Becoming better adapted
Natural selection can result in a population becoming increasingly suited to its environment. Some alleles produce characteristics that improve survival under particular conditions, giving their possessors a selective advantage.
Individuals with favourable alleles are more likely to survive and produce offspring. Their alleles are therefore inherited more often, so the favourable allele and the adaptation associated with it become increasingly common over generations.
When environmental conditions change, a new allele arising by mutation may provide an advantage under the new conditions. Selection can then produce a comparatively rapid change in the population if individuals carrying that allele reproduce more successfully.
Example: sprinting ability in lions
A favourable allele in a lion population could result in a greater proportion of fast-twitch muscle fibres in the legs. This would improve sprinting ability when pursuing prey.
- Lions carrying the advantageous allele are more likely to catch prey and survive.
- These lions produce more offspring.
- The favourable allele is inherited by a larger proportion of the next generation.
- Its frequency rises, so the associated adaptation becomes more widespread.
By contrast, lions carrying an unfavourable allele that makes prey harder to catch have a lower chance of surviving and producing offspring. That allele becomes less frequent.
Across generations, favourable alleles increase in frequency while unfavourable alleles decrease in frequency. The resulting population is better suited to the conditions in which it lives.