Claims of reincarnation are not uncommon, often presented in an appealing manner. Skeptics counsel that because people fear death and are eager to find alternative theories to personal extinction, it is therefore wise to consider any such claim with caution, and to consider the possibility that the claimer has something to gain by the listener's acceptance of the claim.
The scientific evidence for reincarnation is currently fairly weak. The best work in the field has been done by Ian Stevenson, who has found that claims of past lives sometimes correlate with physical birthmarks corresponding to injuries received in the previous life.
The oft-heard skeptical claim that reincarnation is impossible depends on the theory that all mental phenomena are accounted for by physiological processes. There is currently no experimental means to determine the truth or falsehood of this theory. Ockham's razor would seem to dictate that the skeptical view is to be preferred, as it demands no extraordinary new evidence beyond what is already known to science.
Reincarnation is a basic tenet of Hinduism, and also of Buddhism, but the two religions differ on how reincarnation works. Hindus believe that the soul, or atman is what is preserved from one life to the next. Buddhists (or at least Theravada Buddhists) believe in what they call anatman, or the non-existence of the soul. The person is nothing more than an aggregate of material and mental components that separate upon death. However, when the separate, they normally cause a new aggregate to be formed, and thus reincarnation is carried out.
See also: karma,