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The big issues

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Understanding phylogenies

Understanding a phylogeny is a lot like reading a family tree. The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendants of that ancestor. As you move from the root to the tips, you are moving forward in time.

Tree showing ancestor and descendants

When a lineage splits (speciation), it is represented as branching on a phylogeny. When a speciation event occurs, a single ancestral lineage gives rise to two or more daughter lineages.

Where a tree branches, there is a speciation event

Phylogenies trace patterns of shared ancestry between lineages. Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages.

Tree showing unique and shared lineages

Similarly, each lineage has ancestors that are unique to that lineage and ancestors that are shared with other lineages — common ancestors.

Tree showing location of unique and common ancestors

Download this series of graphics from the Image library.

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More details
In some phylogenies, more than two daughter lineages arise from a single ancestral lineage. Find out how to interpret these trees.

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Teach your students about evolutionary relationships and phylogenetics:

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