Karl Ernst von Baer

Biography — Famous Biologists

Karl Ernst von Baer (1792-1876). German zoologist, comparative anatomist, and scientific explorer.

One of the founders of embryology, von Baer discovered the notochord and the embryonic blastula. He also established the fact that mammals develop from eggs. His book, Über Entwickelungsgeschichte der Thiere (On the Development of Animals) surveyed available knowledge of animal development and served as the starting point for the field of comparative embryology.

Together with Heinz Christian Pander, he proposed the now accepted germ layer theory of development, in which three distinct systems of bodily structures are derived from three distinct layers of cells in the embryo, the ectoderm, mesoderm, and endoderm.

Von Baer is perhaps best remembered for his demonstration that the early embryos of very distinct types of organisms are quite similar — this at a time when many still believed that embryos were perfectly formed from earliest inception (see figure, below right). He showed that the various traits characteristic of particular types of organisms appear only later in the course of development. This idea influenced Charles DarwinCharles Darwin, who transferred von Baer's description of embryonic development to the context of evolutionary development — Darwin proposed that generalized forms would evolve into specialized forms as evolution progressed. Von Baer's comparison of embryos also did much to undermine the old idea that humans are sharply distinct from animals, since the embryos from which humans originate are so much like those of other animals.

Karl Ernst von Baer's comparison of embryos of disparate organisms, including a human embryo (rightmost series). The similarity between the earliest stages is obvious. Source: Über Entwicklungsgeschichte der Thiere (click to enlarge)

In addition to his work in comparative anatomy and embryology, Von Baer made important contributions to arctic biology, meteorology, and geography. A resident of Russia at St. Petersburg for much of his life (he was born in nearby Estonia), he was a founder and the first president of the Russian Geographical Society, and a co-founder of the Russian Entomological Society. In 1837 he made an expedition to the island of Novaya Zemlya off Russia's northern coast. He also explored the Caspian Sea and the northern coast of Scandinavia.

Von Baer believed that evolutionary processes can often be saltatory and, therefore, late in life became a prominent critic of the theory of natural selection.

• Major works: De ovi mammalium et hominis genesi (1827); Über Entwicklungsgeschichte der Thiere (vol. 1, 1828; vol. 2, 1837); Beiträge zur Kenntniss des russischen Reiches und der angränzenden Länder Asiens (1839).
• Full name: Karl Ernst Ritter von Baer, Edler von Huthorn.
• Karl Ernst von Baer's exact dates of birth and death: February 28, 1792 — November 28, 1876.