Natural Selection & Evolution Notes

Edexcel GCSE Biology: Revision notes

Key facts

  • Darwin and Wallace developed evolution by natural selection independently and published jointly in 1858.
  • Natural selection: variation, survival of the best adapted, passing on genes, change over generations.
  • Antibiotic resistance is natural selection we can watch happening.
  • Fossils such as Ardi, Lucy and Leakey's finds show how humans evolved.
  • The pentadactyl limb points to a common ancestor, and genetic analysis gave the three-domain system.
  1. 1

    Variation

    individuals differ

  2. 2

    Survival

    best adapted survive and reproduce

  3. 3

    Inheritance

    advantageous genes passed on

  4. 4

    Change

    trait becomes more common

Natural selection leads to evolution

Darwin, Wallace and evolution

Darwin and Wallace independently developed evolution by natural selection, and published it jointly in 1858.

Darwin's On the Origin of Species followed in 1859. The theory was controversial because it conflicted with some religious views, and no mechanism of inheritance was known at the time. Today it underpins all of modern biology.

  1. 1858

    Darwin and Wallace

    Publish the theory jointly.

  2. 1859

    Origin of Species

    Darwin's book sets out the evidence.

Who published the theory of evolution by natural selection jointly in 1858?

How natural selection works

Individuals vary, the best adapted survive and reproduce, and their advantageous genes become more common.

There is variation in a population. The best-adapted survive and reproduce ('survival of the fittest'), passing on advantageous genes. Over generations the proportion with the trait increases, and this can eventually lead to speciation.

  1. 1

    Variation

    exists in a population

  2. 2

    Survival

    the best-adapted survive and reproduce

  3. 3

    Inheritance

    advantageous genes are passed on

  4. 4

    Change

    the trait becomes more common over generations

  5. 5

    Speciation

    can eventually lead to a new species

How natural selection leads to evolution

Why does the proportion of a helpful trait increase over generations?

Antibiotic resistance

Antibiotic resistance is natural selection that we can observe today.

A random mutation gives some bacteria antibiotic resistance. The antibiotic kills the non-resistant bacteria, so the resistant ones survive and reproduce. The resistance gene then becomes common in the population.

  1. 1

    Mutation

    random mutation gives some bacteria resistance

  2. 2

    Antibiotic use

    kills the non-resistant bacteria

  3. 3

    Survival

    resistant bacteria survive and reproduce

  4. 4

    Spread

    the resistance gene becomes common

How resistance spreads

Why is antibiotic resistance evidence for natural selection?

Fossil and tool evidence

Fossils of early hominids show how humans changed over time, and stone tools show growing skill.

Ardi (4.4 million years old) had a mix of ape and human features. Lucy (3.2 million years old) walked upright but had a small brain, so bipedalism came before a large brain. Leakey's fossils (1.6 million years old) are closer to the modern skeleton.

Stone tools become more complex over time. They are dated indirectly, using the rock stratum they are found in.

01234ArdiLucyLeakey's fossilsFossilAge (million years)
Age of each fossil (million years ago)

Ardi

  • Mix of ape and human features

Lucy

  • Bipedalism before a large brain

Leakey's fossils

  • Closer to the modern skeleton

Which fossil showed bipedalism before a large brain?

The pentadactyl limb

Humans, whales and bats share one limb bone structure, which points to a common ancestor.

The pentadactyl limb has a 5-digit bone structure. Humans, whales and bats all have it, despite using their limbs for different functions. This is evidence of a common ancestor.

  1. 1

    Common ancestor

    Had a limb with a 5-digit bone structure

  2. 2

    Human arm

    Used for grasping

  3. 3

    Whale flipper

    Used for swimming

  4. 4

    Bat wing

    Used for flying

One bone structure, different functions

Human

Limb used for:
Grasping and handling
Bone structure:
Pentadactyl

Whale

Limb used for:
Swimming (flipper)
Bone structure:
Pentadactyl

Bat

Limb used for:
Flying (wing)
Bone structure:
Pentadactyl

What does the pentadactyl limb suggest about humans, whales and bats?

Three domains of life

Genetic analysis split the prokaryotes in two, giving the three-domain system that replaced five kingdoms.

Genetic analysis showed that prokaryotes contain two genetically distinct groups. This led to the three-domain system: Archaea, Bacteria and Eukarya.

  1. 1

    Prokaryotes

    Genetic analysis shows two distinct groups

  2. 2

    Archaea

    One domain

  3. 3

    Bacteria

    A second domain

  4. 4

    Eukarya

    Organisms with a nucleus form the third domain

The three-domain system

Archaea

  • Prokaryote cells

Bacteria

  • Prokaryote cells

Eukarya

  • Eukaryote cells

Name the three domains.

Try an exam question

Explain how antibiotic resistance in bacteria is an example of natural selection.

[4 marks]

That's the notes covered.

Carry on to the next subtopic.