Weismann

August Weismann (1834–1914) was a German evolutionary biologist and a central figure in late 19th-century debates on heredity. He argued for germ plasm theory, which posits that heritable information is stored in germ cells (gametes) and that somatic cells of the body do not contribute to the genetic information passed to offspring. Based on this distinction, Weismann contended that acquired characteristics—traits altered during an organism’s life—are not heritable.

In his theoretical framework, the germ line is insulated from somatic changes by a boundary later called the Weismann barrier. He challenged Lamarckian inheritance and emphasized the role of variation arising in germ cells and selection acting on those variations as the driver of evolution. He tested his ideas with experiments on animals, including tail-amputation studies, arguing that loss or modification of a body part did not produce corresponding hereditary changes in descendants.

Among his lasting contributions is The Germ-Plasm: A Theory of Heredity, in which he formalized the idea of the germ-plasm as the source of hereditary material. His views influenced the early development of genetics and the modern understanding of heredity, even as later discoveries in the 20th century—particularly Mendelian genetics and the modern synthesis—expanded or refined aspects of his theory. While the germ plasm concept shaped evolutionary thinking for decades, modern genetics recognizes that some forms of epigenetic inheritance and developmental inheritance can cross the soma-germ boundary in limited cases.

Weismann held academic positions at German universities, and his work helped establish the distinction between heredity and development as central to biology.