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Topic 13: Evolution 1. What is Evolution? 2. Lamarck, Darwin & Wallace 3. Survival of the “Good Enough” 4. Population Genetics & Hardy-Weinberg Law 5. The Power of Natural Selection 6. Microevolution in Large & Small Populations 7. Evidence Supporting Evolution 8. Speciation & Extinction 9. Systematics Topic 12: Lesson 1 Resources: 1. Read Chapter 12.1 pp. 238 2. Does Evolution Really Matter? 3. Zaption – It’s Okay To Be Smart – 12 Days of Evolution WHAT IS EVOLUTION? What Is Evolution? Why does this giraffe have a long neck? Why do these bleeding heart flowers have such a strange shape? Evolution explains the features of all organisms, from microbes to humans. Descendants are Modified Versions of Their Ancestors Evolution is descent with modification—changes in heritable traits from generation to generation. Evolution’s Misconceptions Human Evolution Topic 13: Lesson 2 Resources: 1. Read Chapter 12.2 pp. 238-243 2. Skit – A Conversation between Darwin & Lamarck 3. Worksheet – Darwinian & Lamarckian Thinking LAMARCK, DARWIN & WALLACE Timeline of Evolutionary Thought Lamarck’s Hypotheses • Proposed the first scientifically testable explanation for the change that occurs in species 1. A change in the environment produces a need for change in animals 2. Acquired characteristics will be passed on to offspring 3. If an animal uses a body part often, it will grow in strength and size and vice versa Evolutionary Thought Over the Centuries Charles Lyell • Geologist – Theory of Uniformitarianism – geological features of Earth have changed, and will continue to change – Earth is older than 6000 years – Law of Superposition – new rock layers are above older rock layers Darwin’s Puzzle Chiru Yak Darwin’s Voyage on the HMS Beagle (1831-1836) Darwin the Naturalist • At each port, Darwin would collect samples and analyze them when back onboard Thomas Malthus The Logic of Natural Selection Observations Of Nature • Genetic variation exists within a species Inferences From Observations • Descent with modification • The amount of resources in a given ecosystem limits the population • Struggle for existence • More offspring are born than can survive • Unequal reproductive success On the Origin of Species (1859) • Darwin published his work that summarizes his arguments in support of natural selection • He described dozens of species in support for his ideas Topic 13: Lesson 3 Resources: 1. Read Chapter 12.3 pp. 244-7 2. Lab – Evolution & Natural Selection 3. Lab – Coevolution of Flowers and Pollinators 4. PBS – Surviving AIDS: Delta32 SURVIVAL OF THE FITTEST “GOOD ENOUGH” Nature Selects the Best Suited Individuals This seahorse blends almost perfectly into its habitat. How could an organism like this arise? Each generation, the best camouflaged individuals survive to reproduce. The alleles conferring camouflage become more common in each generation. But natural selection does not create camouflage alleles. Instead, it strongly selects for camouflage alleles that arise by chance. Types of Fitness Ability to attract a mate Ability to catch prey (food) Ability to outrun predators Ability to camouflage for safety Natural Selection Molds Evolution Natural selection operates on the variation present in a population. Since more individuals are born than resources can support, the struggle to survive is inevitable. Some individuals in a population are better than others at surviving and reproducing. Adaptations Provide an Advantage • Heritable traits that provide a selective advantage because they improve an organism’s ability to survive and reproduce Example: Grey Owl – silent flight, neck with large turning radius, sharp talons, great vision/depth perception Natural Selection Does NOT Create Bacteria that are resistant to antibiotics have an adaptive trait that non-resistant bacteria lack. When antibiotics are administered, resistant bacteria are strongly selected for survival. Antibiotics cannot create a resistance allele. The variation in resistance was already present in the population; the presence of antibiotics caused the resistance allele frequency to shift. Evolution Never Stops As environmental conditions change, the phenotypes that natural selection favors will also change. Adaptations that seem “perfect” in one environment would be completely wrong in another. Co-Evolution This orchid and its wasp pollinator have evolved alongside one another for long enough that no other animal can pollinate the flower. But the orchid does not evolve in order to be better-pollinated by the wasp. Neither the orchid nor natural selection has foresight. Topic 13: Lesson 4 Resources: 1. Read Chapter 12.4 pp. 248-9 2. Crash Course – Population Genetics 3. Bozeman Science – Hardy-Weinberg Equation 4. The Penguin Prof – Watch Your P’s and Q’s 5. Bleier Biology – Hardy-Weinberg Practice Problems 6. The Biology Place Lab Bench – Hardy-Weinberg Law of Genetic Equilibrium 7. Hardy-Weinberg Practice Problems POPULATION GENETICS & HARDYWEINBERG LAW Populations Change, Not Individuals Recall that a population is a group of interbreeding organisms of the same species that experience the same environmental changes and the same pressures of natural selection. Gene Pools Are Acted on By Natural Selection Evolution is detectable