Evolution by natural selectionSpec 4.2
In short
Evolution is a change in the inherited characteristics of a population over many generations, and natural selection explains how it happens. Individuals show genetic variation, caused by mutation, and compete for resources. Those best suited to their environment are more likely to survive and reproduce, passing on their alleles, so advantageous alleles become more common over generations.
Evolution is a change in the inherited characteristics of a population over many generations. Darwin explained how it happens using natural selection.
- Individuals in a population show variation. Some of this is genetic, caused by differences in alleles, which arise by mutation.
- More offspring are born than can survive, so individuals compete for resources such as food, space and mates, and some are eaten or die of disease.
- Individuals with characteristics that suit their environment are more likely to survive and reproduce.
- They pass on the alleles for those characteristics to their offspring.
- Over many generations, the proportion of the population with the advantageous alleles increases.
Individuals with a characteristic that gives an advantage are sometimes described as the 'fittest'. This means best suited to their environment, not strongest.
- Natural selection
- The process by which organisms better adapted to their environment are more likely to survive, reproduce and pass on their alleles.
- Evolution
- A change in the inherited characteristics of a population over many generations.
Individuals do not change during their lives to cope with their environment. The advantageous allele has to be there already, and the proportion of individuals with it increases over generations.
Write the full chain in your answer: variation (from mutation), survival and reproduction of the better adapted, alleles passed on, proportion increases.
Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026