Cooking up the perfect insect: Aristotle's transformational idea about the complete metamorphosis of insects

Abstract

Aristotle made important contributions to the study of developmental biology, including the complete metamorphosis of insects. One concept in particular, that of the perfect or complete state, underlies Aristotle's ideas about metamorphosis, the necessity of fertilization for embryonic development, and whether morphogenesis involves an autonomous process of self-assembly. Importantly, the philosopher erroneously views metamorphosis as a necessary developmental response to lack of previous fertilization of the female parent, a view that is intimately connected with his readiness to accept the idea of the spontaneous generation of life. Aristotle's work underpins that of the major seventeenth century students of metamorphosis, Harvey, Redi, Malpighi and Swammerdam, all of whom make frequent reference to Aristotle in their writings. Although both Aristotle and Harvey are often credited with inspiring the later prolonged debate between proponents of epigenesis and preformation, neither actually held firm views on the subject. Aristotle's idea of the perfect stage also underlies his proposal that the eggs of holometabolous insects hatch 'before their time', an idea that is the direct precursor of the much later proposals by Lubbock and Berlese that the larval stages of holometabolous insects are due to the 'premature hatching' from the egg of an imperfect embryonic stage. This article is part of the theme issue 'The evolution of complete metamorphosis'.

Keywords: Aristotle; William Harvey; epigenesis; fertilization; spontaneous generation.

Figure 1.

Aristotle's concept of the perfect or complete state and its implications. (a) The concept of the perfect state leads Aristotle to conclude that a holometabolous insect larva differs from the adult of the same species because it lacks Pneuma. (b) Aristotle concludes that because holometabolous larvae lack Pneuma they must be generated spontaneously (i.e. without fertilization). Even if these insects appear to mate, they do not really do so. (c) Aristotle recognizes that larval–pupal morphogenesis is a gradual process that involves feeding and growth, and in which perfect form develops as a result of the gradual accumulation by the larva of Pneuma from outside of itself. (d) Aristotle considers that pupal–adult morphogenesis is an abrupt process that does not involve feeding and growth, and in which perfect form is generated from a template provided by Pneuma. Aristotle contrasts this with the gradual development of the perfect state in (c). Note, however, that although Harvey later regards non-gradual pupal–adult transformation as necessarily non-epigenetic, contrasting it with gradual larval–pupal development, Aristotle does not draw such a distinction.