by examining the population’s gene pool— the entire collection of genes and alleles. Evolution occurs in a population when allele frequencies change from one generation to the next. Percentage of Alleles in a Population An allele frequency is calculated by the following equation: # of copies of an allele Total # of alleles for the same gene in the population Microevolution Even for the same species, gene pools differ from population to population. The gene pool for a population of Swedes differs from that of a population of Asians. If Swedes migrate to Asia and interbreed with locals, then allele frequencies in the gene pool will change. Evolution, more specifically, microevolution has occurred! What Is Evolution? MICROEVOLUTION MACROEVOLUTION • Change in allele frequencies • Change within organisms over long periods of time in a gene pool (millions of years) • Change within organisms that happens over a short period • Leads to the evolution of new species of time (a few generations) Hardy-Weinberg Equations • Used to predict allele frequency in gamete pool and genotypic frequencies in the next generation p+q=1 (p + q)2 = p2 + 2pq + q2 = 1 Hardy-Weinberg Assumptions 1. 2. 3. 4. 5. 6. 7. 8. Organisms are diploid Generations are non-overlapping Population is infinitely large Mutation does not occur Sexual reproduction Random fertilization Migration does not occur Natural selection does not operate Hardy-Weinberg Equilibrium • A population in Hardy-Weinberg equilibrium is “not evolving” • If the allele frequencies change from one generation to the next the population is evolving Topic 13: Lesson 5 Resources: 1. Read Chapter 12.5-6 pp. 250-2 2. Three Modes of Natural Selection 3. Lab – Sickle-cell Disease 4. Crash Course – Natural Selection THE POWER OF NATURAL SELECTION Three Modes of Natural Selection Stabilizing, Directional & Disruptive modes of natural selection are distinguished by their effects on the phenotypes in a population. Directional Selection One phenotype is favored over another Disruptive Selection • Extreme phenotypes are favored over an intermediate phenotype Stabilizing Selection • An intermediate phenotype is favored over the extreme phenotypes. Natural Selection Can Shape Populations in Many Ways Natural Selection Can Shape Populations in Many Ways However, these three models do not explain why natural selection maintains some harmful alleles in the population. Heterozygote Advantage • Some harmful alleles still exist in the population because they give the heterozygous person an advantage – Examples: Sickle-cell anemia, hereditary deafness/thickened epidermis, thalassemia/heart attacks Topic 13: Lesson 6 Resources: 1. Read Chapter 12.7 pp. 253-5 2. Worksheet – Microevolution & Hardy-Weinberg 3. Video - Rock Pocket Mice MICROEVOLUTION IN DIFFERENT SIZED POPULATIONS Microevolution in Large Populations • English peppered moth (Biston betularia) 5 Mechanisms that affect gene pools 1. Natural selection – allele frequency is dependent upon reproductive success 2. Mutation – one allele changing to another spontaneously and randomly 3. Genetic drift – random change in allele frequency 4. Gene flow – allele movement caused by migration 5. Nonrandom mating – individuals choose who to mate with Natural Selection & Mutation Genetic Drift • In each generation, some individuals may, just by chance, leave behind a few more descendants than other individuals 16.5 Microevolution in Small Populations Population Bottleneck • When a drastic event occurs and the population is reduced for a few generations Example: American bison 1492 population 60,000,000 1890 population 750 2000 population 360,000 Inbreeding Occurs in Small Populations • Inbreeding – increase of homozygosity of alleles caused by genetic drift – Example: California condor – 22 birds were captured and bred at the San Diego Zoo – 384 condors are now living Inbreeding Depression • Inbreeding depression – decreased fertility and survival rate (vigor) caused by inbreeding – Problem in zoos, endangered species, isolated populations, bred animals (dogs, livestock), Gene Flow • Allele frequencies of populations can change due to permanent migration Founder Effect • New populations can be started by migrants so that the genetic makeup or allele frequency differs from the original population – Extreme case: the founding of a new colony by one pregnant animal or one plant seed Founder Effect in the Real World • 1814, 15 people founded a British colony on Tristan da Cunha • One of the colonists carried the allele for retinitis pigmentosa • 1960, 240 descendents, 4 had retinitis pigmentosa, 9 were carriers Nonrandom Mating/Sexual Selection • Individuals choose their mate Showing Off = Reproductive Success At face value, flashing showy plumage, and butting heads with rival males all appear to waste energy. How can natural selection allow for traits that apparently reduce survival? Intersexual Selection Intrasexual Selection Sexual Selection Directly Influences Reproductive Success (Inter vs. Intra) Intersexual Intersexual Intrasexual Choosy Females Effect Allele Frequency &/or Behavior Generations of choosy females have selected for males with nest-building traits or elaborate ornamentation. Finding a Mate > Spending Energy Although the yellow weaver bird uses time and