Chapter 15 EvolutionChapter 15 Evolution

15.1 Darwin’s Theory of Natural 15.1 Darwin’s Theory of Natural SelectionSelection

15.2 Evidence of Evolution15.2 Evidence of Evolution

15.3 Shaping Evolutionary Theory15.3 Shaping Evolutionary Theory

15.1 Darwin’s Theory of Natural Selection15.1 Darwin’s Theory of Natural Selection

Main idea: Charles Darwin developed a theory of Main idea: Charles Darwin developed a theory of evolution based on natural selectionevolution based on natural selectionObjectivesObjectives

Discuss the evidence that convinced Darwin that species could Discuss the evidence that convinced Darwin that species could change over time.change over time.

List the four principles of natural selection.List the four principles of natural selection. Show how natural selection could change a populationShow how natural selection could change a population

Review VocabularyReview Vocabulary Selective Breeding – process by which a breeder develops a Selective Breeding – process by which a breeder develops a

plant or animal to have certain traitsplant or animal to have certain traits

New VocabularyNew Vocabulary Artificial selectionArtificial selection Natural selectionNatural selection EvolutionEvolution

Developing the Theory of Natural Developing the Theory of Natural SelectionSelection

Charles Darwin boarded the Charles Darwin boarded the HMS Beagle HMS Beagle in in 1831, the average person believed the world 1831, the average person believed the world was about 6,000 years old.was about 6,000 years old.Darwin’s role on the ship was as naturalist and companion to the captain. His job was to collect biological and geological specimens during the ship’s travel.During the ship’s five year voyage, Darwin made extensive collections of rocks, fossils, plants and animals.He also read Charles Lyell’s Principles of Geology – a book proposing the Earth was millions of years old.

HMS BeagleHMS Beagle

In 1835, the In 1835, the Beagle Beagle arrived in the arrived in the GalGalápagos Islands off the coast of South ápagos Islands off the coast of South America. America. Darwin began to collect mockingbirds, finches, and other animals on the four islands. He noticed that the different islands seemed to have their own, slightly different varieties of animals.

Galápagos IslandsAlmost every specimen that Darwin had collected on the islands was new to European scientists.

Populations from the mainland changed after reaching the Galápagos.

Darwin Continued His StudiesDarwin Continued His Studies

Darwin hypothesized that new species could appear gradually through small changes in ancestral species.

Darwin inferred that if humans could change species by artificial selection (selective breeding), then perhaps the same process could work in nature.

Natural SelectionNatural SelectionVariation: Individuals in a population show variations. Heritability: Variations can be inherited.Overproduction: Organisms have more offspring than can survive on available resources.Reproductive Advantage: Variations that increase reproductive success will have a greater chance of being passed on.Darwin called his theory Natural Selection.He reasoned that, given enough time, natural selection could modify a population enough to produce a new species.

Basic Principles of Natural SelectionBasic Principles of Natural SelectionPrinciplePrinciple ExampleExampleIndividuals in a population show Individuals in a population show variations among others of the variations among others of the same species.same species.

The students in a classroom look The students in a classroom look different.different.

Variations are inherited.Variations are inherited. Traits are passed down from Traits are passed down from parents to offspringparents to offspring

Animals have more young than can Animals have more young than can survive on the available resources.survive on the available resources.

The average cardinal lays nine The average cardinal lays nine eggs per summer. If each cardinal eggs per summer. If each cardinal lived only one year, in eight years lived only one year, in eight years there would be a million cardinals if there would be a million cardinals if all offspring survived.all offspring survived.

Variations that increase Variations that increase reproductive success will be more reproductive success will be more common in the next generation.common in the next generation.

If having a fan-shaped tail If having a fan-shaped tail increases reproductive success of increases reproductive success of pigeons, than more pigeons in the pigeons, than more pigeons in the next generation will have fan-next generation will have fan-shaped tails.shaped tails.

The Origin of SpeciesThe Origin of Species

Darwin published On the Origin of Species by Means of Natural Selection in 1859.Darwin’s theory of natural selection is not synonymous with evolution.It is a means of explaining how evolution works.Today, biologists use the term evolution to define cumulative changes in groups of organisms through time.

