The exact origins of the belief in reincarnation are obscure. Aspects of it have been found to have arisen independently in countless different regions throughout the world. This has ranged from as early as 1200 BCE - The Iron Age, to the 6th century BCE in India and Greece. Celtic Druids are also reported to have taught a doctrine of reincarnation. In ancient European, Iranian and Indian agricultural cultures, the life cycles of birth, death, and rebirth were recognized as a replica of natural agricultural cycles.
Most commonly, reincarnation has been attributed to Buddhist beliefs. Early Buddhist texts discuss techniques for recalling previous births, acquired largely through intense levels of meditation. Buddha reportedly warned that these recollections can be misleading however, and should be interpreted with care. Tibetan Buddhism has developed a unique "science" of death and rebirth, much of which is set down in what is popularly known as The Tibetan Book of the Dead.