In any population of a species, there is a large amount of genetic variation and nearly all of the genetic variants come 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 be mutated at any time. However, they can also occur due to environmental changes.
The different forms of gene mutations involve adding, deleting, or rearranging a gene’s DNA base sequence. Some mutations can produce an allele that causes a big change in the protein created, which affects how the body works.
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 change lead to a rapid change in the phenotype of a species.
Natural selection is a process through which organisms that are more adapted to their surroundings will survive and reproduce more. This means that their genes will be passed down to future generations.
We can see natural selection in peppered moths. Some peppered moths are pale and some are dark. Before the British industrial Revolution, most of the peppered moth population was pale. This is because pale moths were more adapted to their environment than 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. This meant that pale-coloured moths no longer had an advantage over dark-coloured moths, as they were now more easy to spot by predators on the blackened tree.
Therefore, the dark moths survived and were able to reproduce, passing on this phenotype to the next generation. As more dark-coloured moths survived, the number of dark-coloured moths in the population became larger than the number of pale-coloured moths.
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 trees getting darker gave them an advantage. So, the dark variety became advantageous as the environment changed.