Natural Selection and Classification Review

This lesson brings together all the key concepts from Topic 4: Natural Selection and Genetic Modification. Use it to consolidate your knowledge, practise extended-response questions and check your understanding of how the different topics link together.

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Linking Evolution to Classification

Evolutionary Trees (Phylogenetic Trees)

An evolutionary tree (also called a phylogenetic tree) is a diagram that shows the evolutionary relationships between organisms. It represents how species have diverged from common ancestors over time.

                    Common ancestor
                         │
              ┌──────────┴──────────┐
              │                     │
         Ancestor A            Ancestor B
           │                       │
      ┌────┴────┐            ┌────┴────┐
      │         │            │         │
  Species 1  Species 2  Species 3  Species 4

How to Read an Evolutionary Tree

Feature	What It Means
Branch point (node)	A common ancestor where two lineages diverged
Branch length	Sometimes represents time or amount of genetic change
Tips (ends)	Modern-day species (or extinct species if labelled)
Closer branches	Species that share a more recent common ancestor are more closely related

How New Evidence Changes Classification

Classification is not static — it is constantly updated as new evidence emerges: