In any population of a species, there is significant genetic variation, and nearly all genetic variants arise from mutations. A mutation is a change in a gene or chromosome. Most mutations occur when the DNA of a single gene is altered.
Mutations occur naturally, at random, which means that any gene can mutate at any time. However, they can also occur due to environmental factors.
Gene mutations can involve the addition, deletion, or rearrangement of a gene’s DNA base sequence. Some mutations can result in an allele that significantly changes the protein produced, which affects the organism’s function.
Sometimes, characteristics are controlled by many genes. So, a mutation may only affect a part of a gene that creates a small change in the protein being produced.
Mutations rarely create a new phenotype. However, if it does and the new phenotype is suited to a particular environment, the members of the species that are more adapted to the environment are more likely to reproduce. This can lead to a rapid change in the phenotype of a species.
Natural selection is a process through which organisms that are better adapted to their surroundings tend to survive and produce more offspring. This means that their genes will be passed down to future generations.
The peppered moth is a popular example of natural selection in action. Some peppered moths are pale and some are dark. Before the British Industrial Revolution, most of the peppered moth population was pale. This was because pale moths were better camouflaged in their environment compared to the black moths.
They were camouflaged against the trees, which made it more difficult for predators to spot them compared to the dark-coloured moths. More pale-coloured moths survived and were able to reproduce, passing this phenotype on to the next generation.
However, during the Industrial Revolution, pollution from the factories (especially soot) turned the trees black. As a result, pale-coloured moths no longer had a camouflage advantage, as they became easier for predators to spot against the soot-darkened trees.
Due to this, dark moths had a higher survival rate and reproduced more, passing this phenotype on to the next generations. As more dark-coloured moths survived, they soon outnumbered the pale-coloured moths in the population.
Originally, pale-coloured moths made up the majority of the population. But over time, the dark-coloured moths became the majority.
Although the dark variety always existed, the darkening of the trees provided them with an advantage. So, the dark variety became advantageous as the environment changed.