Biologists in stamps

These UK stamps were issued in (clockwise, from top right) 1965, 1982 and 1996, to commemorate the centenary of Joseph Lister's discovery of antiseptic surgery, the centenary of the death of Charles Darwin, and the work of crystallographer Dorothy Hodgkin (who is backed by her model of vitamin B 12). The Hodgkin stamp is one of a series entitled Twentieth Century Women of Achievement, which includes ballerina Margot Fonteyn and novelist Daphne du Maurier. (Images courtesy of the Royal Mail.)