Misconceptions
Cladograms are frequently misunderstood. Most of these misunderstandings are due to unfamiliarity.
Let’s review the cladogram before going into the common misconceptions. Above, is a common cladogram. The Nodes represent a divergence (events of speciation). Look at the node with the single asterisk (*). At that node organism A and B share a common ancestor. Now look at the node with two asterisks (**). At that node organism A B C share a common ancestor. Distantly related to all and roots the tree at a common ancestor is the outgroup. Although simple in appearance they are not always easily understood among students. Here are some common misconceptions and errors:
“Lower and higher”
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Before students are set to making a cladogram they must understand evolution. They must know that evolution is not a process that drives towards complexity or higher intelligence. Certain organisms are not “more evolved” than others. For example, organism A on the cladogram is “higher” or “more evolved” than organism F.
Reading across the tips
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Looking at just the tips a person might interpret thinking certain species are closely related to each other over others wrongfully. For example, a person might mistake that D is more closely related to C than E since the tips are ordered with D next to C. Also if there seems to be a trend present at the tips, someone might be misled to thinking it an evolutionary trend even though the pattern might not show up at the nodes at all
Similarity vs. Relatedness
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It’s important to tell students that some organisms are closely related but dissimilar in appearance. For example, the bottom cladogram shows sauropsids.
Notice that birds are closely related to crocodilians. Based on just appearance most would assume crocodilians are more closely related to lizards and not place the birds among the reptiles at all!
Siblings vs. Ancestors
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A group can be mistaken to be siblings or decedent from one another. For example, someone might think that birds are descended from crocodilians. In reality neither crocodilians nor birds are descended from the other, but both are descended for a common ancestor at the node.
Long branch= No change
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This is often applied to the outgroup as some people might think since the divergence of the outgroup it has not changed. This is not true, changes occur over time and although a change in appearance may not necessarily be seen they may have changed genetically.