Evolution by Natural Selection — AQA GCSE Biology
The theory of evolution by natural selection explains how species change over time and how new species arise.
The theory of evolution
The theory of evolution by natural selection (proposed by Charles Darwin) 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 within a species show variation because of differences in their genes.
- Those with characteristics best suited to the environment are more likely to survive and reproduce (sometimes called "survival of the fittest").
- The alleles for those beneficial characteristics are passed on to the next generation.
- Over many generations, these beneficial characteristics become more common, so the species gradually changes (evolves).
Speciation
If two populations of a species become so different (in phenotype) that they can no longer interbreed to produce fertile offspring, they have become two separate species. This is speciation.
Why Darwin's ideas were slow to be accepted
- They challenged the religious idea that God made all the animals and plants.
- There was insufficient evidence at the time to convince many scientists.
- The mechanism of inheritance (genes) was not understood until much later.
Exam tips
- Learn the four steps of natural selection and apply them to any example.
- Define speciation (populations can no longer interbreed to give fertile offspring).
- Explain why Darwin's theory was slow to be accepted.
- Antibiotic resistance is a modern example of natural selection.