Natural Selection

This lesson covers: 

  1. Variation in species and its survival impact
  2. The natural selection process
  3. Giraffes and neck length as an example of natural selection

Variation leads to natural selection

Illustration showing two mice and a sheep competing for an apple.

Organisms compete for essential resources such as:

  • Food
  • Water
  • Shelter


This competition is not just among the same species but also across different species.

The natural selection process

Natural selection works through simple steps:

  1. Populations display variation.
  2. Some variations give individuals an advantage for survival in their environment.
  3. Those with advantages are more likely to survive and reproduce, passing on these traits.
  4. Those less suited to their environment will die before reproducing.
  5. Beneficial traits become more common in the population, thanks to natural selection.

An example of natural selection

A useful example of natural selection is the development of long necks in giraffes.

Illustration showing a short-necked giraffe less likely to survive and a long-necked giraffe more likely to survive due to better access to food.

Imagine a group of animals with varying neck lengths eating from trees:

  1. As food becomes scarce, only those with longer necks can reach the higher leaves.
  2. Long-necked animals had better access to food, survived, and reproduced, passing the long-neck trait to their offspring.
  3. Short-necked animals die before reproducing so their trait is not passed on.
  4. Over generations, this trait became more common, demonstrating natural selection.
  5. Eventually all the giraffes in the population have long necks.