Darwin Presents His CaseDarwin Presents His Case

Chapter 15, Section 3Chapter 15, Section 3

Lyell’s InfluenceLyell’s Influence

In attempt to In attempt to explain the past in terms of explain the past in terms of present day processespresent day processes, Darwin went to local , Darwin went to local farmers and animal breeders and observed…farmers and animal breeders and observed…

Variation in the organisms that could be Variation in the organisms that could be inheritedinherited

After many generations, organisms appear After many generations, organisms appear very different from ancestorsvery different from ancestors

Darwin called this process ARTIFICIAL Darwin called this process ARTIFICIAL SELECTIONSELECTION

Darwin was convinced a similar process Darwin was convinced a similar process occurred in nature: occurred in nature:

NATURAL SELECTIONNATURAL SELECTION

1.1. Variation in NatureVariation in Nature No two organisms are exactly alike!No two organisms are exactly alike!

2.2. Struggle for ExistenceStruggle for Existence (Malthus) (Malthus) High birth rates and limited resources will force organisms to High birth rates and limited resources will force organisms to

competecompete Selective pressures (predation, competition, parasitism, Selective pressures (predation, competition, parasitism,

disease, pesticides, etc)disease, pesticides, etc)3.3. Survival of the FittestSurvival of the Fittest

FitnessFitness: an organism’s ability to survive and reproduce: an organism’s ability to survive and reproduce AdaptationAdaptation: any inheritable characteristic that increases an : any inheritable characteristic that increases an

organism’s chance of survivalorganism’s chance of survival Organisms with the best adaptations survive and reproduce Organisms with the best adaptations survive and reproduce

more oftenmore often4.4. Reproduction of Viable OffspringReproduction of Viable Offspring

Offspring must be fertile and reproduce Offspring must be fertile and reproduce

Descent with ModificationDescent with Modification

Darwin then proposed that over long Darwin then proposed that over long periods of time, natural selection produces periods of time, natural selection produces organisms that look different from their organisms that look different from their ancestors.ancestors.

This implies that all living things are This implies that all living things are related to one another.related to one another.

Common DescentCommon Descent: all species, living and : all species, living and extinct, were derived from common extinct, were derived from common ancestors.ancestors.

Darwin’s Evidence of Darwin’s Evidence of EvolutionEvolution

The Fossil RecordThe Fossil Record Fossils are buried in Fossils are buried in

sedimentary rock→ Relatively, sedimentary rock→ Relatively, deeper fossils are olderdeeper fossils are older

Fossils provide evidence of Fossils provide evidence of changing lifechanging life

Paleontologists search for Paleontologists search for transitional fossilstransitional fossils

Geographic Distribution of Geographic Distribution of Living SpeciesLiving Species

The geographic The geographic distribution of animals distribution of animals serves as a clue to how serves as a clue to how modern species evolvedmodern species evolved

Two islands in different Two islands in different parts of the world (with parts of the world (with similar environments) will similar environments) will house species similar to house species similar to the nearest mainland the nearest mainland rather than the other rather than the other islandisland

Ex: Australia’s unique Ex: Australia’s unique plants and animals plants and animals evolved from isolation evolved from isolation from other continentsfrom other continents

Similarities in StructureSimilarities in Structure The forelimbs of all The forelimbs of all

mammals are made of mammals are made of bones that are similar in bones that are similar in origin (skeletal structure), origin (skeletal structure), but may vary in function but may vary in function →→ called called homologous homologous structuresstructures

Vestigial structuresVestigial structures are are remnants of structures in an remnants of structures in an animal that may have had a animal that may have had a function or purpose in function or purpose in ancestral species, but serve ancestral species, but serve no apparent function or no apparent function or purpose in modern speciespurpose in modern species

Similarities in DevelopmentSimilarities in Development

EmbryologyEmbryology: the : the study of embryo study of embryo developmentdevelopment

Animals that are Animals that are more closely more closely related will have related will have more similarities in more similarities in the stage of the stage of developmentdevelopment