Julien d'Huy in Scientific American [h/t: Simon During]:
The Greek version of a familiar myth starts with Artemis, goddess of the hunt and fierce protectress of innocent young women. Artemis demands that Callisto, “the most beautiful,” and her other handmaidens take a vow of chastity. Zeus tricks Callisto into giving up her virginity, and she gives birth to a son, Arcas. Zeus’ jealous wife, Hera, turns Callisto into a bear and banishes her to the mountains. Meanwhile Arcas grows up to become a hunter and one day happens on a bear that greets him with outstretched arms. Not recognizing his mother, he takes aim with his spear, but Zeus comes to the rescue. He transforms Callisto into the constellation Ursa Major, or “great bear,” and places Arcas nearby as Ursa Minor, the “little bear.”
As the Iroquois of the northeastern U.S. tell it, three hunters pursue a bear; the blood of the wounded animal colors the leaves of the autumnal forest. The bear then climbs a mountain and leaps into the sky. The hunters and the animal become the constellation Ursa Major. Among the Chukchi, a Siberian people, the constellation Orion is a hunter who pursues a reindeer, Cassiopeia. Among the Finno-Ugric tribes of Siberia, the pursued animal is an elk and takes the form of Ursa Major.
Although the animals and the constellations may differ, the basic structure of the story does not. These sagas all belong to a family of myths known as the Cosmic Hunt that spread far and wide in Africa, Europe, Asia and the Americas among people who lived more than 15,000 years ago. Every version of the Cosmic Hunt shares a core story line—a man or an animal pursues or kills one or more animals, and the creatures are changed into constellations.
Folklorists, anthropologists, ethnologists and linguists have long puzzled over why complex mythical stories that surface in cultures widely separated in space and time are strikingly similar. In recent years a promising scientific approach to comparative mythology has emerged in which researchers apply conceptual tools that biologists use to decipher the evolution of living species. In the hands of those who analyze myths, the method, known as phylogenetic analysis, consists of connecting successive versions of a mythical story and constructing a family tree that traces the evolution of the myth over time.