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August Weismann
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August Weismann (1834–1914), the great German theorist and experimental biologist of the 19th century, was one of the first biologists to use evolutionary arguments to explain aging. His initial idea was that there exists a specific death-mechanism designed by natural selection to eliminate the old, and therefore worn-out, members of a population[5]. The purpose of this programmed death of the old is to clean up the living space and to free up resources for younger generations. Weismann probably came to this idea while reading the following notes of Alfred Russel Wallace (one of Darwin's contemporaries and a codiscoverer of natural selection), which he later cited in his essay “The Duration of Life
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August Weismann (1834-1914) was a German biologist whose insights effectivly undercut the linchpin of Lamarckian evolutionary mechanics. He claimed, rightly, that inheritance was only a function of the sex cells, and from this, one of the central dogmas of modern biology; that the germ-line cells create both somatic cells and other sex cells. The important implication is that changes to the soma have no effect on the germ-line... ruling out the inheritance of acquired characteristics.
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The biologist August Weismann proposed the continuity of the germ plasm, where phenotypic changes environmentally caused in the soma are not converted into changes in the genotype (Weismann, 1893). The classic illustration of this principle is that even if you cut off the tails of thousands of generations of rats, they will always produce tailed offspring. Similarly puppies of breeds of dogs which consistently over generations have had their tales or ears docked are born with tales and ears.
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August Weismann identifies that sex cells must have divided differently to end up with only half of a chromosomal set. This very special division of sex cells is called meiosis. Weismann's experiments with reproduction in jellyfish lead him to the conclusion that variations in offspring result from the union of a substance from the parents. He refers to this substance as "germ plasm."
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In 1889, German biologist August Weismann showed that Lamarck's [explanation of evolution] was incorrect. Weismann cut off the tails of hundreds of mice for 22 generations. Lamarck's hypothesis [sic] would predict that eventually mice would be born with shorter tails or no tails at all. However, Weismann's mice continued to produce baby mice with normal tails. Weismann concluded that changes in the body during an individual's lifetime do not affect the reproductive cells or the offspring.
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August Weismann was born on Jan. 17, 1834, at Frankfurt am Main. He early showed intense interest in natural history, and while still a schoolboy he made extensive collections of butterflies, moths, beetles, and plants from the country around Frankfurt. He entered the University at Göttingen in 1852 and took a four-year course in medicine.
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August Weismann