Darwin and Wallace

HSC Biology | Free Study Notes

In this lesson

• the observations made by Darwin and Wallace

• the key ideas behind natural selection

• how their work helped develop evolutionary theory

  
  

Who were Darwin and Wallace?

Charles Darwin and Alfred Russel Wallace were naturalists who both developed the idea that species change over time through natural selection.

They worked independently, but both recognised that:

• populations show variation

• the environment creates selection pressures

• individuals with favourable traits are more likely to survive and reproduce

• over time, populations change

Their work became a major part of modern evolutionary theory.

Darwin’s observations

Darwin’s ideas developed through careful observation and collection of evidence.

Examples linked to the syllabus

The syllabus specifically highlights Darwin’s observations of:

• finches of the Galapagos Islands

• Australian flora and fauna 

What Darwin noticed

Darwin observed that:

• organisms in different places often had similar basic structures but different features

• closely related organisms could be adapted to different habitats

• island species often showed clear variation from one island to another

• these differences seemed linked to food sources and environmental conditions

Galapagos finches

Darwin noticed that finches on different islands had different beak shapes.

These beak differences were linked to:

• different food types

• different feeding methods

• adaptation to local environments

This helped support the idea that species are not fixed and can change over time.

Wallace’s observations

Wallace also made important observations about how organisms vary between places.

What Wallace noticed

Wallace observed that:

• species differ across regions

• related organisms are often distributed in patterns linked to geography

• environmental conditions influence which organisms survive best

Why Wallace matters

Wallace independently reached the same broad idea as Darwin, that natural selection could explain evolutionary change.

This is why the syllabus refers to Darwin and Wallace’s Theory of Evolution by Natural Selection, not Darwin alone. 

Key ideas

The main ideas developed by Darwin and Wallace form the basis of natural selection.

Variation

Individuals in a population are not identical.

There is variation in traits such as:

• size

• colour

• beak shape

• speed

• resistance to disease

This variation is essential because natural selection can only act if differences already exist.

Overproduction and competition

More offspring are produced than can survive.

Because resources are limited, organisms compete for:

• food

• water

• shelter

• mates

This creates a struggle for survival.

Selection pressures

The environment creates selection pressures.

These may include:

• predators

• climate

• disease

• competition

• food availability

Some individuals are better suited to these conditions than others.

Survival and reproduction

Individuals with favourable traits are more likely to:

• survive

• reproduce

• pass their alleles to offspring

Over time, useful traits become more common in the population.

Development of evolutionary theory

Darwin and Wallace helped change scientific thinking by showing that species are not fixed.

Before their work

Many people believed species were unchanging.

What their work suggested

Darwin and Wallace argued that:

• species change over time

• adaptation happens gradually as advantageous traits are selected

• biodiversity can be explained by descent with modification

Why this was important

Their ideas provided a scientific explanation for:

• adaptation

• biodiversity

• the origin of new species over time

This is why Module 3 links their theory directly to the changes in and diversification of life and to later topics such as convergent evolution, divergent evolution and speciation. 

Darwin and Wallace

In Module 3, students are expected to:

• investigate Darwin’s observations and data collection

• explain biodiversity using the Theory of Evolution by Natural Selection

• use examples to explain how Darwin and Wallace’s theory accounts for evolutionary patterns 

So this page is a foundation for later pages on:

• natural selection

• speciation

• evidence for evolution

Worked example

Exam-style question

Explain how Darwin’s observations of finches supported the development of evolutionary theory.

Worked answer

Darwin observed that finches on different Galapagos Islands had different beak shapes. These differences were linked to different food sources and habitats. This supported the idea that populations vary and that traits which improve survival in a particular environment become more common over time through natural selection.

Why this works

This answer:

• uses a named observation

• links the observation to adaptation

• connects it to natural selection

Common mistakes

• Writing only about Darwin and ignoring Wallace.

• Listing observations without explaining why they mattered.

• Saying Darwin and Wallace proved individuals change during their lifetime.

• Confusing variation within a population with the sudden appearance of completely new species.

• Treating natural selection as a choice made by organisms, rather than a process driven by environmental pressures.

Quick quiz

1. Who were Darwin and Wallace?

2. What example from Darwin’s work is specifically linked to the syllabus?

3. What did Darwin observe about Galapagos finches?

4. What is one key idea in natural selection?

5. Why was the work of Darwin and Wallace important to evolutionary theory?

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