AQA GCSE Evolution(Biology)

Evolution

Evolution is the change in inherited characteristics of a population over time.

It happens through a process called natural selection.

Over long periods, this can lead to the formation of new species.

Origin of Life

The theory of evolution by natural selection states:

All species evolved from simple life forms. These first appeared over 3 billion years ago. Over time, organisms became more complex.

The Earth was formed about 4.5 billion years ago as a comparison.

Variation

Individuals in a population are not all the same – they show variation.

Variation can be caused by:

Genetics – differences inherited from parents

Environment – conditions in which an organism grows

Some variations make individuals better suited to survive in their environment.

In the diagram below, there are white rabbits and brown rabbits. The white rabbits are better camouflaged and less likely to be eaten by predators.

The brown rabbit stands out, so its more likely to be eaten by a predator.

This gives the white rabbits a survival advantage

Evolution

Evolution is the change in inherited characteristics of a population over time.

In the example above for the rabbits:

Variation
In a population of rabbits, there is variation in fur colour (e.g. brown and white).

Mutation
A random genetic mutation causes some rabbits to have white fur.

Selection pressure
In a snowy environment, white rabbits are better camouflaged.

Survival advantage
White rabbits are less likely to be seen by predators, so more of them survive.

Reproduction
These rabbits reproduce and pass on the white fur allele to their offspring.

Over time (evolution)
The number of white rabbits increases, and the population becomes mostly white.

Above is natural selection, this is the mechanism for evolution. Remember that evolution is the change in inherited characteristics over time.

Speciation (Formation of New Species)

Speciation is the formation of a new species

A species is a group of individuals that can breed together to produce fertile offspring.

Sometimes populations become separated (e.g. by a river).
They experience different environments.
Different traits are selected.
Over time, they become so different they cannot interbreed.
This means a new species has formed.

Term	Definition
Evolution	Change in inherited characteristics of a population over time.
Natural selection	Survival of the fittest
Species	organisms that can interbreed to produce fertile offspring
Variation	Differences in characteristics between individuals of the same species.
Adaptation	A feature that will increase the chance of survival