Fig. 2

Common Ancestry’s paper-based series “Fish or Mammals?” (right) leads students on a data-based exploration of the four lines of evidence for common ancestry: fossils, anatomy, embryos, and DNA. Each new piece of evidence leads to a more-detailed understanding of cetaceans’ relationship with other species, finally revealing that their closest living land-dwelling relative is the hippopotamus. In the online “Interactive Phylogenetic Tree” (left), students explore DNA, which is both a source and a record of evolutionary relatedness. Students choose pairs of organisms on the tree to reveal the number of genes they share (based on published data). This activity reveals the pattern that more closely related organisms, which share a more recent common ancestor, have more genes in common than more distantly related ones