15.3 Darwin Presents His Case

Darwin Presents His CaseThe specimens Darwin brought back had the scientific community in a buzzLearned that Galapagos species are found nowhere else in the worldThey looked similar to South American mainland species but were clearly different

Darwins BookPublished his ideas about species diversity and evolution in On the Origin of SpeciesProposed a mechanism for evolution called natural selectionMany agreed with Darwin while others strongly opposed him

Natural VariationScientists used to believe species were perfect and unchangingDarwin argued natural variation (differences among species) is found in all types of organismsSome cows give more milkSome plants give larger fruit

Artificial SelectionDarwin also studied English farmers and breedersUsed selective breeding to breed the best individualsLargest hogs, fastest horsesDarwin called this artificial selectionStill used today!

Evolution by Natural SelectionDarwin believed that evolution occurred through natural selectionNatural selection = the process by which only the organisms best adapted to their environment will survive and reproduce3 main parts to natural selection

1. The Struggle for ExistenceThere are more living things than resourcesResults in competition Competition = the struggle among living things to get their needs for life

2. Survival of the FittestIndividuals that are better suited to their environments survive (high fitness)Individuals not suited to their environment will die (low fitness)Fitness the ability of an individual to survive and reproduce in its environmentIs a result of adaptations

2. Survival of the FittestAdaptation any inherited characteristic that increases an organisms chance for survivalLong necks in giraffesLong toes / webbed feet in birdsColoring / Camouflage

3. Descent with ModificationEach living species has descended, with changes, from other species over timeImplies all organisms are related to one anotherKnown as common descent

Evidence for EvolutionFossil EvidenceWhen living things from the past are compared to living things today, we can see that change has occurred

Evidence for EvolutionGeographic distribution of living thingsSpecies are located in different parts of the world but share similaritiesBeavers and capybara are similarMuskrat and coypu are similar

Beaver NORTH AMERICAMuskratCapybaraSOUTH AMERICABeaver MuskratBeaver and MuskratCoypu CapybaraCoypu and CapybaraCoypu

Evidence for EvolutionHomologous body structuresLimbs (arms, wings, legs, flippers) have different form and function but are constructed from the same bonesTurtleAlligatorBirdMammalsTypical primitive fish

Evidence for EvolutionVestigial structuresBody parts that no longer have functionsi.e. Pink lump in corner of eyeRemnant of a third eyelid Frogs and turtles have third eyelid to see underwaterAppendixIn many mammals the appendix is used to help digest food

Evidence for EvolutionEmbryologyStudying embryo development to look for similarities and differences

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