How Does Evolution How Does Evolution Happen? Happen?

Chapter 7 Chapter 7

Section 2Section 2

Charles DarwinCharles Darwin

Naturalist (one who studies nature) Naturalist (one who studies nature) on the on the HMS BeagleHMS Beagle

Observations on trip w/ Observations on trip w/ HMS BeagleHMS Beagle helped Darwin form his theory of how helped Darwin form his theory of how evolution happensevolution happens– Collected thousands of plant & animal Collected thousands of plant & animal

samplessamples– Galápagos IslandsGalápagos Islands

Darwin’s FinchesDarwin’s Finches

Noticed many plants & animals on Noticed many plants & animals on the Galápagos Islands were similar to the Galápagos Islands were similar to plants & animals in Ecuadorplants & animals in Ecuador– ExampleExample: Finches (birds): Finches (birds)

Slightly different than those in EcuadorSlightly different than those in Ecuador Beaks different depending on which island Beaks different depending on which island

they are onthey are on Beak of each finch is adapted to the way Beak of each finch is adapted to the way

the bird usually gets food. the bird usually gets food.

PopulationsPopulations

Limited by:Limited by:1.1. StarvationStarvation2.2. DiseaseDisease3.3. CompetitionCompetition4.4. PredationPredation

Only a limited # of a species can Only a limited # of a species can survive to reproducesurvive to reproduce

Offspring of the survivors inherit Offspring of the survivors inherit traits that help the offspring survive traits that help the offspring survive in their environment in their environment

Theory of Natural SelectionTheory of Natural Selection

Darwin’s bookDarwin’s book: : On the Origin of On the Origin of Species by Means of Natural Species by Means of Natural SelectionSelection – proposed the theory that evolution proposed the theory that evolution

happens through happens through natural selectionnatural selection Natural SelectionNatural Selection: the process by : the process by

which organisms that are better which organisms that are better adapted to their environment survive adapted to their environment survive and reproduce more successfully and reproduce more successfully than less well adapted organisms do than less well adapted organisms do

Darwin’s TheoryDarwin’s Theory

1.1. Each species produces more offspring Each species produces more offspring than will survive to reproduce.than will survive to reproduce.

2.2. Individuals within a population have Individuals within a population have slightly different traits. slightly different traits.

3.3. Individuals within a population compete Individuals within a population compete with each other for limited resources. with each other for limited resources.

4.4. Individuals that are better equipped to Individuals that are better equipped to live in an environment are more likely to live in an environment are more likely to survive to reproduce.survive to reproduce.