August Weismann
(1834-1914)
August Weismann was considered by
Ernst Mayrto be the greatest evolutionary biologist between
Charles Darwin and the "modern synthesis" of Darwinian evolution (natural selection) and Mendelian genetics in the 1920's.
Weismann argued that the
variability that drives natural selection involves only the germ cells (the egg and sperm cells that form the zygote). Other body (somatic) cells are not involved in heredity. Germ cells produce the somatic cells and nothing that changes in the somatic cells can be inherited.
Weismann thus denied the Lamarkian theory of evolution, that changes in the body during development and growth can become inherited. It appears to agree with the "central dogma of molecular biology," that transcriptions of DNA sequences into RNA are one-way messengers (mRNA) that travel out of the nucleus into the cytosol where ribosome "factories" translate the messages into polypeptide chains of amino acids (proteins which, if folded properly, become active enzymes).
Genetic information cannot go the other way from soma to germ plasm and on to the next generation.
These standard ideas of genetics in the twentieth century have been changed in the twenty-first by discoveries in "
epigenetics," in which markers can tag genes to suppress or allow transcriptions, thus regulating the production of proteins. And these markers can be duplicated along with the DNA in mitosis and meiosis, so that gene expression and regulation can be inherited by successive generations of cells in development.
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