What is Evolution? Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Understanding evolution as changes in inherited characteristics over time and how all species evolved from simple life forms through natural selection.

• Define evolution as a change in inherited characteristics of populations over time
• Explain how natural selection drives evolutionary change
• Describe the evidence supporting the theory of evolution by natural selection
• Apply the concept of natural selection to explain adaptation in organisms

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 What is Evolution? 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 evolution, one of the most powerful ideas in science.
• A change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species.
• Think of evolution like this: imagine a population of beetles. Some are green, some are brown. Over many generations, you notice more brown beetles and fewer green ones. The population has evolved - its characteristics have changed over time.
• Trap: Many students think individual organisms evolve during their lifetime. Actually, populations evolve over many generations - individuals don't change their inherited characteristics.
• Evolution doesn't happen randomly. There's a mechanism driving it: natural selection. This is where Darwin's genius shines through.
• The process by which organisms with characteristics that make them better adapted to their environment are more likely to survive and reproduce successfully, passing these advantageous characteristics to their offspring.
• Natural selection works like a filter. Picture those beetles again: if birds find it easier to spot green beetles on brown tree bark, more green beetles get eaten. Brown beetles survive longer, reproduce more, and pass on their 'brown' genes. Over time, the population becomes mostly brown.
• For natural selection to work, you need three key ingredients: variation (different characteristics), inheritance (traits passed to offspring), and selection pressure (something that affects survival or reproduction).
• The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago. That's a mind-boggling timescale.
• Imagine compressing Earth's history into a single year. Simple life forms appear in March. Complex cells don't show up until August. Animals with shells appear in mid-November. Dinosaurs rule for just a few days in December. Humans appear in the last few minutes of New Year's Eve.

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.