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BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 13 How Populations Evolve Modules 13.1 – 13.3 From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Clown, Fool, or Simply Well Adapted? • All organisms have evolutionary adaptations – Inherited characteristics that enhance their ability to survive and reproduce • The blue-footed booby of the Galápagos Islands has features that help it succeed in its environment – Large, webbed feet help propel the bird through water at high speeds Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings EVIDENCE OF EVOLUTION 13.1 A sea voyage helped Darwin frame his theory of evolution • Aristotle and the culture of the 1800’s believed that species are fixed • Fossils suggested that life forms change – This idea was embraced by Lamarck in the early 1800s Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • While on the voyage of the HMS Beagle in the 1830s, Charles Darwin observed – similarities between living and fossil organisms – the diversity of life on the Galápagos Islands, such as blue-footed boobies and giant tortoises Figure 13.1A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The voyage of the Beagle Great Britain Europe North America Pacific Ocean Atlantic Ocean Africa Galápagos Islands Equator South America Australia Cape of Good Hope Tasmania Cape Horn Tierra del Fuego New Zealand Figure 13.1B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Darwin became convinced that the Earth was old and continually changing – He concluded that living things also change, or evolve over generations – He also stated that living species descended from earlier life-forms: descent with modification Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.2 The study of fossils provides strong evidence for evolution • Fossils and the fossil record strongly support the theory of evolution – Hominid skull – Petrified trees Figure 13.2A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Scorpion in amber – “Ice Man” Figure 13.2E, F Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The fossil record shows that organisms have appeared in a historical sequence • Many fossils link early extinct species with species living today – These fossilized hind leg bones link living whales with their land-dwelling ancestors Figure 13.2G, H Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.3 A mass of evidence validates the evolutionary view of life • Other evidence for evolution comes from – Biogeography – Comparative anatomy – Comparative embryology Human Cat Whale Bat Figure 13.3A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Molecular biology Human Rhesus monkey Last common ancestor lived 26 million years ago (MYA), based on fossil evidence Mouse Chicken Frog Lamprey 80 MYA 275 MYA 330 MYA 450 MYA Figure 13.3B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DARWIN’S THEORY AND THE MODERN SYNTHESIS 13.4 Darwin proposed natural selection as the mechanism of evolution • Darwin observed that (Natural Selection) – organisms produce more offspring than the environment can support – organisms vary in many characteristics – these variations can be inherited – organisms that are better adapted leave more offspring Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin’s Four Criteria for Natural Selection to Occur • Overproduction of offspring leads to more offspring than environment can support • Variation in those offspring • Variations are inherited • Offspring that are better adapted to environment leave subsequently more offspring Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted • Darwin saw natural selection as the basic mechanism of evolution – As a result, the proportion of individuals with favorable characteristics increases – Populations gradually change in response to the environment Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment – This is called artificial selection Adopt me!! Figure 13.4A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.5 Connection: Scientists can observe natural selection in action • Evolutionary adaptations have been observed in populations of birds, insects, and many other organisms – Example: camouflage adaptations of mantids that live in different environments Figure 13.5A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The evolution of insecticide resistance is an example of natural selection in action Insecticide application Chromosome with gene conferring resistance to insecticide Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow Survivor Figure 13.5B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.6 Populations are the units of evolution • A species is a group of populations whose individuals can interbreed and produce fertile offspring • A population is a group of interbreeding individuals living in same place and same time. – Populations evolve, not individuals!!! Figure 13.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.7 Microevolution is change in a population’s gene pool over time • A gene pool is the total collection of genes in a population at any one time • Microevolution is a change in the relative frequencies of alleles in a gene pool Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.8 The gene pool of a nonevolving population remains constant over the generations • Hardy-Weinberg equilibrium states that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool – To test this, let’s look at an imaginary, nonevolving population of blue-footed boobies Webbing No webbing Figure 13.8A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists Phenotypes Genotypes WW Ww ww Number of animals (total = 500) 320 160 20 Genotype frequencies 320/ 500 = 0.64 Number of alleles in gene pool (total = 1,000) 640 W Allele frequencies 800/ 1,000 160/ 500 20/ = 0.32 160 W + 160 w = 0.8 W 200/ 1,000 500 = 0.04 40 w = 0.2 w Figure 13.8B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Recombination of alleles from parent generation SPERM EGGS WW p2 = 0.64 WW qp = 0.16 Ww pq = 0.16 ww q2 = 0.04 Next generation: Genotype frequencies 0.64 WW Allele frequencies 0.32 Ww 0.8 W 0.04 ww 0.2 w Figure 13.8C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.10 Five conditions are required for HardyWeinberg equilibrium • The population is very large • The population is isolated • Mutations do not alter the gene pool • Mating is random • All individuals are equal in reproductive success Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings What is Hardy-Weinberg Equilibrium???? • It just means that the gene pool is in equilibrium. • Allele frequency is not changing • POPULATION IS NOT EVOLVING!!! Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.11 There are several potential causes of microevolution • Genetic drift is a change in a gene pool due to chance – Genetic drift can cause the bottleneck effect Original population Bottlenecking event Surviving population Figure 13.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – or the founder effect Figure 13.11B, C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Gene flow can change a gene pool due to the movement of genes into or out of a population • Mutation changes alleles • Natural selection leads to differential reproductive success Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Five Fingers of Evolution (Causes of Microevolution) • Small population size • Non-random mating • Mutations • Gene flow (migration) • Natural selection Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.12 Adaptive change results when natural selection upsets genetic equilibrium • Natural selection results in the accumulation of traits that adapt a population to its environment – If the environment should change, natural selection would favor traits adapted to the new conditions Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings VARIATION AND NATURAL SELECTION 13.13 Variation is extensive in most populations • Phenotypic variation may be environmental or genetic in origin – But only genetic changes result in evolutionary adaptation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Many populations exhibit polymorphism and geographic variation Figure 13.13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.14 Connection: Mutation and sexual recombination generate variation A1 Parents A1 A2 A3 MEIOSIS A1 A2 A3 Gametes FERTILIZATION Offspring, with new combinations of alleles A1 A2 A1 A3 and Figure 13.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.15 Overview: How natural selection affects variation • Natural selection tends to reduce variability in populations – The diploid condition preserves variation by “hiding” recessive alleles – Balanced polymorphism may result from the heterozygote advantage Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.16 Not all genetic variation may be subject to natural selection • Some variations may be neutral, providing no apparent advantage or disadvantage – Example: human fingerprints Figure 13.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.17 Connection: Endangered species often have reduced variation • Low genetic variability may reduce the capacity of endangered species to survive as humans continue to alter the environment – Studies have shown that cheetah populations exhibit extreme genetic uniformity – Thus they may have a reduced capacity to adapt to environmental challenges Figure 13.17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.18 The perpetuation of genes defines evolutionary fitness • An individual’s Darwinian fitness is the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals • Production of fertile offspring is the only score that counts in natural selection Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.19 There are three general outcomes of natural selection Frequency of individuals Original population Phenotypes (fur color) Original population Evolved population Stabilizing selection Directional selection Diversifying selection Figure 13.19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.20 Sexual selection may produce sexual dimorphism • Sexual selection leads to the evolution of secondary sexual characteristics – These may give individuals an advantage in mating Figure 13.20A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.21 Natural selection cannot fashion perfect organisms • This is due to: – historical constraints – adaptive compromises – chance events – availability of variations Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings