In this lesson students working in teams classify furniture, share their categories and rationales, then note how their different schemes vary arbitrarily. They then see how living organisms are classified, and note how these groupings are natural, nearly always reflecting the same ancestral relationships in nested hierarchies, regardless of the deeper criteria. Such patterns are revealed with a look at several phylogenetic trees of primates. Finally, teachers are encouraged to give their students lab experience collecting data from a variety of primate characteristics (skulls, chromosomes, and hemoglobin), to see for themselves the congruency of those data sets.