Evolution of Classification and Evolutionary Trees Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Examine how biological developments have impacted classification systems over time and discover how scientists use evolutionary trees to show relationsh...

• Explain how developments in biology have changed classification systems over time
• Describe what evolutionary trees show and how they are constructed
• Interpret evolutionary trees to determine relationships between organisms
• Evaluate the evidence used to create evolutionary trees

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 Evolution of Classification and Evolutionary Trees before testing yourself from memory.

• Imagine trying to organise your music collection. First you sort by genre, then by artist, then you discover some artists don't fit neatly into one genre. Scientists face the same problem with living things — but their 'collection' has millions of species, and new discoveries keep forcing them to reorganise everything.
• For centuries, scientists classified organisms based on what they could see — their physical features. A whale looked like a fish, so it was grouped with fish. But as biology advanced, this simple approach started falling apart.
• Grouping organisms based on observable physical characteristics and behaviour patterns
• The problem with traditional classification became clear when scientists started looking deeper. A whale might look like a fish, but it breathes air, feeds milk to its young, and has warm blood. These features suggested whales were more closely related to mammals than fish.
• Three major developments in biology completely transformed how we classify organisms. Each discovery revealed that appearances can be deceiving when it comes to evolutionary relationships.
• DNA analysis was the game-changer. When scientists could compare the genetic code of different organisms, they discovered shocking relationships. Humans share 98.8% of their DNA with chimpanzees, but only 85% with mice — even though mice are also mammals.
• Protein studies provided another layer of evidence. Scientists found that organisms with similar proteins often shared recent common ancestors, even if they looked completely different. The protein that carries oxygen in your blood (haemoglobin) is remarkably similar to the same protein in a gorilla.
• Fossil discoveries filled in the gaps, showing how organisms changed over millions of years. Fossils revealed transitional forms — organisms that showed characteristics of two different groups, proving they were evolutionary links.
• An evolutionary tree is like a family tree for species. Instead of showing how your relatives are connected, it shows how different organisms evolved from common ancestors over millions of years.
• A branching diagram that shows the evolutionary relationships between different species or groups, with branch points representing common ancestors

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.