How to Read an Evolutionary Tree

Hominid "Family Tree": This evolutionary tree depicts lines of possible descent for hominids. In other words, it proposes relationships among species over time. All trees are hypotheses, and are based on comparison of living species, fossils, and genetic data.

(click to enlarge)

Reading This Evolutionary Tree:

1. Dashed lines show how related species diverged from each other through a common ancestor.

2. Faded lines indicate very unclear origin or descent.

3. Branch points are called nodes. Nodes indicate a species that once lived, and was the common ancestor of two or more descendants.

4. Horizontal lines indicate time.

5. Orange vertical bars indicate how long a species is known, from fossils, to have existed.

Common Misconceptions:

All species on this evolutionary tree are ancestors of Homo sapiens.

This is not true. You can follow the dashed lines back through time to learn which species are proposed ancestors.

Evolution progresses toward a goal.

Evolution does not necessarily follow from simple to more complex, or non-human to human.

Evolutionary trees are fixed.

Evolutionary trees are not fixed. They are based on interpretations of current data. New evidence or new ways of interpreting existing evidence can revise them.