AQA GCSE Theory of evolution(Biology)

AQA GCSE Theory of evolution (Biology)

Theory of evolution by natural selection

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

It occurs by a process called natural selection.

Evolution is supported by evidence such as fossils. The theory was developed over time many scientists contributed to the theory.

Charles Darwin

Charles Darwin was a scientist who developed the theory of evolution.

He travelled around the world on the HMS Beagle; making observations of plants, animals and fossils. He spent many years collecting evidence before publishing his ideas. In 1859, he published his book “On the Origin of Species”

His ideas caused controversy at the time.

Charles Darwin developed the theory of evolution by natural selection after years of experimentation and discussion with other scientists

His ideas were also supported by:

Evidence from fossils

Developing knowledge of geology (the study of rocks and Earth’s history)

Variation

Individuals in a species show variation.

This means:

They are not identical

They have different characteristics (e.g. size, colour, speed)

In the image below we can see variation in coat colour of rabbits

Natural Selection

Individuals within a population show variation, variation can be due to a mutation.

Some characteristics give an advantage, which means that the individual is more likely to survive and reproduce.

They pass on the allele for these advantageous characteristics to their offspring

Over time, the species evolves and more individuals within the population will have the favourable characteristic.

When the term survival of the fittest is used it is referring to the individuals with the advantageous characteristic.

Peppered Moths Example

Below there are two peppered moths a light form and a dark form.

Originally, tree bark was light-coloured.

Light moths were camouflaged
Dark moths were easily seen by predators (birds)

Light moths were more likely to survive and reproduce until the industrial revolution.

During industrialisation, pollution covered trees in dark soot.

Dark moths became camouflaged. Light moths were easily seen and eaten

Dark moths were more likely to survive and reproduce, passing on the allele for the dark colour.

Over time the population gradually changed so there were more dark moths and fewer light moths.

Inheritance

Characteristics are passed on through genes, or alleles from parents to offspring

Darwin did not know how this worked because the mechanism of inheritance was discovered later about 50 years after the theory of evolution.

Why Darwin’s Theory Was Not Accepted

Darwin’s theory was not accepted at first because:

1.It challenged religious beliefs (idea that God created all life)

2.There was not enough evidence at the time

Scientists did not understand inheritance or the mechanism for how genes are passed on at the time. The mechanism for genetics was discovered about 50 years after the theory was published.

Other Theories – Lamarck

Jean-Baptiste Lamarck was a French biologist that suggested:

Characteristics gained during life are inherited:

E.g. giraffes stretching necks to reach food from high trees, which made their necks longer. This enhanced characteristic was then passed onto their offspring who would also have long necks.

We now know this is incorrect in most cases. Although the idea works for some cases, there are many cases where it does not work.

Practice Questions

1.What is meant by the term evolution?

2.Give two reasons why Darwin’s theory was not accepted at first.

3.A population of beetles shows variation in colour. Birds can easily see the green beetles but not the brown beetles. Explain how the population may change over time.