B1b 7 Evolution 7.3 Natural selection

Learning objectives Understand how natural selection works Understand how natural selection works Know what a mutation is Know what a mutation is Understand what is involved in extinction Understand what is involved in extinction

The Peppered Moth

Natural Selection Organisms gain an advantage in competition Organisms gain an advantage in competition Against other species Against other species Against own species Against own species More likely to thrive, survive and breed More likely to thrive, survive and breed Nature has selected the individual Nature has selected the individual

Survival of the fittest Animal always produce too many offspring Animal always produce too many offspring They don’t all survive They don’t all survive Individuals in a species show variation Individuals in a species show variation Due to genes - DNA Due to genes - DNA Those with best suited genes Those with best suited genes Breed, feed, stay alive Breed, feed, stay alive Think about bunnies – what gets passed on and what doesn’t Think about bunnies – what gets passed on and what doesn’t

Mutants Natural mistakes when DNA is being copied Natural mistakes when DNA is being copied Happens when cells divide Happens when cells divide New form of a gene (allele) New form of a gene (allele) Might have no effect Might have no effect Gene might do something different Gene might do something different Introduces variety into the species Introduces variety into the species Increases survival of species Increases survival of species

Evolution in action Antibiotic resistant bacteria Antibiotic resistant bacteria 1. Variation – some strains resistant, some aren’t 2. Competition – non-resistant bacteria killed by penicillin. 3. Survival of the fittest – resistant bacteria survive 4. Passing on of genes – resistant bacteria reproduce - pass on adaptations to offspring Bacteria Penicillin

Extinction Millions of species exist today, but billions have existed Millions of species exist today, but billions have existed Extinct Extinct Changing conditions Changing conditions Organisms adapt to survive – new food, habitat Organisms adapt to survive – new food, habitat Organisms that don’t adapt – die out Organisms that don’t adapt – die out Extinction is essential to balance number of species Extinction is essential to balance number of species

Environmental change Animals adapted to one extreme won’t survive in another Animals adapted to one extreme won’t survive in another Main cause of extinctions Main cause of extinctions Dinosaurs - perfectly adapted Dinosaurs - perfectly adapted sudden change in climate sudden change in climate Too cold Too cold Mammals could survive Mammals could survive

Top 5 extinction events 500 million years ago – trilobites 500 million years ago – trilobites 430 million years ago – plants and fish 430 million years ago – plants and fish 350 million years ago – 70% all species 350 million years ago – 70% all species 225 million years ago – amphibians and invertebrates 225 million years ago – amphibians and invertebrates 65 million years ago – dinosaurs 65 million years ago – dinosaurs Next year – humans? Next year – humans?

Causes of extinction New diseases – organisms have developed immune response – swine flu New diseases – organisms have developed immune response – swine flu New predators – Tibbles the cat New predators – Tibbles the cat New competitors – species replacement New competitors – species replacement Famous case – The Dodo Famous case – The Dodo

Learning outcomes How does natural selection work? How does natural selection work? What is a mutation and what effect can it have? What is a mutation and what effect can it have? What might be involved in an extinction? What might be involved in an extinction?