Greek mythology has changed over time to accommodate the evolution of their culture, of which mythology, both overtly and in its unspoken assumptions, is an index of the changes. In Greek mythology's surviving literary forms, as found mostly at the end of the progressive changes, is inherently political, as Gilbert Cuthbertson has urged.
The earlier inhabitants of the Balkan Peninsula were an agricultural people who, using Animism, assigned a spirit to every aspect of nature. Eventually, these vague spirits assumed human forms and entered the local mythology as gods. When tribes from the north of the Balkan Peninsula invaded, they brought with them a new pantheon of gods, based on conquest, force, prowess in battle, and violent heroism. Other older gods of the agricultural world fused with those of the more powerful invaders or else faded into insignificance.
After the middle of the Archaic period, myths about relationships between male gods and male heroes become more and more frequent, indicating the parallel development of pedagogic pederasty (Eros paidikos, παιδικός ἔρως), thought to have been introduced around 630 BC. By the end of the fifth century BC, poets had assigned at least one eromenos, an adolescent boy who was their sexual companion, to every important god except Ares and to many legendary figures. Previously existing myths, such as those of Achilles and Patroclus, also then were cast in a pederastic light. Alexandrian poets at first, then more generally literary mythographers in the early Roman Empire, often readapted stories of Greek mythological characters in this fashion.
The achievement of epic poetry was to create story-cycles and, as a result, to develop a new sense of mythological chronology. Thus Greek mythology unfolds as a phase in the development of the world and of humans. While self-contradictions in these stories make an absolute timeline impossible, an approximate chronology may be discerned. The resulting mythological "history of the world" may be divided into three or four broader periods:
- The myths of origin or age of gods (Theogonies, "births of gods"): myths about the origins of the world, the gods, and the human race.
- The age when gods and mortals mingled freely: stories of the early interactions between gods, demigods, and mortals.
- The age of heroes (heroic age), where divine activity was more limited. The last and greatest of the heroic legends is the story of the Trojan War and after (which is regarded by some researchers as a separate fourth period).
While the age of gods often has been of more interest to contemporary students of myth, the Greek authors of the archaic and classical eras had a clear preference for the age of heroes, establishing a chronology and record of human accomplishments after the questions of how the world came into being were explained. For example, the heroic Iliad and Odyssey dwarfed the divine-focused Theogony and Homeric Hymns in both size and popularity. Under the influence of Homer the "hero cult" leads to a restructuring in spiritual life, expressed in the separation of the realm of the gods from the realm of the dead (heroes), of the Chthonic from the Olympian. In the Works and Days, Hesiod makes use of a scheme of Four Ages of Man (or Races) : Golden, Silver, Bronze, and Iron. These races or ages are separate creations of the gods, the Golden Age belonging to the reign of Cronus, the subsequent races the creation of Zeus. Hesiod intercalates the Age (or Race) of Heroes just after the Bronze Age. The final age was the Iron Age, the contemporary period during which the poet lived. The poet regards it as the worst; the presence of evil was explained by the myth of Pandora, when all of the best of human capabilities, save hope, had been spilled out of her overturned jar. In Metamorphoses, Ovid follows Hesiod's concept of the four ages.