Continuing his speculations on the development of living things, Lucretius strikes out in bolder and original vein. The past history of man, he says, lies in no heroic or golden age, but in one of struggle out of savagery. Only when "children, by their coaxing ways, easily broke down the proud temper of their fathers," did there arise the family ties out of which the wider social bond has grown, and softening and civilizing agencies begin their fair offices. In his battle for food and shelter, "man's first arms were hands, nails and teeth and stones and boughs broken off from the forests, and flame and fire, as soon as they had become known. Afterward the force of iron and copper was discovered, and the use of copper was known before that of iron, as its nature is easier to work, and it is found in greater quantity. With copper they would labour the soil of the earth and stir up the billows of war.... Then by slow steps the sword of iron gained ground and the make of the copper sickle became a byword, and with iron they began to plough through the earth's soil, and the struggles of wavering man were rendered equal." As to language, "Nature impelled them to utter the various sounds of the tongue, and use struck out the names of things." Thus does Lucretius point the road along which physical and mental evolution have since travelled, and make the whole story subordinate to the high purpose of his poem in deliverance of the beings whose career he thus traces from superstition. Man "seeing the system of heaven and the different seasons of the years could not find out by what causes this was done, and sought refuge in handing over all things to the gods and supposing all things to be guided by their nod." Then, in the sixth and last book, the completion of which would seem to have been arrested by his death, Lucretius explains the "law of winds and storms," of earthquakes and volcanic outbursts, which men "foolishly lay to the charge of the gods," who thereby make known their anger. So, loath to suffer mute, We, peopling the void air, Make Gods to whom to impute The ills we ought to bear; With God and Fate to rail at, suffering easily.