eternal youth
According to the mythology of the Trobriand Islands, human beings used to be immortal, by simply shedding their skin when it grew old. At some point, however, they lost the power to remain youthful forever in a rather trivial incident...
Once upon a time there lived in the village of Bwadela an old woman who dwelt with her daughter and granddaughter; three generations of genuine matrilineal descent. The grandmother and granddaughter went out one day to bathe in the tidal creek. The girl remained on the shore, while the old woman went away some distance out of sight. She took off her skin, which, carried by the tidal current, floated along the creek until it stuck on a bush. Transformed into a young girl, she came back to her granddaughter. The latter did not recognize her; she was afraid of her, and bade her begone. The old woman, mortified and angry, went back to her bathing place, searched for her old skin, put it on again, and returned to her granddaughter. This time she was recognized and thus greeted: "A young girl came here; I was afraid; I chased her away." Said the grandmother: "No, you didn't want to recognize me. Well, you will become old -- I shall die." They went home to where the daughter was preparing the meal. The old woman spoke to her daughter: "I went to bathe; the tide carried my skin away; your daughter did not recognize me; she chased me away. I shall not slough my skin. We shall all become old. We shall all die."
From: 'Magic, Science and Religion' (1948) by Bronislaw Malinowski.