essential to Mahayana Buddhism, the vast majority of contemporary lay Buddhists focus on accumulating good karma and acquiring merit to achieve a better reincarnation in the next life. In early Buddhist traditions, Saṃsāra cosmology consisted of five realms through which the wheel of existence cycled. This included hells (niraya), hungry ghosts (pretas), animals (tiryak), humans (manushya), and gods (devas, heavenly). In latter Buddhist traditions, this list grew to a list of six realms of rebirth, adding demigods (asuras). Rationale The earliest layers of Vedic text incorporate the concept of life, followed by an afterlife in heaven and hell based on cumulative virtues (merit) or vices (demerit). However, the ancient Vedic Rishis challenged this idea of afterlife as simplistic, because people do not live equally moral or immoral lives. Between generally virtuous lives, some are more virtuous; while evil too has degrees, and the texts assert that it would be unfair for people, with varying degrees of virtue or vices, to end up in heaven or hell, in "either or" and disproportionate manner irrespective of how virtuous or vicious their lives were. They introduced the idea of an afterlife in heaven or hell in proportion to one's merit. Comparison Early texts of Hinduism, Buddhism and Jainism share the concepts and terminology related to reincarnation. They also emphasize similar virtuous practices and karma as necessary for liberation and what influences future rebirths. For example, all three discuss various virtues—sometimes grouped as Yamas and Niyamas—such as non-violence, truthfulness, non-stealing, non-possessiveness, compassion for all living beings, charity and many others. Hinduism, Buddhism and Jainism disagree in their assumptions and theories about rebirth. Hinduism relies on its foundational assumption that 'soul, Self exists' (atman or attā), in contrast to Buddhist assumption that there is 'no soul, no Self' (anatta or anatman). Hindu traditions consider soul to be the unchanging eternal essence of a living being, and what journeys across reincarnations until it attains self-knowledge. Buddhism, in contrast, asserts a rebirth theory without a Self, and considers realization of non-Self or Emptiness as Nirvana (nibbana). Thus Buddhism and Hinduism have a very different view on whether a self or soul exists, which impacts the details of their respective rebirth theories. The reincarnation doctrine in Jainism differs from those in Buddhism, even though both are non-theistic Sramana traditions. Jainism, in contrast to Buddhism, accepts the foundational assumption that soul exists (Jiva) and asserts this soul is involved