The world came into existence as the result not of design, but of every variety of combination in the elemental atoms throughout infinite time. Originally all were confused together. Gradually those that had mutual affinities combined and separated themselves from the rest. The earthy particles sank to the centre. The elemental particles of the empyrean (aether ignifer) formed the 'moenia mundi.' The sun and moon were formed out of the particles that were neither heavy enough to combine with the earth, nor light enough to ascend to the highest heaven. Finally, the liquid particles separated from the earth and formed the sea. Highest above all is the empyrean, entirely separated from the storms of the lower air, and moving round with its stars by its own impetus. The earth is at rest in the centre of our system, supported by the air, as our body is by the vital principle. The movements of the stars and of the sun and moon through the heavens are next explained; then the origin of vegetable and animal life on the earth, and the beginning and progress of human society.
First plants and trees, afterwards men and animals, were produced from the earth in the early and vigorous prime of the world. Many of the animals originally produced afterwards became extinct. Those only were capable of continuation which had either some faculty of self-preservation against others, or were useful to man, and so shared his protection. The existence of monsters such as Scylla, the Centaurs, the Chimaera, is shown to be impossible according to the natural laws of production.
The earliest condition of man was one of savage vigour and power of endurance, but liable to danger and destruction from many causes. The first humanising influence is traced to domestic union and the affection inspired by children—
Et Venus inminuit viris puerique parentum
Blanditiis facile ingenium fregere superbum.[389]
The origin of language is next explained, then that of civil society, of religion, and of the arts,—the general conclusion being that all progress is the result of natural experience, not of divine guidance.
The last source of superstition is our ignorance of the causes of natural phenomena—
Praesertim rebus in illis
Quae supera caput aetheriis cernuntur in oris.[390]
Hence the sixth book is devoted to the explanation of thunderstorms, tempests, volcanoes, earthquakes, and the like,—phenomena which are generally attributed to the direct agency of the gods. The whole work terminates with an account of the Plague at Athens, closely following that given by Thucydides.