BIO 200 Lecture Chapter 13, Fall 2016

© 2013 Pearson Education, Inc. Lectures by Edward J. Zalisko PowerPoint® Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition – Eric J. Simon, Jean L. Dickey, and Jane B. Reece Chapter 13 Chapter 13 How Populations Evolve CHARLES DARWIN AND THE ORIGIN OF SPECIES • Biology came of age on November 24, 1859. Charles Darwin published On the Origin of Species by Means of Natural Selection, an assemblage of facts about the natural world. © 2013 Pearson Education, Inc. • Darwin made three observations from these facts. 1. Life shows rich diversity. 2. There are similarities in life that allow the classification of organisms into groups nested within broader groups. 3. Organisms display many striking ways in which they are suited for their environments. CHARLES DARWIN AND THE ORIGIN OF SPECIES © 2013 Pearson Education, Inc. • In The Origin of Species, Darwin – proposed a hypothesis, a scientific explanation for his observations, – used hundreds of pages in his book to describe the evidence supporting his hypothesis, – made testable predictions, and – reported the results of numerous experiments he had performed. CHARLES DARWIN AND THE ORIGIN OF SPECIES © 2013 Pearson Education, Inc. • Darwin hypothesized that – present-day species are the descendents of ancient ancestors that they still resemble in some ways and – change occurs as a result of “descent with modification,” with natural selection as the mechanism. CHARLES DARWIN AND THE ORIGIN OF SPECIES © 2013 Pearson Education, Inc. • Natural selection is a process in which organisms with certain inherited characteristics are more likely to survive and reproduce than are individuals with other characteristics. • As a result of natural selection, a population, a group of individuals of the same species living in the same place at the same time, changes over generations. CHARLES DARWIN AND THE ORIGIN OF SPECIES © 2013 Pearson Education, Inc. • Natural selection leads to evolutionary adaptation, a population’s increase in the frequency of traits suited to the environment. • Natural selection thus leads to evolution, seen either as – a change in the genetic composition of a population over time or – on a grander scale, the entire biological history, from the earliest microbes to the enormous diversity of organisms that live on Earth today. CHARLES DARWIN AND THE ORIGIN OF SPECIES © 2013 Pearson Education, Inc. • Natural selection leads to – a population (a group of individuals of the same species living in the same place at the same time) changing over generations and – evolutionary adaptation. • In one modern definition of evolution, the genetic composition of a population changes over time. CHARLES DARWIN AND THE ORIGIN OF SPECIES © 2013 Pearson Education, Inc. Darwin’s Cultural and Scientific Context • The Origin of Species was fundamentally different from the prevailing scientific and cultural views of Darwin’s time. • Let’s place Darwin’s ideas in their historical context. © 2013 Pearson Education, Inc. The Idea of Fixed Species • The Greek philosopher Aristotle held the belief that species are fixed and do not evolve. • The Judeo-Christian culture fortified this idea with – a literal interpretation of the biblical book of Genesis and – the suggestion that Earth may only be 6,000 years old. • Naturalists were grappling with the interpretation of fossils, imprints or remains of organisms that lived in the past. © 2013 Pearson Education, Inc. Lamarck and Evolutionary Adaptations • Naturalists compared fossil forms with living species and noted patterns of similarities and differences. • In the early 1800s, French naturalist Jean Baptiste Lamarck suggested that life evolves, and explained this evolution as the refinement of traits that equip organisms to perform successfully in their environment. © 2013 Pearson Education, Inc. • Lamarck suggested a mechanism that we now know is wrong. • Lamarck proposed that by using or not using its body parts, an individual may develop certain traits that it passes on to its offspring, thus, acquired traits are inherited. • Lamarck helped set the stage for Darwin by proposing that species evolve as a result of interactions between organisms and their environment. Lamarck and Evolutionary Adaptations © 2013 Pearson Education, Inc. Figure 13.4 Darwin in 1840 North America Great Britain Europe Asia Africa South America Cape of Good Hope Cape Horn Tierra del Fuego Australia Tasmania New Zealand HMS Beagle ATLANTIC OCEAN PACIFIC OCEAN Equator Equator PACIFIC OCEAN Fernandina Isabela Pinta Marchena Santiago Pinzón Daphne Islands Genovesa Florenza Española Santa Cruz Santa Fe San Cristobal 40 km 40 miles 0 0 Galápagos Islands • On his journey on the Beagle, Darwin – collected thousands of specimens and – observed various adaptations in organisms. The Voyage of the Beagle © 2013 Pearson Education, Inc. • Darwin was intrigued by – the geographic distribution of organisms on the Galápagos Islands and – similarities between organisms in the Galápagos and those in South America. The Voyage of the Beagle © 2013 Pearson Education, Inc. • Darwin was strongly influenced by the writings of geologist Charles Lyell. • Lyell suggested that Earth – is very old and – was sculpted by gradual geological processes that continue today. The Voyage of the Beagle © 2013 Pearson Education, Inc. • Darwin reasoned that the extended time scale would allow for gradual changes to occur – in species and – in geologic features. The Voyage of the Beagle © 2013 Pearson Education, Inc. Descent with Modification • Darwin made two main points in The Origin of Species. 