How to Create a Phylogenetic Tree

A phylogenetic tree shows the evolution of a species. As we learn new things in the field of biology, existing trees change. New branches may arise. Old ones may be truncated. So before creating a phylogenetic tree, search for the most current information.

Difficulty:

Moderate

Instructions

Things You'll Need

• Paper Markers

Creating a Phylogenetic Tree

1. Research the species you wish to chart in a phylogenetic tree. Organize all the related species. A chart may help. Try listing the species in the order in which they appeared in one column. In another column, list the approximate date of their appearance. In a third column write the name of the species' direct ancestor. This way, on a single row of your chart you have a species name, its date of appearance and its direct ancestor. This will help you link together your tree.

2. Identify the starting point for your tree, the ancestor common to all else on the tree. Select a starting point for your tree. If you are drawing your tree vertically, you might select a point somewhere along the bottom center of your paper. If you are drawing your tree horizontally, you might select a point along the left middle side of your paper. Left, because charts are typically drawn from left to right.

3. Draw a line outward from the common ancestor. The length of the line can be used to represent the time which this species alone survived--i.e., there were no known descendants. This means you would need to devise a rough scale to keep your line length consistent with time throughout your tree. But not all trees use line length to illustrate time lines.

4. Create forks--however many are appropriate to the particular species. Try to space out your forks evenly (assuming more than one) so they spread like tree branches. Each fork represents one of the evolutionary descendants that came off a common ancestor. Each of these descendants will have only the particular ancestor in common--i.e.,each descendant is considered unique from the other.
   Label each fork with the appropriate species If you choose to use line length to indicate time, remember to keep to your scale.
   Note: You might use different colored markers for each of the first branches coming off the original common ancestor. Then maintain the color pattern within each of these nodes. As the tree progresses, you may find additional places where new color patterns should arise.

5. At each labeled species the process is the same. So repeat the above step until you have placed all the species on your tree.
   For example,sometimes a species simply evolves into a single, yet new species. In this instance you would have a single line continuing outward from the ancestor species to its next evolved descendant.
   In another example, you may find a species produces multiple descendants, requiring more branching. Use the organized chart to help you keep track by locating the ancestors in column three. If you find the same ancestor three times, that means you need three branches--that you have three descendants, their names found in column one, to place on the tree. Note that each of the three branches may have a different length. Use column two, the time the descendant appeared, to dictate the length of your line (branch). Those who appeared sooner would have shorter lines than those who appeared later. Even if you do not use a scale, you can still show order of appearance by using different branch lengths.

Tips & Warnings

• You might also use available software to help you create a phylogenetic tree. See the links below.