Theory of evolution

Inheritance, variation and evolution · The development of understanding of genetics and evolution · note 1 of 7

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Theory of evolutionSpec 4.6.3.1

In short

The theory of evolution by natural selection states that individuals in a species vary, that those with characteristics most suited to the environment are more likely to survive to breed, and that these characteristics are passed on. It was only gradually accepted because it challenged religious belief, evidence was insufficient and the mechanism of inheritance was unknown.

Charles Darwin proposed the theory of evolution by natural selection as a result of observations on a round the world expedition. His ideas were backed by years of experimentation and discussion, and linked to developing knowledge of geology and fossils.

Individual organisms within a particular species show a wide range of variation for a characteristic.
Individuals with characteristics most suited to the environment are more likely to survive to breed successfully.
The characteristics that have enabled these individuals to survive are then passed on to the next generation.

Darwin published his ideas in On the Origin of Species (1859). There was much controversy about these revolutionary new ideas. The theory developed over time, using information gathered by many scientists.

Why the theory was only gradually accepted

It challenged the idea that God made all the animals and plants that live on Earth.
There was insufficient evidence at the time it was published to convince many scientists.
The mechanism of inheritance and variation was not known until 50 years after the theory was published.

Lamarck

Other theories, including that of Jean-Baptiste Lamarck, are based mainly on the idea that changes that occur in an organism during its lifetime can be inherited. We now know that in the vast majority of cases this type of inheritance cannot occur.

Exam tip:

Learn the three reasons for slow acceptance as a short list: religious belief, not enough evidence, no known mechanism of inheritance. A study of creationism is not required.

Written and checked against the AQA GCSE Biology (8461) specification · Updated October 2026

Frequently asked questions

Why was the theory of evolution only gradually accepted?

Triple only The theory of evolution by natural selection was only gradually accepted for three reasons. It challenged the idea that God made all the animals and plants that live on Earth, there was insufficient evidence at the time to convince many scientists, and the mechanism of inheritance and variation was not known until 50 years after the theory was published.

What is the evidence for evolution?

The evidence for evolution includes the fossil record, which shows how much or how little organisms have changed as life developed on Earth, the discovery that characteristics are passed on to offspring in genes, and antibiotic resistance in bacteria, which shows natural selection happening in a short time. This is why the theory is now widely accepted.

How are fossils formed?

Fossils form in three ways: from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent, from parts that are replaced by minerals as they decay, or as preserved traces such as footprints, burrows and rootlet traces. Fossils are found in rocks and show how organisms have changed.

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