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In biology, epigenesis has at least two distinct meanings:
- the structural development in an organism, and in particular the development of a plant, fungus or animal from a seed, spore or egg through a sequence of steps in which cells differentiate and organs form;
- the theory that plants, animals and fungi develop in this way, in contrast to theories of preformationism.
The originator of the latter 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 1759 in favor of epigenesis, though this did not sound the death knell of preformationist ideology.
- http://books.google.com/books?id=IUfAsFSPf6oC&pg=PA173&lpg=PA173&dq=spallanzani+epigenesis&source=web&ots=yRuS8F4bjQ&sig=kqF-9nu4yL1DPAqB9wLmVf3n-UI#PPP1,M1 Marianne Henn & Holger A. Pausch, Body Dialectics in the Age of Goethe, 2003, pp.169-175
- http://www.springerlink.com/index/Q3T8577K012T4281.pdf Al Baxter, Edmund B. Wilson as a preformationist: Some reasons for his acceptance of the chromosome theory, Journal of the History of Biology, 9,1, March, 1976, pp.29-57
- http://www.spallanzani.it/paginanews.asp?id=17 Spallanzani in New York, Spallanzani's Biological Contributions 200 Years After His Death, Columbia University, New York, October 29th, 1999
- http://books.google.com/books?id=-ddVamDO-xcC&pg=PA11&lpg=PA11&dq=epigenesis+controversy&source=web&ots=MqfgfvWLrA&sig=iiQYbdCyxLJOBGC-ou6O5x0hlrQ Ernst Mayr, This Is Biology: The Science of the Living World, p.11