15.2 Evidence of Evolution15.2 Evidence of EvolutionMain idea: Multiple lines of evidence support the theory of evolution.Main idea: Multiple lines of evidence support the theory of evolution.Objectives: Objectives:

Describe how fossils provide evidence of evolution.Describe how fossils provide evidence of evolution. Discuss morphological evidence of evolution.Discuss morphological evidence of evolution. Explain how physiology and biochemistry provide evidence of evolution.Explain how physiology and biochemistry provide evidence of evolution.

Review Vocabulary: Review Vocabulary: Fossil – remains of an organism or its activitiesFossil – remains of an organism or its activities

New VocabularyNew Vocabulary Derived traitDerived trait Ancestral traitAncestral trait Homologous structureHomologous structure Vestigial structureVestigial structure Analogous structureAnalogous structure EmbryoEmbryo BiogeographyBiogeography FitnessFitness MimicryMimicry CamouflageCamouflage

Support for EvolutionSupport for Evolution

The theory of evolution states that all organisms The theory of evolution states that all organisms on Earth have descended from a common on Earth have descended from a common ancestor.ancestor.

The fossil record offers some of the most significant evidence of evolutionary change.

Fossils provide a record of species that lived long ago.

Fossils show that ancient species share similarities with species that now live on Earth.

The Fossil RecordThe Fossil Record

The giant armadillo-like The giant armadillo-like glyptodont, glyptodont, Glyptodon,Glyptodon,is is an extinct animal that an extinct animal that Darwin thought must be Darwin thought must be related to the living related to the living armadillos that inhabit armadillos that inhabit South America, Central South America, Central America, and the America, and the southern United States.southern United States.The fossil record is an The fossil record is an important source of important source of information for information for determining the ancestry determining the ancestry of organisms and the of organisms and the patterns of evolution.patterns of evolution.

Studying Transitional FossilsStudying Transitional Fossils

Two major classes of traits:Two major classes of traits: Derived traits are newly evolved features, such as

feathers, that do not appear in the fossils of common ancestors.

Ancestral traits are more primitive features, such as teeth and tails, that do appear in ancestral forms.

Transitional fossils provide detailed patterns of evolutionary change for ancestors of many modern animals, including mollusks, horses, whales and humans.

Comparative AnatomyComparative Anatomy

Anatomically similar structures inherited from a common ancestor are called homologous structures.The forelimbs of vertebrates are adapted for different uses, but they all have similar bones.Similar structure; different function.

Vestigial StructuresVestigial Structures

Vestigial structures are the reduced forms of functional structures in other organisms.Evolutionary theory predicts that features of ancestors that no longer have a function for that species will become smaller over time until they are lost.Examples: Snake pelvis Examples: Snake pelvis and human appendix.and human appendix.

Analogous StructuresAnalogous StructuresAnalogous structures can be used for the same purpose and can be superficially similar in construction, but are not inherited from a common ancestor.Show that functionally similar features can evolve independently in similar environments.Same function; different structure

Comparative EmbryologyComparative Embryology

An embryo is an early pre-birth stage of an organism’s development.Vertebrate embryos exhibit homologous structures during certain phases of development but become totally different structures in the adult forms.

Comparative BiochemistryComparative Biochemistry

Common ancestry can be seen in the complex metabolic molecules that many different organisms share.

Comparative BiochemistryComparative Biochemistry

Comparisons of the similarities in these molecules across species reflect evolutionary patterns seen in comparative anatomy and in the fossil record.

Organisms with closely related morphological features have more closely related molecular features.

Geographic DistributionGeographic Distribution

The distribution of plants and animals that Darwin saw first suggested evolution to Darwin.

Rabbit Mara

BiogeographyBiogeography

Scientists have confirmed and expanded Scientists have confirmed and expanded Darwin’s study of the distribution of plants Darwin’s study of the distribution of plants and animals around the world in a field of and animals around the world in a field of study now called biogeography.study now called biogeography.Patterns of migration were critical to Darwin when he was developing his theory.Evolution is intimately linked with climate and geological forces.

AdaptationAdaptation

Types of AdaptationTypes of Adaptation An adaptation is a trait shaped by natural selection

that increases an organism’s reproductive success. Fitness is a measure of the relative contribution an

individual trait makes to the next generation. It is often measured as the number of reproductively viable offspring that an organism produces in the next generation.

