Darwin's theory of evolution by natural selectionSpec 3.38
Evolution is a change in the inherited characteristics of a population over many generations. Darwin's theory explains how it happens by natural selection.
- Individuals in a population show variation. Some of this variation is genetic, and arises from mutation and sexual reproduction.
- More offspring are born than can survive, so individuals compete for resources such as food, space and mates. 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.
This is sometimes summed up as 'survival of the fittest'. 'Fittest' means best suited to the environment, not strongest.
Common mistake:
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.
Exam tip:
Write the full chain in your answer: variation, competition, survival and reproduction of the better adapted, alleles passed on, proportion increases.