Earth bore man spontaneously, as the best of her fruits, before even the Moon was. This was the golden race, who lived without cares or labour and lived off the plants and trees they found. They didn't grow old and danced and laughed much. Their spirits still survive as genii of happy music retreats, givers of good fortune and upholders of justice.
The silver races was also divinely created. They ate bread and had a matriarchal society, were quarrelsome and didn't sacrifice to the gods. Zeus destroyed them.
The brazen race fell like fruits from the ash-trees and were armed with brazen weapons. They ate flesh as well as bread and delighted in war. Black Death seized them.
The fourth race was also brazen, but begotten by gods on mortal mothers, making them nobler and more generous. These were the heroes who fought the Trojan War and went on the expedition of the Argonauts.
The fifth race is the race of iron that lives today, the unworthy descendants of the fourth.
Robert Graves, The Greek Myths. Complete Edition.