IODICALS

SCIENCE & TECHNOLOGY
But Pilgrim, like all students of evolution in his day, believed that the best way to judge how closely species were related was to consider all their physical similarities. This view changed during the 1960s, when West Germany's Willi Hennig argued that only similarities that linked species to a common ancestor-"shared derived" characteristics-mattered. Horses, zebras, and rhinoceroses all belong to the order Perissodactyla because they have fewer t...