August Weissmann | Biography

August Weissmann was a German biologist who is best known for his contributions to evolutionary theory, specifically for his germ-plasm theory of heredity. Weissmann was born in Frankfurt, Germany. At the age of 18, he began his study of medicine at Göttingen University which he attended until 1856. After completing his education, Weissmann practiced medicine until 1863, at which time he turned his attention to the study of biology and zoology. In 1867, Weissmann became a professor of zoology at the University of Freiburg. He first served at the medical school associated with the university and later at a new Institute of Zoology. Weissmann remained in this capacity until 1912.

During this time Weissmann explored a variety of areas, most notably the embryology of insects and crustaceans. He is especially noted for his evaluations of the two-winged flies, the Diptera. He also conducted studies of Hydrozoa (a class of invertebrates which include jellyfish) that led to the development of his famous germ-plasm theory. In this theory, Weissmann proposed that the genetic code for an organism is contained in the germ cells (the egg and sperm), which explains how the information can be transmitted unchanged from generation to generation. In accordance with this theory, Weissmann favored the natural selection ideas championed by Charles Darwin, who believed that specific inherited characteristics are passed from generation to generation. An opposing theory, supported by Jean-Baptiste Lamarck and others of the time, postulated that organisms acquired physical characteristics through exposure to their environment, and that they passed on these characteristics to their offspring. Weissmann was the first scientists to conduct experiments to disprove that acquired characteristics can be transmitted from parents to offspring. He did this using an experiment where he cut off the tails of mice for five consecutive generations. He then observed the offspring to determine if this tail-less characteristic was passed on to subsequent generations. These studies confirmed that such environmental stimuli are not passed on in a hereditary fashion. In other studies, Weissmann noted that the process of meiosis involved some form of reduction division because the genetic material did not double when the cell replicated.

Weissmann published his theories in a series of essays that were translated as Essays upon Heredity and Kindred Biological Problems which were published between 1889 and 1892. In 1902, he published Vorträgeuber Descendenztheorie which is still considered to be a valuable contribution to evolutionary theory. He was the first to provide a detailed explanation of the neuro-humoral organ that was later named after him, the Weissmann ring. Weissmann died at age 80 in 1914.