Camouflage allows organisms to become almost invisible to predators. Some species have evolved morphological adaptations that allow them to blend in with their environments.

Mimicry is another morphological adaptation that allows one species to evolve to resemble another species.

Consequences of AdaptationsConsequences of Adaptations

Antimicrobial Antimicrobial resistance - An resistance - An antibiotic is a antibiotic is a medicine that slows medicine that slows or kills the growth of or kills the growth of bacteria.bacteria.Some bacteria have Some bacteria have evolved a resistance evolved a resistance to certain antibiotics.to certain antibiotics.People infected with People infected with resistant bacteria can resistant bacteria can never get rid of it.never get rid of it.

Consequences of AdaptationsConsequences of Adaptations

Some features of an organism might be consequences of other evolved characteristics.

They do not increase reproductive success.

Features likely arose as an unavoidable consequence of prior evolutionary change.

15.3 Shaping Evolutionary Theory15.3 Shaping Evolutionary Theory

Main idea: The theory of evolution continues to Main idea: The theory of evolution continues to be refined as scientists learn new information.be refined as scientists learn new information.

Objectives:Objectives: Discuss patterns observed in evolution.Discuss patterns observed in evolution. Describe factors that influence speciation.Describe factors that influence speciation. Compare gradualism with punctuated equilibrium.Compare gradualism with punctuated equilibrium.

Review VocabularyReview Vocabulary Allele: alternative forms of a character trait that can be Allele: alternative forms of a character trait that can be

inherited.inherited.

15.3 Shaping Evolutionary Theory15.3 Shaping Evolutionary TheoryNew VocabularyNew Vocabulary

Hardy-Weinberg PrincipleHardy-Weinberg Principle Prezygotic isolating mechanismPrezygotic isolating mechanism

Genetic driftGenetic drift Allopatric speciationAllopatric speciation

Founder effectFounder effect Postzygotic isolating mechanismPostzygotic isolating mechanism

BottleneckBottleneck Sympatric speciationSympatric speciation

Stabilizing selectionStabilizing selection Adaptive radiationAdaptive radiation

Directional selectionDirectional selection GradualismGradualism

Disruptive selectionDisruptive selection Punctuated EquilibriumPunctuated Equilibrium

Sexual selectionSexual selection

Mechanisms of EvolutionMechanisms of Evolution

Evolution occurs at the population level, with genes as Evolution occurs at the population level, with genes as the raw material.the raw material.Hardy-Weinberg Principle Hardy-Weinberg Principle states that when allelic frequencies remain constant, a population is in genetic equilibrium. (Even though the number of owls doubled, the ratio of gray to red owls remained the same).

Hardy-Weinberg PrincipleHardy-Weinberg Principle

pp2 2 + 2pq + q+ 2pq + q2 2 = 1= 1

This equation allows us to determine the This equation allows us to determine the equilibrium frequency of each genotype in equilibrium frequency of each genotype in the population: homozygous dominant the population: homozygous dominant (p(p22), heterozygous (2pq), and homozygous ), heterozygous (2pq), and homozygous recessive (qrecessive (q22). Note the sum of these ). Note the sum of these frequencies equals one.frequencies equals one.

Hardy-Weinberg PrincipleHardy-Weinberg Principle

A population in genetic equilibrium must meet five A population in genetic equilibrium must meet five conditions – there must be no genetic drift, no gene flow, conditions – there must be no genetic drift, no gene flow, mating must be random, mutation, and there must be no mating must be random, mutation, and there must be no natural selection.natural selection.

Genetic DriftGenetic Drift

A change in the allelic frequencies in a population that is due to chance.

In smaller populations, the effects of genetic drift become more pronounced, and the chance of losing an allele becomes greater.

Examples: Founder Effect & Bottleneck

Founder EffectFounder Effect

Occurs when a small sample of a population settles in a location separated from the rest of the population

Alleles that were uncommon in the original population might be common in the new population.

