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Branching diagram that resembles a broom head with diagonal lines extending upwards, basic features

This style of tree is often used to show relationships among microorganisms and the earliest forms of life or among genes. The tree shown here depicts the relationships among ants, flies, butterflies, and beetles.  This diagram has the following basic features:

• An arrow showing that evolutionary time flows from the bottom root of the tree (earlier times) towards the top tips (more recent times).
• A root at the bottom from which the other branches emanate. The root represents the ancestor that all the lineages on the tree have in common.
• A branching pattern.  The tree shown here depicts a root with ants, then flies and butterflies, and then beetles splitting off.  The branching pattern represents evolutionary relationships. It tells you how closely related different groups are. Here, flies and butterflies are more closely related to each other than either is to beetles because their branches join more recently than either joins the beetles’ branch. All the insect groups are related to one another, but some are more closely related than others.
• Branching points. Branching points represent the ancestor that all the lineages whose branches join at that point have in common. Three branching points on the tree are highlighted in yellow.  Point 1 appears over the point at which the fly and butterfly branches meet.  When you click it, that point and the two branches emanating upwards from it (the fly and butterfly branches) are highlighted. Point 2 appears over the point at which the beetle branch connects to the shared ancestral branch of flies and butterflies. When you click it, that point and all the branches emanating upwards from it (including the fly, butterfly, and beetle branches) are highlighted. Point 3 appears over the point at which the ant branch connects to the shared ancestral branch of flies, butterflies, and beetles. When you click it, that point and all the branches emanating upwards from it (including the ant, fly, butterfly, and beetle branches) are highlighted. Here, point 1 is the most recent ancestor that flies and butterflies have in common. Point 2 is the ancestor that flies, butterflies, and beetles have in common. Point 3 is the ancestor that all the lineages have in common.
• Tips. Tips represent groups of organisms.  On the tree, the icons depicting ants, flies, butterflies, and beetles are each highlighted. Here, each tip is a major group of insects.

Other buttons at the bottom are labeled “advanced tree features” and “animated video.” A button at the top is labeled “select a tree.”

Branching diagram that resembles a broom head with diagonal lines extending upwards, advanced features

This style of tree is often used to show relationships among microorganisms and the earliest forms of life or among genes. The tree shown here depicts the relationships among 14 unspecified groups of organisms.  This diagram has the following advanced features:

• Highlighted group or name on a lineage. A set of connected lineages is circled and labeled “Name of group.” When a name is written on a lineage, it indicates that the lineages descending from that lineage all belong to the same named group.
• Labeled branch mark. One vertical lineage on the tree has a short horizontal line on it that is labeled “dark wings evolve.” This indicates that a particular feature (such as having dark- instead of light-colored wings) evolved and was inherited by the descendent lineages, the lineages that have that ancestor in common.
• A polytomy is represented by three or more lineages coming from the same branching point. A branching point from which three branches all directly emanate is highlighted along with those descendant lineages. A polytomy indicates that scientists are uncertain about which of those lineages are more closely related.
• Differently colored branches. Three terminal lineages and the branching point from which they arise are colored red, instead of black as the rest of the branches on the tree are. This usually indicates that a particular feature evolved and was inherited by the highlighted lineages. It can also mean that the highlighted branches share the same name.
• Varying branch length. Two branches with different lengths are highlighted. Varying branch length represents the amount of evolutionary change that occurred in that lineage. Longer branches experienced more change.

Buttons at the bottom are labeled “Basic tree features” and “animated video.” A button at the top is labeled “select a tree.”

Animated video

An animated video shows these different styles of branching diagram morphing into another. Each diagram depicts the relationships among ants, flies, butterflies, and beetles. All evolutionary trees, no matter what they look like, represent the same thing: evolutionary relationships.

Buttons at the bottom are labeled “basic tree features” and “advanced tree features.” A button at the top is labeled “select a tree.”

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