B1b 7 EvolutionB1b 7 Evolution
7.3 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 Think about bunnies – what gets passed
on and what doesn’ton and 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?
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