Evolution

Inheritance, variation and evolution · Variation and evolution · note 2 of 5

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EvolutionSpec 4.6.2.2

In short

Evolution is a change in the inherited characteristics of a population over time through a process of natural selection, which may result in the formation of a new species. Individuals best suited to their environment are more likely to survive, breed and pass on their alleles. Populations that can no longer interbreed to produce fertile offspring are separate species.

Evolution: A change in the inherited characteristics of a population over time through a process of natural selection, which may result in the formation of a new species.

The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.

How natural selection works

Individuals in a population show variation in their phenotypes, caused by differences in their genes.
The environment puts pressure on the population. For example, there may be predators, disease or competition for food.
Individuals with phenotypes best suited to their environment are more likely to survive and breed.
They pass on the alleles for the useful characteristic to their offspring.
Over many generations, a greater proportion of the population has the characteristic.

New species

If two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring, they have formed two new species.

Common mistake:

Individuals do not 'adapt' or 'evolve' during their lives. Populations evolve, because the better-suited variants survive and reproduce. Do not write that organisms 'need' a characteristic so they develop it.

Three generations of a beetle population on green leaves. Birds eat more of the easily seen yellow beetles, so the proportion of green beetles rises from 50% to 67% to 83%. — Better-suited individuals are more likely to survive and breed, so their alleles become more common in each generation.

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

Frequently asked questions

How does natural selection lead to evolution?

Natural selection leads to evolution because individuals in a population vary, and those with phenotypes best suited to their environment are more likely to survive and breed. They pass on the alleles for the useful characteristic to their offspring. Over many generations, a greater proportion of the population has the characteristic, so the inherited characteristics of the population change.

What are the 4 stages of natural selection?

The 4 stages of natural selection are: variation, as individuals have different phenotypes caused by their genes; pressure from the environment, such as predators, disease or competition; survival and breeding of the best-suited individuals; and passing on their alleles, so the characteristic becomes more common over many generations. Populations evolve, not individuals.

What is selective breeding in plants?

Selective breeding in plants is when humans choose parent plants with a desired characteristic, such as disease resistance or large flowers, and breed them together. The offspring with the characteristic are then bred again, over many generations, until all the offspring show it. A risk is that it reduces the number of different alleles in the population.

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