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February 5:   Devin Henry (Western University)

“Aristotle and Epigenesis”

Abstract: In a recent paper Aryeh Kosman (2010) makes a “plea for the recognition that Aristotle’s theory [of animal development] is through and through a theory of epigenesis”. What he means by this is that Aristotle rejected the ancient theory of preformationism (the view that the complete organism pre-exists in miniaturized form inside the sperm or egg) in favour of a model in which form and structure emerge gradually during development from an unorganized, amorphous embryo. But there is a more interesting question that Kosman fails to consider. Modern developmental biology now recognizes two senses of “epigenesis” that give rise to what Alan Love characterizes as “a pervasive ambiguity lumbering around in the literature”. In the first place “epigenesis” is used for that familiar idea of the gradual emergence of form and structure. (Call this Epigenesis-1.) But biologists also describe development as “epigenetic” to emphasize the context-dependency of the process itself. (Call this Epigenesis-2.) According to this view developmental pathways are not fixed ahead of time by the genetic program. Rather the genes represent a set of potential pathways, and which pathways are actualized during development is determined in real time as the process unfolds in response to environmental cues (including factors internal to the developing system itself but external to the genome). This model denies the view that development is simply the gradual actualization of a pre-arranged series of changes hard-wired in the genotype so that everything proceeds in a fixed sequence once the process has been triggered. Instead a developing embryo is viewed as a more dynamic and responsive system that reacts to real-time inputs from the internal and external environment (Müller & Olsson 2003). In a word, to say that development is “epigenetic” in this sense is to say that many parts of the organism’s phenotype are determined on the fly as it comes into being. While it is certainly not news to anyone that Aristotle rejected preformationism in favour of Epigenesis-1, it is completely up for grabs whether or not he thought development was “epigenetic” in the sense of Epigenesis-2. This is important because Epigenesis-1 is completely compatible with a rejection of Epigenesis-2. Someone can hold that form and structure emerged gradually from an unorganized, amorphous embryo and yet still think that the process unfolds according to a fixed sequence of pre-programmed changes. In this paper I argue that Aristotle’s theory was not a theory of epigenesis in the sense of Epigenesis-2 but instead viewed the process as much more deterministic than some recent commentators have tried to maintain.

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Date(s) - February 5, 2016
3:30 pm - 5:00 pm

McMaster University, Kenneth Taylor Hall 109


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