Baer , Karl Ernst von

(1792–1876) German–Estonian biologist, comparative anatomist, and embryologist

Baer is generally considered the father of modern embryology. He was born on his family's estate in Piep, Estonia, and received private tutoring and schooling before entering Dorpat University to study medicine. He graduated in 1814 and then studied comparative anatomy at the University of Würzburg, where he was introduced to embryology by Ignaz Döllinger. In 1817 Baer became professor of zoology at Königsberg and in 1834 was appointed academician and librarian of the Academy of Sciences at St. Petersburg.

It was prior to his move to St. Petersburg that Baer did most of his pioneering work in laying the foundation of comparative embryology as a separate discipline. In distinguishing the mammalian ovum within the Graafian follicle he established that all mammals, including man, develop from eggs. He also traced the development of the fertilized egg and the order in which the organs of the body appear and develop, showing that similar (homologous) organs arise from the same germ layers in different animals, thus extending the work of Kaspar Wolff and the German anatomist Christian Pander. His expounding of the ‘biogenetic law’, demonstrating the increasing similarity and lack of specialization in the embryos of different animals as one investigates younger and younger embryos, provided Darwin with basic arguments for his evolutionary theory. Baer was, however, opposed to the idea of there being a common ancestor for all animal life, although he conceded that some animals and some races of man might have had common ancestry. His other notable discoveries included the mammalian notochord and the neural folds as the precursors of the nervous system. Baer intended his embryological work to be, at least partly, a means of improving animal classification by demonstrating vertebrate affinities. Indeed modern zoological classification is now based partly on biogenetic principles. His great work on the mammalian egg, De ovi mammalium et hominis genesi (1827; On the Origin of the Mammalian and Human Ovum) was followed (1828–37) by Über Entwickelungsgeschichte der Tiere (On the Development of Animals), in which he surveyed all existing knowledge of vertebrate development.

A man of wide interests, Baer did much work in other scientific disciplines. He was instrumental in founding the German Anthropological Society and helped to found the Russian Geographical and Entomological Societies.