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

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:

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 RecordA 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

Hyracotherium Miohippus

Neohipparion Equus

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 evolvedHorse 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 evolution2. Outline the Darwin and Wallace

Theory of natural selection3. Discuss the evidence of evolution

from the study of fossils