Chapter 13 How Populations Evolve 0 0 Clown

Chapter 13 How Populations Evolve 0

0 Clown, Fool, or Simply Well Adapted? • The blue-footed booby o Is a type of bird living in the Galápagos Islands

0 • This type of bird possesses many specialized characteristics, called evolutionary adaptations o Which are inherited traits that enhance its ability to survive and reproduce in its particular environment

DARWIN’S THEORY OF EVOLUTION 0 13. 1 A sea voyage helped Darwin frame his theory of evolution • On his visit to the Galápagos Islands, Charles Darwin observed many unique organisms Figure 13. 1 A

0 • Darwin’s main ideas o Can be traced back to the ancient Greeks • Aristotle and the Judeo-Christian culture believed that species are fixed (permanent) and do not evolve

0 • In the century prior to Darwin o The study of fossils suggested that life forms change • Geologists proposed that a very old Earth is changed by gradual processes • Lyell developed a theory of evolution nearly identical to Darwin's • The unifying theme of biology is evolution.

0 • While on the voyage of the HMS Beagle in the 1830 s o Charles Darwin observed similarities between living and fossil organisms and the diversity of life on the Galápagos Islands North America Great Britain Europe Asia ATLANTIC OCEAN PACIFIC OCEAN Pinta Marchena Santiago Pinzón Fernandina Isabela Figure 13. 1 B 0 PACIFIC OCEAN Equator The Galápagos Islands 0 Africa 40 km PACIFIC OCEAN South America Genovesa Equator Australia Andes Daphne Islands Santa Cruz Fe Cape of Good Hope Cape Horn San Cristobal Florenza Española 40 miles Tierra del Fuego Tasmania New Zealand

0 • Darwin’s experiences during the voyage of the Beagle helped him frame his ideas on evolution • Main ideas that Darwin advanced in his works Species change over time Living species have arisen from earlier life forms Modern species arose through a process known as "descent with modification" o New species arise by natural selection o o o

0 13. 2 Darwin proposed natural selection as the mechanism of evolution • Darwin observed that o The Earth is very old. o Populations produce more offspring than their environment can support. o Organisms compete for limited resources. o Organisms vary in heritable ways.

0 • Darwin reasoned that natural selection o Results in favored traits being represented more and unfavored ones less and less in ensuing generations of organisms

0 • Darwin found convincing evidence for his ideas in the results of artificial selection o The selective breeding of domesticated plants and animals Hundreds to thousands of years of breeding (artificial selection) Ancestral dog (wolf) Figure 13. 2 A Figure 13. 2 B

0 • Darwin proposed that living species o Are descended from earlier life forms and that natural selection is the mechanism of evolution African wild dog Coyote Wolf Thousands to millions of years of natural selection Figure 13. 2 C Ancestral canine Fox Jackal

0 13. 3 The study of fossils provides strong evidence for evolution • Fossils and the fossil record o Strongly support theory of evolution A Skull of Homo erectus B Petrified tree E Fossilized organic matter of a leaf Figure 13. 3 A–G C Ammonite casts D Dinosaur tracks F Insect in amber G “Ice Man”

0 • The fossil record o Reveals that organisms have evolved in a historical sequence Figure 13. 3 H

• Fossils form the following processes o The remains of a dead organism are sometimes turned into stone by petrification. o Actual organic material remains if an organism is buried in a medium that prevents bacteria and fungi from decomposing it. o The hard parts of animals that are rich in minerals, such as teeth and the shells of clams, may remain as fossils. o Whole organisms are sometimes preserved in ice or deep within acid bogs.

0 • Many fossils link early extinct species o With species living today Figure 13. 3 I

• The fossil record shows that o the earliest fossils of life are about 3. 5 billion years old. o younger strata are on top of older strata. o within the vertebrates, fish were the first to evolve. o some fossils represent an evolutionary series of changes that provide strong documentation of evolution.

0 13. 4 A mass of other evidence reinforces the evolutionary view of life

0 Biogeography • Biogeography, the geographic distribution of species o Suggested to Darwin that organisms evolve from common ancestors • Darwin noted that Galápagos animals o Resembled species of the South American mainland more than animals on similar but distant islands

0 Comparative anatomy • Comparative anatomy o Is the comparison of body structures in different species • Homology o Is the similarity in characteristics that result from common ancestry

0 • Homologous structures o Are features that often have different functions but are structurally similar because of common ancestry Figure 13. 4 A Human Cat Whale Bat

Anatomy and Embryology • Analogous structures-have closely related functions but do not derive from the same ancestral form. (Different structure; same function. ) o Ex. Bird, bat, and moth wings

0 Comparative Embryology • Comparative embryology o Is the comparison of early stages of development among different organisms

0 • Many vertebrates o Have common embryonic structures Pharyngeal pouches Post-anal tail Human embryo Chick embryo Figure 13. 4 B

