Chapter 22: Descent With Chapter 22: Descent With Modification Modification

A Darwinian View of LifeA Darwinian View of LifeOn the Origin of Species by Means of On the Origin of Species by Means of Natural Selection by Charles DarwinNatural Selection by Charles DarwinAttempts to create a family tree for Attempts to create a family tree for all life on Earthall life on EarthMechanism= natural selectionMechanism= natural selection

Groundwork for Darwin’s Groundwork for Darwin’s TheoryTheory TaxonomyTaxonomy

Linnaeus- group organisms based on similar Linnaeus- group organisms based on similar structuresstructures

PaleontologyPaleontology CuvierCuvier Study of fossilsStudy of fossils

GradualismGradualism Change is slow but continuousChange is slow but continuous

Lamarck’s TheoryLamarck’s Theory First to include gradualismFirst to include gradualism Use & disuseUse & disuse Inheritance of acquired characteristicsInheritance of acquired characteristics

Natural SelectionNatural Selection Population CAN change over generations if Population CAN change over generations if

individuals with better adaptations leave individuals with better adaptations leave more offspringmore offspring

Evolutionary adaptationEvolutionary adaptation Inherited characteristics that enable survival Inherited characteristics that enable survival

and reproduction in a certain environmentand reproduction in a certain environment EvolutionEvolution

Change in genetic composition of a population Change in genetic composition of a population over timeover time

Descent with modification (Darwin’s term)Descent with modification (Darwin’s term) All organisms are related through descent with an All organisms are related through descent with an

ancestral organismancestral organism Modifications in species a result of inhabiting Modifications in species a result of inhabiting

different environmentsdifferent environments

Natural selectionNatural selection RequirementsRequirements

Resources are limited Resources are limited Struggle for existenceStruggle for existence Individuals with Individuals with heritableheritable traits better traits better

suited to environment leave more suited to environment leave more offspringoffspring

Population gradually evolves to exhibit Population gradually evolves to exhibit higher number of individuals with higher number of individuals with beneficial traitbeneficial trait

Natural SelectionNatural Selection INDIVIDUALS DO NOT EVOLVE- INDIVIDUALS DO NOT EVOLVE-

POPULATIONS CAN!!!!POPULATIONS CAN!!!! Environment determines which traits Environment determines which traits

are favoredare favored Biogeography- similarities found among Biogeography- similarities found among

species in similar ecological nichesspecies in similar ecological niches Convergence- unrelated species in similar Convergence- unrelated species in similar

niches have similar adaptationsniches have similar adaptations Divergence- related species in different Divergence- related species in different

ecological niches have dissimilar adaptationsecological niches have dissimilar adaptations Environment Environment does not create does not create

change-change- it selects for individuals who it selects for individuals who alreadyalready possess beneficial possess beneficial adaptationadaptation

Examples of natural selection Examples of natural selection at workat work

Guppy sexual maturation age & Guppy sexual maturation age & predatory pressurepredatory pressure

Drug resistant HIVDrug resistant HIV Insecticide resistance in insectsInsecticide resistance in insects

EvidenceEvidence

Fossil recordFossil record HomologyHomology

related species have similar underlying related species have similar underlying traits that MAY be used for different traits that MAY be used for different functionsfunctions

Homologous structuresHomologous structures Comparative embryologyComparative embryology Vestigial structures (remnant structures)Vestigial structures (remnant structures) Molecular similarities (DNA, protein)Molecular similarities (DNA, protein)