Final answer:
In Hinduism and Buddhism, a soul's rebirth in a higher or lower caste or life form is governed by karma, which is determined by an individual's moral and immoral actions in life.
Step-by-step explanation:
The soul's rebirth in life after death, according to Hindu and Buddhist beliefs, is influenced by karma, which is the spiritual principle of cause and effect resulting from an individual's actions. Positive actions and upholding one's dharma lead to good karma, drawing one closer to God and potentially leading to rebirth into a higher caste or a life with greater spiritual awareness in the cycle of reincarnation. Conversely, negative actions distance a soul from God and can result in reincarnation into a lower caste or form of life. The ultimate objective in both religions is to accumulate positive karma and achieve moksha, which is liberation from the cycle of birth and rebirth.