Africa San Cristobal Española PACIFIC OCEAN Equator South America Genovesa Santiago Fernandina ATLANTIC OCEAN Australia Cape of Good Hope Cape Horn Tierra del Fuego Tasmania New Zealand Natural Selection Darwin proposed natural selection as the mechanism of evolution •Organisms vary in many characteristics that can be inherited •Excessive numbers of organisms lead to a struggle for survival •Organisms produce more offspring than the environment can support What is a Species? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 13-2c Natural selection is supported by evidence from artificial selection African wild dog Coyote Wolf Thousands to millions of years of natural selection Ancestral canine Fox Jackal LE 13-4a –Common embryonic structures in all vertebrates are evidence for common descent Human Cat Whale Bat LE 13-4b Pharyngeal pouches Post-anal tail Chick embryo Human embryo LE 13-5b Chromosome with gene conferring resistance to pesticide Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow Pesticide application Survivor • Examples of evolutionary adaptation reveal three key points about natural selection – Natural selection is more of an editing process than a creative mechanism – Natural selection is contingent on time and place – Significant evolutionary change can occur in a short time Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Studying evolution at the population level – Evolution: change in the prevalence of certain heritable characteristics in a population over a span of generations – Gene pool: the total collection of genes in a population at any one time – Microevolution: a change in the relative frequencies of alleles in a gene pool – Species: a group of populations capable of interbreeding and producing fertile offspring Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 13-9a In addition to natural selection, other events can contribute to evoluti Original population Bottlenecking event Surviving population LE 13-12a A1 Parents A2 A1 A3 Meiosis A1 Gametes A2 A3 LE 13-12b A1 A2 A3 Gametes Fertilization Offspring, with new combinations of alleles A1 A1 A2 and A3 CONNECTION 13.13 The evolution of antibiotic resistance in bacteria is a serious public health concern • Natural selection has led to the evolution of antibiotic-resistant bacteria • Overuse and misuse of antibiotics has contributed to the proliferation of antibiotic-resistant strains Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neutral traits 13.15 The perpetuation of genes defines evolutionary fitness • Evolutionary fitness is the relative contribution an individual makes to the gene pool of the next generation • Survival of genes depends on production of fertile offspring • Selection indirectly adapts a population to its environment by acting on phenotype Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 13-16 Original population Evolved population Frequency of individuals Natural selection can alter variation in a population Original population Phenotypes (fur color) Stabilizing selection Directional selection Disruptive selection 13.18 Natural selection cannot fashion perfect organisms • There are at least four reasons why natural selection cannot produce perfection – Organisms are limited by historical constraints – Adaptations are often compromises – Chance and natural selection interact – Selection can only edit existing variations Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings