What is natural selection?

A process whereby an organism which have well adapted characteristics to a particular environment will survive to a reproductive age to produce offspring.

Types of Natural Selection:-

1) Stabilising selection

The mean is selected for; the extreme phenotypes are selected against.

  • No change in average
  • Reduce genetic variation

Example: babies’ birth weights

2) Directional Selection

The selection of phenotype occurs at one end of the range of variation. The phenotype shifts either to the right or to the left.

  • A change in average
  • Reduce genetic variation

Example: beak shape

3) Disruptive Selection

Extreme phenotypes have selective advantage (be selected for; therefore not eliminated).

  • Genetic variation remains.

Example: beak length

4) Sexual Selection

  • Selection of specific phenotypes or mating behaviour occurs.
  • Usually female animal choose for certain appearance or behaviour.
  • To compete for healthy mate thus produce healthy offspring.

Example: only peacock with dazzling plumage and attractive mating behaviour is allowed to mate.

5) Polymorphism

A condition when a specific trait of a species exists in two or more different forms. (a result of multiple alleles)

Example: ABO blood system, patterns of snail shells, light/dark peppered moth

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