energy making nests for females, this behavior might secure a mating opportunity. Topic 13: Lesson 7 Resources: 1. Read Chapter 13.1-3 2. Worksheet – Comparing Amino Acid Sequences 3. POGIL-Evidence for Evolution 4. Blenny Fish Evolution 5. Crash Course – Evidence for Evolution EVIDENCE SUPPORTING EVOLUTION Fossil Record The physical proof of fossils (eggs, body parts, foot prints, etc.) helps us to understand the sequence of events over time in respect to which organisms were alive, where they lived, what they looked like and so forth Biogeography • The study of the distribution of organisms through time and space • Where Life Lives Convergent Evolution • Two or more unrelated species become more and more alike due to common environmental NORTH pressures, not due to ancestry AMERICA Sugar gliders are marsupials (more closely related to a kangaroo than a squirrel); both creatures live in an environment where gliding quickly from tree to tree is a helpful trait. Sugar glider AUSTRALIA Flying squirrel Divergent Evolution Hyracoidea (Hyraxes) • Adaptive Radiation – two or more related species become less and less related over time Sirenia (Manatees and relatives) Moeritherium Barytherium Deinotherium Mammut Platybelodon Stegodon Mammuthus Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) 34 24 5.5 Millions of years ago 2 104 0 Years ago Comparative Anatomy • Scientists use similarities and differences between organisms to determine evolutionary relatedness Homologous Structures • Organisms that are descended from a common ancestor share common ancestral traits (structural resemblances) that may have developed to perform different functions Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat Analogous Structures • Unrelated (or distantly related) species of animals or plants develop similar traits when exposed to similar environmental pressures • These are seen in convergent evolution and NOT a reflection of shared ancestry Example: the wings of butterflies, birds and bats Vestigial Structures • A Structure that is a remnant of an organism’s evolutionary past and has no current function • Useful indication of common ancestry where one species maintained the use of the structure Embryology • The branch of biology that deals with the formation, early growth, and development of living organisms • The high degree of similarity of these early developmental forms supports that species have arisen from common ancestors Example: the embryonic development of humans and turtles Biochemical • Comparing DNA nucleotide sequences or amino acids sequences in a protein helps reveal evolutionary relationships Topic 13: Lesson 8 Resources: 1. Read Chapter 14.1-5 pp. 282-294 2. Speciation – Mosquitoes 3. Worksheet – Types of Reproductive Barriers 4. Examining the Fossil Record 5. The London Underground Mosquito 6. Crash Course – Speciation SPECIATION & EXTINCTION Speciation • Changes in isolated populations that lead to the formation of new species • At what point are two populations considered separate species? – When they become reproductively isolated from one another (meaning they cannot interbreed and produce fertile offspring) Gradualism & Punctuated Equilibrium Reproductive Barriers Cause Species to Diverge Prezygotic Barriers Do not allow zygote to be formed • Habitat isolation • Temporal isolation • Behavioral isolation • Mechanical isolation • Gametic isolation Postzygotic Barriers Reduce fitness of hybrid • Hybrid inviability • Hybrid infertility • Hybrid breakdown Note- isolation alone isn’t what causes the speciation; once isolated, each population can evolve separately and become different enough from one another that they can no longer mate successfully Geographic Isolation • Habitat isolation – species live in different habitats Temporal Isolation • Species are active or fertile at different times Behavioral Isolation • Different courtship rituals Mechanical Isolation • Mating organs or pollinators are incompatible Gametic Isolation • Gametes cannot unite Hybrid Inviability • Hybrid offspring develops but either dies before birth, or dies before sexual maturity Hybrid Infertility • Sterility – Hybrid offspring are not able to reproduce Hybrid Breakdown • When hybrids reproduce but their offspring cannot Topic 13: Lesson 9 1. Read Chapter 14.6 pp. 294-295 2. The IS: Clad Method of Cladistics 3. POGIL: Biological Classification 4. Organism Classification Project 5. What Did a T-Rex Taste Like? 6. The Evolution of Flight in Birds 7. iTOL 8. Crash Course: Taxonomy: Life’s Filing System SYSTEMATICS: TAXONOMY & PHYLOGENETICS Taxonomy • Describing, classifying, and naming species • • • • • • • • Domain Kingdom Phylum Class Order Family Genus species Used as the scientific name; binomial nomenclature Phylogenetics • Phylogenetics – studying the evolutionary relationships between organisms Homologous structures and DNA sequences can be used to create evolutionary trees (cladogram, phylogenetic tree) Branch point (common ancestor) Lungfishes Amphibians 1 Tetrapod limbs Mammals 2 Lizards and snakes 3 Amnion (membrane that surrounds and protects embryo) 4 Crocodiles Homologous characteristic Feathers Ostriches 6 Birds 5 Hawks and other birds Note- crocodiles & birds share a common ancestor; birds did not evolve from crocodiles. Tree of Life