The late Carl Sagan once asked the Dalai Lama what he would do if science were to cast doubt on a central tenet of Tibetan Buddhism-reincarnation. The Dalai Lama replied with a grin: "It's going to be hard to disprove reincarnation."
The doctrine of reincarnation is not peculiar to Buddhism. It is prominent in other eastern religions as well as in some tropical African cultures. The Pythagoreans made reincarnation a part of their metaphysics; so did Plato (who argued that it accounted for our knowledge of the Forms) and, later, Schopenhauer. It has cropped up in certain Christian heresies and in Jewish Cabbalism. In the US today, more than a quarter of the people surveyed say they believe in reincarnation.
Disproving reincarnation would shake up a lot of world views. But is such a disproof as unimaginable as the Dalai Lama thinks? One might start with a simple observation that, a century ago, the world's population was under two billion; today it is six billion. As a matter of mathematical necessity, most people alive today cannot be re-embodied versions of people who died just before their birth.
Believers in reincarnation get around this demographic argument by surmising that the extra souls came from other species, or from elsewhere in the universe, or by allowing that new souls might be created. The important thing is that, once in existence, a soul is not destroyed by the death of a body it might inhabit.
But that raises a second objection to reincarnation. How can my self, which is so intimately bound up with the structures of my brain, survive its disintegration at death? Reincarnationists have a stock answer to this argument. The brain, they say, is like a radio. When it is damaged, the music becomes distorted. When it is smashed, the music stops altogether. But even then the radio waves are still out there to be received. A new radio can pick them up, provided it is tuned to the right frequency.
If reincarnation cannot be ruled out on empirical grounds, perhaps it can be discredited on a priori ones. Some philosophers have argued that the idea of reincarnation is incoherent. If, for example, I recall having fiddled while Rome burned, that does not mean I am Nero reborn. For me to be Nero, in this view, my body must be physically continuous with his; in other words, I would have to be Nero resurrected.
Many philosophers, however, do not insist on bodily identity as a necessary condition for personal identity. More influential is the Lockean view that psychological continuity-having the "same consciousness"-is enough. So it is at least conceptually possible that I might survive death by having my mental life, say, downloaded into a computer. Or lodged in a new body.
Let's turn the issue around. If it is hard to shake the faith of a believer in reincarnation, is it any easier to shake the belief of a sceptic? Suppose I say that I, for one, have no memories of past lives. The reincarnationist responds that death is a traumatic event and is therefore likely to cause amnesia. Far more convincing would be the existence of people who possessed detailed knowledge of past lives-knowledge which would be inex-plicable unless they had actually lived those lives. As it happens, Ian Stevenson, an 81-year-old psychiatrist at the University of Virginia, has been collecting just this sort of evidence for the last four decades. Underwritten by a $1m grant from the late Chester Carlson, the inventor of xerography, Stevenson has investigated nearly 3,000 cases of possible reincarnation on five continents. Recently, Tom Shroder, a Washington Post editor, accompanied Stevenson on field trips to Lebanon and India. Initially a sceptic about reincarnation, Shroder ended up by writing a sympathetic account of the research: Old Souls: The Scientific Evidence for Past Lives (Simon & Schuster, 1999).
What Stevenson documents are spontaneous waking memories reported by small children which contain intimate details of the life of a deceased person-invariably one who died shortly before the birth of the child in question. In Lebanon, for example, a boy "remembers" being a 25-year-old mechanic thrown to his death in a car accident on a beach road near Beirut. Stevenson verifies the boy's knowledge of the name of the driver, the exact location of the crash, the names of the mechanic's family and friends, and many other details.
Stevenson's cases are uncanny at first blush, suggesting, if not reincarnation, at least ESP. But the evidence nearly always turns out to be contaminated by contact between the child's family and the family of the deceased before Stevenson arrived on the scene. Explanations involving self-deception, wish-fulfilment, and fraud can never quite be excluded. And there is a deeper problem-one that I would call the reincarnation theorist's dilemma. A "memory" of a past life is either checkable by an investigator or not. If the alleged memory is checkable, then the possibility cannot be ruled out that the "reborn" person came to learn of it through the same channels that the investigator subsequently uses to check it. If it is not checkable, then it is indistinguishable from fabulation, and hence has no evidentiary value.
Neither the Dalai Lama's belief in reincarnation nor Carl Sagan's disbelief appears falsifiable. Does that mean that both are equally unscientific?