Examples: Amish & French Canadians

BottleneckBottleneck

Occurs when a population declines to a very low number and then rebounds

Gene FlowGene Flow

A population in genetic equilibrium A population in genetic equilibrium experiences no gene flow, however, few experiences no gene flow, however, few populations are isolatedpopulations are isolated

Random movement of individuals between Random movement of individuals between populations, or migration ipopulations, or migration increases genetic variation within a population and reduces differences between populations

Nonrandom matingNonrandom mating

Rarely is mating completely random in a Rarely is mating completely random in a population.population.

Usually individuals mate with individuals in Usually individuals mate with individuals in close proximity.close proximity.

This promotes inbreeding and could lead to a change in allelic proportions favoring individuals that are homozygous for particular traits

MutationsMutations

A random change in genetic material.A random change in genetic material.

Collective mutations violate genetic Collective mutations violate genetic equilibrium.equilibrium.

Occasionally mutations provide an Occasionally mutations provide an advantage to organisms and become advantage to organisms and become more common in subsequent generations.more common in subsequent generations.

Basis upon which natural selection works.Basis upon which natural selection works.

Natural SelectionNatural SelectionActs to select the individuals that are best adapted for survival and reproductionStabilizing selection operates to eliminate extreme expressions of a trait when the average expression leads to higher fitness. (Birth Weights)Directional selection makes an organism more fit. (Peppered Moths)Disruptive selection is a process that splits a population into two groups. (Lake Erie Water Snakes)

Sexual SelectionSexual Selection

Sexual selection operates in populations where males and females differ significantly in appearance. (Males are largest and most colorful in the group).Qualities of sexual attractiveness appear to be the opposite of qualities that might enhance survival. (More likely target for predators yet bodies enhance reproductive success).Examples: Peacocks & Deer

Reproductive IsolationReproductive Isolation

Two types of reproductive isolating Two types of reproductive isolating mechanism prevent gene flow among mechanism prevent gene flow among populations:populations: Prezygotic isolating mechanisms – operate Prezygotic isolating mechanisms – operate

before fertilization occurs.before fertilization occurs. Postzygotic isolating mechanisms – operate Postzygotic isolating mechanisms – operate

after fertilization has occurred to ensure that after fertilization has occurred to ensure that the resulting hybrid remains infertile.the resulting hybrid remains infertile.

Prezygotic IsolationPrezygotic Isolation

prevents reproduction by making fertilization unlikely.prevents genotypes from entering a population’s gene pool through geographic, ecological, behavioral, or other differencesEastern and Western meadowlarks similar in appearance but their songs separate them behaviorally.

Postzygotic IsolationPostzygotic Isolation

Occurs when Occurs when fertilization fertilization has occurred but a hybrid offspring cannot develop or reproduce.Prevents offspring survival or reproduction.A Liger is the offspring of a male lion and a female tiger. Ligers are sterile.

SpeciationSpeciationA population must diverge and then be A population must diverge and then be reproductively isolated for speciation to occur.reproductively isolated for speciation to occur.Two types of speciation:Two types of speciation: Allopatric speciation - Allopatric speciation - A physical barrier

divides one population into two or more populations. (The Grand Canyon separates the Abert and Kaibab squirrels).

Sympatric speciation - Sympatric speciation - A species evolves into a new species without a physical barrier. The ancestor species and the new species live side by side during the speciation process. (Occurs frequently in plants due to polyploidy).

Patterns of EvolutionPatterns of Evolution

Adaptive Radiation - Adaptive Radiation - Can occur in a relatively short time when one species gives rise to many different species in response to the creation of new habitat or some other ecological opportunity.Follows large-scale extinction events

CoevolutionCoevolution

The relationship between two species might be so close that the evolution of one species affects the evolution of the other species.Mutualism – occurs when two species benefit each other. (Moth and the comet orchid it pollinates exist in a mutualistic relationship).Coevolutionary arms race – one species can evolve a parasitic dependency on another species. (A plant and an insect pathogen that is dependent on the plant for food. The plant evolves a chemical defense; the insect evolves a biochemistry to resist the defense; response continues to escalate.)

Convergent EvolutionConvergent Evolution

Unrelated species evolve similar traits even though they live in different parts of the world.

Occurs in environments that are geographically far apart but have similar ecology and climate.

Rate of SpeciationRate of Speciation

Evolution proceeds in small, gradual steps according to a theory called gradualism.Punctuated equilibrium explains rapid spurts of genetic change causing species to diverge quickly.