Reading phylogenetic trees.

As cladistics, facilitated by genetic comparisons and molecular-clock modeling, has become the dominant taxonomic method, the phylogenetic tree diagram has become nearly ubiquitous, but little explanation is given for its meaning. Where the branch points occur along one axis has meaning; placement on the other axis is a matter of taste.

In a 11 November 2005 short article in Science, entitled The Tree Thinking Challenge, David A. Baum and Susan DeWitt Smith of the University of Wisconsin, and Samuel S. S. Donovan at the University of Pittsburg present a simple phylogeny and ask the reader to, based on that information, determine which of two critters is more closely related to humans. Take their quiz and see how you fare. If you get it wrong, the article--a very quick read--will set you straight and establish a good habit.