0 Molecular Biology • Comparisons of DNA and amino acid sequences between different organisms o Reveal evolutionary relationships Table 13. 4

POPULATION GENETICS AND THE MODERN 0 SYNTHESIS • 13. 6 Populations are the units of evolution A population § Is a group of individuals of the same species living in the same place at the same time § The smallest unit that can evolve. o A species is a group of populations § Whose individuals can interbreed and produce fertile offspring o

0 • A gene pool o Is the total collection of genes in a population at any one time • Microevolution o Is a change in the relative frequencies of alleles in a gene pool

0 13. 7 The gene pool of a nonevolving population remains constant over the generations • In a nonevolving population o The shuffling of alleles that accompanies sexual reproduction does not alter the genetic makeup of the population Figure 13. 7 A Webbing No webbing

0 • Hardy-Weinberg equilibrium o States that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool Phenotypes Genotypes WW Ww ww Number of animals (total 500) 320 160 20 Genotype frequencies 320 0. 64 500 Number of alleles in gene pool (total 1, 000) 640 W Allele frequencies Figure 13. 7 B 160 0. 32 500 160 W 160 w 800 0. 8 W 1, 000 20 0. 04 500 40 w 200 0. 2 w 1, 000

0 • For a population to be in Hardy-Weinberg equilibrium, it must satisfy five main conditions o The population is very large o The population is isolated o Mutations do not alter the gene pool o Mating is random o All individuals are equal in reproductive success

CONNECTION 13. 8 The Hardy-Weinberg equation is useful in public health science • Public health scientists use the Hardy-Weinberg equation o To estimate frequencies of disease-causing alleles in the human population 0

0 13. 9 In addition to natural selection, genetic drift and gene flow can contribute to evolution • Genetic drift o Is a change in the gene pool of a population due to chance o Can alter allele frequencies in a population

0 • Genetic drift o Can cause the bottleneck effect (genetic drift resulting from a disaster that drastically reduces population size)or the founder effect Original population Bottlenecking event Figure 13. 9 A Surviving population Figure 13. 9 B

0 • Gene flow o Is the movement of individuals or gametes between populations o Can alter allele frequencies in a population o Tends to reduce genetic differences between populations

CONNECTION 0 13. 10 Endangered species often have reduced variation • Low genetic variability o May reduce the capacity of endangered species to survive as humans continue to alter the environment Figure 13. 10

VARIATION AND NATURAL SELECTION 13. 11 Variation is extensive in most populations • Many populations exhibit polymorphism o Different forms of phenotypic characteristics Figure 13. 11 0

0 • Populations may also exhibit geographic variation o Variation of an inherited characteristic along a geographic continuum

0 13. 12 Mutation and sexual recombination generate variation • Mutations, or changes in the nucleotide sequence of DNA o Can create new alleles

0 • Sexual recombination o Generates variation by shuffling alleles during meiosis Parents A 1 X A 2 A 3 Meiosis Gametes A 2 A 1 A 3 Fertilization Figure 13. 12 Offspring, with new combinations of alleles A 1 A 2 A 1 and A 3

CONNECTION 0 13. 13 The evolution of antibiotic resistance in bacteria is a serious public health concern • The excessive use of antibiotics o Is leading to the evolution of antibiotic-resistant bacteria Colorized SEM 5, 600 Figure 13. 13

0 13. 14 Diploidy and balancing selection variation • Diploidy preserves variation o By “hiding” recessive alleles • Balanced polymorphism o May result from the heterozygote advantage or frequency-dependent selection

0 • Some variations may be neutral o Providing no apparent advantage or disadvantage Figure 13. 14

0 13. 15 The perpetuation of genes defines evolutionary fitness • An individual’s fitness o Is the contribution it makes to the gene pool of the next generation

0 13. 16 Natural selection can alter variation in a population in three ways • Stabilizing selection Favors intermediate phenotypes • Directional selection o Acts against individuals at one of the phenotypic extremes • Disruptive selection o Favors individuals at both extremes of the phenotypic range o

0 • Three possible effects of natural selection Original population Frequency of individuals Original population Figure 13. 16 Evolved population Stabilizing selection Phenotypes (fur color) Directional selection Disruptive selection

0 13. 17 Sexual selection may produce sexual dimorphism • Sexual selection leads to the evolution of secondary sexual characteristics o Which may give individuals an advantage in mating Figure 13. 17 A Figure 13. 17 B

• Intrasexual selection-secondary sex structures may be used to compete with members of the same sex for mate. • Intersexual selection-mate choice-individuals of one sex (usually females) are choosy in selecting their mates.

0 13. 18 Natural selection cannot fashion perfect organisms • There at least four reasons why natural selection cannot produce perfection o Organisms are limited by historical constraints o Adaptations are often compromises o Chance and natural selection interact o Selection can only edit existing variations