18.3 Selection

2026 📋 Syllabus Objectives

By the end of this topic, you should be able to:

  • Explain what natural selection is and how it works
  • Describe the steps of natural selection using examples
  • Explain how natural selection leads to changes in a population over time
  • Define and explain artificial selection (selective breeding)
  • Describe examples of artificial selection in animals and plants
  • Compare natural selection and artificial selection

📖 Main Content

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1. What Is Natural Selection?

Natural selection is the process by which individuals that are better suited to their environment survive longer, reproduce more, and pass on their useful features to their offspring.

A simple way to think about it: nature "selects" the best individuals to survive.

This idea was first described by a scientist called Charles Darwin, who called it "survival of the fittest". Here, "fittest" does not mean the strongest or fastest — it means the best suited to the environment.

2. Why Does Natural Selection Happen?

For natural selection to happen, three things must be true:

2.1 Variation Exists in a Population

  • No two individuals of the same species are exactly alike.
  • There are always differences (called variation) between individuals — in their size, colour, speed, disease resistance, and many other features.
  • Some of this variation is caused by differences in genes (the instructions inside cells that control how an organism develops).
  • Occasionally, a mutation (a random change in a gene) creates a completely new feature in one individual.

2.2 Organisms Produce More Offspring Than Can Survive

  • Living things reproduce and make more offspring than the environment can support.
  • There is not enough food, water, shelter, or space for every individual to survive.
  • This leads to competition — a struggle between individuals to get the resources they need to stay alive.

2.3 Some Individuals Are Better Suited Than Others

  • Because individuals vary, some are better at finding food, escaping predators, or resisting disease.
  • These better-suited individuals have a greater chance of surviving the competition.
  • Because they survive longer, they have more opportunities to reproduce.
  • When they reproduce, they pass their useful genes on to their offspring.
  • Over many generations, more and more individuals in the population carry those useful genes, and the population gradually changes.

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