The Theory of Natural Selection and the Survival of the Fittest

Evolution is the way in which living things change genetically over long periods of time to produce new forms of life.

 A theologist and also a naturist who devised a theory about evolution

 Much of Darwin’s work was done on the Galapagos islands with Finch birds

 Darwin proposed a mechanism for evolution by natural selection  Alfred Wallace working in Borneo also proposed the same theory so it is called the Darwin – Wallace theory of evolution

 Darwin’s observation…  For all organisms many offspring are produced but  Overall the population numbers remain constant.

 The high number of offspring causes competition between them for resources – only some offspring will survive to become adults!

Competition occurs between different species…

And members of the same species

 All populations of organisms have variations that have arisen by chance - due to sexual reproduction, mutations etc.

 The variations allow some individuals to adapt and survive and reproduce in their environment and pass on the successful traits to their off spring.  This is called natural selection… or survival of the fittest!

How are polar bears adapted to life in an extremely cold climate? White fur acts as camouflage. Large feet spread the body’s weight. The wide paws act as good paddles How are polar bears adapted? Thick fur and a thick layer of body fat insulate from the cold. Small ears help to reduce heat loss. and snow shoes.

Other adaptations that polar bears have evolved to cope with conditions in the harsh polar environment are: How are polar bears adapted? Skin is actually black to absorb any heat transmitted through the hairs. Greasy fur repels water and keeps the bear dry. Eyes have brown irises to reduce the glare from sunlight reflection. Body surface area is small compared to volume to reduce heat loss.

Play evolution movie file from extra material folder

 The fossil Record A fossil is the remains of an organism that lived a long time ago. Clip about fossils forming!

Play fossil.swf file in extra material folder

Fossils show changes in organisms occur over time – evidence that evolution occurs: 1. Some fossil organisms are extinct e.g Dinosaurs

 2. Fossils show changes when compared to modern organisms e.g the modern horse Miohippus Neohipparion Equus Hyracotherium

Miohippus NeohipparionEquus Hyracotherium

 The ancestor of the modern horse evolved 60 million years ago Horse Fossils were 0.4m tall  30 million years ago Horse fossils were 0.6m tall  15 million years ago Horse fossils were 1m tall  1 million years ago Equus – the modern horse evolved Horse fossils were 1.6m tall

3. Modern fossils show increased complexity

Play human evolution movie file from extra material folder

1. Outline the evidence for evolution 2. How do fossils provide evidence for evolution 3. Can you outline the evolution of the modern horse?

Can you………………………… 1. Define evolution 2. Outline the Darwin and Wallace Theory of natural selection 3. Discuss the evidence of evolution from the study of fossils