Evolution A Scientific Explanation for Similarities and Differences between Organisms

Darwin’s Observations Living Organisms resemble extinct fossil forms.Living Organisms resemble extinct fossil forms.

Darwin’s Observations Progressive changes from simpler to more complex organisms can be seen in the fossil record.Progressive changes from simpler to more complex organisms can be seen in the fossil record.

Darwin’s Observations Different island species resemble each other.Different island species resemble each other.

Darwin’s Observations Island Populations resemble those on nearby land. The Galapagos finches resembled the grassquit found on the coast of Ecuador.Island Populations resemble those on nearby land. The Galapagos finches resembled the grassquit found on the coast of Ecuador.

Darwin’s Observations Lands with similar climates have unrelated plants and animals.Lands with similar climates have unrelated plants and animals.

Darwin’s Observations Plants and animals of each continent are distinctive.Plants and animals of each continent are distinctive.

A Flowchart of Evolutionary Reasoning Potential for rapid reproduction Relatively constant resources and population over time Variability in structures and behaviors Some variability is inherited (observations) (conclusions) Competition for survival and reproduction (1) NATURAL SELECTION On average, the fittest organisms leave the most offspring (2) EVOLUTION: The genetic makeup of the population changes over time, driven by natural selection (3)

Darwin’s Theory of Evolution Evolution occurs by natural Evolution occurs by natural selection. selection. Evolution = progressive change in the characteristics of organisms as a result of changes in genetic compositionEvolution = progressive change in the characteristics of organisms as a result of changes in genetic composition

Darwin’s Theory of Evolution Natural selection = mechanism for evolutionNatural selection = mechanism for evolution Process by which those individuals whose traits adapt them to their environment leave a larger number of offspringProcess by which those individuals whose traits adapt them to their environment leave a larger number of offspring An increase in frequency of genotypes that confer a favorable advantage in a given environment. An increase in frequency of genotypes that confer a favorable advantage in a given environment.

Adaptations Traits that make a species survival more likelyTraits that make a species survival more likely Can beCan be –structural: physical features –functional: physiological, biochemical, metabolic features –behavioral mechanisms Natural Selection favors individuals that are well-adapted to the current environment.The adaptations are not “perfect” solutions.

Applying Your Knowledge A.The mechanism for evolution is B.A progressive change in the characteristics of organisms is C.A trait that makes a species survival more likely is called a(n) 1.Adaptation 2.Evolution 3.Natural selection

Evidence for Evolution: Fossil Record

Evidence for Evolution: Geological Sufficient time for evolution based on age of the earthSufficient time for evolution based on age of the earth

Evidence for Evolution: Comparative Anatomy Structures that do not show a common originStructures that do not show a common origin –Analogous structures: superficially similar Structures that show a common originStructures that show a common origin –Homologous Structures: same evolutionary origin despite differences in function –Vestigial Structures: serve no purpose but are homologous to structures in related organisms

Analogous Structures Not homologous; not analogous Homologous; not analogous Not homologous; analogous Homologous; analogous

Homologous Structures Flying Swimming Running Grasping

Vestigial Structures Functional hindlimb in salamander Remnants of hindlimb seen in boa and whale

Evidence for Evolution: Embryology Similar embryonic patterns of developmentSimilar embryonic patterns of development

Evidence for Evolution: Genetics Mutation generates diversityMutation generates diversity Meiosis and Fertilization generate new combinations due toMeiosis and Fertilization generate new combinations due to –Crossing Over –Alternate patterns of chromosome segregation –Unique genotype of fertilizing sperm combined with unique genotype of egg

Evidence for Evolution: Biochemistry Molecular similarities between different organismsMolecular similarities between different organisms

Evidence for Evolution: Molecular Biology Similarities in sequence measured by ease of separating DNA strands by heatSimilarities in sequence measured by ease of separating DNA strands by heat

Evidence for Natural Selection Artificial SelectionArtificial Selection

Evidence for Natural Selection Current Observations – –Development of insecticide resistance in western corn rootworm larvae Western corn rootworm larval bioassay results R LD 50 /S LD 50. Chlorpyrifos Terbufos Methyl Parathion Tefluthrin Carbofuran Resistance Ratios

Natural Selection Data, p. 115 Color 1 P S O Color 1 P S O Color 2 P S O Color 2 P S O Color 3 P S O Color 3 P S O Color 4 P S O Color 4 P S O Color 5 P S O Color 5 P S O 1 st 20 __ __ 2 nd __ __ __ 3 rd __ __________ 4 th 5 th S= Survivors Must Total 25 O= Offspring = 3 x Survivors (Place on cloth) P= Pre-hunt = Survivors + Offspring

Natural Selection Data, p. 115 Plot Pre-Hunt population values for most and least successful colors

Types of Natural Selection Large Size Favored Large Size Favored Directional Selection Average Size Favored Average Size Favored Stabilizing Selection Extreme Size Favored Extreme Size Favored Disruptive Selection Variation reduced over time Variation reduced over time Mean changed over time Mean changed over time Variation becomes polarized Variation becomes polarized Before Selection After Selection Time

Types of Selection Stabilizing: eliminates extremesStabilizing: eliminates extremes

Stabilizing Selection & Balanced Polymorphism SS SS’ S’S’ Dies of malaria SS Lives and reproduces Dies of sickle-cell anemia Dies of malaria Lives and reproduces Dies of sickle-cell anemia Homozygous Normal Homozygous Defective Heterozygous

Types of Selection Disruptive: increases both extremesDisruptive: increases both extremes

Types of Selection Directional: increases one extremeDirectional: increases one extreme

Applying Your Knowledge 1.Stabilizing Selection 2.Disruptive Selection 3.Directional Selection Which type of selection has occurred if The background is sandy with dark rocks and snails are found with either dark or light shell colors?The background is sandy with dark rocks and snails are found with either dark or light shell colors? After spraying with malathion, more fruit flies are found to be resistant to this insecticide?After spraying with malathion, more fruit flies are found to be resistant to this insecticide?

Patterns of Evolution DivergentDivergent –different phenotypes arise as related species encounter environmental differences

Patterns of Evolution ConvergentConvergent –similar phenotypes arise in unrelated species as a result of environmental similarities North American Desert Plants Cactus Euphorbs African

Patterns of Evolution ConvergentConvergent –similar phenotypes arise in unrelated species as a result of environmental similarities Meadowlark of North America Meadowlark of North America Yellow-Throated Longclaw of Africa

Patterns of Evolution Coevolution: species adjust together to maintain relationshipCoevolution: species adjust together to maintain relationship Flowering plants and their Pollinators Predators and their Prey