Chapter 15-3: Darwin Presents Chapter 15-3: Darwin Presents His CaseHis Case

Essential Questions:Essential Questions:How does How does natural variationnatural variation relate to relate to artificial selection?artificial selection?What is What is natural selectionnatural selection and dow does it and dow does it relate to relate to fitness?fitness?What evidence did Darwin presented for What evidence did Darwin presented for evolution by natural selection?evolution by natural selection?

Publication of Publication of On the Origin of SpeciesOn the Origin of Species1858: Alfred Wallace comes up with same 1858: Alfred Wallace comes up with same

ideaideaDarwin publishes 1859Darwin publishes 1859

Natural variation and Natural variation and artificial selectionartificial selectionHumans select desired traits from variation Humans select desired traits from variation

found in naturefound in natureOver time, can change speciesOver time, can change species

Evolution by Evolution by natural selectionnatural selectionStruggle for existenceStruggle for existence

High birth rate means not enough resources for allHigh birth rate means not enough resources for allSurvival of the fittestSurvival of the fittest

Fitness: how well suited org. is to its environmentFitness: how well suited org. is to its environmentAdaptation: trait that increases fitnessAdaptation: trait that increases fitnessOver time, Over time, natural selectionnatural selection causes changes in causes changes in

inherited traitsinherited traitsDescent with modificationDescent with modification

Each species descends, with modification, from Each species descends, with modification, from other speciesother species

Common descentCommon descent

Evidence of evolution by nat. selectionEvidence of evolution by nat. selectionFossil recordFossil record

Geographic distribution of living speciesGeographic distribution of living species

Homologous body structuresHomologous body structures

Similarities in early developmentSimilarities in early development

Summary of DarwinSummary of Darwin’’s Theory (p. 386)s Theory (p. 386)1.1. Variation existsVariation exists2.2. More offspring produced than can surviveMore offspring produced than can survive3.3. Therefore, competition for limited resourcesTherefore, competition for limited resources4.4. b/c of #1, each org. has advantages & b/c of #1, each org. has advantages &

disadvantages in struggle to survivedisadvantages in struggle to survive5.5. Most fit individuals survive/reproduce most Most fit individuals survive/reproduce most

successfullysuccessfully1.1. Most fit traits get passed on most oftenMost fit traits get passed on most often2.2. Less fit traits passed on less oftenLess fit traits passed on less often

6.6. Species change over time due to Species change over time due to natural selectionnatural selection, , new species appear & other species disappear new species appear & other species disappear

7.7. Species alive now descended, with modificaiton, Species alive now descended, with modificaiton, from past speciesfrom past species

8.8. All orgs. are united in a single tree of life by All orgs. are united in a single tree of life by common descentcommon descent