How Evolution Works Through Natural Selection Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Exploring the mechanism of natural selection and how it leads to evolution by selecting variants with advantageous phenotypes for their environment.

• Explain how evolution occurs through natural selection
• Describe the role of variation in natural selection
• Analyse how environmental pressures select for advantageous traits
• Apply the principles of natural selection to real-world examples

Key ideas to keep in view

Use this lesson to stay inside B5.2 Natural selection and evolution while connecting the detail back to the wider B5: Genes, inheritance and selection topic.

• B5: Genes, inheritance and selection
• B5.2 Natural selection and evolution
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from How Evolution Works Through Natural Selection before testing yourself from memory.

• Why do giraffes have long necks? Why are polar bears white? These aren't random features - they're the result of a powerful process that shapes all life on Earth.
• Picture a population of beetles living in a forest. Some are brown, some are green. When birds hunt for food, which beetles are easier to spot against the brown tree bark? The green ones stand out like beacons, whilst the brown ones blend in perfectly.
• This isn't just about beetles - it's about the fundamental mechanism that drives evolution: natural selection. Understanding this process explains how species change over time and why organisms are so perfectly suited to their environments.
• The process by which organisms with favourable characteristics are more likely to survive and reproduce, passing on their advantageous traits to offspring.
• Natural selection works like a filter, but instead of filtering water, it filters traits. For this process to work, four conditions must be met:
• 1. Variation exists: Individuals in a population must have different characteristics. Without variation, there's nothing to select from.
• 2. Traits are inherited: Characteristics must be passed from parents to offspring through genes. Learnt behaviours don't count.
• 3. Selection pressure occurs: Environmental factors must affect survival or reproduction. This could be predators, disease, climate, or competition for resources.
• 4. Differential reproduction: Individuals with advantageous traits must produce more offspring than those without. This is where the 'selection' happens.
• Trap: Many students think organisms 'try' to evolve or that they evolve during their lifetime. Actually, evolution happens to populations over many generations, not to individuals.

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.