Karl Ernst von Baer
On this date, the Estonian-born German biologist and embryologist Karl Ernst von Baer was born. He was an important precursor to Charles Darwin and his theory of evolution.
For more than a century, scientists had attempted to determine the exact nature and location of the mammalian egg. During his research in 1826, Baer discovered the mammalian egg by identifying a yellowish spot within the ovarian follicle visible only with a microscope. He developed this idea in his 1827 treatise, De ovi mammalium et hominis genesi (On the Origin of the Mammalian and Human Ovum).
Baer studied the embryonic development of animals, discovering the blastula stage of development and the notochord. Together with Heinz Christian Pander and based on the work by Caspar Friedrich Wolff, Baer described the germ layer theory of development (ectoderm, mesoderm, and endoderm) as a principle in a variety of animal species. He summarized his findings in his two-volume textbook entitled Über Entwickelungsgeschichte der Thiere (On the Development of Animals) which he published between 1828 and 1837, laying the foundation for comparative embryology.
James Watson (left) and Francis Crick in 1959.
On this date, Cambridge University scientists James D. Watson and Frances H.C. Crick announced that they had determined the structure of DNA, the molecule containing human genes. On the morning of February 28, they determined that the structure of DNA was a double-helix polymer, or a spiral of two DNA strands, each containing a long chain of monomer nucleotides, wound around each other.
In his best-selling book, The Double Helix (1968), Watson later claimed that Crick announced the discovery by walking into the nearby Eagle Pub and blurting out that “we had found the secret of life.”
Watson and Crick’s solution was formally announced on 25 April 1953, following its publication in that month’s issue of the journal Nature. The article revolutionized the study of biology and medicine.
Along with Maurice Wilkins, a colleague, Watson and Crick won the Nobel Prize in 1962 for their discovery.