1. Organisms inhabiting Earth today descended from ancestral species. 2. Natural selection is the mechanism for descent with modification. © 2013 Pearson Education, Inc. EVIDENCE OF EVOLUTION • Evolution leaves observable signs. • We will examine five of the many lines of evidence in support of evolution: 1. the fossil record, 2. biogeography, 3. comparative anatomy, 4. comparative embryology, and 5. molecular biology. © 2013 Pearson Education, Inc. The Fossil Record • Fossils are – imprints or remains of organisms that lived in the past – often found in sedimentary rocks. © 2013 Pearson Education, Inc. The Fossil Record • The fossil record – is the ordered sequence of fossils as they appear in rock layers, – reveals the appearance of organisms in a historical sequence, and – fits with the molecular and cellular evidence that prokaryotes are the ancestors of all life. © 2013 Pearson Education, Inc. • Paleontologists (scientists who study fossils) have discovered many transitional forms that link past and present. • Transitional fossils include evidence that – birds descended from one branch of dinosaurs and – whales descended from four-legged land mammals. The Fossil Record © 2013 Pearson Education, Inc. Biogeography • Biogeography, the study of the geographic distribution of species, first suggested to Darwin that today’s organisms evolved from ancestral forms. • Darwin noted that Galápagos animals resembled species of the South American mainland more than they resembled animals on similar but distant islands. © 2013 Pearson Education, Inc. • Many examples from biogeography would be difficult to understand, except from an evolutionary perspective. • One example is the distribution of marsupial mammals in Australia. Biogeography © 2013 Pearson Education, Inc. Comparative Anatomy • Comparative anatomy – is the comparison of body structure between different species and – attests that evolution is a remodeling process in which ancestral structures become modified as they take on new functions. © 2013 Pearson Education, Inc. Comparative Anatomy • Homology is – the similarity in structures due to common ancestry and – illustrated by the remodeling of the pattern of bones forming the forelimbs of mammals for different functions. © 2013 Pearson Education, Inc. • Vestigial structures – are remnants of features that served important functions in an organism’s ancestors and – now have only marginal, if any, importance. Comparative Anatomy © 2013 Pearson Education, Inc. Comparative Embryology • Early stages of development in different animal species reveal additional homologous relationships. – For example, pharyngeal pouches appear on the side of the embryo’s throat, which – develop into gill structures in fish and – form parts of the ear and throat in humans. – Comparative embryology of vertebrates supports evolutionary theory. © 2013 Pearson Education, Inc. Molecular Biology • The hereditary background of an organism is documented in – its DNA and – the proteins encoded by the DNA. • Evolutionary relationships among species can be determined by comparing – genes and – proteins of different organisms. © 2013 Pearson Education, Inc. Figure 13.11 Percent of selected DNA sequences that match a chimpanzee’s DNA Chimpanzee 100% 96% 92% Human Gibbon Orangutan Gorilla Primate Old World monkey NATURAL SELECTION • Darwin noted the close relationship between adaptation to the environment and the origin of new species. • The evolution of finches on the Galápagos Islands is an excellent example. © 2013 Pearson Education, Inc. Darwin’s Theory of Natural Selection • Darwin based his theory of natural selection on two key observations. 1. All species tend to produce excessive numbers of offspring. 2. Organisms vary, and much of this variation is heritable. © 2013 Pearson Education, Inc. Natural Selection in Action • Examples of natural selection include – pesticide-resistant insects, – antibiotic-resistant bacteria, and – drug-resistant strains of HIV. © 2013 Pearson Education, Inc. Figure 13.15-1 Chromosome with gene conferring resistance to pesticide Insecticide application Figure 13.15-2 Chromosome with gene conferring resistance to pesticide Insecticide application Figure 13.15-3 Chromosome with gene conferring resistance to pesticide Reproduction Survivors Insecticide application Evolutionary Trees • Darwin saw the history of life as analogous to a tree. – The first forms of life on Earth form the common trunk. – At each fork is the last common ancestor to all the branches extending from that fork. – The tips of millions of twigs represent the species living today. © 2013 Pearson Education, Inc. Figure 13.17 Tetrapod limbs Amnion Feathers Lungfishes Mammals Amphibians Lizards and snakes Crocodiles Hawks and other birds Ostriches Amniotes Tetrapods Birds Common ancestor of lineages