Phenogram vs. Cladogram — What's the Difference?

Phenograms, also known as phenetic trees, are constructed based on the overall similarity between species, which can be morphological, biochemical, or genetic. They represent the degree of similarity using various statistical methods, without necessarily reflecting evolutionary pathways. Cladograms, in contrast, are based on the concept of shared derived characteristics, known as synapomorphies. These are traits that are present in an ancestral species and its descendants but absent in more distant relatives. Cladograms are used to hypothesize evolutionary relationships and show how closely species are related based on their evolutionary history, rather than just similarity.

While phenograms focus on similarity, which can result from convergent evolution (where unrelated species evolve similar traits), cladograms emphasize actual evolutionary relationships. This distinction is crucial because similarity does not always indicate common ancestry. For example, the wings of birds and insects are similar but evolved independently.

The construction of a cladogram involves identifying unique characteristics that define groups of organisms, then organizing these groups based on when these characteristics appeared in their lineage. This method helps clarify the evolutionary branching points, or nodes, which represent common ancestors.

Both phenograms and cladograms are tools in systematics, the study of the diversity of life and the relationships among living things. However, cladograms are considered more informative for understanding evolutionary relationships because they are based on the principle that characteristics appearing in recent common ancestors are more significant for classification than overall similarity.