Theory Biosci. (2002) 121: 247±251 Ó Urban & Fischer Verlag http://www.urbanfischer.de/journals/theorybiosc Editorial: Haeckel and Modern Biology Michael K. Richardson, Jonathan E. Jeffery Institute of Evolutionary and Ecological Sciences, Leiden, The Netherlands Address for correspondence: Prof. Dr. Michael K. Richardson, Institute of Evolutionary and Ecological Sciences, Leiden University, Kaiserstraat 63, 2311 GP Leiden, The Nether- lands Received: May 22, 2002; accepted: June 21, 2002 The symposium Haeckel and Modern Biology was held at the Sixth Inter- national Congress of Vertebrate Morphology in 2001 in Jena, Eastern Ger- many. It brought together historians and biologists to consider the work of Ernst Haeckel and its relevance to modern biology. Jena was an appro- priate setting because Haeckel spent much of his academic career as a pro- fessor in its University. Haeckel's fame rests on his work as a naturalist, systematist, theoretician, philosopher and popular science writer (Bo Èlsche 1906; Uschmann 1954; Heberer 1968; Krauûe 1984; Weindling 1989; Richards 1992; Nyhart 1995). In this introduction, I suggest some reasons why this work is still relevant to modern science 1 , and outline some of the issues discussed by the speakers. Biologists still make use of Haeckel's important and magnificently-illu- strated monographs on marine organisms (e. g. Haeckel 1862; 1872; 1877; 1881; 1888). Not only are the illustrations and descriptions in these works important, but some of the taxonomic categories Haeckel employed for certain groups of sponges, medusa and radiolaria are still in use. Haeckel developed theories in the field of evolutionary developmental biology, such as the Gastraea Theory and Biogenetic Law . These theories gained a new relevance, years after Haeckel's death, when their scientific value was reassessed by several influential writers (including de Beer, 1930; Gould, 1977). Another reason why Haeckel is of interest to modern biologists is that he was the first to outline a phylogenetic tree covering the whole animal kingdom. He did this by adapting the methods of the old comparative anatomy to promote a new evolutionary morphology. 1431-7613/02/121/03±247/$ 15.00/0 1 In this article, I have not followed the order in which the talks were presented at the sympo- sium.