August Weismann

August Weismann (1834–1914) was a German evolutionary biologist who argued that hereditary information passes through reproductive cells, not through changes acquired by the body.

Germ-plasm theory: A theory that hereditary material resides in reproductive cells and passes between generations through an unbroken lineage. This is Weismann’s best-known account of how heredity persists across generations.
Continuity of the germ plasm: The hypothesis that hereditary material passes through successive generations of reproductive cells without being produced anew by the body. It captures the lineage principle at the heart of Weismann’s account.
August Weismann’s mouse-tail experiment: A multigenerational experiment in which Weismann cut off mouse tails and observed that offspring were born with tails. He used it to argue that mutilations do not alter hereditary material in reproductive cells.
Neo-Darwinian synthesis: The twentieth-century framework that joined Mendelian genetics with Darwinian natural selection. Its rejection of inheritance of acquired characteristics echoed Weismann’s position, though its genetics differed.
Germ line: The lineage of cells that gives rise to an organism’s eggs or sperm and transmits hereditary material. Weismann treated this lineage as continuous across generations.
Weismann barrier: The proposed restriction preventing information acquired by somatic cells from entering the germ line and being inherited. The barrier formalizes the separation Weismann argued for between body and reproductive cells.
Lamarckism: An evolutionary theory that attributes adaptation partly to the inheritance of characteristics acquired during an organism’s life. Weismann’s account directly opposed its proposed route from bodily change to heredity.
Mendelian inheritance: The transmission of traits according to inheritance patterns described by Gregor Mendel’s experiments. Mendelian genetics later supplied a more precise account of hereditary transmission than Weismann’s hypothetical germ plasm.
Somatic cell: Any cell of an organism that is not a reproductive cell or its direct precursor. His theory separated these body cells from the hereditary lineage.
Natural selection: Differential survival and reproduction cause heritable variants to become more or less common in populations. Weismann made natural selection the main explanation for adaptive change rather than inherited bodily modification.

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