Preformationsim
<p >In the <a href="http://en.wikipedia.org/wiki/History_of_biology" title="History of biology" >history of biology</a>, <b>preformationism</b> (or <b>preformism</b>) is the idea that organisms develop from miniature versions of themselves.</p>
<p>
Instead of assembly from parts, preformationists believe that the <a href="http://en.wikipedia.org/wiki/Platonic_forms" title="Platonic forms" class="mw-redirect" >form</a> of living things exist, in real terms, prior to their <a href="http://en.wikipedia.org/wiki/Ontogeny" title="Ontogeny" >development</a>.<sup id="cite_ref-SEP_0-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Preformationism#cite_note-SEP-0" >[1]</a></sup> It suggests that all <a href="http://en.wikipedia.org/wiki/Organism" title="Organism" >organisms</a> were created at the same time, and that succeeding generations grow from <a href="http://en.wikipedia.org/wiki/Homunculus" title="Homunculus" >homunculi</a>, or <a href="http://en.wikipedia.org/wiki/Animalcule" title="Animalcule" >animalcules</a>, that have existed since the beginning of creation.</p>
<p>
<a href="http://en.wikipedia.org/wiki/Epigenesis" title="Epigenesis" >Epigenesis</a><sup id="cite_ref-OED1_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Preformationism#cite_note-OED1-1" >[2]</a></sup>, then, in this context, is the denial of preformationism: the idea that, in some sense, the form of living things comes into existence. As opposed to "strict" preformationism, it is the notion that "each embryo or organism is gradually produced from an undifferentiated mass by a series of steps and stages during which new parts are added." (Magner 2002, p. 154) <sup id="cite_ref-Magner_2-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Preformationism#cite_note-Magner-2" >[3]</a></sup> This word is still used, on the other hand, in a more modern sense, to refer to those aspects of the generation of form during ontogeny that are not strictly genetic, or, in other words, <i><a href="http://en.wikipedia.org/wiki/Epigenetics" title="Epigenetics" >epigenetic</a></i>.</p>
<p>
The historical ideas of preformationism and epigenesis, and the rivalry between them, are obviated by our<a href="http://en.wikipedia.org/wiki/Genetics" title="Genetics" >contemporary understanding</a> of the <a href="http://en.wikipedia.org/wiki/Genetic_code" title="Genetic code" >genetic code</a> and its <a href="http://en.wikipedia.org/wiki/Nucleic_acid" title="Nucleic acid" >molecular basis</a> together with <a href="http://en.wikipedia.org/wiki/Developmental_biology" title="Developmental biology" >developmental biology</a> and <a href="http://en.wikipedia.org/wiki/Epigenetics" title="Epigenetics" >epigenetics</a>.</p>
<p>
<a href="http://en.wikipedia.org/wiki/Pythagoras" title="Pythagoras" >Pythagoras</a> is one of the earliest thinkers credited with ideas about the origin of form in the biological production of offspring. It is said<sup id="cite_ref-johnston_3-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Preformationism#cite_note-johnston-3" >[4]</a></sup> that he originated "spermism", the doctrine that fathers contribute the essential characteristics of their offspring while mothers contribute only a material substrate. <a href="http://en.wikipedia.org/wiki/Aristotle" title="Aristotle" >Aristotle</a> accepted and elaborated this idea, and his writings are the vector that transmitted it to later Europeans. Aristotle purported to analyse ontogeny in terms of the material, formal, efficient, and teleological causes (as they are usually named by later anglophone philosophy) – a view that, though more complex than some subsequent ones, is essentially more epigenetic than preformationist. Later, European physicians such as <a href="http://en.wikipedia.org/wiki/Galen" title="Galen" >Galen</a>, <a href="http://en.wikipedia.org/wiki/Realdo_Colombo" title="Realdo Colombo" >Realdo Colombo</a> and <a href="http://en.wikipedia.org/wiki/Girolamo_Fabrici" title="Girolamo Fabrici" class="mw-redirect" >Girolamo Fabrici</a> would build upon Aristotle's theories, which were prevalent well into the 17th century.<sup id="cite_ref-Magner_2-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Preformationism#cite_note-Magner-2" >[3]</a></sup></p>