to the right Homologous trait shared by all groups to the right 2 1 3 4 6 5 THE MODERN SYNTHESIS: DARWINISM MEETS GENETICS • The modern synthesis is the fusion of – genetics with – evolutionary biology. © 2013 Pearson Education, Inc. Populations as the Units of Evolution • A population is – a group of individuals of the same species, living in the same place at the same time and – the smallest biological unit that can evolve. © 2013 Pearson Education, Inc. • The total collection of alleles in a population at any one time is the gene pool. • When the relative frequency of alleles changes over a number of generations, evolution is occurring on its smallest scale. Populations as the Units of Evolution © 2013 Pearson Education, Inc. Genetic Variation in Populations • Individual variation abounds in all species. – Not all variation in a population is heritable. – Only the genetic component of variation is relevant to natural selection. © 2013 Pearson Education, Inc. • Variable traits in a population may be – polygenic, resulting from the combined effects of several genes, or – determined by a single gene. • Polygenic traits tend to produce phenotypes that vary more or less continuously. • Single-gene traits tend to produce only a few distinct phenotypes. Genetic Variation in Populations © 2013 Pearson Education, Inc. Sources of Genetic Variation • Genetic variation results from processes that both involve randomness: 1. mutations, changes in the nucleotide sequence of DNA, and 2. sexual recombination, the shuffling of alleles during meiosis. © 2013 Pearson Education, Inc. Sources of Genetic Variation • For any given gene locus, mutation alone has little effect on a large population in a single generation. • Organisms with very short generation spans, such as bacteria, can evolve rapidly with mutation as the only source of genetic variation. © 2013 Pearson Education, Inc. Analyzing Gene Pools • A gene pool – consists of all the alleles in a population at any one time and – is a reservoir from which the next generation draws its alleles. • Alleles in a gene pool occur in certain frequencies. © 2013 Pearson Education, Inc. • Alleles can be symbolized by – p for the relative frequency of the dominant allele in the population, – q for the frequency of the recessive allele in the population, and – p + q = 1. • Note that if we know the frequency of either allele in the gene pool, we can subtract it from 1 to calculate the frequency of the other allele. Analyzing Gene Pools © 2013 Pearson Education, Inc. • Genotype frequencies can be calculated from allele frequencies (if the gene pool is stable = not evolving). • The Hardy-Weinberg formula – p2 + 2pq + q2 = 1 – can be used to calculate the frequencies of genotypes in a gene pool from the frequencies of alleles. Analyzing Gene Pools © 2013 Pearson Education, Inc. Figure 13.20 Figure 13.21 Allele frequencies Genotype frequencies Sperm Eggs p  0.8 (R) q  0.2 (r) p  0.8 R q  0.2 r RR p  0.8 R q  0.2 r p2  0.64 rR pq  0.16 q2  0.04 rr pq  0.16 Rr (RR) p2  0.64 q2  0.04 (rr) 2pq  0.32 (Rr) Population Genetics and Health Science • The Hardy-Weinberg formula can be used to calculate the percentage of a human population that carries the allele for a particular inherited disease. © 2013 Pearson Education, Inc. Population Genetics and Health Science • PKU – is a recessive allele that prevents the breakdown of the amino acid phenylalanine and – occurs in about one out of every 10,000 babies born in the United States. • People with PKU must strictly regulate their dietary intake of the amino acid phenylalanine. © 2013 Pearson Education, Inc. Figure 13.22 INGREDIENTS: SORBITOL, MAGNESIUM STEARATE, ARTIFICIAL FLAVOR, ASPARTAME† (SWEETENER), ARTIFICIAL COLOR (YELLOW 5 LAKE, BLUE 1 LAKE), ZINC GLUCONATE. †PHENYLKETONURICS: CONTAINS PHENYLALANINE Microevolution as Change in a Gene Pool • How can we tell if a population is evolving? • A non-evolving population is in genetic equilibrium, also known as Hardy-Weinberg equilibrium, meaning the population’s gene pool is constant over time. • From a genetic perspective, evolution can be defined as a generation-to-generation change in a population’s frequencies of alleles, sometimes called microevolution. © 2013 Pearson Education, Inc. MECHANISMS OF EVOLUTION • The main causes of evolutionary change are – genetic drift, – gene flow, and – natural selection. • Natural selection is the most important, because it is the only process that promotes adaptation. © 2013 Pearson Education, Inc. Genetic Drift • Genetic drift is a change in the gene pool of a small population due to chance. © 2013 Pearson Education, Inc. The Bottleneck Effect • The bottleneck effect – is an example of genetic drift and – results from a drastic reduction in population size. • Passing through a “bottleneck,” a severe reduction in population size, – decreases the overall genetic variability in a population because at least some alleles are lost from the gene pool, and – results in a loss of individual variation and hence adaptability. © 2013 Pearson Education, Inc. Figure 13.24-1 Original population Figure 13.24-2 Original population Bottleneck event Figure 13.24-3 Original population Bottleneck event Surviving population