Epigenesis (biology)

Epigenesis (biology)

In biology, epigenesis has at least two distinct meanings:

  • the unfolding development in an organism, and in particular the development of a plant or animal from an egg or spore through a sequence of steps in which cells differentiate and organs form;
  • the theory that plants and animals develop in this way, in contrast to theories of preformation.

The originator of this theory of epigenesis was Aristotle in his book On the Generation of Animals. Though the theory seems an obvious fact to us in today's genetic age, however, the theory was not given much credence in former times because of the dominance for many centuries of Creationist theories of life's origins. However, during the late 18th century an extended and controversial debate by biologists finally led epigenesis to eclipse the long-established preformationist view. The embryologist, Caspar Friedrich Wolff, famously refuted preformationism in 1795 in favor of epigenesis, though this did not sound the death knell of preformationist ideology.

Vestiges of the issue still persist, which has been succinctly summarized as follows: "where preformation stated that the germ cells of each organism contain preformed miniature adults that unfold during development, epigenesis held that the embryo forms by successive gradual exchanges in an amorphous zygote. Although both traditions tried to explain developmental organization, religious and metaphysical arguments on the conception of embryonic matter as either active or passive determined the scope of their respective explanations. It is shown that these very arguments still underlie the use of gene-centric metaphors in the molecular revolution of the 20th century."

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