Methodology of a Cladistic Analysis
HOW TO CONSTRUCT CLADOGRAMSHere is an outline of the steps necessary for completing a cladistic analysis. Don't be fooled, however, by the simplicity of these steps. Seeing a real cladistic analysis out to fruition can be a difficult and time consuming task.
Choose the taxa whose evoutionary relationships interest you. These taxa must be clades if you hope to come up with plausible results.
Determine the characters (features of the organisms) and examine each taxon to determine the character states (decide whether each taxon does or does not have each character). All taxa must be unique.
Determine the polarity of characters (whether each character state is original or derived in each taxon). Note that this step is not absolutely necessary in some computer algorithms. Examining the character states in outgroups to the taxa you are considering helps you determine the polarity.
Group taxa by synapomorphies (shared derived characteristics) not plesiomorphies (original, or "primitive", characteristics).
Work out conflicts that arise by some clearly stated method, usually parsimony (minimizing the number of conflicts).
Build your cladogram, which is NOT an evolutionary tree, following these rules:
All taxa go on the endpoints of the cladogram, never at nodes.
All cladogram nodes must have a list of synapomorphies which are common to all taxa above the node (unless the character is later modified).
All synapomorphies appear on the cladogram only once unless the character state was derived separately by evolutionary parallelism.
To accomplish the task of creating a good cladogram, you must use your judgement. Ask yourself the following questions and answer them carefully.
Could a supposed synapomorphy be the result of independent evolutionary development?
Are your characters chosen well?
Should you consider other characters?
Should you consider additional taxa?
Continue your journey by selecting one of the topics below.
Methodology of Cladistics
