NPR had a fascinating story about how the tree of life, our representation of the relationships between all species of living things, past and present, has changed over time. The original Linnaean taxonomy was based on “shared physical characteristics” while the modern taxonomy is based on shared characteristics of DNA. The differences in the structure of the taxonomies tell us not to “judge a book by its cover”—organisms with very different DNA may share superficial physical characteristics, while organisms with similar DNA may look physically different. Furthermore, the modern taxonomy adds information absent from the original: it quantifies the differences between branches on the tree.