7.3.2 Natural Selection

Key Concepts

1. Niche:

• A species' role within the environment, including how it obtains resources and interacts with other species.
• Species with overlapping niches compete with one another. The better-adapted species outcompetes others, surviving and reproducing.

2. Overproduction of Offspring:

• Many organisms produce more offspring than can survive, e.g., fish lay thousands of eggs.
• Intraspecific competition (competition within a species) occurs due to limited resources.

3. Survival of the Fittest:

• Individuals with advantageous alleles are better suited to their environment, survive longer, and reproduce more successfully.
• Variation in genotypes and phenotypes increases a population's ability to adapt to environmental changes.

Process of Natural Selection

4. Variation:

• A population shows phenotypic variation due to genetic differences.

5. Environmental Change:

• A change occurs, altering the selection pressure (e.g., predators, food availability, climate).

6. Selective Advantage:

• Some individuals possess advantageous alleles that improve survival or reproduction.

7. Reproduction:

• These individuals survive, reproduce, and pass advantageous alleles to their offspring.

8. Evolution:

• Over generations, allele frequencies shift in the population, favouring traits that improve survival in the current environment.

Example:

• Peppered Moths:
  • Before industrialisation, light-coloured moths camouflaged with lichen-covered trees and were less likely to be eaten by predators.
  • After industrialisation, soot darkened trees, giving dark-coloured moths a selective advantage.