Darwin and Wallace: Developing the Theory of Evolution Revision Notes | GCSE AQA Higher Biology

1. The Revolutionary Idea That Changed Everything

Before 1858, most people believed species never changed. Then two British naturalists proposed something radical: all life forms gradually change over time through a process called natural selection. This wasn't just another scientific theory - it revolutionised how we understand life itself.

What makes this story fascinating is that Charles Darwin and Alfred Russel Wallace developed virtually identical theories independently. Darwin had been working on his ideas for over 20 years when Wallace's letter arrived, forcing Darwin to finally publish his groundbreaking work.

2. Darwin's Journey to Discovery

Charles Darwin began developing his theory during his voyage on HMS Beagle (1831-1836). As the ship's naturalist, he observed finches on the Galápagos Islands with different beak shapes perfectly suited to their food sources. This sparked a crucial question: why were closely related species so perfectly adapted to their environments?

Darwin spent decades collecting evidence. He studied domestic breeding, noting how farmers selected animals with desirable traits. If humans could change species through artificial selection, perhaps nature did something similar through natural selection.

The key insight came from Thomas Malthus's essay on population growth. Malthus argued that populations grow faster than food supplies, creating competition for resources. Darwin realised this competition would favour individuals with advantageous traits - they would be more likely to survive and reproduce.

3. Wallace's Independent Discovery

Alfred Russel Wallace was collecting specimens in the Malay Archipelago (modern-day Indonesia and Malaysia) when he independently developed the same theory. Unlike Darwin's gradual realisation, Wallace's breakthrough came suddenly during a fever in 1858.

Wallace was studying the geographical distribution of species when he noticed a pattern: closely related species were often separated by geographical barriers like mountains or seas. This suggested species changed over time as they adapted to different environments.

Like Darwin, Wallace was influenced by Malthus's ideas about population pressure. During his fever, Wallace suddenly realised that in the struggle for survival, those with favourable variations would survive while others would perish. This was natural selection.

4. The 1858 Joint Publication

In June 1858, Wallace sent Darwin a manuscript outlining his theory. Darwin was shocked - Wallace had described almost exactly the same mechanism Darwin had been developing for decades. This created a dilemma: who should get credit for the discovery?

Darwin's friends, geologist Charles Lyell and botanist Joseph Hooker, arranged a solution. On 1st July 1858, they presented both Darwin's and Wallace's work to the Linnean Society of London. This joint presentation ensured both men received credit for independently discovering natural selection.

The joint publication had an immediate impact on Darwin. Realising he could no longer delay, he began writing a 'short' version of his theory. This became 'On the Origin of Species', published in November 1859 - just over a year after the joint presentation.

5. How Natural Selection Actually Works

Both Darwin and Wallace identified the same four-step process that drives evolution. Understanding this mechanism is crucial for GCSE exams, as questions often test whether you can explain each stage clearly.

Worked example: The Four Steps of Natural Selection

Explain how natural selection leads to evolutionary change in a population over time.

1. Individuals in a population show variation in their characteristics — This variation is caused by genetic differences and provides the raw material for selection
2. More offspring are produced than can survive due to limited resources — This creates competition for food, mates, territory, and other resources
3. Individuals with advantageous characteristics are more likely to survive and reproduce — These 'fitter' individuals have better adaptations to their environment
4. Advantageous characteristics are passed to offspring, becoming more common in the population — Over many generations, the population evolves as beneficial traits increase in frequency

Answer: Natural selection causes populations to evolve by favouring individuals with advantageous characteristics, which become more common over time through inheritance.

Trap: Many students think individual organisms evolve during their lifetime. Actually, evolution happens to populations over many generations. An individual giraffe doesn't grow a longer neck - populations of giraffes gradually develop longer necks over thousands of years.

6. Exam Technique: Getting Full Marks

Questions about Darwin and Wallace appear regularly in GCSE exams. Examiners test whether you understand the historical development of evolutionary theory and can explain natural selection clearly.

Common exam mistakes include confusing evolution with adaptation, thinking individuals evolve, or forgetting Wallace's contribution. Practice explaining natural selection using specific examples like antibiotic resistance in bacteria or pesticide resistance in insects.

The work of Darwin and Wallace transformed biology from a descriptive science into one that could explain the diversity of life. Their theory of natural selection remains the foundation of modern evolutionary biology and continues to be supported by evidence from genetics, fossils, and molecular biology.