These activities, prepared for key stage 5 students (ages 16-18) and also suitable for key stage 4 (ages 14-16), show that physical appearance is not necessarily the best way to classify mammals. DNA structure is examined to show how similarities and differences between DNA sequences of mammals can be used to establish evolutionary relationships. Some real DNA sequences are compared to illustrate that the whale is surprisingly closely related to mammals such as the hippo, camel and cow, a relationship confirmed by fossil evidence. Finally, an analysis of haemoglobin sequences of primates shows the close relationship between humans and other great apes such as the chimpanzee. (Contains 4 figures and 5 tables.)