Natural Selection & EvolutionEdexcel GCSE Biology: Revision notes

Section 1

Darwin, Wallace and the Theory of Evolution

Darwin and Wallace independently developed evolution by natural selection, publishing jointly in 1858; Darwin's On the Origin of Species followed in 1859. Controversial due to conflicting religious views and lack of a known inheritance mechanism. Now underpins all modern biology.

Key termsnatural selectionOn the Origin of Species

Exam tip

Name both Darwin AND Wallace.

Section 2

Darwin's Theory

Variation exists in a population
Best-adapted survive and reproduce ('survival of the fittest')
Advantageous genes passed on
Proportion with the trait increases over generations
Can lead to speciation

Key termsvariationspeciation

Common mistake

Organisms don't 'choose' to evolve — selection acts on existing variation.

Section 3

Antibiotic Resistance as Evidence

Random mutation gives some bacteria resistance; antibiotic use kills non-resistant bacteria, resistant ones survive/reproduce, resistance gene spreads — natural selection observed today.

Key termsantibiotic resistance

Section 4

Fossil Evidence for Human Evolution

Fossil	Age	Significance
Ardi	4.4 mya	Mix of ape/human features
Lucy	3.2 mya	Bipedalism before large brain
Leakey's fossils	1.6 mya	Closer to modern skeleton

Key termsArdiLucyhominid

Exam tip

Order: Ardi (oldest) → Lucy → Leakey's finds (youngest).

Section 5

Stone Tool Evidence

Tools become more complex over time, showing increasing skill. Dated indirectly via the rock stratum they're found in.

Key termsstratum

Section 6

Pentadactyl Limbs

Same 5-digit bone structure across species (humans, whales, bats) despite different functions — evidence of a common ancestor.

Key termspentadactyl limbcommon ancestor

Think of it like this

Same building blocks rearranged for different jobs — wing, flipper, hand.

Section 7

Genetic Analysis and Three-Domain System

Genetic analysis showed prokaryotes contain two genetically distinct groups, leading to the three-domain system: Archaea, Bacteria, Eukarya, replacing the five-kingdom system.

Key termsthree-domain systemArchaea

Common mistake

Five kingdoms and three domains are different classification levels.

Must Know

Darwin & Wallace: natural selection, published jointly 1858.
Variation → survival/reproduction → gene passed on → speciation.
Antibiotic resistance = observable natural selection.
Fossils: Ardi (4.4mya) → Lucy (3.2mya) → Leakey (1.6mya).
Pentadactyl limb = common ancestor evidence.
Genetic analysis → three-domain system replaced five kingdoms.

That's the notes covered.

Carry on to the next subtopic.