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Understanding phylogenies (1 of 4)

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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 descendents of that ancestor. As you move from the root to the tips, you are moving forward in time.

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A phylogeny. Descendants are numbered 1, 2, 3, and 4 at the top. The very bottom of the phylogeny shows the ancestor. The top of the phylogeny shows recent species. The lower down a phylogeny, the further in the past the species is.

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This image is part of a series:

This image shows two parallel line connected at the bottom point by a horizontal bar. From a point in the middle of the horizontal bar, a blue line descends directly downward. The point in the middle of the horizontal bar that connects with the blue bar is the speciation event. The blue bar is the ancestral lineage.

Understanding phylogenies (2 of 4)

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.

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A phylogeny with descendents A, B, and C. A shares a speciation event with B and C. B shares a speciation event with C. There is a dotted line moving from the bottom of the phylogeny towards the speciation event of B and C; this represents the shared history of B and C. The line leading to B is green, representing the unique history of B. The line leading to C is blue, representing the unique history of C.

Understanding phylogenies (3 of 4)

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.

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Shows the same phylogeny of A, B, and C as the previous one. The point representing the speciation event of A and B&C also represent the common ancestor of A, B, and C. The point showing the speciation event of B and C also represents the common ancestor of B and C. A point along the line to C represents a unique ancestor of C.

Understanding phylogenies (4 of 4)

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

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