Twins appear in the mythologies of many cultures around the world. In some they are seen as ominous and in others they are seen as fortuitous. Twins in mythology are often cast as two halves of the same whole, sharing a bond deeper than that of ordinary siblings, or otherwise shown as fierce rivals. Twins can represents some "other" aspect of the Self, a doppelgänger or a shadow. Often the twin is the "evil twin" , or one may be human and one semi-divine. The twin may be a brother, or a soul-mate, such as the "civilized" Gilgamesh and the "wild" Enkidu.
Many cultures have mythic or folkloric explanations for how twins are conceived. In Greek mythology, some twins were conceived when a woman slept with both a mortal and a god on the same day. One of her offspring thereafter had godlike qualities, and the other was an ordinary mortal, such as Heracles and his twin brother Iphicles. In several Native American cultures women avoided eating twin fruits like double almonds and bananas because it was thought to increase the likelihood of twins. In other cultures, twins were attributed to superior virility of the father.
Twins can represent the dualistic nature of the universe. In Greek mythology, Apollo and Artemis are twins, and Apollo was adopted as the sun god with Artemis as the moon goddess. In Xingu mythology of Brazil, the twin brothers Kuat and Iae forced the evil king Urubutsin to give light to the world, and Kuat became the sun with Iae as the moon. In one version of the Egyptian creation myth, the earth god Geb and the sky goddess Nut were twins. In Zoroastrian mythology, the twins Ahriman and Ahura Mazda represent the spirits of evil and good respectively. Cultures with rival twin heroes often follow this pattern of split moral forces. In a myth of several northeastern Native American tribes, Gluskap, the creator god and cultural hero, has to defeat Malsum, his evil twin, who was the ruler of the demons.
Twins can also be shown as having special powers and deep bonds. In Greek mythology, Castor and Pollux share a bond so strong that when Castor dies, Pollux gives up half of his immortality to be with his brother. This etiologically explains why their constellation, the Discoursi or Gemeni, is only seen half the year, as the twins split their time between the underworld and Mount Olympus. In an aboriginal tale, the same constellation represents the twin lizards who created the plants and animals and saved women from evil spirits. To the Dogon of Mali in West Africa, twinship represents completeness and perfection, symbolized by the deity Nummo. Nummo is actually a set of twins, male and female, and because the creation of the world required a sacrifice, humans can only be one half of the whole, male or female. In many Native American stories, twins are often partners on adventures such as quests.
Jobes, Gertrude (1962). Dictionary of Mythology, Part 2. New York: Scarecrow Press, Inc. pp. 1614–1615.
Maria Leach, ed (1972). Standard Dictionary of Folklore, Mythology, and Legend. New York: Funk & Wagnalls. pp. 1134–1136.
John M. Wickersham, ed (2000). Myths and Legends of the World, vol 4. New York: Macmillan Reference USA. pp. 76–79. ISBN 0-02-865438-2.