How Does Evolution Happen

Ch.5, Sec.2

Charles Darwin

18311831Naturalist on HMS Naturalist on HMS BeagleBeagle

Collected Collected plant/animal plant/animal specimensspecimens

Traveled to Traveled to Galapagos IslandsGalapagos Islands

He noticed He noticed animals/plants on animals/plants on Galapagos similar but Galapagos similar but not identical to not identical to mainland speciesmainland species

Main species Main species observed were observed were finchesfinches

FinchesFinchesDifferent from Different from mainlandmainland

Different from Different from others on islandothers on island

Mainly shape of the Mainly shape of the beakbeak

QuestionQuestionWhy were the Why were the finches on the finches on the island similar, but island similar, but not identical to the not identical to the ones on the ones on the mainland?mainland?

Thomas MalthusThomas MalthusHumans have the Humans have the potential to potential to reproduce beyond reproduce beyond food suppliesfood supplies

Darwin noticed…Darwin noticed…Species produce Species produce more offspring than more offspring than can survivecan survive

Limited # survive Limited # survive and reproduceand reproduce

Why?Why? ADAPTED

Natural SelectionNatural SelectionProcess by Process by

which evolution which evolution may occurmay occur

STEPS OF STEPS OF NATURAL NATURAL

SELECTIONSELECTION

1) Overproduction1) OverproductionSpecies produce Species produce

more offspring than more offspring than will survivewill survive

Ex. - frogsEx. - frogs

2) Genetic Variation2) Genetic VariationIndividuals are Individuals are slightly diff. from slightly diff. from

each othereach otherSome are better Some are better

adaptedadapted

3) Struggle to Survive3) Struggle to SurviveCompetition for Competition for

resourcesresourcesSome better Some better

adapted to obtain adapted to obtain resourcesresources

4) Successful 4) Successful ReproductionReproduction

Well adapted Well adapted == survival survival ==

reproductionreproductionSpecies continuesSpecies continues