Karl Ernst von Baer - Discovered the Mammal Egg

Dr. Karl Ernst von Baer established the field of embryology, the study of how living things grow and develop from a tiny egg or seed into a fully formed baby, animal, or plant.

He was born in 1792 in what is now Estonia, into a large Baltic German noble family. As one of ten children, von Baer was sometimes raised by relatives. From a young age, he loved nature and plants. Although he received private tutoring and went to school, he was far more interested in studying the natural world than in military training.

Von Baer attended the University of Dorpat in his hometown, where he first studied medicine. Later, he continued his studies in Germany. There, he met scientists who were interested in how embryos form and develop before birth. His curiosity about the earliest stages of life led him to focus on how animals begin their existence.

In 1826–1827, von Baer made one of the most important discoveries in biology. While examining the ovaries of a dog under a microscope, he saw a tiny yellow spot inside a small sac. After careful study, he realized it was the mammalian egg, the first one ever identified and described. That same year, he published a scientific paper, De ovi mammalium et hominis genesi (On the Genesis of the Ovum of Mammals and of Man), to share his discovery with the world.

After this breakthrough, von Baer began comparing embryos from many different animals. He found that they all go through similar stages early in development. Between 1828 and 1837, he published his famous book Über Entwickelungsgeschichte der Thiere (On the Developmental History of Animals), in which he introduced four laws of embryology, now known as von Baer’s Laws. These laws showed that embryos start with general features common to a large group of animals and later develop the special traits of their own species. This idea went against the popular belief of the time that embryos “replayed” the adult stages of simpler animals as they developed.

Von Baer also discovered the notochord, a stiff rod of cells that appears early in vertebrate embryos. The notochord helps guide the development of the backbone and nervous system. He showed that embryos from fish, birds, reptiles, and mammals are so similar in their earliest stages that it can be hard to tell them apart. He also described the three germ layers, ectoderm, mesoderm, and endoderm that form early in development and later become all the different parts of the body. These ideas became the foundation of modern embryology and developmental biology.

Von Baer’s interests went beyond embryology. He taught zoology and anatomy, helped found the Russian Geographical Society, and studied topics like geography and fish conservation. He worked as a professor in Königsberg, Germany, and later became a member of the Imperial Academy of Sciences in Saint Petersburg, Russia. His achievements were recognized across Europe. In 1831, the French Academy of Science awarded him a medal, and many other scientific organizations honored him during his lifetime.

Although von Baer disagreed with some parts of Charles Darwin’s theory of evolution, Darwin admired his work. Darwin especially valued von Baer’s insight that embryos of different species look alike early in development because they share common beginnings, not because they are repeating the life stages of other animals.

Karl Ernst von Baer died in 1876, leaving behind a remarkable scientific legacy. His discovery of the mammalian egg, his laws of embryology, and his research on germ layers and early development helped transform embryology into a modern science. His work laid the foundation for understanding how animals and humans develop and influenced later ideas about evolution. Today, von Baer is remembered as the father of comparative embryology and one of the most important scientists of the 19th century.

References:
Barnes, By: M. Elizabeth, et al. “Karl Ernst von Baer’s Laws of Embryology.” Karl Ernst von Baer’s Laws of Embryology | Embryo Project Encyclopedia, embryo.asu.edu/pages/karl-ernst-von-baers-laws-embryology.
“Karl Ernst von Baer.” Encyclopædia Britannica, Encyclopædia Britannica, inc., www.britannica.com/biography/Karl-Ernst-Ritter-von-Baer-Edler-von-Huthorn.
“Karl Ernst von Baer: EBSCO.” EBSCO Information Services, Inc. | Www.Ebsco.Com, www.ebsco.com/research-starters/history/karl-ernst-von-baer.
S; Brauckmann. “Karl Ernst von Baer (1792-1876) and Evolution.” The International Journal of Developmental Biology, U.S. National Library of Medicine, pubmed.ncbi.nlm.nih.gov/23319342/.

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"Portrait of Karl Ernst von Baer. Wellcome M0017373.jpg" by Wellcome Images licensed under CC BY 4.0 / Cropped from original

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