Hume ... famously told Boswell that he was no more afraid of his own extinction after death than he was of the nonexistence that had preceded his birth. (Christopher Hitchens)
When it comes to reincarnation, there's not a lot of hard evidence about. In fact there's not a lot of hard evidence about concerning anything to do with an existence outside of our life on this earth in a physical body.
When I compare my sense of who I am now with the "pre-mystical" self that I recall as a youth and young adult, the biggest difference is what I would describe as a sense of immortality. Like Woody Allen, I am no longer afraid of death. I just don't want to be around when it happens.
There is no way that I could have arrived at this conclusion by any logical process, but the difference is a profound one. It is tempting, but, I think, ultimately foolish, to try and "prove" the existence of life after death now that I'm so certain of it. But no argument convinced me thoroughly beforehand. As no argument could unconvince me now.
Much experience of this kind is contained for our species not in logical argument but in myth, in story, in image, in music, in ritual, and in fable. As the sign on the T-shirt said, "I have given up my search for truth and am now looking for a good fantasy."
As a minimum gesture in the direction of rationality we do like our fantasies to be as self-consistent as possible, but that is the most we claim for them.
Most fantasies hold that there is a part of a human being, the body, that comes into existence at conception and disappears at death, and that there is another part, the soul or spirit, that lives on. Christianity, broadly, embraces this theory.
Some such theories hold that a soul comes into existence with the conception (or birth) of a human being, has one "lifetime" in a human body, and then lives in eternal punishment (Hell) or eternal bliss (Heaven) depending on the circumstances of that one life.
The Roman Catholic Church, for example, teaches that a child that dies without being received into the fold through baptism does not make it into Heaven. (Baptism, is, consequently, one of the few rites of the Church that does not require one to be a priest to perform it.)
Most of the thousands of subfantasies in this "one chance only" group, like the Roman Catholics, also claim to be the sole owners of the path to the promised eternal bliss. "My way, or the highway — to Hell"
A key problem in these groups has been to determine at what point a "soul" is created, and at what point it joins with its human body. Possession of a soul is what differentiates man from the rest of creation in many theories and entitles him to special treatment as a result.
More than One Life
Other theories hold that when a human being dies, his immortal part passes, either immediately or after an interval of some kind, into a new body. If the theory permits only human to human transference, this process is called reincarnation. If it permits transference between any two life forms, this process is known as transmigration. Many subtheories of these permit the possibility of transmigration between different worlds.
All of these theories, once we stop with them, generate a host of further questions.
For example, one might ask Christians - or Muslims - whether souls come into being as a function of conception, ie, does conception generate a soul as well as a body, or whether souls are created separately by God, and then joined with their bodies, at conception or at some "later" stage.
(This might seem trivial except that, for many people, one of the problems around abortion and contraception - or spontaneous miscarriage for that matter - is deciding at what point a fetus acquires a human soul.)
(Consider also, that identical twins begin as one fertilised egg and separate after conception. If a soul is created at the moment of conception, do identical twins share a soul? If not, there must surely be a period of time, for all fetuses during which they are without a soul, inside which period division into twins may occur? What about Siamese twins?)
If, as many do, we assert that the fetus has a soul from the moment of conception, or even soon afterwards, then what determines whether the soul of a fetus that miscarries spends eternity in heaven or hell?
What are we to do about fetuses that come into being in vitro, and are preserved in laboratories, potentially for years, unable, one assumes, to find release as in death or fulfilment as a living growing, aging, human being.
What determines, besides chance, whether a soul is born into comfortable or miserable circumstances, to Christian or Muslim or New Age or atheistic parents? What determines whether a soul is born into a healthy or a severely deformed body. (See John 9.)
All at Once or Ad Hoc
We might also like to ask whether all souls were created at once "in the beginning", as part of the "heaven and the earth", or do they come into existence as required.
(Dammit. Let's go for broke: Did souls, like the rest of our physical world, evolve? Were they present in primitive forms as life began its long upwards journey from the primeval slime? At what point along the evolutionary path did souls become recognisably human? For, on the basis of the subtle-body theories put forward, there should be some equivalent, even in inanimate forms such as rocks, of each of the subtle bodies.)
