Aristotle on chance and spontaneous generation. A discussion note

In Physics II. 4,6 Aristotle deals with the technical concept of chance. Here a number of specific characteristics are ascribed to the chance happenings. At the same time, in his biological works Aristotle presents his notorious theory of 'spontaneous generation' Most scholars assume that this theory ought to be in line with the doctrine of chance, as this is presented in his Physics. It is clear, however, that spontaneous generation lacks (at least some of) the features a chance happening ought to have. For instance, spontaneity is not unusual. My purpose here is to address the exegetical problem at hand, in particular to sketch out an argument according to which the discrepancy between Aristotle's doctrine of chance and his theory of spontaneous generation is merely an apparent one.