B1b 7 EvolutionB1b 7 Evolution7.3 Natural selection7.3 Natural selection

Learning objectivesLearning objectives Understand how natural selection Understand how natural selection

worksworks Know what a mutation isKnow what a mutation is Understand what is involved in Understand what is involved in

extinctionextinction

The Peppered MothThe Peppered Moth

Natural SelectionNatural Selection Organisms gain an Organisms gain an

advantage in advantage in competitioncompetition Against other speciesAgainst other species Against own speciesAgainst own species

More likely to thrive, More likely to thrive, survive and breedsurvive and breed

Nature has selected Nature has selected the individualthe individual

Survival of the fittestSurvival of the fittest Animal always produce too many Animal always produce too many

offspringoffspring They don’t all surviveThey don’t all survive

Individuals in a species show variationIndividuals in a species show variation Due to genes - DNADue to genes - DNA

Those with best suited genesThose with best suited genes Breed, feed, stay aliveBreed, feed, stay alive Think about bunnies – what gets passed on Think about bunnies – what gets passed on

and what doesn’tand what doesn’t

MutantsMutants Natural mistakes when Natural mistakes when

DNA is being copiedDNA is being copied Happens when cells divideHappens when cells divide

New form of a gene New form of a gene (allele) (allele) Might have no effectMight have no effect Gene might do something Gene might do something

differentdifferent Introduces variety into Introduces variety into

the speciesthe species Increases survival of Increases survival of

speciesspecies

Evolution in actionEvolution in action Antibiotic resistant bacteriaAntibiotic resistant bacteria1.1. Variation – some strains Variation – some strains

resistant, some aren’tresistant, some aren’t2.2. Competition – non-resistant Competition – non-resistant

bacteria killed by penicillin.bacteria killed by penicillin.3.3. Survival of the fittest – Survival of the fittest –

resistant bacteria surviveresistant bacteria survive4.4. Passing on of genes – Passing on of genes –

resistant bacteria resistant bacteria reproduce - pass on reproduce - pass on adaptations to offspringadaptations to offspring

Bacteria

Penicillin

ExtinctionExtinction Millions of species exist today, but Millions of species exist today, but

billions have existedbillions have existed ExtinctExtinct

Changing conditionsChanging conditions Organisms adapt to survive – new food, Organisms adapt to survive – new food,

habitathabitat Organisms that don’t adapt – die outOrganisms that don’t adapt – die out

Extinction is essential to balance Extinction is essential to balance number of speciesnumber of species

Environmental changeEnvironmental change Animals adapted to one extreme Animals adapted to one extreme

won’t survive in anotherwon’t survive in another Main cause of extinctionsMain cause of extinctions Dinosaurs - perfectly adaptedDinosaurs - perfectly adapted

sudden change in climatesudden change in climate Too coldToo cold Mammals could surviveMammals could survive

Top 5 extinction eventsTop 5 extinction events 500 million years ago – trilobites500 million years ago – trilobites 430 million years ago – plants and fish430 million years ago – plants and fish 350 million years ago – 70% all species350 million years ago – 70% all species 225 million years ago – amphibians 225 million years ago – amphibians

and invertebratesand invertebrates 65 million years ago – dinosaurs65 million years ago – dinosaurs Next year – humans?Next year – humans?

Causes of extinctionCauses of extinction New diseases – organisms have New diseases – organisms have

developed immune response – swine developed immune response – swine fluflu

New predators – Tibbles the catNew predators – Tibbles the cat New competitors – species New competitors – species

replacementreplacement Famous case – The DodoFamous case – The Dodo

Learning outcomesLearning outcomes How does natural selection work?How does natural selection work? What is a mutation and what effect What is a mutation and what effect

can it have?can it have? What might be involved in an What might be involved in an

extinction?extinction?