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Natural Selection. Key words: characteristics, ‘fittest’. Starter. How the giraffe got its neck. How does Darwin’s theory explain a giraffe’s long neck?. Due to natural variation, the ancestors of modern giraffes would have had necks of different length. . Explain how Darwin would have
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Natural Selection Key words: characteristics, ‘fittest’
Starter How the giraffe got its neck How does Darwin’s theory explain a giraffe’s long neck? Due to natural variation, the ancestors of modern giraffes would have had necks of different length. Explain how Darwin would have explained the giraffe’s neck Giraffes with longer necks would have been able to reach more food than those with shorter necks. As a result, the long-necked giraffes were more likely to be healthy and live to produce more high-quality offspring. This, in turn, would increase the chances of their long-necked characteristic (an adaptive trait) being passed on to future generations.
Objective • What is natural selection? • Success Criteria • By the end of the lesson I: • can explain that organisms in a species all vary from each other • can explain that some organisms are more likely to survive and breed as they have ‘better’ chanracteristics.
What do you think ‘Natural Selection’ is defined as? Natural selection occurs when successful characteristics, produced by chance (random) mutations, enable organisms to survive and breed.
ANOTHER EXAMPLE The peppered moth The peppered moth is a common insect in Britain with two forms: the dark form and the light form. The light form has small black specks just like it has been dusted with pepper. This is variation. 300 years ago most peppered moths were the light form. After the industrial revolution the dark form became commonest in city areas. Why?
Natural selection of dark form in industrial areas Tree surfaces are dark because of air pollution Pale lichens are killed by sulfur dioxide Dark moth less likely to be seen and eaten by bird predators Dark moths more likely to survive to breed Repeated over generations
Natural selection of light form in clean areas Tree surfaces are pale. Pale lichens grow on the tree bark. Light moth less likely to be seen and eaten by bird predators Light moths more likely to survive to breed Repeated over generations
Weaker members of the species may die from Disease Lack of food (or being caught by predators) Variation in the climate (a very wet/cold/hot period of weather) The survival of organisms with the ‘best’ characteristics is known as ‘survival of the fittest’. The ‘best’ characteristics can be Fastest Ability to find food Fight off disease Survive a short changein weather well EXAM TIP
Draw a flowchart to explain the natural selection of oysters from Malpeque Bay (1915-1940) p113 in text. EXAM TIP A disease killed most of the Oysters in Malpeque Bay, Canada Fortunately a few of the shellfish carried a mutation which made them resistant to the disease. These were the only ones to survive and breed. Repeated over generations.
What happens when habitats change? Adaptive evolution ensures that individuals within a species have traits allowing them to survive and reproduce in their habitat. If the habitat changes, however, successful traits can become a disadvantage. For example, if global warming caused Arctic snow to melt, brown rabbits may be better camouflaged and so more likely to survive than white rabbits. Individuals that fail to reproduce, compete effectively for food or survive against new predators will eventually die out. If the last individual of a species dies, the species is extinct.
Objective • What is natural selection? • Success Criteria • By the end of the lesson I: • can explain that organisms in a species all vary from each other • can explain that some organisms are more likely to survive and breed as they have ‘better’ chanracteristics.
