=278.= The seventh and last of the subordinate powers of the soul, according to the Stoics, is that of procreation. This part of their system is of great importance, not only for the study of human nature, but even in a higher degree for its indirect bearing upon the question of the development of the universe through ‘procreative principles’ (σπερματικοὶ λόγοι), or, as we have termed them above, ‘seed powers[78].’ That all things grow after their kind is of course matter of common knowledge; no combination of circumstances, no scientific arrangement of sustenance can make of an acorn anything but an oak, or of a hen’s egg anything but a chicken. But in the common view this is, at least primarily, a corporeal or material process; whereas the Stoics assert that it is not only a property of the soul, but one so primary and fundamental that it must be also assumed as a first principle of physical science. Before approaching the subject from the Stoic standpoint, it may be well to see how far materialistic theories, ancient and modern, can carry us. [Sidenote: Heredity.] =279.= Lucretius finds this a very simple matter: ‘Children often resemble not only their parents, but also their grandparents and more remote ancestors. The explanation is that the parents contain in their bodies a large number of atoms, which they have received from their ancestors and pass on to their descendants. In the chance clashing of atoms in procreation Venus produces all kinds of effects, bringing about resemblances between children and their forebears, not only in the face and person, but also in the look, the voice, and the hair[79].’ This account has a generally plausible sound until we bear in mind that it is the fundamental property of atoms that, though their own variety is limited, they can form things in infinite variety by changes in their combination and arrangement. They are like the letters out of which words, sentences, and poems are made up; and we can hardly expect to reproduce the voice or the spirit of an Aeschylus by a fresh shuffling of the letters contained in the _Agamemnon_. On the contrary, seeing that the atoms contained in the bodies of parents have largely been drawn from plants and animals, we could confidently reckon upon finding the complete fauna and flora of the neighbourhood amongst their offspring. Lucretius in effect postulates in his theory that particular atoms have a representative and creative character, passing from father to child in inseparable association with the marks of the human race, and endowed with a special capacity of combining with other like atoms to form the substratum of specifically human features. In giving his atoms these properties he is insensibly approximating to the Stoic standpoint. [Sidenote: Modern theories.]