If all were created simultaneously, we then have to inquire about the nature and quality of their existence during the "interval" between the beginning of creation and their birth as humans.
If, on the other hand, souls are created on an ad hoc basis as required, we still have to identify some point of creation, of coming into existence, for something that we maintain will continue to exist after the death of its human expression.
Are questions with a "time" component irrelevant when we are discussing existence outside of this creation. If such is the case, what is the nature of this non-temporal existence? Ideas get slippery.
Reincarnation itself poses a number of further questions and transmigration a few more still. (Though alongside the possibilities offered elsewhere they can seem eminently rational.)
If all souls were created together in the beginning, we have to assume a fixed number of souls. Given our best estimates of the total number of human beings that have ever lived (120 billion or thereabouts) and the current world's population (5-6 billion and rising) that limits reincarnation from one earth-human to another to about 20-25 times around, in a significant number of which lives they probably lived for less than a year.
That's a lot less than the hundreds and thousands of lives spoken of by many New Age writers as necessary to grow in spiritual wisdom. You can perhaps see why some theories look to include other worlds beside earth in the equation. At the other extreme, the Vedic writings maintain that there are 8,400,000 species of living beings and that each soul spends time in all of them.
Or are there new souls still coming into being? (Some traditions do speak of "old souls").
What animates non-human life forms, such as insects, animals and plants, or bacteria or viruses for that matter? What is the relationship between this "spark of life" and the human soul?
Any answer we provide to these questions provides us with simply more questions.
Once I have rejected the notion that life just is, and has no obvious meaning or significance or value, it seems to me that reincarnation makes a good deal more sense than most other theories about what happens before and after — or outside of — our time in this world. Whether it makes enough sense is perhaps a separate question.
What evidence is there to support the notion of reincarnation, apart from the fact that the alternatives sound even more improbable?
Past Life Recall
One school of thought has it that because people "recall" past lives, either spontaneously or via hypnosis, this is evidence for reincarnation. Maybe, but I doubt it. Personally, I believe that memories of a specific lifetime are included in the part of us that dies and decays into it's original building materials.
Without being (conventionally) Christian, I tend to regard such past-life recall as more akin to possession by some kind of superphysical entity. (Leave demons, devils, evil spirits and other value-laden descriptions out of it at this point.)
In my early dabbling in this field, I employed a "regression" technique in reverse on some of my more adventurous clients, and obtained some very interesting reports of "future" lives. Go figure....
(In any case, a good deal of alleged "past-life" recall has been shown to be fraud, or if not fraud, explicable without recourse to the superphysical or to previous existences. But not all of it.
There is one extremely interesting report from Dr Helen Wambach which describes her regression of nearly 1100 clients who reported on their "past lives". Whether these lives were previous existences of the clients themselves, I continue to doubt, for quite separate reasons. What is interesting is that the lives they "recall" are statistically distributed almost exactly according to patterns we would expect from our current knowledge of population numbers and social makeup.)
My personal belief set allows for the existence of persons whose death process is for one or another reason incomplete, who exist as superphysical beings in a fashion that does permit them to recall at least their immediate past life.
Note that Dr Wambach reports on people alive now who recall one or more previous lives, but she does not report that any of these previously existing persons have any awareness of earlier lives still.
Theoretically, if Dr Wambach's clients can recall past lives, at least some of the persons whose lives they recall should also be reporting on earlier lives still, but only the living client is reporting past lives.
So my guess is something more akin to possession rather than recall. The possessing entities do not have access to their own past lives. And I don't believe that living persons here on earth have access to theirs either.
We do perhaps have some evidence here for the persistence of some part of us beyond physical death.
(It might be argued that possessing entities are also available for possession in their turn, but my observation is that possession seems normally to occur for purposes associated with access to physical existence.)
Jesus accepted the idea of reincarnation
See Jesus and Reincarnation. Given the opportunity to pooh-pooh reincarnation, Jesus did not do so. It did not seem to be a concept he found obviously wrong, if the writer of John's gospel is to be believed. Not hard evidence, by any means, but some might find it authoritative.