Phylogenetic trees: reading shared ancestry — Biology, 14–17
How biologists use evidence to show which species share more recent ancestors. Biology, 14–17 years.
A map of relatedness
A phylogenetic tree is a diagram of branching lineages. A branch point means that two groups share an ancestor, and groups that meet at a more recent point are more closely related.
Why draw the branches?
Names and appearances can mislead: dolphins look like fish, but their bodies and DNA link them to mammals. Trees give scientists a testable way to compare evidence and reconstruct family history.
Reading one tree
Imagine a tree where birds and crocodiles join at one branch, while lizards join earlier. Birds and crocodiles share the more recent common ancestor, so they are the closer pair in this tree.
The tree is not a ladder
A common mistake is calling one living species “more evolved” because it appears at the top or end. That feels natural because we read lists from bottom to top, but every tip is a modern survivor of its own branch.
Trees in real research
Scientists compare DNA, fossils and body structures to build trees. The results can guide conservation, reveal disease origins, or show which crops have useful wild relatives.
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