How Did Darwin Develop the Theory of Evolution?

Darwin developed the theory of evolution by natural selection using observations from a worldwide expedition, years of experimentation and discussion, and evidence from geology and fossils.

Darwin’s observations

Charles Darwin observed that individuals within the same species showed variation—differences in their characteristics. He also recognised that organisms produce more offspring than can survive, creating competition for limited resources.

Darwin combined these observations with developing scientific knowledge about geology and fossils. This evidence suggested that Earth was very old and that living organisms had changed over long periods.

The theory of natural selection

Darwin proposed the following process:

1. Individuals within a species show variation.
2. Some variations make individuals better suited to their environment.
3. These individuals are more likely to survive and reproduce successfully.
4. They pass the alleles for their advantageous characteristics to their offspring.
5. Over many generations, these characteristics become more common in the population.

This process is called natural selection. Over a long period, it can cause populations to change and may eventually result in new species.

Example

Imagine a population of insects with different colour variations. Birds can easily see the lighter insects on dark tree bark. Darker insects are more likely to survive, reproduce and pass on alleles for dark colour. Over generations, the proportion of dark insects increases.

Publication and acceptance

Alfred Russel Wallace independently proposed evolution by natural selection. Joint writings by Wallace and Darwin were published in 1858, prompting Darwin to publish On the Origin of Species in 1859.

Darwin’s theory was accepted gradually because it challenged existing beliefs, there was limited evidence at the time, and the mechanism of inheritance and variation was not yet understood.

Exam mistake: Do not say organisms deliberately adapt because they “need to”. Natural selection acts on inherited variation already present in a population.

Scope assumed: AQA GCSE Biology 8461 separate science, Higher Tier. This content is biology only but is studied at both Foundation and Higher Tier.